HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 29, 2010, 10:09 AM
Registered User
United States, TX, Houston
Joined Mar 2010
28 Posts
Discussion
Bungee Launch Help?

I had a e-flite Bae Hawk 15. I just purchase a Jetapult Launcher at fanjetusa. so my question is it ok to use nose gear as a hook to the bungee silicon tubing wire?
tracytown is offline Find More Posts by tracytown
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 29, 2010, 12:30 PM
Effumall
kelberts's Avatar
Joined Nov 2005
3,619 Posts
Why not just hand launch it?
kelberts is offline Find More Posts by kelberts
Reply With Quote
Old Mar 29, 2010, 12:54 PM
Matrix 90 & 100mm sport jet
Getmore Rc's Avatar
Merritt Island Fl
Joined Aug 2008
1,046 Posts
Quote:
Originally Posted by tracytown View Post
I had a e-flite Bae Hawk 15. I just purchase a Jetapult Launcher at fanjetusa. so my question is it ok to use nose gear as a hook to the bungee silicon tubing wire?
No you will not get the lift. The hook is always farther back
near the wing
Getmore Rc is offline Find More Posts by Getmore Rc
Reply With Quote
Old Mar 29, 2010, 01:19 PM
crash rc plane is my job....
bobby67's Avatar
Florence area,Tuscany, Italy
Joined Jan 2009
326 Posts
This is a good bungee lunch at very low cost, easy to build:
Never use the landing gear, i believe the hook is about 2 centimeter before wing leading edge.
bobby67 is offline Find More Posts by bobby67
Reply With Quote
Old Mar 29, 2010, 02:08 PM
Registered User
USA, CT, Farmington
Joined Nov 2003
887 Posts
Your tow hook should be half way between the nose and the CG. If the tow hook is too far forward, you get a very shallow angle of attack. The opposite is true if the tow hook is too far back.
imodel is offline Find More Posts by imodel
Reply With Quote
Old Mar 29, 2010, 03:04 PM
Registered User
United States, TX, Houston
Joined Mar 2010
28 Posts
Thanks, I was almost trying to hand launch this thing but the plane seem to be heavy so I did not doing it. does anyone have a picture of how the tow hook look like or where to buy one?

Thank you very much
tracytown is offline Find More Posts by tracytown
Last edited by tracytown; Mar 29, 2010 at 03:12 PM.
Reply With Quote
Old Mar 29, 2010, 03:08 PM
EDF Jets 70mm,90mm Luv SAPAC !
Wake Forest NC USA
Joined Jul 2009
20 Posts
bungee

Coming from someone who has "cartwheeled" plenty of bungee launches "imodel" is right on and also not too tight on the bungee or you will get gymnastics (like me) not a launch...but really the landing gear is no way to do it. Follow these instruction about installing a hook. Get a small block of wood and drill small hole deep. take 3 inches of hard coat hanger wire (the thick kind) or similar and drill hole for it in fuse at designated location(see posts above) glue (epoxy only) block inside fuse and push coat hanger wire through hole drilled in fuse into hole in block of wood. bend wire as hook. done. Dont try to glue the block of wood on the outside, it will just rip off the fuse. Believe me...

I gave up on shortcuts
fatjet is offline Find More Posts by fatjet
Reply With Quote
Old Mar 29, 2010, 04:37 PM
Registered User
LuvEvolution7's Avatar
St.Catharines, Ontario
Joined Jan 2009
10,377 Posts
Quote:
Originally Posted by imodel View Post
Your tow hook should be half way between the nose and the CG. If the tow hook is too far forward, you get a very shallow angle of attack. The opposite is true if the tow hook is too far back.
actually, according to Nick Ziroli, the hook should be about 2/3 distance between the nose and the balance point. the way we used to do it on gliders, was to turn it upside down and hang it at various points along the fuse. the best position is acheived when the glider hangs almost level with a slight nose down attitude. for all intents and purposes, this postition is about 2/3 between the nose and the balance point (CG). hope that helps you out.

Rich
LuvEvolution7 is offline Find More Posts by LuvEvolution7
Reply With Quote
Old Mar 29, 2010, 06:46 PM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,459 Posts
Rich, tow hook position and cat launch position is very different. A tow position allows level pull, no climb. What imodel says is correct place to start. Hanging the jet with the nose up, the jet should have approx 15deg pos away from the zip line. Just about all of my jets are approx 50-60% back from the nose to the CG.

