Tailwheel Shimmy, Aircraft
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- čas přidán 10. 05. 2024
- This is my thoughts on what causes tailwheel shimmy. This is not the only video that supports my thoughts. I watch almost all of them on this site. Some videos are at a bad angle to see what's causing the shimmy. Most of them show the same problem as I mention here.
- Auta a dopravní prostředky
When we built the prototype FW 190 we had a high speed ground loop from a poorly designed tail wheel. Good thing we had Mira Slovak as our test pilot.
In the late 50's Mira Slovak was my hero, here in Seattle.
@@hankus253 I knew Mora for year's. First met him in Cour d lane at the hydro races. He crashed and my mom helped put him back
together, got together with him at Santa Paula a/p where he had a hanger. I got to fly with him several times.
You know he high jacked his airplane back in the early 60s. That's how he got to the USA.
Nice to see someone from the original WAR group. Thanks for posting, and stopping in.
@@Dynodon64 hi Don't. I just stumbled across your FB and have been watching you closely. I guess it is because I was going to build the first Corsair, my favorite plane. But WAR had some problems like the tail wheel and other things that made me back away.
I have to say you are doing an absolutely wonderful job. I really enjoy
Watching you.
One of these days I'll look for some early W.A.R. pictures and post them.
Keep up the good job.
I visited the Lear Jet Factory (in 1965) in Wichita, KS. There, I talked to an engineer who explained the five causes of shimmy for both nose wheel and tail wheel. He said (Number one) is ANY looseness between the structure and the wheel will cause shimmy. Boy, do I see it in the video. No 2 is wheel/tire out of balance or out of round. No 3 defective shimmy dampener. (On tail wheels it sometimes is a friction plate within the vertical shaft) No 4 is loose or worn wheel bearings. No 5 is wear or looseness in the steering system.
As an aircraft mechanic, I have been correcting wheel shimmy since I got my A&P in 1966. Haven’t lost one yet 😅
I can't argue with that.
I love your corsair Don! You've done an amazing job building her!
Thank you.
Thanks for this comprehensive explanation on tail wheels. It was always a guess for myself and most people as to troubleshooting. All I knew was when they didn’t work it was hard to ignore.
Had that happen once on our Kitfox while doing a high speed taxi. Thought the rudder peddles were attacking me....then back to the hanger to fix the issue....way no fun to experience
This in undamped, or poorly damped, motion. The initial loading up (torsion) on the leaf spring caused the spring to (as it is designed to do, albeit not in torsion) resist and (hopefully) damp out the motion. Problem is, it is being excited by more input. It isn’t phugoid motion, but it looks close.
You are right. The problem is that the leaf spring in the video isn’t constrained in torsion - which it needs to be to work.
As for stoping shimmy (and phugoid motion) there are two issues. The first, you are sorting by constraining. The other issue is to make sure you don’t excite a natural frequency. This second issue requires weight placement to change the natural frequency. This is what motorbike steering dampers,do.
I am sure you will sort it, you always do.
I agree with what you said about the subject. This is clearly the wrong leaf spring for this application. I don't have a shimmy problem with my set up. Just thought I would make a video on it. Thanks for the input.
here's my take; there is very little to no tension on rudder to tail wheel spring after tail is down , the rudder was slightly crabbed to one side on contact ,as weight is applied to tail spring the spring are no longer in play and results in shimmy. I had this on my Skybolt but would stop if you applied a little fwd stick. make sure you have some tension under load .I also had a small safety cable thru spring in case of spring failure. ( in my case one side came off ). this was with a larger tailwheel. great workmanship on your plane, have fun.
Yes I think more tension on the springs can help, but not with this one. The leaf spring is way to soft for that large wheel assembly.
The issue is that the plane of the swivel "disc" has a negative angle causing the shimmy. The swivel disc or plane must have a positive angle relative to the ground. It's in the Tony Bingelis books and worked on our Champ and the Pietenpol I built.
I think that positive caster can help, but I don't believe it is absolutely needed. My friends WAR P-47 has a lot of negative caster, and he has never had a shimmy problem. Mainly due to the tailwheel being retractable, has the tailwheel mount cradled by the retract frame. So it can not twist, or move sideways. It's rigid, unlike a leaf spring only attached at one end.
😮 Look like scary stuff.
@@ronnydowdy7432 The owner should be scared with this one.
The only Tailwheel shimmy you’ll be doing is listening to music in your garage.
Funny you should say that, I muted the video because they were playing, Shake Rattle and Roll song through the whole thing.
1:00 although you may be playing that video at normal speed, it appears that that original video is half speed or slower. I’ve had wheel shimmy plenty of times, the only way to stop it is to lift the tail again and set it down at a slower speed.
