Sorry I didn't get to this sooner.
Fred's post included a lot of key information about torque burners. It IS a lot like having one or two partial motors on the airplane. Typically one or two pins are used, spaced about 1/3 or 1/4 of the length of the motorstick. I liked to have the first one at 1/4 from the front of the prop hook and the second one the same distance back.
The flight profile of the torque burner is pretty interesting to watch. At State science Olympiad in 2004 my first flight did 4 minutes without getting higher than 12'. That was the conservative run. The second flight did 5:01 after climbing all the way to 23' and coming down. With the 48cm biplanes my best torque burner time was 5:29 in a 21' gym.
Usually the plane will climb about half the height of the gym on the first 'burner' then towards the end of the first burner, the plane will drop about 5' then climb back to the same height. When the second one goes off, half of the motor winds are remaining and the goal is to reach full height without hitting followed by a nice slow decent.
The hardest part of playing with torque burners is probably the winding process. How do you get the rubber onto the wire in the first place? What I did was to take a piece of tubing (I used the stuff that I made o-rings out of, but anything like a straw will do) and tried my best to space it in the rubber where it would end up on the torque burner wire. That is to say that you place the piece of tubing in-between the strands of motor perpendicular to the rubber. Much of this requires looking at the drawing I've uploaded to the Files section. Typically, you stretch the rubber to the normal length, then work to get a feel for how far you have to reach so that when you're fully wound, the piece of tubing should line up with the piece of wire that is attached to the motorstick. Then simply insert the torque burner wire into the tubing and slide the rubber up off of the tubing. Now the wire should be in the middle of the two strands of rubber.
As the torque decreases, a mixture of pulling and sliding happens. The rubber in front of the wire wants to pull forward the rest of the knots which are behind the wire. The rubber pulls forward, the wire bends slightly, and the rubber slips downward off of the wire, bringing more knots forward to unwind.
Things you can change to affect the timing are wire diameter ( though you'll quickly find that wire too thick or too thin results in a plane on the ground with 75% of winds left), wire length(same result usually), or the best way to change the timing is distance from the prop.
Before actually going out and trying it, which may result in a lot of frustration, try just bench testing a few and recording results. Just take a prop and motorstick and play with and practice winding and hooking it up. Record times when the burner deployed and total prop run time. This will help build your intuition and give you a much better feel for how it will work on a real live model.
You'll find that you can use a lot more torque and winds--much like a vp prop. I generally used less pitch than flying regular up and down flights.
Feel free to ask questions, I'm not sure how well I explained most of it.
Brett
----- Original Message -----
From: soccers56
To: Indoor_Construction_at_yahoogroups.com
Sent: Monday, January 08, 2007 6:05 PM
Subject: [Indoor_Construction] Torque Burners
Hi,
I'm doing the Wright Stuff for science olympiad, and our ceiling for
all of the sites is pretty low. I was trying to build a torque burner
to perhaps get better flight times, but i haven't had much luck with
that. I can't seem to get it to work right, because it doesn't drop
once the first part of the motor is used up. Does anyone have a
picture/sketch/diagram of their torque burner, along with some
instructions on how to use it? That would help a lot.
Thanks.
[Non-text portions of this message have been removed]
Received on Wed Jan 10 2007 - 09:43:36 CET
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