RC India

RC Models => Self-designed, DIY and College Projects => Topic started by: PankajC on August 28, 2009, 11:48:17 AM



Title: Scratch Build - Cub Trainer
Post by: PankajC on August 28, 2009, 11:48:17 AM
 I have 1mx1m of 10mm and about 4ft x 6ft 2.5 mm foam from my scouting for depron suppliers in Delhi.
Well finally decieded what to do with the EPP / Bio foam that I purchased. I am going to build a Cub Trainer with electric power.
The build vs buy debate has been going on in my mind for a long time, finally tilted to build. Its going to be a scratch build after almost 20yrs, first RC build and first EPP build at that, so in general its very exciting (provided I get time off from office and kids et all)....

Now the overall specks are something like this

Wingspan = approx 46 inch. I do not know the wing loading thing, but the width of wing is approx 7.5 to 8 inch
Length of plane = approx 33 inch.

control 4 channel.

I am thinking of having 2 part wing with carbon and/or fiber glass rods to strengthen it. Since there would be 2 parts, then I guess I would need 2 servos to control the aileron. So I think I shall settle for 4 of 17gm servos.
I am also looking at battery of about 3C1P with 30-40 C drain and rating of about 4000 - 5000mAH. So the weight of the battery alone should be close  to 400-500gm..... I think taking all materials into consideration the all up weight is going to be in the region of about 1.2 to 1.5kg, so back calculating from there - I need a motor of about 400-500watts (100-150 watts per pound rule), which in turn would require about an 60A ESC

What am I missing here???  what prop to use - but then its a long way off. Lets see if I still have it in me to complete a build.

So began cutting the foam into managable blocks. Posting the photos of cut EPP pcs....

Pankaj





Title: Re: Scratch Build - Cub Trainer
Post by: martian2121 on August 28, 2009, 07:03:53 PM
http://f4k3url.com/lazy-bee (http://f4k3url.com/lazy-bee)
Dear Pankaj,
Check this out........... excellent project for depron or biofoam............. light, quick to build and gr8 fun to fly...... 8)
Edwin


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on August 28, 2009, 08:44:57 PM
I second that really looks great never saw this one on RCG.
The plane looks  very nice and the under cambered wing will really make it a great plane.



Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on August 28, 2009, 08:57:00 PM

I think for a foam plane the battery you are considering is too heavy if the set up is a single motor one .
If it were a double motor set up like twin star the capacity you are talking of should be OK

With a 48 " wing span and a 33 " fuse your set up  the battery should   be around  3s 2200 OR 2650  mah  at best .

17 gms servos seem OK for this size of a foamy .

The motor could be a 2217/8 1000 to 1100 KV

Prop : 10 to 11 inch.

If I were to build it as trainer I would  go for rudder elevator with under cambered wing  rather than aileron to start with .
After I got it right in terms of flying  , I will then make another KFM or Aerofoiled wing  for the same fuse as version 2 with aileron's  .

sai

Sai


Title: Re: Scratch Build - Cub Trainer
Post by: b4ggu on August 28, 2009, 11:02:04 PM
Hi Pankaj,

I sure would like to see how your model evolves. I am also into Depron quite a bit in 6mm and 3mm thickness of sheets. I think the 10mm will be too thick and heavy.

I use hotmelt  glue and it works very well as hinges and for sticking but adds the weight.

I wish you success in your venture and look forward to the finished article images.

Where abouts in Delhi do you fly? Did you buy your foam in Pahar Ganj area? Please will you let the other modellors know the where they can get the DEPRON sheets (Actual producer's name of Bio Foam).


Do you know Kuldip who is also into scratch building and flies a few miles out from DLF.

You know what.. you just reminded me of my childhood days in Delhi...

Looking at images of the Bio Foam gave me a glimpse of your floor. I grew up in Delhi's Darya Ganj area and had the same floor in my room... Now this is going back 35 to 40 years.. Good old days.
I have had a few PICO STICKS for over 10 years and have enjoyed it very much in the past years from time to time. In fact I am on my 3rd one now as the power system that it comes with used to cost half the price of kits so I always used to buy another kit when my motor burnt out or broke. Here is a thought based on slow stick and Pico stick..
To get the curves on the wings like lazy bee what if you were to make bows out of BAMBOO SKEWER STICK and wrap it with bio foam or Depron sheet 2 or 3 mm thick. The second option would be Depron warped over ribs in balsa  It does bend to shape when you blow it with hair dryer, but will it keep the shape when the bows are removed ??????

Good Luck

Deepak



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on August 31, 2009, 03:29:48 PM
Well managed to cut some formers with the 10mm foam. Like with any other foam material, the edges are not smooth, but still the formers seem to be fitting nicely even without sanding

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on August 31, 2009, 05:49:32 PM
I second that really looks great never saw this one on RCG.
The plane looks  very nice and the under cambered wing will really make it a great plane.

I took the hard copies of this beauty 8) 8).....and will start working on this today itself... canopy and other will made by Balsa, the only problem i may face is fabricating the wing  :'( :'( :'(, i have 6 mm depron  :'( :'(........But...... {:)} {:)} {:)} {:)} {:)} {:)}


Title: Re: Scratch Build - Cub Trainer
Post by: tg on August 31, 2009, 07:51:31 PM
Use a heat gun to get the under-camber


Title: Re: Scratch Build - Cub Trainer
Post by: allthatido on September 01, 2009, 03:08:16 PM
pankaj
where did you source the depron from in  delhi???


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 01, 2009, 05:15:38 PM
Use a heat gun to get the under-camber

I tried , but it require a lot of patience to make an under-camber out of 6 mm depron, and that too on a wing with 30" or more length. major difficulty come when bending the depron and simultaneously holding the heat gun or hair drier  :D. for easiness i have to make a hot water tub along with some weight to bend. i hope you understand what i mean.
Sandeep


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 04, 2009, 12:50:18 PM
Wings contruction started....

I am thinking like this...
Thick foam base reinforced with carbon/fiberglass rods, foam ribs and then covering the top with a thin foam... wonder if it will work ???


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 04, 2009, 12:53:26 PM
images of a rib....


Title: Re: Scratch Build - Cub Trainer
Post by: mpsaju on September 04, 2009, 01:34:25 PM
Pankaj

Will not the pull of the foam bend the rib out of shape. I would think it better to use use Coro as a rib. Otherwise, why dont you think of coro for the whole under-cambered wing. Would be easy to construct but a little heavier, but also more durable.

Saju


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 04, 2009, 02:50:11 PM

Will not the pull of the foam bend the rib out of shape. I would think it better to use use Coro as a rib. Otherwise, why dont you think of coro for the whole under-cambered wing. Would be easy to construct but a little heavier, but also more durable.

Saju

Not sure about bending, I had been planning a thick foam (remember i am using 10mm foam) for ribs and the base of wing with about 2-3 rods for strength. Then again, I could use coro for base and ribs....


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 04, 2009, 03:32:15 PM
I am not able to understand, how to cut and make the monoblock. the sketch of monoblock is not clearly understandable. Please help.
SAndeep


Title: Re: Scratch Build - Cub Trainer
Post by: martian2121 on September 05, 2009, 09:12:33 AM
If you could post the sketch, perhaps we could try to work it out..........
Edwin


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 08, 2009, 10:51:26 AM
.....
With a 48 " wing span and a 33 " fuse your set up  the battery should   be around  3s 2200 OR 2650  mah  at best .
.......

