Designing a removable one-piece horizontal stabilizer with advanced composites (self-study)

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bhooper360

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My plane’s stabilizer is slightly wider than the average Airstream trailer, so it's designed to be removable. That way I don’t have to worry about it when I’m driving.

This part of the aircraft was the most persistently frustrating to design. It’s because there are so many control components and load-bearing components close to each other. I didn’t see any existing on the search, except BoKu explaining about the Libelle. Here is my (WIP, work in progress) design and a few sketches. Critique it, or not.

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Goals:
  • Twice the number of individual components, or fewer, as compared to a fixed installation.
  • After installation, the stabilizer must align within 0.3 degrees without using a measuring tool.
  • Strength requirements --
  • Theoretical ultimate load, 4470 lbs
  • Static loading approximation, linear deflection: up to 1500 lbs
  • Weight approximation, for the elevator and h. stabilizer: 25 lbs
Principles:
  • Reduce complexity.
  • Minimize failure points.
  • Make the structure easier to analyze.
  • Respect the limitations and best practices of composite materials.
 

WonderousMountain

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Something I'm doing on Stubby Bipe is shoving the Stabilizer forward to get it out of the way of the Vertical Fin. Extending the fuse looked like work. Control horns aren't that helpful at my loading. Sketching does look clean.
 

TiPi

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If you can handle a T-tail with single-piece elevator, the connctions become quite simple:
single pivot at the main or front spar
actuator rod to rear spar
trim if required
anti-servo tab if required

The Spacek SD-1 uses that concept, 3 pins to be pulled for removal (anti-servo tab on top of elevator). But it is a very small & light aircraft.
Added: on the SD-1, the elevator pivots on the main spar bracket, the actuator is connected to the front spar bracket.
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bhooper360

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If you can handle a T-tail with single-piece elevator, the connctions become quite simple:

In Amerika, its called an all-moving stabilizer. Or stabilator?

But it is a very small & light aircraft.

In the PW-5 you can wiggle the whole stabilizer slightly, it's no problem. Maybe bad for asymmetric loading condition, but the wings will fall off before then anyway.

the T-tail still has an advantage if it allows the control linkages to be separate, thereby maximizing the moment arm according to WonderousMountain.

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The Libelle has the more similar system to what you're building, where the pivot point is load-bearing.

Anyway, I discovered the maintenance manual for the Extra. The only composites-specific thing is that they put all the loads through the rectangular spars, the skins do not transfer loads between the two halves.

extra.png

Control horns aren't that helpful at my loading.

Yeah, under a certain wing loading you're really better off if you step onto the wing and move them by hand.

Sketching does look clean.

Thank you.
 
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wsimpso1

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This is why so many sailplanes have a T-tail. The The vertical fin stays put, the horizontal attaches with a fixed pin and threaded in pin. The elevator on many sailplanes are auto hookup. Rock simple, very reliable, and completely confirmable after attaching.
 

bhooper360

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The elevator on many sailplanes are auto hookup. Rock simple, very reliable, and completely confirmable after attaching.

The way memories are stored and recalled is a topic that is both fascinating and also somewhat relevant. For instance, after tightening all twelve points on his twelve-point ratcheting harness, a pilot may run through a physical, printed checklist, recollect a specific tactile or visual sensation, and reach the absolutely correct conclusion that he had personally attached a particular component.

If, subsequently, substantial pieces of the glider's empennage are seen either dragging across the pavement or they are completely absent, it's a fact highly likely to be remarked upon by one of the other six people also waiting in line for a tow.
 

Riggerrob

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May I suggest a horizontal stabilizer that pivots to lay longitudinally during trailering?
This folding scheme is similar to the main-wing fold mechanism on a Back Yard Flyer or CV-22 Osprey tilt-rotor.


Start with a T-tail. Try hollowing out one side for the vertical stabilizer. The hollow lays between the vertical fin's front and rear spars. This triangular hollow makes it easy to install a third, diagonal spar in the fin. Make that hole triangular so that it allows a triangular panel to lay flush in flying configuration. The forward edge - of the hatch - is vertical and holds hinges.
Two structural pins attach the stabilizer front and rear spars to the fin. They automatically engage as you "extend" the stabilizer.
Add an extra locking pin to the rear spar joint. Make that locking pin buig anc cumbersome and paint it a hideous color that emmbarrassingly visible except when perfectly installed.

