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Druine D.31 Turbulent


Timo Starkloff
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  • 3 weeks later...

What about a nice pair of ski? Last weekend we‘ve had the first snow. It’s already gone, but I want to be prepared for the next time. Even the original Turbulent is flown with ski (and with floats, but that’s something for next year, maybe).

The first job is to make a model for the ski from plywood.

Not much progress on the pilot and exhausts, yet. There were other things to do. I was flying indoor again a week ago, something which works better each time. I still need some more accumulators and maybe I try 3S350 35C. This would spare another 10 grams, to be spent again on the pilot.

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They are very neat Timo (as usual). They will probably work on wet grass too, if not so realistic.

I was offered a pair of skis for my full sized Turbulent many years ago when I was a member of the Tiger Club at Redhill. One of the problems was that when there was a decent snowfall I couldn't get to the airfield but when it began to thaw, it was too thin and slushy, when the skis would quickly freeze onto the snow. Full application of power with the stick fully back and full rudder waggle would break the skis free from the snow and the flight could then commence. So I never did do any Turb on ski flying myself, sadly. sad

Post some pictures of your model flying when you get more snow, it will look very festive.

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  • 2 weeks later...

I‘ll try to get some pictures, Piers. Unfortunately the ski are finished now but no snow in our region.

Pilot and exhausts still missing, but I finished the cockpit panel and it looks quiet good. Maybe I manage to put a FPV camera in the cockpit, a realistic view is great then.

Merry Christmas everyone!

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Edited By Timo Starkloff on 25/12/2017 10:58:40

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  • 1 month later...

Bad winter for flying with skis - temperatures change every few days or hours, so no nice snow surface and no flight test yet.

But end of February is a indoor model airshow and I'll try to finish the Turbulent concerning pilot and engine. The pilot from foam is once again covered with balsa filler, made fluid with some water.

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With a small M3 screw the pilot is easily detachable, in case of indoor weight saving or placing a FPV camera inside the cockpit. No new inflight pictures yet, but the looks of the Turbulent are much improved by the pilot.

Now only the engine tubes and wires and details around the canopy are missing.

We just have had enough snow for taking some pictures on skis, sadly this snow was mainly in forest area so no chance of flying there.

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  • 3 weeks later...

I'm constantly changing projects now Getting carbon tubes for the Whirlwind lasted longer than expected, but last week I received a 6mm ABS tube from Aeronaut via my local model shop. Otherwise it would have been 2.50€ for the tube + 5€ or more for shipping.

Bending the 3mm ABS tube for the cockpit frame with a heat gun was quiet easy, but not so for the 6mm tube. It gets soft qiet fast, but there is no way to get a a smooth radius. So I rememberedthat sand is used for bending stell tubes. In my case I closed the ends with tape and filled the tube with sand (knocked a bit against it to get it really full). And after two or three tests, the result was still not perfecct but good enough for use on the model. And after some colouring and adding wires, the motor looks perfect realistic. Amazing, I have to say

Another small but easy to add detail are the wires for the brakes from fuselage to the wires. I saw them on a picture when looking for the shape of the motor tubes. I just took a 0.14mm² wire and fixed it with cyano.

Flying indoor is still possible, although the weight steadily increased to about 370 grams by adding all thos scale details (including the small 3S350 accumulator on board). Last sunday our indoor space was a bit limited and I took the pilot out (-20 grams). The result was an much easier behaviour at low speeds. And I'm ooking forward to fine spring weather to fly the Turbulent outside. The few flights until now have been really satisfying.

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Your VW flat four is looking great, Timo.

What an achievement with your project. yes

Then, of course adding some details as you are doing, gets the weight up as well.

Regarding the bending of the ABS tube, instead of sand, maybe you could try a soft metal wire introduced into the plastic to have it bent nicely... ? Just maybe?

Cheers

Chris

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  • 1 month later...

Possibly, Chris, but I would need one with 5mm diameter. All in all I’m really satisfied

Finally spring is here. Or already summer? More than 30C yesterday and today! I took a short movie of the outdoor Turbulent. It flies absolutely great outside, even with a bit of wind. But I still have to optimize the propeller. Smaller should be better for higher speed, in case of wind and for aerobatics.

**LINK**

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  • 7 months later...

It’s now one year of flying with the small Turbulent. The project to build a plane for flying indoor and outdoor was quiet challenging, but worked fine. Since summer I’m working on a plan for the German FMT magazine, but it will take some time to get it finished since I’m also busy with building the Whirlwind.

In summer I had to change the motor. Outdoor you fly longer periods with a higher power setting and there is no motor cooling. On one hot summers day the Hacker motor stopped working. The new one is a Aerodrive SK3-2822-1090, a few grams heavier but it can run a long time on full power. And it’s better suited to slow flying with less rpms per volt.

For indoor flying I use a Graupner Slow-Fly-Prop 9x3” and a small 3S350 accumulator. The pilot could be taken out to have another 20 grams less, if necessary. The center of gravity is a bit to the rear and the flaps are set on about 50 degrees. I need a large gym for relaxed flying, but can do some more manoeuvres than only flying circles. Touch and go, figure eight, kind of a wing over, and for more adrenaline some high speed rounds with flaps retracted.

Outdoor flying can be done with any accumulator from 3S350 to 3S1300, the prop is a smaller Graupner Slow-Fly 6x4. CoG is a bit forward and flaps are needed only when flying tight manoeuvres in a small space over the airfield.
The 6% thin airfoil with a small incidence is working fine up to medium wind conditions. I fact, the limiting thing is the motor power available, the model still flies fine.
Really good looking is the landing gear during low passes or turns away from you, when you see the lower side of the model. Starts are best from a flat surface but als possible from grass with some elevator to prevent a nose over. Landings are easy and there is no chance to provoke a stall with a spin. Best description of flying characteristics is: Easy but not boring!

So what lessons learned for the next model? The main focus will be on indoor flying and therefore a much slower speed. Bigger wing area and less weight. An airfoil slightly cambered on the lower side for a bit more lift without flaps. Less and smaller servos (actually 6x D47 with 5 grams each), maybe only 2S accumulator for indoor flying since I don’t need full power there. Rudder linkage with a thread instead of cfk tube. Lighter covering. And a lighter pilot puppet.

Timo

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  • 2 months later...

Yesterday I've been to the small indoor meeting in Crailsheim, South-West Germany and made the first flight with skis. Everything went fine and I didn't notice a different behaviour (no wind, of course). Snow ist difficult in our part of Germany, only a few days have been white here and that was either too short or too windy.

Last December I had a collision with a foam plane. Pilot at the other end of the gym thought to fly some rounds with me without having a talk before... So that was a test for robustness. Only minor damage occured which was repaired in two hours (hinges of one flap came out, wood of the wing holder inside the fuselage broke and the motor came off). The tough Turbulent flew fine again afterwards

If there is interest, I can post some pictures of the indoor meeting in an extra thread.

Timo

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Edited By Timo Starkloff on 24/02/2019 17:57:00

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  • 10 months later...
  • 11 months later...

Finally weather conditions were perfect and I was able to fly the Turbulent with skis in snow. I made a test flight with them already a year ago indoor, but until now never outside. It was great to fly, no change of flying characteristics and touch and skimming across the snow surface doing touch and goes was just great

Only one small inflight picture since I was alone and flying plus taking photos isn't that easy with an agile model.

Timo

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Edited By Timo Starkloff on 19/01/2021 05:50:21

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