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1:5/5 A6 Intruder Flying Stab

Old 01-18-2022, 10:50 AM
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Flite-Metal
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Default 1:5/5 A6 Intruder Flying Stab


Looking for some recommendations (assistance) in sourcing flying stab bearing and tube (aluminum) for support of my A6's flying stab
cradle. Most turbine and EDF jets are bought with the flying stab mechanism pre-installed...as we are doing.
.................................................. .......................................
By virtue of the design of the stab drives I must use high tensil aluminum alloy tube (schedule 7000) with /FG/or phenolic sleeve. Note image
of cradle and drive mechanism below. All I have found so far are C/F tube and sleeve. I must use aluminum tube. Using a cradle within fuse
where each stab is driven by an individual servo. Gator sells fiberglass only...no aluminum.

Tapered L.E. Stab Spec:
Root: 16” x 1.75” thickest.
Ttip: 8.25” x .75” thickest.
Ea. leading edge span: 18.75”
Ea. trailing edge span: 18.75”

Old 01-31-2022, 05:16 PM
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Ron S
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I stumbled on this thread... I did a search on 7075T6, which is pretty good stuff, and this place (I've never ordered from them) has some evidently, at a very reasonable price. I suspected 1/2" OD is good enough for you, I don't know your estimated loads so I did not do a bending analysis.

I normally go thru Online Metals, but they do not carry 7075 tubing. Going thru an aerospace supplier might get pricey.

Interesting website...


Note: 5/8" OD might be another option, depending on your loads.

Last edited by Ron S; 01-31-2022 at 05:20 PM. Reason: added note.
Old 02-01-2022, 07:13 AM
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Default Flying Stab Cradle & Components.

Thanks Ron

You are the second person to recommend 7075T6. That price surprises me. Will definately follow up on this today. Will post
a drawing of what I resolve as the simplest/most serviceable cradle design. Working on the bearings.






Last edited by Flite-Metal; 02-02-2022 at 04:05 AM.
Old 02-03-2022, 01:16 PM
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Can not use the 7075 due to lack of sleeve availability.. So:

Thanking you in advance for your feedback.Name:  smiley14.gif
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Size:  489 Bytes Should there be concern for a heat treat hex head 4-40 bolt inserted through both sides of a 1/2 inch c/f tube at right angle which is the control arm for half a flying stab on a plane anticipated to have an air speed of 70~75 mph?

Tube is located at 25% of the stab MAC. Lock nuts are on each side of 4-40 bolt where it passes through C/F tube. Is there concern for bolt threads enlarging the drilled hole? Do I need to sleeve bolt or use a 1/2 inch shanked bolt?
Old 02-05-2022, 08:28 AM
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Hi Ed,
If you can move your pivot tube, just a bit AHEAD of the 25% MAC point, that would be a bit better. Locating the pivot point at 23-24% for example. This way, if there's a bit of difference between your calculated 25%MAC point and the real location, it just adds a bit of conservatism. Also, if the H stab were to become detached from the servo, the H stab would have a greater likeliness of moving to a streamlined position, instead of possibly flipping to 90 degrees.

You can refer to the AMA document for Large Scale Models (modelaircraft.org, Media..., AMA Docs, Large Model Program, PDF Document 520-A). This is for the large model signoff, but it is good for any size model, and there's a section in there for approximating control surface and flying stabilator loads. You may have your own methods, but this is good as another sanity check.

I'd be a bit worried about using a 4-40 thread as a control arm thru a CF tube - mainly about the small dia screw bearing into the CF tube, and wearing the hole to a large size, resulting in slop. If you could sleeve the inside of your CF tube with another piece of telescoping CF tube, (to build up the wall thickness), that would help. Sleeving the bolt can help too as you suggest. I'd probably stay away from 4-40, and see if 6-32 is do-able.

I would want to make that arm on the tube longer, also. This way you can use a servo arm that isn't real short... Short servo arms and short arms on the control surface will make your tail "looser". (Think of it as, if you have .01" tolerance between a clevis and servo arm hole, if the arm is short, that's a lot of angle - if the arm is longer, you've just reduced your angular slop). You're probably gonna need only about 45 degrees max throw on your H stab. A servo is 90 degrees nominal, so you're already looking at H stab arm should be around twice the length of your servo arm (ballpark).

You can also check with Sierra Precision to see if they have (in stock!...) any clamp-type control arms for 1/2" tube.