Sai

Sai,

How does one determine the max battery aH - is it weight or something else? What would (most likely) to happen if I were to use a higher aH rating battery - say a 4000aH?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 08, 2009, 12:55:35 PM
If you could post the sketch, perhaps we could try to work it out..........
Edwin
The sketch is available at
http://f4k3url.com/lazy-bee
Sandeep


Title: Re: Scratch Build - Cub Trainer
Post by: martian2121 on September 08, 2009, 07:19:18 PM
SORRY buddy, never realised u were workin on the link that I had posted. As far as the lazy bee is concerned, just get the wings correct. thats all that matters. As for the fuse, trust ur intution and keep it as light as possible. make the tail also very light. dont pay too much attention to detail.......... (bad advice probably, but thats how i did mine)
Edwin


Title: Re: Scratch Build - Cub Trainer
Post by: Pikle6 on September 08, 2009, 08:34:34 PM
hey guys beware of the link posted above the plane just doesn't have enough vertical stabilization so increase the rudders length and you are all set

subbu


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 09, 2009, 01:33:43 PM
What started off as a build thread for one, has now turned into a log for two scratch builds ( one with Sandeep as well)  ;D ;D

loading images of tail assembly. The problem is I am not getting the proper finish (check the closeup image) ... I think I would need to apply some sort of a coat on top and then sand the bits. On its own, the fins look too fiberous. Was thinking of covering the model with areldite - but then a) its too thick for a thin layer b) not sure about the increase in weight.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 09, 2009, 03:41:15 PM
Building this cubs wing is real challenge for me. i have build fuse and monoblock (i dont know how correct it is), will post the pictures tomorrow.
to build the wing with under-camber, first i am cutting the long wing into 10 small pieces. then each small piece is sliced into 3mm approx.
all 10 small piece is then hot aired and given the shape of the required wing shape, after completing, all wing pieces are hot glued to form the complete wing. although shape of wing is slightly ugly, but i hope it will give proper lift to the cub.
Will post the pictures tomorrow.
Sandeep
 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 09, 2009, 04:57:03 PM
Well Sandeep, I am using ribs for the aerofoil, what I did was that I cut out a number of them using a coro sheet rib as a template and them sanded them together. Next challenge is to actually fit it.....



Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 10, 2009, 11:30:14 AM
Here are the Pic of my Built:
(http://img39.imagefra.me/img/img39/2/9/10/sandeepm/f_10dhjm_eadef5a.gif) (http://imagefra.me/)
(http://img40.imagefra.me/img/img40/2/9/10/sandeepm/f_11dv1km_ede6616.gif) (http://imagefra.me/)
(http://img39.imagefra.me/img/img39/2/9/10/sandeepm/f_vsb40b10acem_0048b75.gif) (http://imagefra.me/)
(http://img40.imagefra.me/img/img40/2/9/10/sandeepm/f_wp4f4bc1an1m_d1c3ae6.gif) (http://imagefra.me/)
(http://img39.imagefra.me/img/img39/2/9/10/sandeepm/f_senlxkp46m_b421027.gif) (http://imagefra.me/)
(http://img38.imagefra.me/img/img38/2/9/10/sandeepm/f_t83akjata7m_043e2af.gif) (http://imagefra.me/)
(http://img39.imagefra.me/img/img39/2/9/10/sandeepm/f_dkim_a720833.gif) (http://imagefra.me/)

Please don't ask how i build the mono block  :o, it was the toughest time for me to think the mono block design


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 10, 2009, 11:54:45 AM
Looking great..........

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 10, 2009, 12:04:11 PM
It Should Fly GREAT also  ;D, i have a small doubt in one small corner of my small mind of its capability.

Sandeep


Title: Re: Scratch Build - Cub Trainer
Post by: tg on September 10, 2009, 12:46:35 PM
You should apply 3M 2 inch or 4 inch tape span wise on the wing to remove the warps. And add more ribs to ensure a clean and constant camber for the wing. Why did you cut the wing into sections. Not enough foam or only strips?


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on September 10, 2009, 01:04:37 PM
Wonderful build. {:)} {:)} I am sure it will fly as good as it looks.


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 10, 2009, 01:47:44 PM
You should apply 3M 2 inch or 4 inch tape span wise on the wing to remove the warps. And add more ribs to ensure a clean and constant camber for the wing. Why did you cut the wing into sections. Not enough foam or only strips?
I have to cut the wings into section as i have to slice my 6mm depron into 3mm, since my blade is not such long to slice the entire width, i have to cut them into sections.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on September 10, 2009, 03:51:25 PM
Yup, the best/worst part of a scratch build is finding the right tool and material for the job.

Right now, am finding it difficult to comeup with suitable material for firewall that can sustain a 550W 42mm outrunner weighing about 140gm..... I wonder if I would be able to takeoff...  ???



Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on September 30, 2009, 11:05:01 AM
Here are the final built Pics of Blazy Bee:
1.
(http://img38.imagefra.me/img/img38/2/9/30/sandeepm/f_efe0c4h3m_5ff5688.jpg) (http://imagefra.me/)
2. Thanks to Subu, who made the wing for my Blazy bee.....  {:)} {:)} {:)}
(http://img03.imagefra.me/img/img03/2/9/30/sandeepm/f_efe0c4h4m_e08c285.jpg) (http://imagefra.me/)
3.
(http://img39.imagefra.me/img/img39/2/9/30/sandeepm/f_ettecglmfm_11f9caa.jpg) (http://imagefra.me/)
4.
(http://img39.imagefra.me/img/img39/2/9/30/sandeepm/f_efe0c4h6m_1325163.jpg) (http://imagefra.me/)
5.
(http://img02.imagefra.me/img/img02/2/9/30/sandeepm/f_efe0c4h7m_99719a3.jpg) (http://imagefra.me/)

Maiden will be on 2nd
Video will be posted on 5th Oct.
Sandeep


Title: Re: Scratch Build - Cub Trainer
Post by: sahilkit on October 01, 2009, 10:27:57 AM
what is the AUW ?


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on October 01, 2009, 01:26:48 PM
 :( , i don't have option to check the AUW.. will try with my local shop here..


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 07, 2009, 04:43:44 PM
Aaaaahh!!! feels good to be back to the build log after a long gap. Well as I write I do see a lot of new icons/smileys.

Anyway, finally ordered Lipo from HC. Was wanting to know about A123 cells and how to program the ESC for these, but for the lack of knowledge ordered Lipos instead. Have also ordered TowerPro ESC after seing the pictures of them on Subbu's space shuttle log.

So the order looks like this
  2 x 3AH batteries
  2 x 40A Esc - one extra just in case!!!!
  11x7 props
  50W charger
  charge bag
  4 mm bullet connectors - and some more bits and pcs.....

So another long wait for the materials to arrive - I don;t think they have dispatched it yet.

In the mean time, back to building the cub. Its taking up quite a lot of time and the joins are not as smooth as what we get in balsa models. This is the first time I am building a foam model and more than half the time I am wondering on the strength and trying to add some more material to it. At this moment, my main concern/fear is that I may be over engineering the model to an extent that it becomes too heavy to take off - that would be painful.  I guess I should try to get hold of a balance to check the weight of the model - am thinking of a spring balance but wonder where I can get one.


BTW, Sandeep. Good to see the finished version of Lazy Bee - did you manage to maiden it yet?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: sandeepm on October 08, 2009, 10:08:26 AM
Yes Pankaj , i maiden the blazy bee..but unfortunately due to low height of Vertical stabilizer...it wobble in air and crashed badly.....i have put new vertical Stabilizer and will try this Saturday again.... hopefully it should fly now.... :thumbsup:


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 08, 2009, 10:26:23 AM
OK,

One of the primary requirements that I had while starting on the scratch build was the 2 part wing system that could be assembled or disassembled easily. I took me a while to figure out how I could do this.