Yes, I have seen videos where they tell you to lift the wheel up and let settle again. To me, that's just a band aid to the real problem. But it works for you, good.
@@Dynodon64 well I agree that it isn’t the solution to the issue, but in that moment, it’s the ONLY solution other than let it beat itself to breakage.
@@thomasaltruda Yes, it's what you need to do if you want to live with the shimmy, as is.
This is the only channel that I don’t care if I get blocked.
Then why bother coming here? Thanks for the commenting, though, it helps with CZcamss algorithm to promote my channel.
Maybe the flexibility inherent in the video wheel is their problem which you won't have because your design is stiffer overall.Your yoke and rigid mounting seem more in line with the real F4U which has a very solid shock absorbed rear strut more like yours. Wow the little things one gets into when building a plane.
Yes this plane needs a stiffer leaf spring. My WAR Corsair has a caged wheel assembly, so I don't have this problem. No shimmy in mine.
Flew a Stearman for 30 yrs. Never had shimmy. If the lateral springs are too weak, the resonant frequency is low. Stiffer springs raise this frequency and provide a dampening effect. If your fix isn't adequate, add a damper.
Thats my point exactly. Thanks
It looks to me that the spring is being moved by the wheel.
Not the other way around.
Yes the weight of the wheel is moving the spring. That's part of my point. The spring is too soft. It should not flex so easily. Flex in the leaf spring is allowing to wheel to pull it from it's neutral position.
Thanks Don!
G'day Don,
Yay Team !
I must be weird, because I
"Got it" in the last Video when you mentioned the Tailwheel-set inducing a
One-Wing Low condition...
The way I visualised it,
Weight on the 3 Wheels "should" be a Triangle with the Tailwheel on the Perpendicular which bisects the "Baseline" running from Mainwheel to Mainwheel...
Whenever the Tailwheel, at the far end of it's Fork, mounted on the end of the Leafspring at the back of the rear Fuselage is deflected Left or Right ; the Rear Contact Point on the Ground is displaced Left or Right from the Centreline,
Causing more weight (55% ?) to bear on one Mainwheel or the other - inducing that One-Wing Low "set" which you mentioned...
As I see it, the Leaf-Spring is behaving as a
Torsional Pendulum, whereby any Deflection left or right of Centreline by the Tailwheel Fork displaces the Contact-point of the Tailwheel from the Centreline, inducing a Twisting moment in the whole Fuselage - which then causes the
Tailwheel's Castoring Axle to
Lead the Wheel into attempting to chase the Centreline,
In the Yaw Axis...
But coupled Inertia leads to the Tyre overshooting the mark, &
Heterodyning with the Elastic Modulus of the Fuselage...,
Plus the
Torsional Twistiness of the
Leafspring, to
result in the
Offset Axis of the
Out of phase
Compound (double)
Pendulum resulting from the Leafspring swinging in Roll as well as bending in Pitch oscillations, energising the Tailwheel Forks to
Oscillate
Violently, as it attempts to use the
Leaf-Spring as a Lever with which to attempt to
Twist off the entire
Tail...
My prescription would be to do up the Friction Locknut on that Tailwheel Castoring Axle, to attempt to damp the Tailwheel's Response-Times - when it's invited to go into the
WigWag Mode...; and/or to add Stiffness to that Leafspring in the Torsional Mode.
Either a thicker, stiffer Leaf-Spring setup...; or come up with one of the Leaves having an "U-Section" rather than being flat - so that the other Leaves "nest" inside the "Fences" and those "fences" or "webs" along the edge of the "Main Leaf" should (?) render the whole thing too stiff to be able to
Twist the Wheel any further off-centre than the degree induced by the Yaw-displacement of the Castoring Forks.
I amputated all such worries, by using a Bungee-Sprung, Steel-shod, Wooden Tailskid which was locked to the Fin-Post so stayingCentral in Yaw - but allowing 60° of up/down movement in the Skid, against the Bungee..., and the forward end of the Skid featured a "Sprag" which by using Full-Back Stick and Propeller-Blast, or passing Slipstream on the Elevators, the resulting Downforce stretched the Bungee, pushing the Skid's "leading Edge Sprag" down into the Turf,
As a "Brake".
Such was my Hypothesis.
In fact, I never noticed any great ability to control the Braking with application of Full Back Stick ; but it failed to fail, kinda thing - it did the job and it never ever shimmied (!).
Keep on keeping on...
Stay safe.
;-p
Ciao !
Sounds like, to me , you nailed it. I like the U shape idea for the leaf to nest in. But I think in the case of this plane, it needs a stiffer leaf spring to start with.
@@Dynodon64
Thanks !
Yep, that should fix it, either way...
But, it might perhaps be worth adding a bit of Friction to the Tailwheel Fork's Castoring Axle , in case that damps it's
Wiggle-Waggling enough to delay it's tendency to
"Return Swing, &
Overshooting the Centreline..."
