Tomorrow we will complete the glider.
Please give me a feedback :
a) ok
b) too easy , I knew it all, waste of time.
c) helpful?
d) any other feedback, please

modified thread reply #66

A CLARIFICATION

STAB TILT

I had not mentioned this so far, as in the initial stages I feel it is more important that the tail parts are perpendicular to each other, than to incorporate more advanced features.

However, since it has been mentioned, let me explain.

Stab tilt means the stab is installed on the fuselage with one tip higher than the other (say 1/8” for this size). It makes the model turn towards the higher tip during glide.

Normally we would use rudder to turn (in a model without ailerons)
This works ok on a chuck or hand launch glider.
In a catapult glider, the launch speed is several times the glide speed.
So the rudder offset required for turn in the glide has excessive effect at launch speed.

What we need is a method to have a turn in the glide without excessive turn at launch.
This achieved with stab tilt.
In the glide, the speed is low, so to remain aloft, the model flies at a high angle of attack.
Actually the model is in a more or less horizonal attitude. But because it is descending, the airflow is not head on, but slightly from below. When this upward airflow hits a tilted stab, it produces a small sideways component. A stab with left tip higher will move to the right, causing the model to turn left.
This is used for turn during glide.

In the launch, the speed is high, so the model needs only a small angle of attack.
The airflow is therefore nearly head on, and the sideways effect of the tilted stab is negligible.

In a nutshell, stab tilt is a way to have a turn in the glide without excessive turn at launch.

 As Mr. Iyer concludes "In a nutshell, stab tilt is a way to have a turn in the glide without excessive turn at launch.".

So, in a CLG, rudder is effective during launch at high speeds and stab tilt is effective at low gliding speeds. So the piece of ruder tab cannot be too big. The dimensions given are first guess. Hence stuck with glue stick, not CA. You may have to modify it.

In a CLG, to glide well in circles (turn) , it has been known not to depend on the rudder as it can lead to spiral in.

Wing Dihedral is very vital, make sure you get it exact. your dihedral angles are already made by Mr. Iyer.

Lay the the two halves very close on a tape. Make a carboard piece three inches tall. Before adding any glue just move one half up and assure that it bends to exact 3 inches while the other is flat on the table. I would tape the flat piece so it does not move on you.

At this time please observe that when you prop the the wing halves together at 3", THERE is no visible gap between the two halves which will now be glued. They must mate to a single joint, see photo below.

When happy glue the leading edges and trailing edge with CA and make sure the upper half is still sitting at 3 inches. When satisfied, glue the mid portion of the wing and let the CA cure for about 2 minutes. Your dihedral is complete, gently remove the tape from the wing

Photos:

Now we have to install the wing onto the fuse. But your wing has a V shape and needs to be glued onto a flat fuse. So tape a nail file on the table and move the wing gently back and forth on it to produce a flat at the V. Be gentle and check several times that you are not removing too much wood. You just want a flat that you can feel on your finger tips. Go very slow on this step and check often. The photo below may give an illusion that on half of the wing is flat on the table. Both halves are off the table, you sanding with the wing perpendicular (straight up on the V ) on the table.

Producing a flat:

Now comes a very vital gluing of the wing to the fuse. Trace the fuselage on a thick carboard. NOW is the TIME to measure the fuse height ( from bottom to top) where the leading edge and trailing edge will be glued. They must be EQUAL. If at all, the trailing edge maybe a bit lower than the LE height, BUT not by much, a difference about the thickness of a hair. In no case the fuse height at LE on the fuse be higher than TE height.

Add 1 and 1/2 inch to the traced fuse (dihedral is 1.5 inches on each tip). Cut out the template, then cut it at the center so you get two, one for each tip.

Make sure the fuse is again taped perpendicular  to your flat building board or mat. Use a glue stick and rub it two or three swipes on the the fuse between where the LE and TE will be glued. Mount the wing on the fuse. Use the toothpick method to put CA on the TE and LE of the wing. Let it cure. See photo below

A GOOD TIME TO CHECK AND MAKE SURE THAT THE DISTANCE BETWEEN THE WING LE AND STAB TE IS 3.5 INCHES.

Mr Iyer has already marked these on your fuse.

Photos:

After the glue is set at the both the LE and TE , remove the glider from mat. Now put CA at the remainder of the wing from the bottom. This is called fillet,  Your glue stick glue should hold the wing correctly.

Now the time has come to install the Washin on LEFT SIDE OF THE WING ONLY.

From your good match sticks cut a piece gently that is 2 cms long, 2 mm wide and about 1 mm thick. Use the glue stick again and glue it away from fuse at a distance of 6 cm from the fuse. Again, vital that you use the glue stick as it may have to be modified in the trimming and gliding phase.

Balance the plane.

Mr. Iyer has included (I think) a pin with a thread on it. Pierce the pin at the CG location which is exactly 1 and 1/8 inch from the wing TE. Take a bit of clay and roll it into a cylinder. Place the clay on TOP of  the fuse nose. Add and subtract as needed small amounts of clay so that the glider balances with a slight nose downwards about a couple degrees, NOT Much more that.

