Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

CG Problem - rush!

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Old 06-09-2007, 07:44 AM
  #1  
nexxa
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Default CG Problem - rush!

I almost finish my new scratch build Protype V. 3 1/2 pound, OS46 FX on tune. APC 9X8

I have some difficulty to calcul my CG.

Here is the wing, somebody can help me.
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Old 06-09-2007, 07:53 AM
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evan-RCU
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Default RE: CG Problem - rush!

3.8-4.2 back from the front of the wing assuming your drawing includes the ailerons. I would start at 3.8" better safe than sorry...
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Old 06-09-2007, 09:41 AM
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Default RE: CG Problem - rush!

That is a GREAT looking plane! What is it?
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Old 06-09-2007, 05:17 PM
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Default RE: CG Problem - rush!

Use this method and apply it to your wing planform. Probaby start at 25% of the mean Aerodynamic Chord.

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Old 06-10-2007, 03:44 AM
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nexxa
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Default RE: CG Problem - rush!

Thanks for the answer.

Today is the maiden day!

Its a Scratch Build 'Lifes a Drag'. Inspire by a pathern plane. Not the most efficient airfoil and thicness for speed, but I looks like!!
I will post the first fly report with final pictures!

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Old 06-11-2007, 07:55 AM
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Default RE: CG Problem - rush!

Flight Report

Wing loading! What is wing loading!!!
Like I said, that was a prototype! My fifth one. Four of them were a success, but this one was an In the entire project I never take care of the weight, normally, a normal airframe without hardware came out under 2 pounds. I was okay 1.9 pound, with landing gear, gas tank, control rods.... After adding radio gear, engine, spinner, prop, tune pipe the airplane came out at 4.9 pounds!!! It’s ok on a normal plane with 400 square inch wing, but with my small wing, the wing loading came out at 45 oz by square feet!!! Just a bit too MUCH!!!

Finally to keep it in the air, I need to fly it almost full throttle. On an untrimmed plane it was tricky, and very scary. The plane was so sensitive.... And for the landing, imagine landing your plane at half throttle, on grass, with wheel pants…

I made two tests flights, with minor correction to CG, and a lot of expodential... I didn't crash it, but I will not put it in the air any more... Like somebody suggest me, I could modified my wing by adding 4 inches at the end (wing extension) plus adding wing tips to reduce the wing loading. But there is other projects waiting....
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Old 06-11-2007, 08:09 AM
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Default RE: CG Problem - rush!

So where did the CG end up? Congrsts on a semi sucssesfull flight!
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Old 06-11-2007, 08:54 AM
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Default RE: CG Problem - rush!

Finally, I start my CG at 3.7" and I finish at 3.5". At full speed it was very stable, not too sensative, but pratically impossible to land on a 250 feet runway! All test flights was finished at the end of the field in long grass with a couple of flip!.

This project was fun to build, and give me big boost of adrenaline. Maybe one day I will make some mods on it to make it flyable.
I will work now on my unfinish Enforcer, Viper 500 and Reno P51....

Thanks.
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