On its own, the wing assembly is not complete, but have got the base with reinforced carbon. The load carrying  spar is a 6mm x 6mm square carbon tube. The leading edge is has a 2.5mm fiber rod
 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 08, 2009, 10:33:39 AM
Closer inspection of the wing join...

I have done is cut 4 pcs of 2 inch length of 5mm carbon tube. The outer has been reinforced by a strong silk thread with epoxy. This was done to increase the friction between the surfaces as well as to provide extra protection to the small carbon pcs.  Inside the two tubes, have inserted a reinforced fiberglass rod with enough traction that it fits tightly. These have then been joined with epoxy to form the 'male' part of the connector.

Once the 'male' connector was ready,, applied grease to extender fiberglass rods and slipped in the other 5mm tube. This entire contraption was joined by epoxy all the while holding the wing at an angle to form the dihedral.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 08, 2009, 10:35:45 AM
So, now after drying, when I just join the wing using these connectors.... I get the following....



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 08, 2009, 10:41:44 AM
I shall now put the ribs on this base and cover it with 3mm biofoam......

On the fuse, the basic form has taken place, I shall now work on putting on the wheels and also giving shape to the cowl.. For the engine mount, I do have an X mount supplied with the motor. In order to install it, I have a 6x6mm carbon tube connected to a small laminated sheet (used for mounting the electrical switches at homes). The drills are in place to accept a self thread screw to attach the X mount.
 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 08, 2009, 10:44:53 AM
For housing the servos in the parcel tray, I have first pasted a balsa sheet on the parcel tray with large holes to accommodate the servo housing. The servo itself has been installed on a smaller piece of balsa then the entire setup has been screwed to the parcel tray. Well I could have used less balsa on the parcel tray but what the heck........


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on October 08, 2009, 11:32:44 AM
Good going Pakaj. This is one of the "neatest" build I have seen in RCindia. Keep it comming.

-Ismail


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 21, 2009, 10:06:24 AM
Been busy building the model....

For wings, I have used fiberglass rods as spars and thermocol ribs, then have covered with a 2.5mm bio foam sheet. The top surface was first heat treated with a blow drier to give a rough shape to te aerofoil...
 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 21, 2009, 10:08:29 AM
finally glued the top layer for form the wing... At the base, cut out a small square for a pc of balsa to act as the tray for the servo


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 21, 2009, 10:11:37 AM
Some more of the fuse being built.. The cowl and the nose assembly


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 21, 2009, 10:17:05 AM
finally all the pcs together...... Tried to check the weight, but since I do not have a kitchen scale at home, tried with a contraption of balancing against a 600ml pet bottle filled with water (so the wt should be around 650gm) the model with motor,wheels and servo is almost the same wt. The only thing missing is prop, esc and battery.... so the all up wt should be within 1200gms which was the target set at the start.....


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on October 21, 2009, 01:01:37 PM
 {:)} 

What prompted you to add this type of wing tips ?


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 21, 2009, 03:29:13 PM
Actually, I could not figure out a way to gradually taper the wing tip, so next best I could do was to build a block and file away to glory  ;D ;D ;D ;D


Title: Re: Scratch Build - Cub Trainer
Post by: tg on October 21, 2009, 04:01:12 PM
Instead of that you could have continued the upper surface of the wing all the way to the end and taper the under side instead. Thats done on virtually all ARF trainers. The wing has a level surface end to end and the taper is on the lower surface.


Title: Re: Scratch Build - Cub Trainer
Post by: martian2121 on October 21, 2009, 09:56:54 PM
Dear Pankaj, Gr8 work............. but looks like u have really complicated a very simple build model! The bee is not a model basically designed for durability...... except the original Clancy's balsa bee. Urs looks ready for battle. Gr8 effort but seems way too heavy!


Title: Re: Scratch Build - Cub Trainer
Post by: allthatido on October 22, 2009, 12:50:31 AM
Pankaj

Great build...could you please post some pics of the fuse internal ribs or bulkheads...also where did you get those landing gears from..Waiting for the video.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on October 22, 2009, 12:30:03 PM
Dear Pankaj, Gr8 work............. but looks like u have really complicated a very simple build model! The bee is not a model basically designed for durability...... except the original Clancy's balsa bee. Urs looks ready for battle. Gr8 effort but seems way too heavy!

Quite right on the overdoing part.... First timer for foam and I was kind of skeptical on its durability - even holding the foam firmly puts a dent. So tried to give extra protection. As per the weight- the AUW should be in the region of 1050-1250gm and with a out-runner capable of delivering 500W, I think it will take off... I am worried about the landing   :headscratch:

Anyways, still some weeks off before I maiden - primarily because, I had left out the battery and ESC while ordering the rest of the parts from HC. I wanted to try out the A123 batteries, but till the end I could not locate an ESC (with guide) that would take in these batteries. Hence settled for Lipo. So the order would probably reach in couple of weeks time.

Till then, would be finishing the model - work remaining is on finishing the wing with flaperon and wing tips. Then giving the model the final sanding and applying WBPU for gloss...




Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 10:29:04 AM
So while I am waiting for the parcel to be delivered - which contains ESC,Prop and Lipo, I decided to try my hand in painting the model (not that I am good with brush anyway).

First part of the deal was to get hold of WBPU. I had read this is available easily, but it turns out that the local paint/harware shops had not heard of it. All PU they had was thinner based. I went the Home Town stores and did locate a water based Polyurethane called Varthane (seems to be a US brand). 1ltr was being sold at Rs.2700/- so I gave up the idea. Then I tried calling the Pedilite industries - the folks who make fevicol and acrelic paints. It turns out that they do have a WBPU - in fact two versions, interior and exterior. The product range is called SHOWCASE AQUA. It is a milky liquid and quite colorless when applied.

I bought the interior version for less than Rs.400 for a lt.
 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 10:37:36 AM
The first attempts to apply WBPU for finishing, did not go too well. I noticed that the liquid was entering pores of thermocol which meant that a) there would be more consumption and b) the finish would not be smooth.

So I tried another route.

I got hold of thin tissue paper for covering the balsa frames (the one that was used as a material to apply dope) from India Hobby center in Delhi. The intent was to cover the model with tissue and then apply WBPU. Since there was no frame hence the entire paper was getting wet and also since this paper expands when wet, I was having trouble covering large portion. So I came up with a plan......

I cut the tissue into series of 8 inch by 5 inch pcs and then applied a coat of WBPU after slight dilution with water. Then placed the tissue and ironed out the wrinkles from the surface - to the max extent possible. The next tissue was placed with a slight overlap of about 2-3 mm and followed the same process. After the entire surface was covered, 2 coats of diluted wbpu was applied and left to dry.
The finished surface looks like this..... (the second is a close up)


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 10:44:23 AM
Next part was to apply paint.

First  attempt was made with universal stainer mixed with WBPU. I was thinking that maybe both are water based, so the result might be acceptable - turns out I was wrong. Next I got hold of acrylic colors and applied the same with suitable masks and sufficient dilution

The result after the first couple of coats is this.

This is the bottom of the fuse, with color applied except on the battery bay. Notice how tight the paper appears along with the few wrinkles..


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 10:47:03 AM
The wings looks like this....



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 10:53:33 AM
And finally the finished model looks like this......

