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PSS Dash-7 (DHC-7) build blog


Ben-Erik Ness
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Any sweep back/sweep forward modifies the Mean Aerodynamic Chord so that using 'what looks right' for CG position at the root rib is incorrect.

 

This glider has pronounced sweep back, I had to move the battery from the nose to between the wings, a rare case of a model turning out nose heavy.

 

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If you look at the Schleicher K7 and K13 gliders they have swept forward wings, the CG is pretty much on the instructor's seat (rear seat). This means that there is very little or no change in CG when they step out to send the student pilot solo.

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  • 2 weeks later...

I know we've chatted on messenger, but just to reiterate - 15% static margin is a lot.  8 or 9% is much more like it - even my "less than stable" F100 flies with it at 8%, and that has very little tailplane area.

 

Good luck on the maiden - you're doing the right thing using the calculators online, they've never let me down.

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Thanks for all input on CG. I may have done a major f-up... And it messes with my CG. I have 2 degrees positiv eincidence on the main wing... Why? I because I have that on a powered plane of slightly smaller size, and i flies great.

 

I have consulted a few "experts", both knowlegable modellers and professional glider designers, and they all end up with roughly the same calgulation (incdence calculated into the equation. So my CG ends up at 15omm from the leaning edge at the root. I feel calmed and confident that it will work.

As you know nose heavy planes are a pain to fly, a tail heavy plane only flies once...

 

I'm waiting for stickers for livery and windows, and two new servos that I have to change, one of the Futaba 3150 actually burned during a test - without load...

 

My favourite slope where maiden will find place is still covered in snow, and the weather the last tree days has not helped ?

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  • 1 month later...

Snow has left us and flying season is here!

Decals are on as well ?

 

In order to get the Dash-7 flight ready, I decided to cut lose the mid flaps, remove the lover hinge and top hinge them in stead. This will give both flap movement and better aileron control.

 

CG has been set at 150mm from the leaning edge, and I had to add 850g of ballast in the nose to acheive that... Not too happy with that, but can't blaim anyone else than the designer. She ends up a tad over 5Kg ready to fly - so I will need more than a light brezze to fly her.

 

This weekend I should of course have been at the Grat Orme, and one day this bird just might fly there! Fabolous pictures.

 

Next weekend we have a slope meet coming up, and for the first time I had to check if thefuse fits in the car. I'm a lucky man ?

The weather forcast gives us flying wind, bun not too optimistic about maiden, I don't think it will be enough wind at these slopes for this kind of plane.

Time will show!

 

Thanks for all input so far!

 

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Edited by Ben-Erik Ness
adding photos
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  • 5 weeks later...

 

Time for some reflections after yesterdays maiden flight:

 

  • CG was spot on at 150mm from the leaning edge at root
  • The re-hinging, from bottom to top hinge on the second set of flaps gave me full authority over the aircraft
  • The setup of butterfly for braking up before landing was also spot on.
  • If flew very nicely, no bad habits on the first flight (20 minutes)
  • The second flight had to be abandoned, due to the clevis attached to one of the main flaps snapped loose out of it's rudder horn. In the future I will bring spares. They are easy to replace and I have plenty. making a stronger horn will make repairing much worse and expensive
  • It looks good in the air. Penetrates quite well. Keeps speed quite well too.
  • Next is dummy engine pods with spinners!
    Looking forward to the next flight for this one

 

 

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  • 1 year later...

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