This is also the time to assure that one half of the wing is not heavier than the other. If the left side is slightly down, that maybe OK. If the right side is heavy make a note of it. I am sure it will balance horizontally from wing tip to wing tip flat.

It is important that you put the clay so that it does not touch lower end of the fuse. During gliding and testing or even normal flying, when the glider touches the ground, the clay will either pick up dust  or rub off and you will wonder why the glider is no longer flying correctly.

Also, adjust the CG by putting the clay a bit behind the nose as seen in the photo. During glide test adjusting, if you need more nose weight, just move the clay 1 mm forward each time. If it dives, move the clay 1 mm in each step to the back. This way you are not guessing how much is too much, add or subtract. Adding and subtracting clay can be a frustrating experience, but here you are just moving the clay pillow back and forth.

Congratulation.

You have now completed building your glider with the stab tilt, washin, rudder off set and correct CG.

Next we get into gliding and trimming.

Hope you took the time for your build and measured each critical dimensions correctly and that using the glue stick and toothpick for CA initially has helped you to get a light and true plane which will be easier to trim and glide.

PS : Resist the urge to glide the model inside your house. You will ding it or worst break it.

You can wrap around clay with cello tape to keep clay in place  even during hard landing.  You can do this after you are satisfied with the balancing.

@ Dreamliner: Excellent idea and a  good point. That will definitely do it. But we are trying to keep overall weight down and fewer parts too.

My glider took 0.5 grams of clay to balance it. So very small quantities will be needed in Mr. Iyer's kit.

CLARIFICATION

In elucidating the build process in detail, some new issues have gotten introduced, that I had not mentioned earlier.

So let me put the concepts into a logical sequence.

1. For a newcomer to the hobby, a chuck glider is the most inexpensive introduction
2. It should be based on a known successful design
3. A kit is easier than building from scratch
4. An ARF kit saves the newcomer a lot of work, and can be ready in a few minutes

My kit meets these criteria.

Now we come to assembly, which involves:

5. Sticking the wing halves together at the correct dihedral angle. In the kit, the joining surfaces have already been sanded to the correct angle. And the wing halves are temporarily taped at the bottom. All that is required is to keep one panel flat, lift the other tip 3”, and glue the joint.

6. Attaching fin to fuselage, ensuring that it is upright and dead straight. Already done in the kit.

7. Attaching the stab to the fuselage. I’ve recommended that it be perpendicular to the fuselage/fin.
No need for stab tilt at this stage. (More on this later)

8. Attaching wings to fuselage.
You can sand a little flat at the bottom of the wing centre, to increase the contact area.
Align the wing centre line accurately with the fuselage (ie, centered on the fuselage and trailing edge perpendicular to fuselage.
Glue initially only at leading edge and trailing edge with small drops of Feviquik.
Check alignment.
Then run a bead of glue down the bottom of the wing fuselage joint.
I had suggested Feviquik, but due to lack of contact area, Allfix (from Fevicol) or Fevicol may be better.

9. Balance. Stick a pin into the top of the wing centre 1.75” back fromthe leading edge, same as 1.25” ahead of the trailing edge. Add nose weight (with clay provided in kit) till it balances level.

Now its ready for a test glide

Next: How to test glide

Much later: use of trim tab wedges, stab tilt, washin etc.
As these are things that come into play only after the test glide is satisfactory.

 

Hi all,

Very comprehensive and clear build and trim instructions by Free Flight and further concept elucidation and applicability of instructions to the kit by KK.
I learnt quite a few things too regarding CLGs.
It can't get better than this.
And this is what any forum should be about - sharing expertise and experience.
Reminds me of how I was struggling in getting even 15 secs on rubber powered models - and was the mentored by Bill Gowen - one of the masters of indoor on the Hippocketaeronautics forum - for almost 4 months -  at the end of which there was that eureka moment when it all came together.
Kudos to KK and Free Flight.
I sincerely hope this effort triggers at least a few to delve deeper into HLG and CLG - which is a world by itself.
Regards

Wow! Learned a LOT ! stab tilt , washin etc ... - new insights . Very thankful  for properly guiding us .

Thanks Glidiator and S174 for the your kind words. So let's have fun flying this plane.

I have made an assumption (sorry) that all of you are right handed. If you are left handed, your changes will be the opposite. Right and left as discussed  are from the pilot's point of view ( In any model flying). Assume you are the pilot sitting in the cockpit facing the nose. Your right is the glider right.

In a CLG flight there are 3 steps :
1) The launch with the rubber band that goes at extremely high speeds. Small wraps will have a distinct effect here.  This called the launch phase.
2) Once the glider reaches to the top called apex, it will slide its left wing down ( so called roll out) . This called transition.
3) Start gliding at a much lower speed. This the glide phase.