Ball rod ends may not have slop initially, but they will develop some looseness over time. I'm not sure if you are using all metal ball rod ends, or nylon ones. Once you get to looking for ball rod ends for #6-8 thread sizes, you'll find they are really hard to come by, for some reason. If you plan on using nylon ball rod ends, Dubro I think makes Monster ball rod ends for 6-32 thread...
Old 02-05-2022, 09:39 AM
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Originally Posted by Ron S View Post
Hi Ed,
If you can move your pivot tube, just a bit AHEAD of the 25% MAC point, that would be a bit better. Locating the pivot point at 23-24% for example. This way, if there's a bit of difference between your calculated 25%MAC point and the real location, it just adds a bit of conservatism. Also, if the H stab were to become detached from the servo, the H stab would have a greater likeliness of moving to a streamlined position, instead of possibly flipping to 90 degrees.

You can refer to the AMA document for Large Scale Models (modelaircraft.org, Media..., AMA Docs, Large Model Program, PDF Document 520-A). This is for the large model signoff, but it is good for any size model, and there's a section in there for approximating control surface and flying stabilator loads. You may have your own methods, but this is good as another sanity check.

I'd be a bit worried about using a 4-40 thread as a control arm thru a CF tube - mainly about the small dia screw bearing into the CF tube, and wearing the hole to a large size, resulting in slop. If you could sleeve the inside of your CF tube with another piece of telescoping CF tube, (to build up the wall thickness), that would help. Sleeving the bolt can help too as you suggest. I'd probably stay away from 4-40, and see if 6-32 is do-able.

I would want to make that arm on the tube longer, also. This way you can use a servo arm that isn't real short... Short servo arms and short arms on the control surface will make your tail "looser". (Think of it as, if you have .01" tolerance between a clevis and servo arm hole, if the arm is short, that's a lot of angle - if the arm is longer, you've just reduced your angular slop). You're probably gonna need only about 45 degrees max throw on your H stab. A servo is 90 degrees nominal, so you're already looking at H stab arm should be around twice the length of your servo arm (ballpark).

You can also check with Sierra Precision to see if they have (in stock!...) any clamp-type control arms for 1/2" tube.

Ball rod ends may not have slop initially, but they will develop some looseness over time. I'm not sure if you are using all metal ball rod ends, or nylon ones. Once you get to looking for ball rod ends for #6-8 thread sizes, you'll find they are really hard to come by, for some reason. If you plan on using nylon ball rod ends, Dubro I think makes Monster ball rod ends for 6-32 thread...
Ron,

Thanks for the feedback which is actually confirmation of this 23% of MAC setup, I may have posted an image where the axle appeared closer to 25%.


A tapped hardwood plug is inside CF tube to prevent wollowing out the hole via thread abrasion (per recommendation from another thread).There are all metal roller rod and ball rod ends on servo to CF tube connections. I am using a short (3"~5") fiber glass arrow shaft between servo and CF tube connection to assure there won't be flex. I was at a loss for a 1/2 inch dia aluminum control arm since Yellow Aircraft is no longer a source (F-18). Good idea to call Darryl to see if he has them in stock. Surprised to learn robotic parts for it do not exist.

I was trying to not have to add another access hatch directly beneath the CF junction...but it has to be. Stab removal during transport is wise due to width and removal if there was an issue with linkage. Access panel and surround of opening will be glass and CF laminate to assure no flex. The fuse at that location has a vacuum bagged CF, poly foam, and glass sandwich. Each stab is driven with a 25kg servo.
Old 02-07-2022, 10:30 AM
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Ron,

I now have domestic resource for the 1/2 ID CNC'd Control Arms Pairs @ $38.00 USD ;^)

.......

Last edited by Flite-Metal; 02-08-2022 at 05:14 AM.
Old 02-09-2022, 04:52 AM
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Default Final Stab Cradle Configuration




Last edited by Flite-Metal; 02-09-2022 at 07:21 PM.
Old 02-09-2022, 04:53 AM
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Default Final Stab Drive




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Old 02-09-2022, 07:57 PM
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Default Flying Stab Index Inquiry

The A6 flying stabs are removable for ease of transport. .50 I.D. aluminum control arm clamps around .50 diameter aluminum tube.
Wood dowel is inserted to prevent tube collapse. A pair of wheel collars are each side of control arm tto snug up against counter
sunk
bearings in stab cradle frame to retain inboard end of aluminum tube.

