RC India

Any one tried Bungee launch on an electric glider  ??? :headscratch:

yes,
i tried on my dynaflite daydream,
broke the wing  :violent: :violent:
there is a special attachment to be attached to the wing tip to disguss launch !!
is bungee launch similar to disguss launch ??? :discuss: :discuss:

You mean discus launch??, yes a thick dowel is passed through about 1 - 2 inches inside of the wing tip so that about 1 inch extends above and below the wing.

Bungee launch is not like a discus launch. A launching system called high start is used to launch sail planes to heights like 500 ft are so.

Rao

Mr Rao is absolutely Right  Bungee launch is a system for launching Gliders and even EDF's  as shown in this thread and the Video below  :

http://www.rc-airplane-world.com/launching-rc-gliders.html#bungee

http://www.youtube.com/watch?v=faDb3WIjVHI

I am looking at this seriously for  getting more time endurance   in the case of a glider .

I might be wrong  but I am assuming that in the case of  Gliders  due to the design  and large wing spans  a good bit of the current actually consumed by the glider  is on  take off and gaining  altitude , hence should we be able to give the aircraft a High Start  by using a Bungee launcher we could conserve a good bit of this power  as the motors could be turned on just enough ( say around 1/2 or 1/4th throttle )  to soar.
Assuming you use a low KV ( around 1000 KV )  which  consume relatively low current  we can then extend the  flying time ( endurance ) of the glider  by around 20 - 25 % .

Should be useful if you ever think of a SPAD cularis  >:D :headscratch: >:D

Amir ,
You cannot discuss launch any glider  they have to be designed for discuss launch  , check it out at the link in the above post

ok.
i have done bungee launch also on my daydream..
but the experience was not more satisfying than a bl motor.
if u r planning for it then i wud suggest to use motor only,

Amir ,
Since you say you did bungee launch I would like to know a few info.

1) What was the total length of the Byngee
2) What was the length of the stretchable cord
3) What was the length of the non stretchable Nylon cord
4) What was the ratio of 2) : 3) above
5) what was the percentage of elongation possible
6) what was the AUW  and Wing Span of the glider you attempted to launch.

The reason I am asking this is because  from what I have read these are technical parameters that are important when it come to bungee launching

eg the elongation is normally 300 % which means if the total length of the Bungee is 100 ft then the glider has to be launched with the bungee stretched to a length of around 300 ft . Normally if the stretchable length is around 10 ft then the nylon length has to be around 100 ft .

Sai

1:3, arnd 300 feet total length

stretched or without stretch
I have added some other factors what is the material of the stretchable part  ???

i dnt remember exactly.,
it was ready made one of mr. Gaurav
i think he got frm hobbico.
strechible part u can use petrol fuel pipe used in bikes.. but its diff to arrange such huge length.

Is the question itself not incorrect?
Why would one need to bungee launch an electric glider? I presume if it is an elecric powered it would be capable of propulsion?

Capt ,
Read further down the reason for this question is explained :

Quote
I might be wrong  but I am assuming that in the case of  Gliders  due to the design  and large wing spans  a good bit of the current actually consumed by the glider  is on  take off and gaining  altitude , hence should we be able to give the aircraft a High Start  by using a Bungee launcher we could conserve a good bit of this power  as the motors could be turned on just enough ( say around 1/2 or 1/4th throttle )  to soar.
Assuming you use a low KV ( around 1000 KV )  which  consume relatively low current  we can then extend the  flying time ( endurance ) of the glider  by around 20 - 25 % .
Un quote

BTW  not only are electric gliders bungee launched  so are EDF Planes .

The technique of doing this is called "" HIGH START ""  the motors are switched on after the bungee drops so it is like a giving the glider momentum without using battery

Helps in reducing power drain for take off which  is normally the highest rate of discharge on the  batteries during the entire sortie.

sai

Rc hybrid : rubber + electric !!

yes seems a viable option for electrics as the motor can be started up at any time during the flight.

I sure am going to try it some time soon

sai

Sai sir,
Thanks for clarifying, since the reasons were not mentioned i had to ask that.
Now coming to the very reason why EDF' use the bungee to launch is not to conserve energy and prolong flight time alone but also due to the fact that the EDF alone is incapable of accelarting the planes to flying speed on takeoff and hence the additional/lone boost froma length of rubber. Once the plane is at flying speed the EDF can sustain it as when flying the blades unlaod sufficently to rev up more and deliver higher thrust.

Also you do not need to use your motor at all when high starting (unless your length of rubber is old and weary and no longer up to its task ;)) as the high start would impart enough velocity to the projectile being catapulted      

Could not wait for a glider to try the high start .

 >:D So we did a small mod to my good old faithful Multiplex easy cub by attaching a"  L " hook made from cycle spoke to the bottom of the fuse at the CG Point . Attached the Bungee Launcher with a Parachute to the hook , Hammered in a  steel rod into the ground stretched the Bungee launcher  to around 250 - 300 ft  and let go the easy cub   :giggle:

This technique can surely give you a "" High ""  ;) :D  Start  .