So how does this all look when all is said and done. See my video below. When you play it on Youtube, go to "Full Screen" and in setting put the "playback speed" at 0.25 lowest setting and watch the short video. You will see the glider shoots up to the right , transitions or falls on the left wing level and starts the glide with left turn. All this WITHOUT loosing height. That is vital

This called a right-left CLG flying for a right handed person. For a left handed person it will be a left-right CLG flying.

PS : Notice in the video that the bottom of my wing is colored BLACK. This so that it stands out clear in its attitude against a sunny sky. The red color on top of the wing is so that it visible clearly on ground and I can find it. Do not go heavy on the color , just smartly with a non water based marker pen. Keep that weight down on the glider.

Hold on guys. One more step before you go out for the glide test. At home, check once again that :
1) No warps have been introduced in the wing, stab and rudder
2) Balance on pin and thread. Assure the CG is correct !

Now make a small box to carry : a) extra clay b) Feviquick and a GLUE Stick for sure , c) small match  sticks already cut in similar dimensions as in build d) An extra set of rubber bands e) The nail file or sandpaper on a popsicle ( ice cream) stick. I would advise you carry the plane to the field in a box as I have broken it once just carrying it to the field . Very upsetting.

Pick a good place to fly. Prefer a good open park with few or no  trees.  The field must be grassy, not concrete, gravel, stones or black road top (asphalt) . Our planes do not like hard ground to come down upon. I only know Mumbai. So I would go to either Mahalaxmi race course, gym khanna grounds, Azad or Oval maidan ( next to the university tower) or similar places.

Finally, pick a very calm day, hardly any wind. Your first glide test must be in the late evening . When you get to the field, drop a leaf or bundle of grass from the ground from shoulder height. It must fall within 4 feet of you. Note the direction in which it fell. That is where the gentle breeze is coming from. You WILL LAUNCH directly into the gentle breeze.

A free flight pilot must develop to be patient. I watch the weather everyday, when it is calm , I pack my box and go to fly.

READY ! Let us go.

The Glide Test :

1) Face the breeze to test glide, i.e., launch the glider directly into the wind.
2) Raise the glider to eye level , so you can see that you are launching it at a correct angle nose down and WINGS LEVEL..
3) Aim a point about 30 feet away from you and push the glider gently with your arm , do not flick it with your wrist. PRACTICE.
4) When launching make sure that the nose is VERY slightly down , definitely not up.

If all goes well. you should see that the glider is " floating" down gently and perhaps a little turn to the left. As you launch it gently the glider will perhaps raise it nose VERY slightly as it is going forward.  That is good, means you have enough decalage (more on that later).

Your glider should land about 30 to 40 feet away from you. Less is not so good, but longer means your glider is very close to being ready for launch trims.

If that happens, you have successfully completed your test glide. It has never happened to me ever on the first glide even though , say, I have built Tich CLG about 5 times in my life.  

NOW : Very Vital :  Do not make judgements based on a single glide. Repeat this test glide , I do it 5 times, each time expecting the same glide pattern. Do not make changes based on a SINGLE GLIDE. Moreover, make only one change at a time. Else you do not know what worked or if the change was correct or ENOUGH.

Attached below is the link for Glider testing. This one is for the indoor CLG ( Where the indoor guys call it ELG or Elastic Launch Gliders) and they fly Right-Right. We want a left turn as we will fly outdoors RIGHT-LEFT pattern outside.  But the video  shows what a stall is, what a dive is and why.

In this Video They adjust wing differently than we will. Plus you have no Stab tilt as instructed by Mr. Iyer. Your left turn will be adjusted by a clay on the left wing tip. DISREGARD those parts of the video.

So like me, you did not get a perfect glide. That is OK.

1)If the glider stalled , add a bit of clay to the nose , each time about the size of a pin head. ( Remember : Patience Development). If you used my technique in the build, slide the clay to the front to the nose, about 1 mm at a time. Each time confirm the glide, that is you made the correct change and got the same response several times.

2) If the glider dived, remove a small bit of clay (again about a pin head) and re establish the glide.
 
3) It is diving to the right or left at once. Not good. Talk to us and we can have another discussion on that.  Probably a warp has developed mainly at the rudder, rarely at the wings as Mr. Iyer has doped and finished your wings. ALSO CHECK : Make sure that the WASHIN wedge we put on the left wing with a glue stick has NOT FALLEN OFF.

Now our glider needs to have a gentle LEFT turn as we fly Right-Left. This will be achieved by putting a very small amount of clay on the lower side of the left wing tip. Start with about 2 pin head size and re establish the glide. At the end of say 20 to 30 feet are you getting a gentle left turn with a nice floaty glide?

If the answer is yes Congratulations on the GLIDE Test Part.

Please note : GLIDE Test is essential to move forward. But a good glide test is only the beginning and NO GARUNTEE that the CLG will fly good. So next we work on the launch Phase. More on that tomorrow as you digest and practice this.