GOD, Where is the parcel from HC....  :banghead: :banghead:


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 09, 2009, 11:00:04 AM
That looks awesome  :thumbsup:  {:)}


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 09, 2009, 11:32:01 AM
Thanks Anwar!!! Words of encouragement from more experienced folks always help...


Title: Re: Scratch Build - Cub Trainer
Post by: ujjwaana on November 09, 2009, 01:12:24 PM
As they say it - Fundoo Pankaj. Do share the link for the plan etc for RC toddlers like me.
when did you placed HC/HK order ? did you chose EMS or Air parcel ? packages getting held at customs for little less than month is not uncommon.

May be you can still fine tune CG etc in the meanwhile  8)

-Ujjwal


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on November 09, 2009, 01:46:20 PM
Superb!!.. :thumbsup: :thumbsup:

 Must fly better than how it looks.. Enjoy.


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 10, 2009, 09:20:42 AM
Hi Pankaj,

Nice build there :thumbsup:, I just wanted to know How many man hours did you invest in building that plane, and also as Ujjwal requested can you please share the link for the plan? I would also be interested in building it, of course once I get the license that I have been waiting to get for flying in bangalore. :banghead:


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 10, 2009, 10:25:23 AM
Hi Pankaj,

Nice build there :thumbsup:, I just wanted to know How many man hours did you invest in building that plane, and also as Ujjwal requested can you please share the link for the plan? I would also be interested in building it, of course once I get the license that I have been waiting to get for flying in bangalore. :banghead:

Vinay,

Actually I did not count the hours..... there were a lot of them, specially trying to figure out the wing join. I started around end of August and then there was one month where I could not attend to this as I was on tour. My usual time was an hour or two almost every day.

The plan itself was downloaded from rcgroups - the original plan belongs to Scott. I have forgotten the exact location of the plan, but the build log is here http://www.rcgroups.com/forums/showthread.php?t=245311

The plan (which I downloaded from rcgroups ) in pdf form is 1.25mb which I am not able to attach (Anwar !!!! Help ). It called for 6mm depron and since I had 10mm compressed thermocol and 2.5mm biofoam, made some alterations - like increasing the size by about 30% and adding aileron ( hope it flies though). But go ahead and build and do let us all know how things go.....

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 10, 2009, 11:11:15 AM
The plan (which I downloaded from rcgroups ) in pdf form is 1.25mb which I am not able to attach (Anwar !!!! Help ).

Just paste the link to the original PDF, where ever it is.  It does not make any difference to your browser where you download the PDF from, and saves us from being in the shadow of plagiarism  ;)


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 10, 2009, 11:53:00 AM
Anwar,
Like I said, I kind of lost out on the link where the plan was downloaded. Hence was trying to upload a the file itself. BTW, I did mention the original owner and the post where it was downloaded from :) just to be safe.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: ujjwaana on November 10, 2009, 02:16:10 PM
Gosh!! That thread by Scot is two parts of 32 pages each and i have already doenloaded around 30 Zip/PDF/images!! It would be great that people post a consolidated Zip file containing all the files and a Doc form building guide... I know this is much of an ask. Even in SW industry, we barely maintain any decent doc of product containing over a million lines of code!

I would try go thru the entire post and create consolidated package.

-Uj


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 10, 2009, 07:23:46 PM
Would prefer it to be hosted on a free file hosting service, and then we can put a link here, along with proper source/copyright attribution as suggested by Pankaj.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 12, 2009, 08:07:19 PM
Folks some help/ideas required.

BTW, the battery and the rest of the package finally arrived and was trying to fix everything when I got confused on where the balance point should be - 25% of the chord from the LE or 33%? If the bird get slightly tail heavy, then as I see it I have the following options
1) move the battery forward
2) move the wing back
3) redo the tail and try to make it lighter
4) increase the cord
5) add weight to nose.

Which of the options should one chose and why?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on November 12, 2009, 09:31:10 PM
Move the battery forward if possible  Why  the easiest thing to do provided you have space . If that is not enough or possible , I would add  nose weight like the lead you get at Wheel balancing guys  . Normally these two should work for  cases up to  around 45% from LE  .
You should be OK with CG any where between 30 - 35 % from LE.

 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 12, 2009, 09:36:06 PM
Thanks Sai,
One question I was actually trying was why the weight addition instead of moving the wing back? Adjustment in the wing position does not add weight to the model. Is there a problem in doing so?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on November 13, 2009, 06:09:52 AM
From the looks of your models it looks like wing  movement might  not be that easy OR might spoil the aesthetics if that is  a possible option then it is preferred to weight addition


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 13, 2009, 08:43:04 AM

Anyway, finally ordered Lipo from HC. Was wanting to know about A123 cells and how to program the ESC for these, but for the lack of knowledge ordered Lipos instead. Have also ordered TowerPro ESC after seing the pictures of them on Subbu's space shuttle log.

So the order looks like this
  2 x 3AH batteries
  2 x 40A Esc - one extra just in case!!!!
  11x7 props
  50W charger
  charge bag
  4 mm bullet connectors - and some more bits and pcs.....

So another long wait for the materials to arrive - I don;t think they have dispatched it yet.

Pankaj

Folks some help/ideas required.

BTW, the battery and the rest of the package finally arrived.

Pankaj

Hello Mr. Pankaj,

Slightly off topic, looks like it has taken literally 35 days for you to get your package? Just Asking because its been 21 days and Iam still waiting for my package(Air Parcel) from HC. Were all the items available when you checked out or were there any back orders? I was wondering if I should check at the local post office or wait for another week?

~Vinay


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 13, 2009, 10:17:16 AM
Vinay,

In general I have noticed that after the Hongkong post's site says that the material has landed in India, it takes about 25-30 days to land up at my door. This time, the package was possibly opened by the custom authority as the packing was ripped open and the entire parcel was tied by rope. Luckily, all components were intact.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 13, 2009, 12:05:09 PM
Thanks Mr.Pankaj, That clears my major doubt. :)


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 15, 2009, 07:21:24 PM
Hello Mr Pankaj, Exprianced Builders, :)

Prior to getting my radio stuff, I had some time to go through the theory. Iam writing this based on my readings and not based on my experiance(as its 0 :D), All the stuff that I have written below may be totally wrong.

1)As I measured from one of the photos posted here by you. I measured using the scale on my monitor and noted that the right wing is a tad smaller than the left wing? Is this on purpose or PROBABLY due to some inclinaiton occured during taking the photograph. Just a second thought, is it there to counteract the torque or something?

2)From what I measured the ratio of length to breadth is 6.42:1, And based on what you have mentioned on the first page, 46". Based on that Iam calculating the chord length to be approximately 7.1 Inches
  and the area to be 44 X 7 = 308 sq inches. = Approximately 20 Dm. 44" wing span and not 46" because of the curve at the wing ends.
  
3)Considering Approximately a wingloading of 35 to 40 Grams per Dm and since its a trainer let's consider it to be 40 Grams/dm = 40 X 20 = 800 Grams AUW.
And at 35Grams/Dm, lets consider it to be 700 AUW. Considering the AUW from 700 Grams to 800 Grams, It would be equivalent to 1.54 to 1.76 Pounds.

4)Consiering the trainer charecterisitics that it should fly slowly and steadily, the power per pound should be approximately 80Watts that should be around 123 to 140 watts for the above weights. Let it be at 160 watts maximum for now so as to prolong the battery life and keep it light so a small battery would suffice. Since its a trainer we need more thrust than speed. So a lower KV High torque Motor should do fine.

