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General control line discussion => Open Forum => Topic started by: Larry Fulwider on January 02, 2010, 09:08:06 PM
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Let’s suppose a well-intentioned (but ill-informed) genie sneaked into Dave Fitzgerald’s workshop and mistakenly dialed in 2 degrees of up elevator at neutral flap. What would Dave have to say the next time he flew the airplane?
What would the spectators see?
Thanks to the open communications of the “good guys”, most of the rest of us know to put a tad of positive incidence in the stab, and/or a little elevator droop at neutral flap.
What is missing is a description of the flight characteristics of a plane hooked up wrong. Does this erroneous flight trim produce any special characteristics so that a knowledgeable observer might, just by watching a flight, say; “Hey, that bad boy’s got hisself a dose of some up elevator at neutral flap!”
Same thing, but a knowledgeable flyer picks up the handle and upon landing immediately heads for the airplane to look for the dreaded up-elevator / negative stab incidence at neutral flap error.
Can anyone think of two or three phrases to describe maneuvers, or parts of maneuvers, where we can most easily see the problem?
Larry Fulwider
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Larry, great questions, I think? Just for us newbies, exactly what is postive stab incidence? Would the stabilizer be tilted up in the front or the back?
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Let’s suppose a well-intentioned (but ill-informed) genie sneaked into Dave Fitzgerald’s workshop and mistakenly dialed in 2 degrees of up elevator at neutral flap. What would Dave have to say the next time he flew the airplane?
What would the spectators see?
You would see some very shaky pullouts on the wingover, and the rest of the corners much softer than normal. But still a pretty good score. What may not be obvious is that a lot of the skill, and the difference between really good pilots and the truly competitive guys is the ability to adjust a little to accommodate the airplane/engine/conditions. Not for the judges, but for the way the airplane is currently flying.
What is missing is a description of the flight characteristics of a plane hooked up wrong. Does this erroneous flight trim produce any special characteristics so that a knowledgeable observer might, just by watching a flight, say; “Hey, that bad boy’s got hisself a dose of some up elevator at neutral flap!”
Same thing, but a knowledgeable flyer picks up the handle and upon landing immediately heads for the airplane to look for the dreaded up-elevator / negative stab incidence at neutral flap error.
Can anyone think of two or three phrases to describe maneuvers, or parts of maneuvers, where we can most easily see the problem?
From the outside the most obvious problem is usually that the attitude of the airplane is nose-up when upright, and nose-down when it's inverted.
Brett
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Larry, great questions, I think? Just for us newbies, exactly what is postive stab incidence? Would the stabilizer be tilted up in the front or the back?
Front, the net effect being some "down" elevator.
Brett
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You could possibly also see some tracking and hunting problems, as well as some strange looking angles of the fuse on the flAT manouvers
Randy
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You could possibly also see some tracking and hunting problems, as well as some strange looking angles of the fuse on the flat maneuvers
Randy
I fully concur with Randy's post...I was plagued with all the above on my Novi 4...about 3 degrees, down elevator (flaps neutral) cured the airplane problems, now! if only the pilot could fly the darn thing. #^
Norm
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You would see some very shaky pullouts on the wingover, and the rest of the corners much softer than normal. But still a pretty good score. What may not be obvious is that a lot of the skill, and the difference between really good pilots and the truly competitive guys is the ability to adjust a little to accommodate the airplane/engine/conditions. . . .
. . .
Brett
Aahhh, so it wouldn't surprise me to find this as a trim problem in some "competitive" Intermediate or even some Advanced flyers models. I think that was the primary answer I was looking for. The signs are subtle.
A middle of the pack Advanced flyer would perhaps describe the plane as "not quite right" or "hard to fly" but might not be able to give any specifics. Is that a fair picture?
Larry Fulwider
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. . .
From the outside the most obvious problem is usually that the attitude of the airplane is nose-up when upright, and nose-down when it's inverted.
Brett
OK, now that makes sense, and even an Intermediate might spot that. Make sure I got this, if the elevator is closer to neutral in level flight, the out of trim model will have a flap position (slanted up) normally associated with a little down elevator. Naturally, the unflapped chord line would have to have more positive incidence to compensate.
I can imagine that being fairly noticeable, depending on the fuselage shape. Regardless of fuselage shape, it would likely be noticeable either upright or inverted, as the visual difference should be noticeable.
Larry Fulwider
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I think it's more subtle than that...Randy Smith's post is close.
Several summers ago, one of our NW Skyraider members, Jerry Day (two time West Coast Sprint Car Championship driver) asked me to fly his kit-built Profile Cardinal. I did one inside loop, scared the poo out of me, and flew it out in level flight. We dialed in one half turn of down elevator, and I flew it again. It wasn't perfect (and I wouldn't know if it was), but it was a truly magical transformation, and I did a bunch of tricks, tho it wasn't the whole pattern. I remember the triangles being tremendous fun. #^ Steve
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Larry, great questions, I think? Just for us newbies, exactly what is postive stab incidence? Would the stabilizer be tilted up in the front or the back?
Ray,
The explanation I got when I first heard of positive stab was that the air flow over the wing was not straight when it reached the stab but still flowing down. Incidence on the stab puts it inline with the air flow.
Having the stab above the center line of the wing gets it out of the turbulence where the air flow over the wing comes together.
This makes sense to me but perhaps I have it wrong. Thoughts?
George
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The explanation I got when I first heard of positive stab was that the air flow over the wing was not straight when it reached the stab but still flowing down. Incidence on the stab puts it inline with the air flow.
That may be a small part of the issue but that doesn't explain why tiny amounts of incidence improve the tracking both upright and inverted. I think (as expounded on at extraordinary, even Fancheresque lengths in my SN articles and SSW posts on the topic) is the pitch component of precession. The airplane is continually yawing to the left, which creates a continuous positive pitch torque - which is compensated for by the positive incidence or drooped elevator.
That's my theory. But even if you don't buy that completely, just look at the side view of any typical stunt plane. Nothing is really symmetrical about it, so there's no particular reason to expect that 0-0 alignment is any better than something else.
Brett
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I did a bunch of tricks, tho it wasn't the whole pattern. I remember the triangles being tremendous fun. #^ Steve
I love it when P/A is referred to as "doing a bunch of tricks." Kind of puts it all in perspective. We are grown men playing with our toy airplanes, making them do tricks. That is really what it is all about. ;D ;D ;D ;D ;D
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Now if there was just a little electronic gizmo to take up the slack................. LL~ ;D
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I love it when P/A is referred to as "doing a bunch of tricks." Kind of puts it all in perspective. We are grown men playing with our toy airplanes, making them do tricks. That is really what it is all about. ;D ;D ;D ;D ;D
No, it was truly "a bunch of tricks". Nothing very P. about them, only A., Mr. Pacini. It surprised me that only a half turn on a ball-link would change the plane so completely...it made an impression. I don't want youse guys to think you need to crank in 3 turns...a little dab with do ya...sometimes two dabs. Work up to it. When it's good, stop right there. H^^ Steve
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That may be a small part of the issue but that doesn't explain why tiny amounts of incidence improve the tracking both upright and inverted. <SNIP> Brett
So, what would be surmised in a scenario, where dialing in elevator droop cured the instability in upright level flight, but left the plane with an inverted level flight that would rise upwind and fall downwind more that one would want? Dialed in too much droop? Not enough? Other factors?
EricV
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...as expounded on at extraordinary, even Fancheresque lengths...
Brett
H^^ H^^ H^^ H^^ ;D
Brett, you have a way with words...
George