I have built so many planes thru the years that had stab higher than the wing.  When I got the plans and built Bill Irvin's Cotton Candy, I wondered about the stab, wing engine all on a center line down the fuse.  That plane was one of the best I had.   So if you are wondering about the high stab on a Mustang there is no worry other than trimming for some blanking out of the stab during some maneuvers.  Of course to me I never really worried about whare a stab was mounted as long as it stays on the plane.

Lot's of planes have been "In Line" designs, where the thrust line, wing centerline, and stab centerline are all on the same line. Some like this arrangement, but it seems most shy away in favor of the stab being a bit higher than the wing.

There are good reasons most modern designs have the thrust line a bit higher than the wing centerline, with the stab also higher.

I'd go further in explaining the reasoning, but don't want to presume being an "Expert".

There are several designs with wing, tail and thrust lines in line, and some seem to fly well. Mike Pratt's P-Force, now ARF'ed by Sig, is one such model that seems to fly quite well. Mine, built from his short kit several years ago, does OK. Some feel that behavior around neutral in straight flight is better with the stab not aligned with the wing chord, since it avoids the turbulence and perhaps some down-wash from the wing.

Whatever the height of the horizontal tail, other dimensions must be attuned to it, including the longitudinal c.g. location. Downwash from the wing can affect the elevator's neutral setting and input, perhaps the desired stab incidence and/or down-thrust, and definitely changes the neutral point of the aircraft. The vertical center of drag is affected, since the drag on a raised stab tends to pitch the plane up (as does gyroscopic precession), to balance drag on the landing gear and a raised thrust line, which tend to pitch it downward. It's pretty complicated, but I think that except at the highest levels, c.g. placement and elevator setting are probably sufficient to trim a plane for any reasonable stab height. You should do a search on SSW Forum's archives, where this question has been discussed in detail more than a couple times by some of the best minds in CL stunt.

One thing thing I believe true though is that you cannot make the plane symmetrical even with everything in line. Symmetrical architecture is no more aerodynamically symmetrical than the best balanced/trimmed "conventional" designs. I like the in-line idea, but have no expectation that aerodynamic adjustments can make up for P-factor, gyroscopic precession and even landing gear drag/polar moment. So I think that regardless of how well anyone thinks "inside" maneuvers match "outside" maneuvers, they really don't. The human mind and senses adjust in a marvelous way for physical asymmetries. For instance, raising the stab may avoid wing/tail interference to some extent upright or level, but somewhere inverted or doing outside maneuvers, those wakes will interfere. Still, I have to admit that my present project started out fully "in-line", but I raised the stab before completing the fuselage work. Oh, well...

SK

I believe that if investigations were to be made, you would find that the wing was is primarily directed down from the trailing edge of the wing as a function of lift production.
In all the reading I have done, well that which I can remember?, the wing wash is actually DOWN wash, and as such would travel below the stab. I am sure there is some turbulance behind the wing, but as for the accelerated air mass, it will be moving downard. Howard, or Ted , Brett or someone will correct me if I am wrong I am sure,,

One thing thing I believe true though is that you cannot make the plane symmetrical even with everything in line. Symmetrical architecture is no more aerodynamically symmetrical than the best balanced/trimmed "conventional" designs. I like the in-line idea, but have no expectation that aerodynamic adjustments can make up for P-factor, gyroscopic precession and even landing gear drag/polar moment. So I think that regardless of how well anyone thinks "inside" maneuvers match "outside" maneuvers, they really don't. The human mind and senses adjust in a marvelous way for physical asymmetries. For instance, raising the stab may avoid wing/tail interference to some extent upright or level, but somewhere inverted or doing outside maneuvers, those wakes will interfere. Still, I have to admit that my present project started out fully "in-line", but I raised the stab before completing the fuselage work. Oh, well...

The biggest effect of the in-line arrangement I noticed with the Yatsenko Shark was in takeoff and landing.

I'm guessing that having the engine low made the gear taller than it would be otherwise.  I didn't notice anything I'd attribute to the different tail location.  I hope we hear from Brett or Igor on this topic.

I'm guessing that having the engine low made the gear taller than it would be otherwise.  I didn't notice anything I'd attribute to the different tail location.

Aha! As it happens I've just revised the new "simple" model from upright to inverted engine for just that reason.

 . . .
. . .  It's pretty complicated, but I think that except at the highest levels, c.g. placement and elevator setting are probably sufficient to trim a plane for any reasonable stab height. You should do a search on SSW Forum's archives, where this question has been discussed in detail more than a couple times by some of the best minds in CL stunt. . . .