A second tube with an anti-rotation paddle on outboard end is embedded in horizonal stab. Inboard end of stab tube is slipped over
outboard end of stab cradle tube. The slip tolerance tubes are drilled and tapped to receive 4-40 hex head bolt. From the tube specs
below I welcome your recommendation for wall thickness and proper slip tolerance of the two aluminum tubes.



Old 02-11-2022, 06:06 PM
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Hey Ed,
In post #8, I have some questions or clarifications:

1.) What is the purpose of the 4-40 Hex Head screw? Is that taking (or transferring) all of the torque loads out from the stabilator, and dumping it to the control arm? If so, #4 is a pretty small screw. Loadwise it will likely be okay. But I think it will wear the tube after some flying cycles - I think you'll wallow out the holes... #6s might help because the load will be spread over a larger surface area on the screw. I'm also assuming if this screw is removed, that is what allows you to remove the H stab (and CF tube?) I guess also adding another screw will halve the load, and probably the wear too.

2.) Are you still using a CF tube? It looks like perhaps the tube is sliding over the aluminum and wood setup that is attached to the control arm. If so, I suspect the CF tube will get the short end of the hole wallowing from the 4-40 screw... I'm guessing the black outline you show is a CF tube. ?

3.) More importantly, is there a way where you can move the outboard-most plywood wall closer to the green fuselage side? The farther apart you can space those plywood / bearing assemblies from each other, the easier your structure will be able to take the bending load from your H tail.

4.) Are your H Stabilators going to pivot/operate as tailerons (meaning, you are also using them for roll)? Or will they only move in unison, like one big H stabilator? If they move together, you might be better off using a single common inner tube that operates both the LH and RH sides. Plus, this will allow you to get rid of 2 bearings (weight savings). You can still use 2 servos if you want, and 2 control arms. And there are ways to address the issue of servos fighting each other... If the tail operates as a Taileron, then this idea won't help of course. I'm not familiar with how they operated on the full scale.
Old 02-11-2022, 06:44 PM
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Regarding post #10, If the tube assembly that resides inside the fuselage is .500 OD, then the outboard tube that will be attached to the H stab will have to be greater OD ...So in your table, it looks like you'll need something in column 3 (.625 OD).

You will probably want to try the 0.625 OD X .058 wall AL 6061 tube. That will give you 2 X (.063-.058) = 0.01" slop inside the tubes. It would be nice if it were a bit tighter, but that is the best option you have. If that is too sloppy, you could wrap the outer portion of the .500 tube with a single wrap of something like, Flite Metal... I know a guy...

If the outer tube is .058 wall thickness, then for the tube inside the fuselage, I'd want a wall thickness equal or greater than the .058" on the outer tube. I'd go with the .500 OD X .065 wall 6061 tube.

Then your next wear point would be where you notch the tube over your paddle. The notch can get stressed, and also the paddle. Is the paddle plywood? Can it be something harder?

These are things that can be made and played around with, before making your final version. I'd buy some short pieces of the stuff first and play around with it a bit, to see if you're happy with the stackup.
Old 02-12-2022, 06:19 AM
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Default Stab Cradle Drawing/Specs

First of all...thanks Ron for your contributions to this thread! The reason for posting is to benefit from the experience of others in specs we have never worked within. There are no answers without seeking the generious "experience based" knowledge. These drawings are not to scale nor are the materials and specs a fixed item. They are in constant revision until the half rear fuselage lay-up is done. Half fuselage enables assurance rear formers and fittings are proper to enable embedding during lay-up.

The final tubing spec is: .500 x .058 wall aluminum outside tube, 3/8 aluminum inside tube resulting in .0040 slip tolerance. This subject to sourcing. Tubing vendor will send short lengths to permit check of slip fit.

Now that the final tubing spec is known bearings can be sourced. The bearing OD and width will effect the revised drawing. That area of the drawing is a WIP. Bearing/tubing support is made from multiple hardwood ply layers. The actual number of layers will be determined by bearing cross section and available interior fuselage width. Final drawing rev. is 50% complete. From this comes .svg perimeter line drawings for laser cut ply. My editor permits conversion of analog drawings to .svg and other formats for cutting and printing.

6-32 heat treat hex head is the better choice. 6-32 will resist cross threading as well. All areas to be clamped and drilled for threading are hardwood plugged. Stab paddle is planned to be a pair of G-10 with a single layer of C/F veil laminated between...though that too is open to suggestion. We are trying to stay away from cutting solid C/F within our facility for sake of not having to deal with shards.

