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  • December 17, 2017, 10:20:10 PM

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Author Topic: Drag Vs Handling  (Read 448 times)

Offline Motorman

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Drag Vs Handling
« on: November 26, 2017, 09:18:14 PM »
Was thinking of building a box fuselage with the motor mounted on the front with no cowling. I'm wondering if the extra drag will effect the way it tracks and how smooth it flys level.

MM
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Online Howard Rush

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Re: Drag Vs Handling
« Reply #1 on: November 27, 2017, 12:50:27 AM »
I'd guess that it won't.
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Offline Trostle

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Re: Drag Vs Handling
« Reply #2 on: November 27, 2017, 08:57:21 AM »
I agree with Howard's assessment.  Our stunt ships represent a huge "drag machine".  When you look at all of the drag our models have with their thick wings, landing gear, flaps, hinge line gaps and control lines (where lines are probably more than half the total drag the engine has to pull), the incremental amount of drag due to an exposed engine and box fuselage is negligible.  Certainly no worse than a profile fuselage where the engine and tank are completely exposed.

Keith

Offline Motorman

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Re: Drag Vs Handling
« Reply #3 on: November 29, 2017, 04:06:49 PM »
I built two planes identical except one is a profile. The profile flys much worse. I thought it was drag but I found the open warren truss fuselage is so flexible vs the CF push rod, I'm getting random elevator inputs I don't want. Still looks fantastic when the sun hits it ;D. I'll have to box in the sides and try again.

MM
There will be a sunny day and we will fly our airplanes.

Offline Ted Fancher

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Re: Drag Vs Handling
« Reply #4 on: December 05, 2017, 07:03:17 PM »
I built two planes identical except one is a profile. The profile flys much worse. I thought it was drag but I found the open warren truss fuselage is so flexible vs the CF push rod, I'm getting random elevator inputs I don't want. Still looks fantastic when the sun hits it ;D. I'll have to box in the sides and try again.

MM

Yup! Too bad as it looks very cool.  An alternative you might want to try would be to add diagonals to the existing ones to make triangular shaped "true" warren truss type structures.  Find some way to test the resistance to twisting before and after adding them (with the covering removed so you're comparing apples to apples) so you can evaluate whether the fix is likely to be adequate without adding the sheeting.  If the increase in resistance after versus before is significant you might want to recover and try a flight or two.  Doing so "will" add some torsional resistance over the existing structure.  If it is still questionable go ahead and add the sheeting which should be a sure bet.

Ted

Offline Paul Smith

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Re: Drag Vs Handling
« Reply #5 on: December 05, 2017, 08:39:56 PM »
I have noticed that profile Pathfinders have a bend in the fuselage induced by rudder offset that bends the body rather than aiming the nose.  This can't be a good thing.  It can't help but have some action on the flippers.

Why the big boys fly full body stunters.
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Online Tim Wescott

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Re: Drag Vs Handling
« Reply #6 on: December 06, 2017, 03:21:29 PM »
Yup! Too bad as it looks very cool.  An alternative you might want to try would be to add diagonals to the existing ones to make triangular shaped "true" warren truss type structures.  Find some way to test the resistance to twisting before and after adding them (with the covering removed so you're comparing apples to apples) so you can evaluate whether the fix is likely to be adequate without adding the sheeting.  If the increase in resistance after versus before is significant you might want to recover and try a flight or two.  Doing so "will" add some torsional resistance over the existing structure.  If it is still questionable go ahead and add the sheeting which should be a sure bet.

It's not a torsion thing.  It's the fuselage bending from side to side, which actuates the elevator -- the further the pushrod pivot points are from the fuselage, the worse the bending.  Mark Scarborough found this out a few years ago with a profile that misbehaved in the wind.  I think he actually had a camera mounted on the wing watching the tail as he flew, at one point. 

He put strakes on the fuselage from TE to tail, and the flight performance was vastly improved.  There's a rather long thread in the rules section about it, because the width across the strakes was well over the regulation 3/4" for a profile fuselage.

Motorman: do it up with really thin fiberglass sheets back there.  They won't be as rigid as carbon fiber, but they'll be translucent!
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Online Tim Wescott

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Re: Drag Vs Handling
« Reply #7 on: December 06, 2017, 03:29:36 PM »
Was thinking of building a box fuselage with the motor mounted on the front with no cowling. I'm wondering if the extra drag will effect the way it tracks and how smooth it flys level.

MM

Sounds like Tom Niebuhr's Hobo.  I suspect that any issues will be too minor for ordinary humans to detect, although someone who qualifies for top 20 day at the Nats may be able to tell.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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