. . .

SK

Serge --

I think in one of the SSW threads (or another somewhere) wasn't it generally agreed that higher stab location "required" more positive stab incidence? I don't recall any recommended numbers, but stab incidence was "Kentucky Windage Linear" with stab height.

  Larry Fulwider

3 / 4 mm up in 3 1 / 2 in on mine . as baseline . as in not less than .

Mr Rabe uses 3 / 4 Deg. as hes shifting a bit of air, diheadral etc .

Flat wing'd require not as much .say 1 / 2 whichever way .

What I have seen recently is that Martin Simons shows the aircraft neutral point moving rearward for higher stab locations. He gives the following for a stabilizer efficiency factor:

1) .9 for a T-tail
2) .6 for a "normal tail
3) .3 or .4 for a tail near the wing wake.
4) .95 - 1.0 for a canard or foreplane

Incredible.  That suggests that the air slows down 20% behind a wing.  Does this square with the Cd of a stunt wing?

Howard-

Not having studied this yet, I just had the impression that he was referring to the direction of the relative wind. I thought he meant that the closer the stab to the wing's wake, the more negative its aoa (not angle of incidence) and thus more upward it would pitch the nose with  increased wing aoa. In other words, he seemed to be implying that the tail was less stabilizing when placed nearest to the wing chord level. I'll get around to finding out what I'm talking about sometime, but unfortunately not tonight during club newsletter editing week.

SK

Howard-

He just termed his symbol the "stabilizer efficiency." I used the word "factor", because that's how he used it. Here's the page...

SK

Serge,

Yep, that's the one.  It doesn't have downwash in it.  d(epsilon)/d(alpha) is the downwash effect, which he's simplified to a constant.  http://naca.central.cranfield.ac.uk/reports/1939/naca-report-648.pdf gives the lowdown on wake location and strength and downwash angle.  I'm kinda curious about whether having the tail above the centerline makes a difference between inside and outside loops, but wading through those charts is too much work for me.   

Howard-

Thanks for the link. When I have time, I'll look through this one. I may even have it , but last look would have been over ten years ago. Despite what has sometimes been said here, there has been some interesting and probably relevant work done by the researchers of long ago. I'm really curious about the vertical range of downwash effects. CRS gets in the way!

SK

Gyro moment is very small and needs only very small fraction of tail AoA to compensate. But if you will look to flow field analyze of 18% airfoil in 0 AoA, on place where we have tail, you will see also small fraction of down wash (java foil exports coordinates, so it is easy to calculate). But we have also landing gears with some amount of drag and prop with thrust line over the wing, what easily eliminates gyro moment and even more.

I mean - the bigest reason for down elevator and down offset of motor is P-factor. It is possible to trim also by prop down offset to some extent. So I will foloow what David says - give a little bit negative incidence to stab. The rest is "trimmable" either by elevator, or I use also motor offset. It is extremaly visible on my indoors ... I recomment to do indoors in winter, it gives very good trimming practice and sometimes open eyes

It might be interesting to mount one below the wing centerline to see what happens.  Would it need negative incidence relative to the wing? 

Yes, for the wing effect.  Some of the engine effects would have the opposite sign. 

Maybe ..You would use that with pusher props???   

Ha ha...  what do you want to bet that planes still need down elevator, even with pusher props?  Doooooh!!!!

Down elevator is not down elevator at all...  it is down flap.  Look at the umpteen million in flight pictures of stunt planes.  They all have flat elevators and down flap in level flight.

Ha ha...  what do you want to bet that planes still need down elevator, even with pusher props?  Doooooh!!!!

Maybe not...  hmmmmm.

A symmetrical airfoil gets lift from angle of attack.  You can fly a Ringmaster level. It will even do stunts.  Here's the Impact data from Gary James's Xfoil run.  Black is zero flaps.  "Alpha" is angle of attack.  

I have thrown out hte *inline* question before, also.  I had a Junar (Billy's smaller design) that was inline.  It had some good qualities.  The Sky Writer is inline as were most of the Chinese planes I saw in '04 were, IIRC.  That design (and updated) has won quite a few WC's.  From what I understood in '04, the Chinese were still basically flying the same numbers and all as Xaing's original Sky Writer.  Fo curse they had replaced the *ST style .60* with four strokes.

Maybe it is all what we are use to doing.

Anyhoo.......
Big Bear