From what I see from your order from HC

  2 x 3AH batteries (Assuming 3S 1P) = http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=9265 = 260Grams.
  
  1 x 40A Esc = http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2165&Product_Name=TURNIGY_Plush_40amp_Speed_Controller = 33 Grams
  
  Considering you ordered this motor = http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7076&Product_Name=TGY_AerodriveXp_SK_Series_35-30_1400Kv_/_470w = 100 Grams Including Prop
  
  4 X 17 Grams Servos = 70 Grams + A reciever 10 Grams So AUW of electronics = 260 + 33 + 100 + 70 + 10 + 27(Misc) = 500 Grams.
    
  Prop 11 X 7. I cant really comment there since Iam unsure of the Motor KV/Model you might have ordered.
  
  That means this allows the AUW of the model Alone to be around 200 to 300 Grams to Fly considerable well and fly at slow speeds.
  
  Unable to calculate flight time due to lack of KV/Motor info.
  
6)I was wondering If the following gear would do:
  
  1 X 1.3 AH = http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=9272 = 115 Grams Battery. = 1.3 X 20C = 26 A peak Discharge current. So its safe for the motor we are using below.
  
  1 X 30 A ESC = 25 Grams
  
  1 X http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2111 = 65 Grams with Prop
  
  3 X 9 Grams HXT Servos = 27 Grams
  
  Prop Size for the above motor
  9x4.7 10.7V 12.2A 8574rpm 730g
  10x3.8 10.4V 16.0A 6717rpm 850g
  
  Since the above thrust is almost equal to the weight of plane calculated above(very good thrust) we need not even go to full throttle to avoid buring the motor or better use a smaller prop.
  
  Now considering the AUW of the electronics I mentioned = 115 + 25 + 65 + 27 + 10 + 18Grams(Miscellaneous, small since smaller elctronics) = 260 Grams.
  
  That means this allows the AUW of the model Alone to be around 440 to 540 Grams to Fly considerable well and fly at slow speeds.
  
  Flight time calculation at half throttle = 70 Watts = 11.1V X 1.3 A = 15 Wh approx. 15/70 = 0.214 * 60 Mins = 12 .8 Mins. Let's consider it to be 11 Mins.
  


Guys all the above calculaitons is based on the Theory I have read and including the electrical losses what so ever. I have NO PRACTICAL EXPERIANCE WHAT SO EVER

Everybody Please COMMENT!!!
Comments are very useful for beginners like myself (:|~

 Ashta Sir, Expecting your comments also, As you are still the only one I have met in person who has built so many planes from Scratch.

  


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 15, 2009, 07:26:14 PM
Now my question is, whats the AUW of the model Alone that you built Pankaj sir? Only you can tell us that. :)

Pankaj sir, looks like you forgot to blur out your phone number ON the parcel Pic  >:D


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 16, 2009, 03:28:23 PM
Dear vinay,
pl pardon me. i am unable to recollect our meeting. pl give some clue.

According to me what you have given below is far more than just theory it is very very practical and true. You have taken so much pain and troubles to go to such details in depth. congrats.
coming to the point. ( pl excuse me, if there are few mistakes, did not spend enough time reading this thread)

1. I went thru quickly the RCGROUPS thread that pankaj has given.
2. This says an auw of 14 OZ aroud 400 grams max.
3. At the begining of the thread Pankaj says it is 1 to 1.2 KG
4. This is too gross a discrepancy. So this plane  show different flying characteristics than what is designed.
5. The gear that you have selected is Good if the plane is in the 15-20 Oz range.
6. The motor could be even blue wonder 1300 KV to make things bit lighter.

in my opinion just like  Wing span/ Chrd dimns etc. weight of the palne is also an importnat (most imp?) spec. to be respected to get the designed results.
ashta





Everybody Please COMMENT!!!
Comments are very useful for beginners like myself (:|~

 Ashta Sir, Expecting your comments also, As you are still the only one I have met in person who has built so many planes from Scratch.

 



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 16, 2009, 09:43:24 PM
Astha/Vinay,

At the start of the thread I had mentioned my assumptions for the weight. I started with a 3S1P 3-5AH rating and then back calculated from there to get a assumption on the weight. Yes, foam is light, but the rest is not, and glue also adds weight.  I started also with a 130-140% model of Scott's design. So a couple of iterations made me realize that the AUW would be 1000gm+

The motor is 1050Kv. The model is http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2100


Whether this will ultimately takeoff? I am hoping it does so :) else it will be back to the drawing board.

In the meantime there is a problem.....

I have purchase DX6i the unit came with AR6200 receiver. The manual says I need to bind the receiver to the Tx, but the diagram is something that I cannot understand. The diagram has a battery connected to a switch with a charge plug where the bind plug is inserted, but I do not have a switch, I have a ESC with BEC. So the direction given does not match with an electric setup with ESC. So how does one bind the RX?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 17, 2009, 11:06:46 AM
OK, bound the Rx to the Tx and here's how
http://www.rcindia.org/beginners-zone/connecting-servo-to-receiver-and-binding/msg8982/#msg8982


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 17, 2009, 01:41:45 PM
dear pankaj,
any way it is a great build and very nice looking plane. All the best for your maiden.
Many times i have saved my bulids by hand launching to tall grass with every thing loaded powered on but zero throttle to test the glide. May be you can try that.
I do not know about Ar6200.

best regards
ashta



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 20, 2009, 12:23:33 PM
All Electrical Gurus

Need help in understanding the LiPO.

In one of the threads, Anwar suggested that I fly the model for about 5 mins and measure the charge that goes in to determine the flying time available. While I have not maidened my model yet, what I did was to wire up the motor and try it out.

The following thing I observed.
If I suddenly apply full throttle in one jerk, the motor produces a high screech and turns in a considerable slow speed and keeps jerking. However, there is no problem if I go from min to max in about 4-5 sec. Is there a problem with the motor?

I had tied the model to a chair (normal wodden dining chair, weighing about 7-8ks) and started applying throttle, at full throttle, the motor began to pull the chair along the floor (very slowly). does the thrust seem good enough to take off a model about 1.1 - 1.2Kg?

I have a fully charged 3C1P at 12.59V as shown by the charger, I run the motor at about half the throttle for 4 mins. The voltage drops to about 11.8 and then when I charge it, the charge that went in was 1666. So how much wattage did my motor draw?

 
The more I get closer to maiden, the more doubt keep coming in my mind...... First model after such a long time, first RC model, first time handling electric ...... excited and stressed out at the same time... :D


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on November 20, 2009, 08:10:49 PM
Have you set up the ESC for max and Min throttle ?

Some ESC's require you to set the Max and Min throttle  position before the Motor is ready for action  should be there in the instructions

When you give a burst what you say should not happen  and the possible explanation is  the current draw is very very high  can't say for sure .

Proping down might be required .



Sai


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 20, 2009, 09:59:34 PM
If I suddenly apply full throttle in one jerk, the motor produces a high screech and turns in a considerable slow speed and keeps jerking. However, there is no problem if I go from min to max in about 4-5 sec. Is there a problem with the motor?

It is possible that the ESC is preventing an overload.  Your setup may be borderline in terms of wattage. Try a smaller prop, if you have one, as a quick test.

I had tied the model to a chair (normal wodden dining chair, weighing about 7-8ks) and started applying throttle, at full throttle, the motor began to pull the chair along the floor (very slowly). does the thrust seem good enough to take off a model about 1.1 - 1.2Kg?

That seems to be pretty good thrust.