The H-stabs do not function with the spoilerons. As for a single stab shaft I was concerned about servo functional conflict. Using serial bus with down stream satellite receivers permits me to dial-in differential. Though weight is always a concern I am more concerned with this the most critical component within the A6 Intruders. Cantilevering 10 ft fuselages is by no means simple.

The original "Flight Of The Intruder" movie 6's were not designed to survive more than a couple of flights each. Basically second cousin to 2x4 bearing surfaces driven by a single servo. In fact they survived multiple flights each...leaving two of them as survivors...thankfully! 33 years ago the word recip-powered DF giant scale jet left a lot to be imagined, much less flown. It was common for movie jets to be "flown" along stainless wire or filmed short flights in the desert or from cliffs. For all the effort and expense of modeling the A6's at 1:5.5 the net was less than a minute of film.
.
...


Last edited by Flite-Metal; 02-12-2022 at 06:52 AM.
Old 02-12-2022, 01:12 PM
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A better perspective of the stab/fuse. Shorter airfoil in background is the root. Stab paddle is gold running through shaft. I am working on the revised head-on view.

Last edited by Flite-Metal; 02-12-2022 at 01:14 PM.
Old 02-13-2022, 07:53 PM
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Default Final Stab Cradle Design

Final design of the stab cradle and paddles. Paddle is two G-10 with CF veil between to maximize T/C of the sandwich. Until the half rear fuselage lay-up occurs I can only measure exterior dims of the closed rear fuse to estimate available interior width. Below...in green, is the virtual fuselage shape representing the area along which the cradle rails are Hycel'd to interior of the fuse permitting cradle to be retained with 6-32 hex head heat treated bolts.

An additional bottom access hatch has to be created to permit adjustment of cradle mounted hardware. If required the entire cradle can be removed through either the existing hatch, or if necessary...through removed rear fuselage.



Last edited by Flite-Metal; 02-14-2022 at 01:34 PM.
Old 02-20-2022, 07:36 AM
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I had someone who assumed the inner telescoptic tube ended just inboard of the 6-32 hex head bolt connecting the inside to the .0500 outside tube. Below is a revised illustration showing the actual config. Additionally the cradle is a box frame to distribute torque/stress..

Old 02-28-2022, 04:26 PM
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Default Darryl's (Sierra) 1/2 Inch Control Arms :^)

They arrived...excellent 1/2 inch control arms. Darryl did an excellent job making these. The fact it is threaded all the way through and the arm is centered permits adjustment/ inspection access 180 degrees out. There's nothing more frustrating with hex set hardware than the adjustment access is usually in the wrong place.

Last edited by Flite-Metal; 03-01-2022 at 12:27 AM.
Old 03-04-2022, 07:02 AM
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Default Production Stab Control Arms

Correction, thread in the above stab control arms is in the arm side. In our production arms the bolt is inserted through clearance hole on the control arm side. The clearance hole tolerance is only 2 1/000's. This permits arm adjustment through bottom hatch.

Last edited by Flite-Metal; 03-04-2022 at 07:06 AM.
Old 07-12-2022, 05:15 AM
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.
Its been a while since I updated the flying stab progress. Currently creating the cut files after confirming rudder dims. This whole area is immediately above and ahead of the bottom access hatch.
.
.
The above illustration shows how far off the movie models stab pivot point was from a proper aerodynamically balanced stab. The pivot point must be ahead of MAC to prevent flutter and hyper sensitivity. The original location was exactly 14" ahead of the fuselage rear. This was offset by a second attachment point of the servo...ahead of the pivot point...inside each stab neutralizing flutter. The movie model creator was not concerned about the gaping holes in the top of each stab. Hey..who's going to notice from 100 feet away looking through a camera lens...

To create a more scale appearance with reduced stab sensitivity I chose to move the pivot forward 2.75" and the entire flying stab mechanism "inside" the fuselage rear. The control arms are immediately above the access hatch for ease of internal adjustment. If necessary, the entire stab cradle is removable for ease of maintenance.
.
.

Last edited by Flite-Metal; 07-12-2022 at 05:17 AM.
Old 08-04-2022, 04:49 PM
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Old Yesterday, 02:35 PM
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Default .0635 Adjustable Stab Gap



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