Monday, May 12, 2014

Unwinding With a Free Flight Discus Launch Glider

For me the model aviation hobby stays interesting if I take on new types of projects which present new challenges.  This past winter I built a discus launch free flight glider known as the Maxima 30 designed by Len Surtees. I have flown radio controlled DLG gliders before but I found out that it is more of a challenge when you have no control of the glider when it leaves your fingers.  Launching a glider by spinning around while holding one wing tip can give tremendous launch height, but can also result in plane-breaking crashes as the glider hits the ground at high speed. 

Construction of the wing uses solid sections of balsa that require shaping but there are large sections of the wing which use balsa ribs. Carbon fiber strips run the length of the wing both top and bottom and the dihedral breaks are reinforced with fiberglass. Covering was with a material known as Polyspan which worked well and appears to be very tough.

As of yet I had not installed a dethermalizer (DT) in a model plane which presented a new challenge that I have much to learn about. The Smoothie MK III was included with the kit but I have had trouble gluing the arm to the rotary damper part of the timer. I ended up building by own arm out of tubing. In testing using a rubber band pulling on the rotary timer I could not get it to run for more than 30 seconds. If less tension was used it would stop. Switching to tiny springs I had purchased for this purpose worked much better and would give a much longer time before the DT would pop up.

DT Set

DT Popped Up

Learning to launch the Maxima has been more difficult than I expected, even after watching a DVD I purchased from the National Free Flight Society about DLG and Catapult gliders. The crashes normally are because you let go of the glider wrong and it curves the opposite direction it should and crashes shortly after launch or it stalls and does not recover before hitting the ground. Luckily the ground has been fairly soft lately because of all the rain. Still I have broken the glider the glider several times either at the balsa and carbon boom pivot point joint or in the nose where it is cut out for the DT. One time the DT broke free from the nose and was lost in the grass, will have to install a new one.

DT Broke Free and Lost

The last time flying I did not have to make any repairs hopefully my launch technique is improving. Transition at the top of the launch could be better; either it goes downward too fast or into a series of stalls.  There is an adjustment screw under them boom that can be tweaked to adjust the glide. Any type of model free flight glider is more difficult to launch and adjust than one would think because it flies in two entirely different speed modes, high speed for launch and then a slow glide. 

Dive Too Steep

Soaring High

Hopefully I will have a future updated report on this where I can brag of many long flights without crashing.

5/12/2014 Update

Many times tips from someone that has had success can make all the difference. I found this thread on Hip Pocket website that was very helpful "TLG Beginner's Launch Guidance". The one thing I notice was the glider should be launched with very little angle upwards and the glider climbs upwards naturally. I was launching at a rather steep angle. With this knowledge I tried flying again but the recovery at the top of the launch was still poor.

Another idea I had was to give the glider more right turn to help it recover. I increased the  rudder shim with some masking tape wadded up.  This really helped and with a little adjustment of the pitch trim the glide recovery was much better. Too good in fact for the small field in the breeze, it drifted diagonally across the entire field and landed in the road. 

This time I called it enough before I lost the glider. That evening I installed another balsa rudder shim and replaced the DT.  Think I am making some real progress now.

5/12/2014 Update

New post on my progress.

Bill Kuhl

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