I have a fully charged 3C1P at 12.59V as shown by the charger, I run the motor at about half the throttle for 4 mins. The voltage drops to about 11.8 and then when I charge it, the charge that went in was 1666. So how much wattage did my motor draw?
 
The more I get closer to maiden, the more doubt keep coming in my mind...... First model after such a long time, first RC model, first time handling electric ...... excited and stressed out at the same time... :D

Hmm... My suggestion was meant to help determine the safe maximum flying time, and had little to do with wattage (at least I did not intend it that way).  If you can specify the size of your battery (in mah), you can now determine how long you can safely fly. Remember that it is an approximation, as the duration depends on your flying style.  You will get better values if you did a regular flight and then checked the charge that was put back into the battery.

Good luck with your maiden  :thumbsup:


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 21, 2009, 12:51:51 PM
As per spec this motor can take with 3 cell even a 12X8 prop. What prop are u using? if it is smaller, that may not be the problem.
Also look for proper connection, Gold bullet connectors 3 wires, and battery connection Deans. Any loose conact can show up the problem.
I always measure current with different props and ensure with in safe limits on any new electric plane.
 In any case it may be a good idea to have an expreienced flier do the maiden for you.

Wishing you good luck
ashta


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 21, 2009, 07:37:36 PM
Ashta,

If Pankaj is using 11X7 Prop as mentioned in the Previous post then he is getting approximately 1.2 KG of Static Thrust (if run at banglore's altitude.) which is pretty good for the Plane he has designed. Since he has built the plane like a TANK with all the reinforcements, I think it should hold on  ;D

ALSO,
Since the plane has a semi symmetrical aerofoil, what should be the Thrust to weight ratio for a trainer? I read somewhere that the thrust should be atleast 2/3 the weight of the plane for a trainer, Correct me if Iam wrong. :headscratch:

Also is it possible for the Thrust of 1.2KG to pull a 8 KG Chair? ???

Pankaj,
When I measured the Wing span on the monitor with a scale, I noted that the left wing was longer than the right? Is that true, or probably a photography angle mistake?


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 21, 2009, 08:27:17 PM
Battery load....

I programmed the ESC for high voltage threshold, and the cut off (motor speed) to 'cut off'. Then switched on the UP timer on the Rx for timing.

At full throttle, the 3S1P 3000mAH Lipo runs for 4 1/2 mins. The motor gets real hot, but one can touch it. The battery is warm, the esc is around room temperature. BTW kept the ESC outside the model to allow the battery to move forward.

After, the motor cuts off, I put it on charge after a gap of 10 mins. The voltage shows 10.8 with individual battery packs around 3.6 and 3.59

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 21, 2009, 08:30:10 PM
Motor Screeching .... seems to be a timing issue.

by default, the ESC came with LOW timing. the ESC instruction said, change to medium for 6 or higher poles and for better efficiency, change the timing to High. I just changed the timining to High and tried the motor.

When I quickly give the max throttle, there is a slight delay before the motor responds, but there is no screeching noise. I have not run the motor for full battery load, but tried this around 5 times - going from 0% to 100% and back to 0% on the throttle. Everytime the motor responded with a slight delay, but no noise....

I guess, the problem was of timing.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: vinay on November 21, 2009, 09:36:37 PM
Yup, the problem is due to timings, I have read in many forums that increasing the timings will solve problems on higher wattage motor. I wanted to suggest this earlier but since Iam a baby in this field I didnt want to suggest something wrong and burn up you ESC motor >:D

Also Try keeping the ESC in the normal start mode, rather than soft start. This may solve your other problem of delayed starting, If the problem still exists then there may be a problem with compatibility with ESC and motor? ???  :headscratch: Well not sure. ;D Are you using Turnigy plush 40A ESC?

Also High timings are used to get more power to the motor, but it will reduce the efficiency, and will heat up the motor,

Its necessary to keep the timings as low as possible the motor can take without screeching for higher efficiency.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 23, 2009, 10:04:58 PM
Managed to fry atleast something before maiden :banghead: :banghead: :banghead:

http://www.rcindia.org/beginners-zone/fried-motor/msg9174/?topicseen#msg9174


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 24, 2009, 01:35:27 AM
Oops :(

I was going to write that if timing change alone fixed the issue, that would still indicate that you have a border-line power system. 


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 24, 2009, 08:08:26 AM
OK, in case I have a border line power system, how do I figure it out? Any indication (other than a fried motor)? What solves - reduce blade dia or pitch or what?


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on November 24, 2009, 09:35:58 AM
Things getting too hot and the ESC warning you by cutting off are good indications.

Reducing pitch or dia are both helpful.


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 24, 2009, 11:38:37 AM
vinay/pankaj,
1. Sorry to hear that the motor is burned.
2. But it does not matter. it is very easy to rewind the motor. make this opportunity to learn that.
if interseted pl read thru ( may be u hve seen this already)
You can normally finish rewinding it in 30 mins.
3. Some how the whole system is taking toomuch current for sure. Tetsing with out using an ammeter is very risky. Another thing i do is to use bench power supply 12V which can give only 3- 4 amps so that every thing is safe. When u use a large capacity battery, there is no current limit.
4. 75 W per pound should be good enough to get it air born.
5. to pull an 8KG chair, 1.2 kg thrust may be enough. I think that it depends on the friction. For example if the chair has wheels!/ it is on smmoth surface etc.
so one can use a spring weighing m/c and tie one end to the chair and pull. Find out what is the force required.

Pankaj, you can call me 9448073127 if u need any help in rewinding the motor.

ashta




Ashta,

If Pankaj is using 11X7 Prop as mentioned in the Previous post then he is getting approximately 1.2 KG of Static Thrust (if run at banglore's altitude.) which is pretty good for the Plane he has designed. Since he has built the plane like a TANK with all the reinforcements, I think it should hold on  ;D

ALSO,
Since the plane has a semi symmetrical aerofoil, what should be the Thrust to weight ratio for a trainer? I read somewhere that the thrust should be atleast 2/3 the weight of the plane for a trainer, Correct me if Iam wrong. :headscratch:

Also is it possible for the Thrust of 1.2KG to pull a 8 KG Chair? ???

Pankaj,
When I measured the Wing span on the monitor with a scale, I noted that the left wing was longer than the right? Is that true, or probably a photography angle mistake?


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 24, 2009, 05:27:01 PM
dear pankaj,
thanks for talking to me.
From what you said and from the photo of the motor that you have shown, one cannot conclude that the Motor is burned.
So do not dismantle it unless confirmed.
For confirmation u need one more motor and an esc. pl take help from Delhi, fliers.
pl check the motor and the esc seperatley and confrim which one has gone bad.
you need only about a max of 200W to take ur plane airbrne.

best regards
ashta



Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 24, 2009, 06:21:50 PM
Many thanks Ashta, cleared a lot of doubt. Will be much more careful henceforth.
Actually kicking myself in the butt..... I had envisaged that I would end up making mistake - so had ordered 2 lipo, 2 esc, but got only 1 motor...

Anyways ordered one from Sai 2820/6 with a smaller prop, should be good enough replacement. and also would keep the weight same.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on November 24, 2009, 07:07:46 PM
dear pankaj,

you need only about a max of 200W to take ur plane airbrne.

best regards
ashta


Pankaj ,
2820/6  is a 555 watts  and weighs 130 gms 2217 is around 300 watts weighing 70 gms  this motor is adequate power for my multiplex easy cub.