You can install external V-bracing struts to the front and rear spars of the horizontal stabilizer. If the V- struts are on the right side (of the fin), you pull a locking pin (from the rear strut, then pivot the right stabilizer forward to lay over the fuselage center-line.
Elevator controls automatically connect when the elevator bell-crank slides into the cradle that is mounted inside the fin.

Disadvantage: this folding scheme will increase you folded length by a meter/yard or so. If you don't want the extra trailer length, chop off one side of the stabilizer, so that it looks like the asymmetric tail on a BV.141. The double length stabilizer then lays over the fuselage center-line with negligible extra trailer length.
 
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WonderousMountain

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My fuse looks really good as is so I don't want to mod it.
There's this nice flat triangle for mounting the stabilator.
Your BALANCING Horns look dumb, but go ahead & print.
Screenshot_20220205-080039_kindlephoto-2853821.png
 

Victor Bravo

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Look at the sailplane systems. Mini-Nimbus, Nimbus 2, Standard Cirrus for the one-piece stabilator, AS-W20 B&C, Libelle, Ventus and many others for the stab/elevator system.

I owned a Minni-Nimbus, and the tail went on with one "lever", no hardware, no nuts or bolts, went on or off in fifteen seconds, and was LBA certified to 135 knots IIRC.
 

ClaudeR

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Just in case this might possibly be of some help, here is a picture showing where the horizontal stabilizer and elevator attach on my Hornet airplane. I'm not sure what type of plane you are designing and parameters, so this might not be appropriate. The Hornet is a Light Sport airplane similar to a Quad City Challenger.

The HStab slides on the round tube (#1 in the picture) and is free to rotate on it. The rear part of the stab is connected at #2, and allows for using the entire stab surface as trim (ie: the trailing edge of the stab moves up and down for trim function, which rotates the stab around the round tube). The elevator control horn attaches at #3.

If you look closely at the outside end of the round tube you'll see a small hole. This is for a small bolt to go through once the stab is on and secures the stab on the tube.

Claude

Hornet HorzStab Attachment-B.jpg
 

Riggerrob

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Another alternative is a fixed horizontal stabilizer slightly less than 8 feet in span. The elevator is a single piece, completely separate that hangs aft of the rudder (Try to picture the tail on a Volksplane. The elevator span is 10 to 12 feet, but since it is removed, does not affect trailer width. The elevator might include balance horns to improve control authority.
Try to think of it as a small horizontal stabilizer with an additional 4 times area as a full-flying stabilator.
Automatic control hook-ups could be as simple as a pair of arms extending aft of the stabilizer that press on the top and bottom skins of the elevator.
 

bhooper360

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I’ve identified some knowledge gaps and shortcomings with my approach.

Biggest knowledge gap is flutter failure modes and fluttertesting which is a big deal since my V_dive is 300 mph. It’s within my capability to create the exciters and process the accelerometer data independently, but like many things in life it requires actual commitment and not requires talking about it on the Internet.

Regarding ultralight assemblies: Because the mass of my horizontal stabilizer is over 20% of the mass of the rear fuselage, the oscillations will interfere on the fundamental. If it is attached with bolts the amplitude will be small, but adding a degree of freedom can promote destructive flutter. The elevator by itself weighs one order of magnitude less than the mass of the rear fuselage, so it creates harmonic oscillations. The T-tail is a related aeroelastic issue: The spars don’t line up with the node, which gives rise to complicated and extremely harmful mathematics equations.

If you open the manual for a Cirrus or a Giles (both composite aircraft) you will see instructions to create a one-piece bonded assembly using epoxy resin. From parking the trailer, to being on the line waiting for the starter’s signal, I want to be ready within four hours. Also, I want to use the same HS more than once. So I can’t use a bonded assembly. That is what I mean by “removable.”

15-second control hookups, is a great feature that can save lives. It will not be including it on this one-off aircraft, as my initial impression is that the costs outweigh the benefits.