If a Fibre, Leather, or a Nylatron Washer in the Stack were to stiffen up that Castoring Axle ; it might perhaps cure the problem - though thae Friction Washer would have to be seen as a replaceable item - to be swapped out any time the Shimmying starts to reappear...(?).
One last attempt at a
Minimalist
Solution...,
Perhaps...(?!).
Keep in keeping on...
Stay safe.
;-p
Ciao !
It'll be interesting to see what yours does, when you pick up the tail and set it back down, for the first time.
My tailwheel doesn't shimmy, and I don't think it will. Because my wheel assembly is captive with the retract arms, so it can't twist or move side to side.
I think the problem is there is a lateral bend that makes the contact point of wheel be displaced of centerline of leafspring creating a rotational moment but once wheel rotates the contact point changes side creating the opposite and so on.
If the lateral bend of the leaf spring were just that, and no twisting, Then I wouldn't expect the wheel to shimmy. I think the lateral movement away from the center of the leaf spring wouldn't matter. The caster would just turn to match the forward movement of the plane. It would just be off center. But it the lateral movement allows leaf spring to twist, then you will get shimmy.
Very interesting 👍 Good to know
shimmy shimmy ya shimmy yam shimmy yay. no one wants a loose tail
That spring does not appear to be secure in it's mounting. The spring should not have the ability to roll from side to side, inducing shimmy. Maybe the mounting structure on the video airplane needs to be beefier. I have a Stinson 108-3. The tail weight is over 100 pounds. The spring is bolted into the steel tube frame at the tail. If that spring has the ability to roll or move laterally, then you've got a problem with the mounting. As other tailwheel videos explain, stagger will definitely cause shimmy. The vertical axis of the pivot should lean slightly aft from the vertical. If it leans forward, that will induce shimmy. That's the shopping cart phenomena we're all familiar with. Finally, the tailwheel in the video appears to be a Scott 3200 or the Alaska Bush version of that tailwheel with the bush tire. After rebuilding my tailwheel I called Alaska Bush to ask what the torque of the nut on the spindle bolt should be. They said to tighten all the way, and then back off about 3/4 turn to get desired resistance to turning. In the case of the heavy tail Stinson, you don't want that to be real loosey goosey. You want some resistance to turning back there which will help prevent the thing from starting to shimmy.
I think a much larger leaf would go a long way with this one. To skinny for that wide wheel assembly.
How about at tighter assembly and a harder thinner tire.
That still wouldn't help this one. It needs a stiffer/larger leaf spring.
But your locking tail wheel will stop that? or would parallel arms and a spring shock be better?
On this example, a bigger leaf spring is needed. This one twist way to easy for that big wheel assembly.
It seems easy enough to stiffen it up, but the problem would be adding stiffness without greater weight.
Can't have one without the other. Plus, if it's a certified plane, you are stuck it, unless there is a STC'd replacement for it.
Learning new things about a tail dragger airplane I didn't know it was a big problem.
Why can't someone invent a tail dragger wheel design like a car's A arm with a nitrogen gas strut? I think that would solve some issues. I have seen it done on the Drago Light Sport aircraft using nitrogen gas struts on the main landing gear wheels.
If the tailwheel leaf spring was captive at the wheel end, then you would never see this problem. My tailwheel is captive at both ends of the leaf spring, so it won't shimmy, unless the axle comes loose.
what plane was that? a tiger moth? i was waiting for that tire to burst !
The video didn't have any details in it. Just search tailwheel shimmy. It will come right up.
Are you going to put a camera on yours to check for shimmy?
No mine doesn't shimmy.
@@Dynodon64 well nm. Glad you don't.
Tail wheel geometry: drive.google.com/file/d/1iD27sbOxZgCXBIZ8KfUigvl8VkT9PAnQ/view?usp=sharing
Thanks, I'll check it out.
Given what I have seen so far, I am sure this is nothing Don can’t sort out.
This video doesn't have anything to do with my Corsair. I don't have a shimmy problem. I just researched it to see if I might get some by changing to a larger wheel. It's just meant for anyone else who might be looking into shimmy fixes.
I'm ready to take it up. Want me to fly it for you?
I got this, but thanks for the offer.
Multi leaf spring and beef up the attaching point so it doesnt stress a small area. That stuff you have on there now is rinky dink trash throw that in the garbage.
Maybe you should get someone that knows what they’re doing.
I think Don is more than capable my friend.
@@tatumdanielsThat’s your opinion.
@@fishbustin7926 enough to respond to moronic comments
These are the most boring General Aviation videos I’ve seen.
@@fishbustin7926 Thanks for that obvious observation. It’s also my opinion that it’s embarrassing that you’ve left multiple comments on this video 😂