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Old Sep 29, 2007, 05:15 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
Help!
bungee launch question

I have tried with 2 attempts to launch My JHH F14 and failed.

My weight is 8lbs The pull on the bungee is set at 50lbs.

My tries would come off the ramp (14in high) and fall into the grass causing drag and snag! A sled.

I changed the ramp from the first attempts to a higher angle.


I would like to run some pics by any of you to give some feedback as to goods and bads.

Thank-you
Jonathan
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Old Sep 29, 2007, 05:17 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
basic questions for Me are,

Too short?
Too much flex?

Confused................. It won't take many more crashes and it has never flown
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Old Sep 29, 2007, 05:22 PM
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KHorton's Avatar
Raleigh, N.C.
Joined Dec 2001
311 Posts
bungee

What are you using for bungee cord? That does not look like bungee tubing normally used.
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Old Sep 29, 2007, 05:26 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
The tubing was purchaced from Mark at Aerofoam.

The set-up was designed and bought there
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Old Sep 29, 2007, 05:27 PM
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KHorton's Avatar
Raleigh, N.C.
Joined Dec 2001
311 Posts
bungee

What are you using for bungee cord? That does not look like bungee tubing normally used. Can you post a pic of your entire set-up, that would be helpful. For starters, your ramp angle is way to steep. You only need about 15 degrees. You want the jet to come off the ramp in its normal flight profile, straight and slightly climbing, not shot to the moon at high alfa.
Keep trying you'll get it right. Might want to try a lighter, simpler jet until your setup is correct.
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Old Sep 29, 2007, 05:29 PM
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KHorton's Avatar
Raleigh, N.C.
Joined Dec 2001
311 Posts
Are you launching with wings extended?
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Old Sep 29, 2007, 05:34 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
The jet is set up with retracts but My field is only grass, and it's too thick.

Wings are extended during take-slide
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Old Sep 29, 2007, 05:37 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
pics of the hose
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Old Sep 29, 2007, 05:51 PM
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Doug Bateman's Avatar
Swarthmore, PA 19081
Joined Dec 2004
2,838 Posts
Jonathan, How long is your bungee tubing? You should have about 25-30 feet. For this jet it should be 1/2" diameter minimum. One end of this bungee is staked into the ground, the other end is tied to a length of 1/8" cord that needs to be about 25 feet long. This is what you hook the jet onto, not the bungee. The cord is light and will allow the jet to climb as it leaves the ramp, the bungee is to heavy and will drag the plane to the ground every time. I have a post i will try to find with info and my design. Doug
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Old Sep 29, 2007, 06:32 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
Mark at Aerofoam sold Me a 1/4 in wall X 25ft mandrill dipped tubing. one end is staked to the ground and the other is attached to that pink mason line (50 ft).

the mason line is attached to the hook and foot pedal for release.

This set-up is designed to launch 14lbs UAVs, and what was said to be more than necessary.

I am thinking of raising the rear of the launch ramp to make it at that 15 deg angle,
this way the jet has more off of the ground hight.
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Old Sep 29, 2007, 07:01 PM
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KHorton's Avatar
Raleigh, N.C.
Joined Dec 2001
311 Posts
I guess if it works the way he says it works but I have never heard or seen anyone using 50 ft of string. Are you doubling over the tubing. I use 25 ft of tubing doubled over and pulled back 13-14 steps to launch 3lb jets. No trouble what so ever. I for one don't use but about 6" of string and have never had any trouble with the tubing pulling the jet down into the grass.
Here are some pics of my setup.
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Old Sep 29, 2007, 07:03 PM
turbonut's Avatar
upland CA
Joined Dec 2004
7,171 Posts
try putting a flat board on the ramp..the bunggie may be pulling the nose down on the plane and you need to have a positive angle of attack as the plane leaves the ramp..if the pull of the bunggie is pulling the nose down the plane can climb..
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Old Sep 29, 2007, 07:08 PM
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KHorton's Avatar
Raleigh, N.C.
Joined Dec 2001
311 Posts
Question, How far down range does the place go before hitting the ground?
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Old Sep 29, 2007, 07:09 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
I thought of the board turbo, It does seem to pitch the nose down at launch.

My other thought is to have someone hold the tail the the jet as I go WOT, They will need to hold back mabey 4 lbs or whatever WOT is. then when I step on the pedal the other 50lbs will yank it from their hold and I'll be at full throttle and have an extra push/pull off the ramp.
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Old Sep 29, 2007, 07:11 PM
6 planes 2 jets 2 helis
Pacoson71's Avatar
United States, MA, Charlton
Joined Sep 2002
865 Posts
KHorton first run went 5 mabey 6 ft off the ramp then hit grass, I was at WOT at mabey 2 ft after ramp.

The second, I was on throttle quicker and it landed 10 to 15 ft past
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