I will be shipping tomorrow think it over .
Rgds
Sai


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 24, 2009, 09:27:42 PM
I am not sure... reason is that my earlier motor weighs 135gms and with this weight, the plane was balancing around 25-30% mark - with the battery right up in front. If I takeout about 60gm of weight I think I would either have to redo the tail part or add extra weight to the nose.

Since redoing the tail part seems cumbersome at this moment, I thought that if I am adding extra weight might as well be productive - just in case I require and hence my decision to opt for 2820 when 70gm motor could have done..

So do you agree? if not then I shall change the order.




Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on November 25, 2009, 05:26:47 PM
Many thanks Ashta, cleared a lot of doubt. Will be much more careful henceforth.
Actually kicking myself in the butt..... I had envisaged that I would end up making mistake - so had ordered 2 lipo, 2 esc, but got only 1 motor...

Anyways ordered one from Sai 2820/6 with a smaller prop, should be good enough replacement. and also would keep the weight same.

Pankaj

dear pankaj,
i got the following spec for the motor from the net.
Pl note 37A @60seconds.

Be exremely carefull, while doing static test.

al the best to u

ashta


"
For sport and aerobatic models weighing 2-6 lbs. The XTRM 2820/06 is a 1000 KV Brushless Outrunner with a current capacity of 37 amps @ 60 seconds. A maximum efficiency of 82%, a no load current @ 10vdc of 2 amps and an internal resistance of 59 Mohms. This outrunner has a 4mm shaft and is designed to run on 8-14 NiCad/NiMH cells or 3-5 LiPo cells. Includes Radial Mount, 4mm Collet type prop adapter and 3.5mm Gold Plated Bullet Connectors. This motor weighs 5.1 oz. and the dimensions are 35 x 45mm.

Recommended Prop:

11x6 on 3 cells
13x6 APC e on 3 cells = 69 oz. thrust
10x5 on 4 cells

Recommended Model Weight:

1000 - 2500 grams (35 - 88 oz.)

Recommended ESC:

XTRM 50A


Title: Re: Scratch Build - Cub Trainer
Post by: rcforall on November 25, 2009, 06:49:50 PM
Yes Same specs as the Manufacturer in China is the same Xtrm is another brand name like BP, Suppo , Grayson etc
http://hangitrc-estore.webasyst.net/shop/category/brushless-combos/

Sai


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on November 25, 2009, 08:43:15 PM
Astha,
I do not plan to load more than 10x5 prop on 3S1P so I guess, the current would be lot less and so would the wattage....

While we are waiting for the motor to arrive, maybe you could start another thread on motor repair ;)

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 03, 2009, 09:52:47 AM
Maiden Unsuccessful. :( :( :(

I did not know whether hand launching could have been done, so I tried ground take off - maybe the surface was uneven or what I did not understand, but the moment the model gathered speed, it started wobbling left-right and then it lifted only to sharply turn left and crash / cartwheel ....

awaiting suggestions on what all could be wrong.


Title: Re: Scratch Build - Cub Trainer
Post by: chanvivek on December 03, 2009, 09:58:30 AM
sorry about your crash pankaj!! My only doubt regarding this incident (provided the build is proper) is that you must have pulled up elevator before the plane picked up enough airspeed which would cause the exact behavior which you have described!! I could be wrong though!!

- Chan


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on December 03, 2009, 10:42:46 AM
Oops  :(

It would be better if you pick an area with tall grass next time to see if the craft is underpowered (as described by Ashta).  Launch it into the tall grass and see if there is enough power to continue flying.  If not, all that is going to happen is a soft crash into tall grass.


Title: Re: Scratch Build - Cub Trainer
Post by: tg on December 03, 2009, 03:28:54 PM
Should check the landing gear, the wings being level and aligned with the rest of the airframe and same for rudder, elevator. Why not post pics of the model now?


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on December 03, 2009, 05:49:21 PM
That model was too good to have a crash. As it is said in SPADs if it looks about right (TLAR) then it will fly.

As Chan said, I think you took off too early and the airspeed wasn't enough. It sounds like a tip stall and it could happen even in take-off esp when there isn't enough airspeed. Basically, one half of your wing is not producing the required lift. Did you do a take-off roll on cross wind?

-Ismail


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 04, 2009, 10:26:33 AM
Ismile/Chan,

Yesterday was a relatively no wind situation in the ground from where I was trying to take off. I applied half the throttle with 10x5 prop, it shot off like a bullet and then started wobbling left/right and it was lifting off the ground on its own when I applied little bit of elev and then I think, it stalled.

Now analysing, the possibilities I can think of are as follows
1) uneven runaway was causing the wobble
2) alternative, the aerofoil is uneven (hand made so at best could be an approx match) and/or the flaperons were not aligned.
3) I applied too much elev at low speed hence the stall. In an attempt to startoff, I did not even apply flaps which could have provided the necessary lift. This is the first attempt at RC and the feeling is totally different from when one is on sim.

While constructing, I had not fortified the firewall too much, so when the model cartwheeled and the prop hit the ground, the firewall broke and so did the cowl. With that it ripped off the 2-side tape holding the ESC. Also the undercarriage was held lightly so the base came off taking some thermocol with it. 

It seemed a mess at the first glance, but after my nerves calmed down, I noticed that the damage is very little. Have managed to get the firewall back in action in about 1 hour, rest should be done today/tomorrow kind of a timeframe

Now, I think I shall do the following -

First find a reasonably even surface and just let the model run along and observe and report back to the forum for ideas, OR, will try to hand-launch with full throttle and figure out what happens and report. Third option?? open to suggestions


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on December 07, 2009, 12:04:14 PM
dear pankaj,
i have the following suggestion.
1. Arm the Plane fully with the Battery/ RCVr etc.
2. Find a place with lot of grass to take the weight of the plane.
3. With all the control surface aligned, do a glide test, several times by just throwing the plane in to the wind, with out power and carefully see how it glides. By looking at it normally one can judge very well, how it will fly.
4. For example if the plane has a tendency to turn left/ nose down etc, you will get that indication when you throw the plane.
4. Once you sort out these issues, the plane will generally fly well,  If you do not have much thrust angle issues.
5. After this you can again throw the plane with Power say half the throttle (You will gradually get a feeling, when you hold the plane and give throttle about the thrust) and see how it goes and cut the throttle soon so that it will glide in to the grass.
6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 07, 2009, 12:10:17 PM
dear pankaj,
i have the following suggestion.

6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta


Hmm......
Finding a suitable high-grass field is an issue in Delhi - at least not within 15km radius from where I stay

Beside, I am kind of worried about chucking a 1kg+ plane into ground, as a plane of this weight would require some speed even to glide.
Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: tg on December 07, 2009, 12:34:02 PM
This is what I had asked long back in another thread. How do ppl do the initial trimming of  big model planes. I agree, many hours of work and/or lots of Rs./- being tossed into the sky isn;t a great approach.  ???


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on December 07, 2009, 02:51:06 PM
While it may sound strange, the actual method used in our fields are something like this.

1) Make sure the CG is about right on the ground.  If not, fix it by moving things around, or adding weight.

2) If you are not confident about handling pretty much any emergency, hand it over to some really good flyer around.  He does the initial flight, and adjusts the trims till the plane flies level pretty much hands off.  A runway of good size (ie, long!) is a useful thing, since it helps to gauge the speed the model can attain on the ground itself.  BTW, this is usually for models that are .40 size or higher.

For nitro models, there is the additional checking of whether the engine will quit at different orientations by tilting the aircraft by hand in different directions as some high throttle.

