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Touring Motor Gliders Association (TMGA)
Andreas Clauss

Aerodynamics

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Andreas Clauss

Hello, It's now 16 months since I got my Phoenix 49U15. Over time I realised that I'm using the short wings a lot, fast and easier to land on short strips. However, when I'm with the long wings I'd like to glide and travelling is more an exception. 

Martin is working on 17m wingspan but in order to change the characteristic of the plane one would need to replace the existing landing gear with a retrofit, retractable version. Anybody tried this yet?

 

 

 

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Eric Greenwell

The only thing I know about retractable gear is Martin used it on an electric powered prototype based on the Phoenix. Retrofitting a retractable gear to a Phoenix would take a lot of engineering,  probably add significant weight, and cost a lot of money to do it. It would improve the cruise performance while gliding, but not improve the climb rate much while thermalling. Powered operation would only benefit from reduced fuel consumption, as the Vne is already the limit on cruise speed.

There is one feature of retractable gear that might be important to soaring performance: it would possible to land safely in a soft field without tipping over when the wheels dug in, so you could risk the engine not restarting. As it is, when the engine is off, I stay within easy reach of an airport, which can really affect where I can go to reach thermals.

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Andreas Clauss

Have look at this. The solution on page 1 is less complicated but aerodynamically it's less efficient.

Page 2 is more complicated to manufacture but it features less drag and for the emergency case you mentioned, the small wing is ideal.

Eventually you also need to modify the bottom engine/muffler cover and extend it into the undercarriage wing. 

The idea is not to modify the fuselage, just optimise the airflow and reduce drag.

This is an idea but maybe there are a few Phoenix owners that can get together and create a kit (landing gear + bottom cover). Together with Martins 17m wing a glide angle of 40 at 110 km/h can come within reach.

 

Retractable Landing Gear.pdf

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TeriStar

Looks like you are working too hard to make too little improvement in drag and at the sacrifice of weight gain.s  Just spend a little on improving the landing gear leg air flow by taper trailing edge legs and better fuselage fairings like fixed-gear Reno racers do. 

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Andreas Clauss

Teri, Thanks for your comment. The challenge on the aerodynamics is that you never really know. I appreciate that designing a new landing gear is a lot of work. As soon as we can fly again in Europe I'll make some small modifications on the scale you mentioned, taping some areas, and then we see.

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