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Old 10-09-2011, 11:55 AM   #1
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BiPlane Advice

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My grandfather has passed down a biplane that he used to fly for years. It is in kinda of rough shape although appears to be mechanically sound. I am a relatively new pilot but I feel like I can handle this plane with a little help on what to expect. Right now my biggest concern is figuring out how to balance a biplane in general. I am not sure what this aircraft actually is so I am not sure where the cg is supposed to be. From what I have read Typical CG on a bipe is directly above the lower wings leading edge.....If anyone has some insight or advice on flying biplanes in general or even this plane specifically I would appreciate it.

Thank you
Derek Petre

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Old 10-10-2011, 10:02 AM   #2
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Re: BiPlane Advice

Taking into consideration the two different shape of the wing platforms I would guess the G of G should be half way between the lower leading edge and the lower front spar. The leading edge of the lower wing would probably be nose heavy, but it would be possible to fly it with the C of G there. Caution flying this aircraft without the cowling could cause serious control problems.

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Old 10-10-2011, 11:38 AM   #3
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Re: BiPlane Advice

thank you for the advice. I used an old laundry detergent bottle and made a front cowl for it. I also took your advice on the cg. I will be flying it today so I hope all goes well (knock on wood)
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Old 10-14-2011, 09:18 AM   #4
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Re: BiPlane Advice

MAC (Mean Aerodynamic Chord).....

That's what you'll need to find and you've presented almost the toughest case

Step 1 - Top Wing: Measure back 25% of the chord from the leading edge at the root (middle) AND at the tips and make a mark. For instance, if the distance from the leading edge to the trailing edge is 10", measure back from the leading edge 2.5".

Draw a straight line between the two points. Find the middle of that line, mark it and you have MAC for the top wing. (It's the average of the two points)

Step 2 - Bottom Wing: Because the bottom wing is not swept, the MAC is 25% behind the leading edge anywhere along its span.

Step 3 - From the mark you made at the middle of the MAC line on the top wing (step 1), make a line vertically to meet the MAC of the bottom wing (step 2). Some do this with a piece of string.

The mid point of that string is the C of G for that airplane.

Be warned that the procedure only puts you in the ballpark because it's not the "perfectly complete" method (which also involves proportioning by wing area, etc). The airplane will fly and be controllable but may not be quite right. Final adjustments can be made after flight trimming tests.

What I can't figure out is how the lack of cowl affects flight if the aircraft is balanced without it. I have a 'Bipe that is nearly identical to yours and it's never had a cowl.
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Old 10-15-2011, 01:51 PM   #5
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Re: BiPlane Advice

Agree regarding no cowl...should not pose a problem based on my experience with my Astro Hog bipe. Flys very well with open engine bay, BTW which houses a ST90. Unlimited vertical!

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Old 10-15-2011, 06:53 PM   #6
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Re: BiPlane Advice

Derek - one word of advice re flying bipes vs single wings, bipes typically have more drag with those two wings so when you back off on throttle the plane will slow quicker than a single wing. Keep a bit of throttle on during your landing approaches. If you back off to idle some of them drop like a brick or stall quickly. Keep a couple of clicks of "juice" on as you bring her down.
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Old 10-16-2011, 09:42 PM   #7
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Re: BiPlane Advice

So with some advice that I did receive I have taken the plane out and it did seem to fly well. Just as some of the advice indicated it did seem to stall very quickly while turning at lower speeds, I did manage to compensate for this before the plane fell out of the sky. I also found that on take off the plane wanted to pull left which appeared to be effected by the amount of power that I imputed. It also seemed to pull very hard right as soon as I cut the power. I am still pretty new to flying and would assume that is would be some what normal, although i have never had a plane pull to the extent. On the third flight everything was going along well as I did nice and straight pass by. Until the plane rolled right and went inverted on its own, I tried to correct and the plane did not respond until mere feet above the ground when it rolled out level and went in belly first destroying the lower wing and the upper wing supports.

I am really not sure what happened, it appeared to lose radio transmission but I am not really sure. I did find near the wreckage the crystal that was in the receiver as it had fallen out. It is possible I guess that this would have fallen out on impact but I suspect maybe it may have came out in flight causing the plane to lose control. I have the receiver mounted in the plane with the face of it pointing down. I am not sure if I possibly did not push the crystal in all the way or if mounting the receiver like this might have caused it. I do have the receiver glued to some 1/4 inch white foam to avoid vibration from where it is mounted.

The plane is repairable but I think i would like to fly it as single wing plane instead of the bi wing it looked pretty cool with the upper wing broken off hahaa.
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