For smaller models (electrics), it is just a matter of some one experienced gauging if there is enough thrust by holding the model in their hands at full throttle, and the other big checks are making sure the CG and control surfaces are aligned.  After that, the experienced flyer takes off, and deals with any issues with his thumbs.  After all "trim" is just the same as "certain amounts of appropriate controls kept applied". The flyer then puts in the appropriate amounts of whatever trim is needed on each control/channel in the TX, while the model is still in the air.





Title: Re: Scratch Build - Cub Trainer
Post by: anwar on December 08, 2009, 12:09:40 PM
BTW, tall grass seems the best option if you are doing test flights on your own, and you are not experienced enough to handle eventualities.  We do not have that around us either :(


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on December 08, 2009, 01:14:29 PM
dear pankaj,
i have the following suggestion.

6. You can do all these with out damaging the plane, if you are able to locate a place with lot of tall grass. Bangalore Jakkur has lot of grass and it works very well there.

7. It may not be a good idea to try take off from ground initially.
ashta


Hmm......
Finding a suitable high-grass field is an issue in Delhi - at least not within 15km radius from where I stay

Beside, I am kind of worried about chucking a 1kg+ plane into ground, as a plane of this weight would require some speed even to glide.
Pankaj

The idea is to throw the plane so that it can glide for say 10 -15 feet. You can use any thing like grass, a hay stack or even paddy field ( be carefull if it is watery). Prcatically what i do is sit down holding the plane up and slowly throw it and see..
As long as it is a trainer, it should fly say at 10KMH and is OK for test glide.








Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 08, 2009, 02:41:47 PM
Repair update...

Finished the first round of repairs and took it for field testing. The idea was to try and let the model roll in the ground to see whether or not the wheels are aligned. Suddenly the model collapsed. That is when I noticed one major build flaw in the fuse ---- The mounting of undercarriage.

The basic flaw that I did not use spring steel/piano wire for UC, instead went ahead and got hold of hard plastic strips. This I joined using  3" x 1" x 3mm balsa  :banghead: :banghead: :banghead: It simply does not have the holding strength to counter the force generated by the length of the UC - simply ripped off at the slightest jerk.

Since to insert a piano wire UC strut was not possible, I replaced the 3"x1" balsa mount with a bakelite peice of similar size, bolted the UC struts and then pasted 2 cycle spoke length wise across the fuse with epoxy and reinforced with 3" transparent tape. 

Another major issue discovered today is that the material I have used may not be biofoam/depron. I enquired with the BioPac office in Mumbai and they confirmed that they do not have resellers in Delhi. So, the vendor who sold me the foam sheet did not tell the truth (nothing new in Delhi) and all the while I have been building with a material that just another form of thermocol and hence is very very brittle.

I am just wondering whether I need to start all over again.....

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: tg on December 08, 2009, 02:58:03 PM
Foam of any type needs bracing and let me add, depron is brittle, unlike thermocole which is much more flexible and the high density versions are even better.


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 15, 2009, 12:18:55 PM
 :headscratch: :headscratch: :headscratch:Something is wrong and I am unable to get a hang of it.

Last Sunday went in for another field trial, located a fairly flat ground and started to test for speed taxi. Somehow, still not able to come to terms of hand-launching this bird.

When I the model starts to move slowly, it is fine, the moment I apply substantial throttle - it spins to the left. Slight adjustment of the tail wheel and the model spins to right on throttle. I figure this could be a combination of 2 problems a) wheel alignment and b)motor alignment.

So I brought the plane back and tested the same without the wings on the home floor and without the tail wheel. This time the tendency was to waver to right. So I add washers on the right side mount and adjust the wheels slightly. Now, the plane still tries to turn right, but this tendency is when the speed is low, when I apply throttle, its almosts straight.

Question is that when building a scratch model, how does one get on with the alignments? Even when following a plan, the cuts and thickness is not 100% accurate. So what precaution one should take?


Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on December 15, 2009, 12:43:38 PM
little right/ left/up/down thrust issues exist in all planes. What i do for a tractor set up is to give some 2 deg down and 1 or 2 degree right thrust and assemble.
Rest alignments problems if any gets corrected during the trim. so do not give toomuch focus for this.
just make the plane visually straight and clean.


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on December 15, 2009, 01:03:03 PM
What prop size are you using on this model? Not that this is important but usually the wing span should be more than 3 times the prop dia. This will avoid any torque effect on the model once the wing gains lift.

The motor mounting angle (5 deg or so) would not have any effect on the model when tracking on ground. I suspect that your landing gear wheel does not have enough toe-in. Go have a look behind a load carrying auto. (Ape from bajaj??) and you would clearly see what I mean. IOW, when you look at the face of the model the two wheels should converge at an angle of 5 to 10 degrees.

Here is a good picture to explain it better:
http://www.spadtothebone.com/misc/toein.htm

-Ismail


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 15, 2009, 03:20:22 PM
Thanks Izmile, I have an direct opposite of a toe in :D. I guess that needs to be corrected asap.

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on December 15, 2009, 10:05:39 PM
OK, corrected the wheel mount to give it a toe-in.

Noticed something peculiar. when it taxis slowly, the plane has a tendency to turn right sharply, but when i apply substantial throttle, then it goes almost straight.

Anyone knows what the problem is?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: izmile on December 15, 2009, 10:15:58 PM
Check your tail wheel.

 BTW, its very difficult to tune the landing gear. Of all my builds the weakest link is the landing gear. Once you fine tune it, it would not last forever. The next landing (or hard landing) it will change and you would keep tinkering with it. I would suggest you to go and fly rather than look for 100% perfection. It simply dosen't exist.


Title: Re: Scratch Build - Cub Trainer
Post by: anwar on December 15, 2009, 11:17:12 PM
BTW, its very difficult to tune the landing gear.

I would suggest you to go and fly rather than look for 100% perfection. It simply dosen't exist.

+1. 

My experience is that you can get a decent level of landing gear accuracy on the bigger planes. 

On the smaller ones, think of them as just something to prevent the belly from rubbing on the ground.  On these (especially foamies), rudder action is your friend in terms of steering on the ground (instead of relying on any wheel).


Title: Re: Scratch Build - Cub Trainer
Post by: tg on December 16, 2009, 11:52:57 AM
hand launch??


Title: Re: Scratch Build - Cub Trainer
Post by: Ashta on December 19, 2009, 05:07:05 PM
from my experienec on electrics, i never try to taxi it for long distance. i ensure that it takes off at max of 10 feet and more like 3-4 feet most of the times.
so only that much accuracy reqmnts, in terms of wheel alignments.
if the plane has enough thrust to weight ratio, that much should be good enough. mainly landing wheels in that case comes handy more for a proper landing and saving the props.
with a bit experience or with the help of an experienced pilot, one will easily get a feel about it once u hold the plane in your hand and slowly increase the throttle.
ashta




OK, corrected the wheel mount to give it a toe-in.

Noticed something peculiar. when it taxis slowly, the plane has a tendency to turn right sharply, but when i apply substantial throttle, then it goes almost straight.

Anyone knows what the problem is?

Pankaj


Title: Re: Scratch Build - Cub Trainer
Post by: PankajC on February 07, 2010, 07:46:44 PM
This model discarded ... another started here :

http://www.rcindia.org/self-designed-diy-and-college-projects/scratch-build-trainer-part2/


Title: Re: Scratch Build - Cub Trainer
Post by: alok roxx on May 30, 2011, 09:06:51 PM
umm, pankaj sir, could u tell me the inclination angle of the wings with the horizontal?? 
the general stats like wingspan and weight would help too.