Stabilators, all-flying stabilizers, etc.

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Matt G.

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Continuing discussion of stabilators/all-flying stabilizers from the "Elevator protruding at large deflection" thread. Perhaps a moderator can move the other similar posts here? :)

DangerZone said:
Would it be possible to find one Schleicher Ka6E sailplane close nearby and install servos first to see how it behaves?
Not practical. A mod like that would require a bunch of paperwork and a signoff by an A&P IA.

I just discovered that Mechanics of Flight by Warren Phillips discusses stability and control for aircraft with a stabilator, so I'm going to be picking up a copy of that.
 

DangerZone

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Continuing discussion of stabilators/all-flying stabilizers from the "Elevator protruding at large deflection" thread. Perhaps a moderator can move the other similar posts here? :)



Not practical. A mod like that would require a bunch of paperwork and a signoff by an A&P IA.

I just discovered that Mechanics of Flight by Warren Phillips discusses stability and control for aircraft with a stabilator, so I'm going to be picking up a copy of that.
I see what you mean, administration can be a major obstacle...

Isn't that book about high speed/performance aircraft, could info from this book be applicable to a slow speed glider..?
 

Matt G.

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Did a Google books search and found that the topic is discussed in that book. Also, based on the reviews on Amazon, there appears to be a lot of stuff in there that's applicable to GA aircraft. I'll know more next week when it gets here.
 

clanon

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"The HT spar is a tube about 2-3" in diameter that also functions as the pivot"

A pic or drawing of that would be nice to see
:ponder:
 

BJC

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"The HT spar is a tube about 2-3" in diameter that also functions as the pivot"

A pic or drawing of that would be nice to see
:ponder:
Stabilator attach brackets in a T-18. The spar is tubular, about 2" dia.

http://thorp18.com/forum/images/postedimages/Stephen%20Peirce/DSC072.JPG


BJC
 

BJC

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Stabilator attach brackets in a T-18. The spar is tubular, about 2" dia.

http://thorp18.com/forum/images/postedimages/Stephen Peirce/DSC072.JPG


BJC

Stabilizator here:

http://thorp18.com/forum/images/postedimages/leewwalton/0426_2.jpg


BJC
 

Marc Bourget

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I just discovered that Mechanics of Flight by Warren Phillips discusses stability and control for aircraft with a stabilator, so I'm going to be picking up a copy of that.
Matt, I believe you would have appreciated an opportunity to speak with the inventor of the Stabilator, John Thorp. If you have access to the Sport Aviation archives, John wrote a series of articles on Building the T-18 in which, in one, he discusses the concept behind the Stabilator. The 25% hinge line [for those folks living in Rio Linda:^) ] is at/close to the aero center of pressure allowing you to move the stabilator with very little force. The spanwise control surface is an anti-servo tab. It's angular motion is more than that of the main body, and increases so you perceive a growing back-force the more you displace the stabilator. I own his personal T-18, 18JT and the "feel' is wonderful, especially the proportional rise as you get to larger deflections.

Because you don't have the aerodynamic "argument" between the horizontal tail and the elevator, the stabilator can be smaller, lighter and require less drag - all desirable goals.

That being said, the original spar was a single tube, but this was later changed to a "tube-in-a-tube" to address, in part, a flutter issue that developed. It turned out that a full span anti-servo tab has less issued than a split servo tab as was installed on the T-18. The T-18 flutter issues centered around frequency "coupling" that rose out of the additional "modes of freedom" (my inexpert term) introduced by the split servo tab - which was installed as a part of providing better spin recovery. If you wish to install a split servo tab, you would be wise to budget for a full, professional level, engineering "study", (based on the impressive quality and content of your other posts, I believe you already understand my comment)

I feel I can speak with some authority after 15+ years of regular conversations with John after he retired and moved to Lockeford, CA.

mjb
 

Kingfisher

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Originally Posted by Kingfisher
Also, one needs to design the hinge point in the fuselage to take up the bending loads (unless it is a t-tail).



Quote Matt G.:"Can you expand on this a little more? The horizontal tail loads bending loads would be taken up by the horizontal tail spar, and would not be transferred to the attachment at the fuselage. There is probably some asymmetric load case that the horizontal tail should be analyzed for that would put the fuselage in torsion through the HT pivot. Is that what you meant?"

See attached pic. As mentioned above in Marc's post, the challenge is probably more from dynamic loads/oscillations caused by play in the
system. Static loads during steady flight and manoeuvring should be fairly low.
thur530marks 1.jpg
 

cheapracer

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Matt, I believe you would have appreciated an opportunity to speak with the inventor of the Stabilator, John Thorp.
Besides all the other inventors 60 years before him.


an anti-servo tab. It's angular motion is more than that of the main body, and increases so you perceive a growing back-force the more you displace the stabilator.
I believe the fitment of an anti-servo device is law in some categories?

I noticed one pilot on another had put a small reflex tab on either side of his, central (to each side), each about 4" span, 3" long and an 1" high with an ever increasing radius on the under and top sides, almost to about 70 degrees I guess.
 

FritzW

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The stabilators on the VP-1 and VP-2 are good examples. Maybe not as light as they could be but very simple and very effective.

Most airplanes from the Wright Flyer through the beginning of WW1 had stabilators, ...not sure who inverted them.
 

Matt G.

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That being said, the original spar was a single tube, but this was later changed to a "tube-in-a-tube" to address, in part, a flutter issue that developed. It turned out that a full span anti-servo tab has less issued than a split servo tab as was installed on the T-18. The T-18 flutter issues centered around frequency "coupling" that rose out of the additional "modes of freedom" (my inexpert term) introduced by the split servo tab - which was installed as a part of providing better spin recovery. If you wish to install a split servo tab, you would be wise to budget for a full, professional level, engineering "study", (based on the impressive quality and content of your other posts, I believe you already understand my comment)
By 'split' I am assuming you mean 'left and right sides because the vertical stabilizer is between them'...is that what you meant? This may be a good argument for a T-tail if I go this route, however, that has its own set of pros and cons. What is VNE for the T-18, out of curiosity?

Kingfisher said:
See attached pic. As mentioned above in Marc's post, the challenge is probably more from dynamic loads/oscillations caused by play in the system. Static loads during steady flight and manoeuvring should be fairly low.


Actually, this picture is still as unclear as your previous post. Are you referring to a loads asymmetry between the right and left horizontal tail that would put the fuselage in torsion? Having the structure react those loads would not be unique to stabilator. A conventional horizontal tail would apply the same loads to the fuselage attachment, it's just that the attachment would be designed differently for a stabilator th
an it would be for a conventional horizontal tail.
 

DangerZone

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Stabilizator here:

http://thorp18.com/forum/images/postedimages/leewwalton/0426_2.jpg


BJC
Interesting, so this thin aluminum tube is the only thing holding the all moving elevator? How is torsion compensated for, is there a rear atachment where the trim tab should be or is this the only connection between the two elevator sides?
 

clanon

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dino

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I would think the main ingredients for an all flying tail would be:

1) Pivot axis at 25% chord
2) 100% mass balance
3) Anti-servo tab

Dino
 

cheapracer

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Are those things on each side weights ? :ponder:
Oh, you mean the mass balancers - yes weights to balance the assembly as the pivot is aprox at 25% chord point.

Here's the one that suits the previous stabilator I showed above, an adjustable lead weight on the end of a fulcrum arm, sitting on the floor in this case, presumably the stab is rear up. ...
 

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