It was exciting  with every try we improved  and in the 4th try we  achieved around  60 to 70 ft  altitude without power till we turned on the motor after the bungee detached itself 1/2 throttle was enough to maintain the altitude and glide into headwind .

This was with a light plane like Easy cub , hence I see great potential to used this on heavier Powered electric gliders like the easy glider , cularis etc .
The critical part here is the L hook has to made in such a way that  with a slight up elevator  at the top end of the launch the bungee chute should slip off other wise the results could be a disaster.
On 2 attempts the bungee slipped of early   8-)

Sai

Description in words is not enough  >:(  Where are the videos  :P

No Videos this time , next time may be forgot to take the camera  :violent:

sai from where did you get the bungee launch setup ( home made ??? )

I have used a Hi-Start for over 200 flight on my Dynaflite Daydream glider.
Though I am sure you must have searched the basics of it on the net, here are a few details from my setup :
1. Mine has a 350 feet of fishing line ( nylon twine )  and 100 feet of surgical rubber tubing.
2. At the field i clamp the spool to the ground with a hook and then attach the twine to the airplane via a hook , located at CG
3. I stretch the rubber tubing to 3 times. ie total length : 750 feet. Launch the plane into the wind. Usually takes my glider up to a good height, and if its a good day (thermals), i have had upto 10 minutes of flight.

I still love glider flying, and i believe it teaches a lot about flying. How to balance it, how it feel the wind affecting the plane, how to reduce drag . With a motor upfront, you would not be able to appreciate these subtle aspects of flying.

Here is a high start from Tower: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXE636&P=ML
I have one of these as well and they work great.

-Gaurav

Sahil ,
This is the one I have :
http://www.r2hobbies.com/proddetail.php?prod=rcps71902

But after having a look at it I think making a home made one should be easy , I plan to go  to a surgical shop  and buy the surgical tubing  which is basically the same tubing used in our local catapults , fishing line should not be a problem getting as well. Apart from these you need a few small rings and hooks which can be made from  bending cycle spoke or even ready made curtain rings I guess .

It can be made quite easily nothing hi-tech about it  I got myself one from R2 hobbies  to see what it is . I think the proportion on the stretchable part to the non stretchable part is what that needs some attention that is all.

Gaurav  8) , I think this technique has  good potential for  Electrics especially considering that a  reasonable  part of the battery can be conserved with a high start.

I would be interested in knowing the AUW of you glider  and the average  altitude you achieve  with a high start  as I tried this with  an Easy Cub which is a standard airframe with a wing span of 54 " and AUW of around 800 gms ,with  my limited experience I got a feeling yesterday that a heavier and larger plane should do better than the easy cub as it was far smaller and lighter than the kind of plane this bungee was designed for.
Hence knowing your  glider details will help a great deal.

sai

Sai sir,
Just a few word of caution for you and anyone else who is planning to use the high start technique.
1. Be very carefull of the stake driven in the ground when the bungee is stretched out. If the strake is not driven in proper or the earth is soft the stake can hurtle towards the person stretching the bungee with potentially fatal results.
2. High starts have the capability to rip off the wings of light models under full velocity
3. The ring should be tempered steel and not spoke material as this may deform and open up during stretch
4. The hook apart from being right angled also needsto be curved down a bit down at the rear (open end) this helps in the hook sliding off when the stretch is gone and glider is moving forward. All those who have been in tow line gliders would already know this.

Thanks Capt , We took  the mentioned precautions yesterday as they were all the things that came up when I was reading about bungee launching.

Sai

thanks sai n captain

sai is your site working rcforall.in  ???

For now, it redirects to the eBay store.  Soon, it will be a new standalone site  8-)

Ok, i will weigh my 2M glider and post the AUW here later. However how did you assume that a heavier plane would do better than a lighter one ? In my opinion the lighter the plane the better ( in any scenario, including Hi-Starts) . With a heavy plane, you would not gain altitude as much as you would gain with the same, lighter airplane. Of course having a large wingspan would  help in gaining altitude. I use my 2M glider and been very happy with this way of launching.

Very very well said. #1 could be disastrous  ! I will add to this to ensure that the hook is placed at the CG, and the plane released carefully with a bit of forward velocity (run a few steps and release ) to ensure it does not stall at the time of release.

Gaurav,
The reason for heavy plane gaining more speed and hence more lift is due to mass. Take a catapult and now try a projectile of same size but one made of foam and one of say clay whic one gains more speed? You have your answer.
Also it is not necessary to fix the tow hook at CG, in fact you can play around depending on wind and ballast conditions. If you would have come across the GP Spirit series glider you can actually change the hook position in few seconds at the field. Also why do you need to run  while launching  from histart? The plane is going to shoot like an arrow the moment you release it under tension only thing you need to ensure is that the angle is not too steep,best is to launch parallel to ground and then blip the elevator to gain height     

Tow hook should be ahead of CG.  Closer to CG means less stable but greater height. forward away from CG means less height and more stability.  tow hook right on CG will make the model more or less unstable.