Tape a hook in the approx position and hang as discribed. Adjust to suit. Mount perm. If you have a backing of 1/4" ply, inside the fuse, a 3/16" carbon dowel works great, epoxied in. A small tab of plastic or thin ply at the base of the hook allow protection from the pull ring.

Fuzz
St. Martin is offline Find More Posts by St. Martin
Reply With Quote
Old Mar 29, 2010, 06:50 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
4,387 Posts
Yep, Fuzz got it right. You need to position the hook so that the inertia of the model makes it rotate to the correct angle of attack when the bungee is accelerating it. This will depend on the 3D position of the CG, not just the longitudinal position of it, as a high CG will tend to rotate the model more than a low CG. If the hook is too far back the model will tend to rotate to too high an angle of attack, causing the wing to be stalled no matter how fast the launch is (remember, wings stall at a given angle of attack, not airspeed), with the result the model does the dreaded bungee death roll.

Stu.
stumax is offline Find More Posts by stumax
Reply With Quote
Old Mar 29, 2010, 07:07 PM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,459 Posts
G'day, Stu!
St. Martin is offline Find More Posts by St. Martin
Reply With Quote
Old Mar 29, 2010, 08:07 PM
Registered User
Flip Flop's Avatar
United States, UT, Syracuse
Joined Oct 2009
550 Posts
Hey guys, I am new to bungee launching and am going to be trying it soon. I was wondering how you determined the amount of pull on the cord? I've heard before that it was about 5lbs of pull for every 1lb the plane weighs. Is this correct?
Thanks
Flip Flop is offline Find More Posts by Flip Flop
Reply With Quote
Old Mar 29, 2010, 09:56 PM
Registered User
LuvEvolution7's Avatar
St.Catharines, Ontario
Joined Jan 2009
10,377 Posts
Fuzz, I totally agree with you. what I disagree with is the fact that that is where I used to put the hook for bungee launching a glider. if you are using up to 60% on your plane, is that not close to 2/3? if you look at Nick's Turbinator that is designed for bungee launch, he puts the hook at 2/3 between nose and CG. I'm not saying you are wrong at all, but the man is a God in the RC world and I think I'm more inclined to go with him here.

for a more technical reason, we can go further............since we are talking about moments of inertia, too far forward and it's gonna give you a nose down attitude on launch. too far back and you get too nose high. either of those and you are facing a crash with every launch. 60-63% (2/3) gives the best happy medium................in other words, it's gonna give you a bit of nose high at launch, without getting too high in A0A.

there's obviously a reason why Nick chose that hook position with his Turbinator, right? and the reason is, is because it's the most aerodynamically sound position to place it.

Rich
LuvEvolution7 is offline Find More Posts by LuvEvolution7
Reply With Quote
Old Mar 29, 2010, 09:59 PM
Team White Llama!
gundamnitpete's Avatar
Joined Jan 2008
8,144 Posts
Quote:
Originally Posted by kelberts View Post
Why not just hand launch it?
The eflite hawk will not handlaunch.
gundamnitpete is offline Find More Posts by gundamnitpete
Reply With Quote
Old Mar 29, 2010, 10:14 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
4,387 Posts
Quote:
Originally Posted by St. Martin View Post
G'day, Stu!
G'day Steve!

Rich, the reason I don't like the "2/3 from the nose" or similar method is that it depends on the length of the nose. What if it's an F5 or F104? Glider launching is a totally different ball game. It happens much slower and you're on the line for a lot longer. A glider launch is designed to get height, whereas a jet launch is designed to get speed.

Stu.
stumax is offline Find More Posts by stumax
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale PRo Bungee Launch System Artsloper Aircraft - Electric - Jets (FS/W) 2 Jun 26, 2010 01:40 PM
Discussion Bungee launch height. mikey100 Australia 2 Nov 16, 2009 05:17 AM
For Sale Bungee launch dbcaster Aircraft - Electric - Jets (FS/W) 4 Oct 30, 2009 01:31 PM
Discussion Bungee Launch Hooks Leadfoot Pusher Prop Jet Models 0 Oct 23, 2009 12:29 PM