Another alternative is a fixed horizontal stabilizer slightly less than 8 feet in span. (...) The elevator span is 10 to 12 feet, but since it is removed, does not affect trailer width. The elevator might include balance horns to improve control authority.

fokker-dr1-triplane-IRNYL[1].jpg

Additional goals:

  • Assembled within four hours
  • No destructive flutter modes up to V_dive
 
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J.L. Frusha

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fokker-dr1-triplane-IRNYL[1].jpg


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You're making this design problem a good bit harder than it might be by arranging the tail so that the aerodynamic centers and hinge lines of the vertical and horizontal surfaces are so close to one another. If you stagger them a bit, you can make the tail less structurally and mechanically crowded.

Aesthetically, I prefer it when the AC of the horizontal is forward of that of the vertical, but that's just me. But if you go that route, installing the tail into a slot in the vertical like in the Libelle becomes possible, even if you discard the Libelle's elegant though somewhat complex method of supporting the horizontal tail from the inboard elevator hinge points.

Regardless, as others have suggested, a survey of sailplane practice will yield lots of valuable design ideas. We've been at this a while, and have developed a variety of ways of solving this set of problems.

One thing I suggest, regardless of how you proceed, is to try hard to arrive at a solution that incorporates an automatic control connection for the elevator. Every year one or two sailplane pilots are seriously injured or killed in accidents involving unconnected or inadequately connected control surfaces. I consider it an ethical imperative to incorporate autoconnects in any design to be built or used by others.
 

Peterfyg

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IMG_20220207_141813586_HDR.jpg IMG_20220207_141859372.jpg
LS series glider tailplane attachment, might be relevant. The trailing edge of tailplane has a plate with 2 conical sockets, pulled tight by a bolt through the thumbwheel. Front fixing is spherical bearing, locktited, and Rear facing pin embedded in a pocket in the underside of the tailplane. Once assembled it is rock solid. This one is low mileage, only been assembled 600 times in its 30 year life
 
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Riggerrob

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Yes Dear BoKu,
This grumpy old, retired naval flight deck crew member agrees that all controls should automatically self-connect ... even if they do not have fancy hydraulic folding actuators.
Auto-connecting flight controls do require some fore-thought and maybe a fancy fitting or two, but are worth the extra cost if they prevent one (loss of control) crash.

Master Corporal (retired) R. Warner, Air Frame Technician, CD, BA, etc.
Bent wrenches on Sea King helicopters and CF-18 jet fighters.
 

Peterfyg

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Agree with auto connect controls, but if not appropriate or practical at least put the joint where you can see it, like a lot of the old wooden gliders, not hidden with no line if sight like the early plastic gliders
Here is the auto connect for the LS glider, elevator arm with 2 ball races, engaging in a slotted bellcrank, relatively build ableIMG_20220209_133348641_HDR.jpg IMG_20220209_133158939_HDR.jpg
Coincidentaly I have just scrapped a dead sailplane fitters with the autoconect drive of the type Boku referred to in the libelle sailplaneIMG_20220210_184018446.jpg
The c bracket joins the 2 halves of the elevator which slot onto the 2 pins on fitting on the right, which in this case is bolted to the top of the fin post. The inner elevator bearings are substantial, and also form the main tailplane attatchment

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The front mount is typically a drilled tab on the lower surface connected to the fin by a spring bolt. This system is fitted to a few thousand sailplanes, but seems considerably more challenging to fabricate as a one off. I don't know if either system would be suitable above the typical sailplane VNE.
 

cluttonfred

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If interested in a low-tech approach that has worked for almost 60 years on about as many flying examples (including on the original prototype in continuous use almost all that time), I can take some snaps of the Clutton FRED plans to highlight the removable horizontal and vertical tails.
 

TFF

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If you have a tractor prop airplane on conventional gear, it can become extremely nose heavy when you take the tail off. I had to install my tail when I installed my engine, because pushing it out of the hangar it would try and flip. I wanted to keep it compact in the hangar, but someone not aware could put it on its nose pushing it a couple feet, without ballast. Most sailplanes are CG aft with no pilot. Tractor airplanes are usually CG forward.
 
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