Where does the TO shake come from?

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MarcE
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Where does the TO shake come from?

Post by MarcE »

Evening everyone,

I've always wondered where the violent panel shake comes from in the Bo during lift off/initial climb? I've flown that aircraft during various subversions of P3Dv4 and am now close to "new 100 hours" in P3Dv5. While in v4 I had the massive problem of a - in my opinion very exaggerated - nose swing to the left as soon as the main wheels left the ground this behaviour has reduced significantly in v5, I have no idea why. But the panel still shakes violently during TO - and only the panel directly in front of me. I would interpret it as a stall effect if I wouldn't climb normally at 90ish knots. I know the take off dynamics have been a topic here several times and I tried to find an answer but without much luck. So where does that behaviour come from? I cannot recall anything comparable neither in any flightsim model nor in any aircraft I've flown myself or as a passenger. Is that something that happens with a V-tail only?

I use Active Sky and FSUIPC as those addons who COULD imo have to do with it. everything else is much younger so I can exclude it.

Thanks and cheers
Marc

Jarek
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Re: Where does the TO shake come from?

Post by Jarek »

It's a wheel balance issue, perhaps could be made fixable, but seems that it is what it is.

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AKar
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Re: Where does the TO shake come from?

Post by AKar »

Have you tried braking the wheels before retracting the landing gear?

-Esa

MarcE
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Re: Where does the TO shake come from?

Post by MarcE »

Ok that‘s the last thing I would have expected. Nope, I haven‘t, so as long as the wheels are turning it will shake? That would explain why it becomes less shortly after and then stops.

Tomas Linnet
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Re: Where does the TO shake come from?

Post by Tomas Linnet »

The shaking is just yet another feature of Accu-Sim :D I remember a post just after the V35B was released, saying that GA aircraft wheels isn’t dynamically balanced like a wheel in a car, so what you see/feel is perfectly normal. (I’m not a real world pilot)
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Nick - A2A
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Re: Where does the TO shake come from?

Post by Nick - A2A »

Yes, this was behaviour that Scott noticed in the real aircraft while performing flight tests and decided to simulate. A little tap of the brakes just after the wheels leave the ground should stop the shaking.

Incidentally, the reason why it's only the section of panel directly in front of you that moves around is because this part is the shock-mounted 'floating panel' which helps protect the sensitive gyro instruments from vibration.

Thanks,
Nick
A2A Simulations Inc.

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Ron Attwood
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Re: Where does the TO shake come from?

Post by Ron Attwood »

Nick - A2A wrote: 13 Nov 2020, 06:09 Yes, this was behaviour that Scott noticed in the real aircraft while performing flight tests and decided to simulate. A little tap of the brakes just after the wheels leave the ground should stop the shaking.

Incidentally, the reason why it's only the section of panel directly in front of you that moves around is because this part is the shock-mounted 'floating panel' which helps protect the sensitive gyro instruments from vibration.

Thanks,
Nick
That was only recently pointed out to me by one of the beta testers. I smile every time now. Lovely touch. :D
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MarcE
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Re: Where does the TO shake come from?

Post by MarcE »

Hmkay... it seems pretty exaggerated to me. That‘s a 8‘‘ diameter after all, not 18‘‘. The fearing on the front wheel of our club‘s 172 used to buffet in the air stream which led to vibrations of the pedals. But I‘ve never felt anything because of rotating wheels. Anyway, I can live with that knowledge, at least I don‘t think it‘s a stall anymore 😂

Thanks guys!

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DHenriques_
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Re: Where does the TO shake come from?

Post by DHenriques_ »

Just something to remember;

Not all aircraft require a brake tap or brake use OF ANY KIND after rotation with the gear either before or while in transit. Most large airplanes such as airliners use scrubbers and other means to stabilize the wheel rotation as the gear retracts.
The P51 for example, has a notation in the Dash 1 that actually tells you NOT to use brakes after takeoff due to high wheel speeds vs heat transfer.
It's worth noting that heat transfer is the universal issue with any use of brakes on an airplane.
The bottom line on this is that before doing it pilots are encouraged to check their flight handbooks for notation pro or con on ANY aircraft being flown.
Dudley Henriques

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AKar
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Re: Where does the TO shake come from?

Post by AKar »

Yeah, the most common scheme in airliners is a pair of friction pads in nose wheel well, and an automatic application of hydraulic wheel brakes on gear retraction. The puff of brake dust is sometimes clearly visible when the gear is selected up.

-Esa

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DHenriques_
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Re: Where does the TO shake come from?

Post by DHenriques_ »

AKar wrote: 13 Nov 2020, 09:04 Yeah, the most common scheme in airliners is a pair of friction pads in nose wheel well, and an automatic application of hydraulic wheel brakes on gear retraction. The puff of brake dust is sometimes clearly visible when the gear is selected up.

-Esa
The fastest ground speed I've ever experienced at rotation on takeoff would be the T38. At normal gross weight that would be around 160 knots.
The Talon is definitely a "don't touch the brakes after rotation" airplane. If you do the next landing should require a runway from New York to Chicago. LOL
Dudley Henriques

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AKar
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Re: Where does the TO shake come from?

Post by AKar »

Certainly varies from aircraft to aircraft, sure. The closest to that one I'm familiar with would be the F/A-18. It automatically brakes the wheels on retraction as they don't have quite enough room to keep spinning in their bays, and probably to avoid gyroscopic forces during the retraction as well, as the main gear is mechanically rather complex in that type.

-Esa

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DHenriques_
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Re: Where does the TO shake come from?

Post by DHenriques_ »

AKar wrote: 13 Nov 2020, 09:38 Certainly varies from aircraft to aircraft, sure. The closest to that one I'm familiar with would be the F/A-18. It automatically brakes the wheels on retraction as they don't have quite enough room to keep spinning in their bays, and probably to avoid gyroscopic forces during the retraction as well, as the main gear is mechanically rather complex in that type.

-Esa
Yes, the Hornet's gear system was designed by twelve insane engineers that management locked in a windowless room and denied them food and water for 30 days straight. I believe the same crew engineered the gear on the Cessna 210. LOL :-)
DH

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AKar
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Re: Where does the TO shake come from?

Post by AKar »

Except that the Hornet's is a sturdy one - when it's within the tolerances and works! :mrgreen:

Landing incidents resulting in runway a excursion at worst due to planing link not locking were not... entirely impossible, I recall. Perhaps that's why they threw a proxy switch for the very purpose of monitoring the workings of those linkages! :)

-Esa

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Oracle427
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Re: Where does the TO shake come from?

Post by Oracle427 »

Some 172s and 182s I have flown have a brief but noticeable vibration after liftoff. The mains and the spring struts all start to wobble together and it magnifies the sensation. When I flew as a backseat passenger for the first time I watched the mains and was surprised at how much the spring struts wobbled due to the wheel rotation.

Edit: correct sprint struts to spring struts and corrected sprint gear to spring struts.
Last edited by Oracle427 on 13 Nov 2020, 18:55, edited 2 times in total.
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