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Cessna 210 "Centurion" family development topic

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Re: Cessna 210 "Centurion" family development topic

Postby Johan G » Mon Sep 20, 2021 6:57 pm

I am under the impression that:
  • Static friction would be the force you would need to get the wheels to roll
  • Dynamic friction is for movement with locked brakes
  • Rolling friction would be the force you would have to apply to keep the wheels rolling at a constant speed

It could very well be that I have that I static and dynamic friction are the other way around, as the JSBSim manual states that in general static is greater than dynamic that is greater than rolling friction.

From pp. 39-40 of the JSBSim reference manual:
The ground tangential reaction is thus obtained by the formula

Ft = u * Fn

where u is the friction coefficient and Fn is the normal force described above. JSBSim uses a
different value for u depending on the state of the contact point. Three properties describe these
different values: <static_friction>, <dynamic_friction> and <rolling_friction>. The static coefficient
is used when the contact point is at rest, while the dynamic coefficient is used when the contact
point is sliding. The last coefficient, <rolling_friction> is only relevant for the BOGEY contact type;
it models the resistance of the wheel to its rolling. Experience shows that, in the general case, the
static friction coefficient is higher than the dynamic coefficient which, in its turn, is much higher
than the rolling coefficient, which typically has a value of about 0.02.
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Re: Cessna 210 "Centurion" family development topic

Postby TheEagle » Mon Sep 20, 2021 7:15 pm

dany93 wrote in Mon Sep 20, 2021 6:15 pm:No. The static friction is at rest, with the brakes "ON".

Ahhh, so that's what I should increase if my plane starts rolling with the brakes "ON" and max power ? Other planes don't do that - would be good if the C210 does this IRL.
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Re: Cessna 210 "Centurion" family development topic

Postby S&J » Mon Sep 20, 2021 9:07 pm

can anyone point to where I'll find data on the FTH of this engine.
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Re: Cessna 210 "Centurion" family development topic

Postby MariuszXC » Mon Sep 20, 2021 10:41 pm

Actually, rolling friction is a bit of a misnomer. There is a quite good read at Wikipedia on this subject: https://en.wikipedia.org/wiki/Rolling_resistance
and a table with typical rolling resistance coefficients is here: https://www.engineeringtoolbox.com/roll ... _1303.html
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Re: Cessna 210 "Centurion" family development topic

Postby TheEagle » Mon Sep 20, 2021 11:22 pm

S&J wrote in Mon Sep 20, 2021 9:07 pm:can anyone point to where I'll find data on the FTH of this engine.

Maybe, if you tell me what an FTH is ? :wink:
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Re: Cessna 210 "Centurion" family development topic

Postby S&J » Tue Sep 21, 2021 9:38 am

<static_friction> 0.80 </static_friction>
<dynamic_friction> 0.05 </dynamic_friction>
<rolling_friction> 0.01 </rolling_friction>
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Re: Cessna 210 "Centurion" family development topic

Postby S&J » Tue Sep 21, 2021 9:48 am

TheEagle wrote in Mon Sep 20, 2021 11:22 pm:
S&J wrote in Mon Sep 20, 2021 9:07 pm:can anyone point to where I'll find data on the FTH of this engine.

Maybe, if you tell me what an FTH is ? :wink:


It's the alt to which the turbocharger is able to generate it's maximum manifold pressure, after which MP drops off with increased alt.
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Re: Cessna 210 "Centurion" family development topic

Postby dany93 » Tue Sep 21, 2021 10:26 am

Johan G wrote in Mon Sep 20, 2021 6:57 pm:I am under the impression that:
  • Static friction would be the force you would need to get the wheels to roll
  • Dynamic friction is for movement with locked brakes
  • Rolling friction would be the force you would have to apply to keep the wheels rolling at a constant speed

This is not my opinion for the static friction.

Reminder:
Definition of the (general) friction coefficient: u = tan((Ft / Fn), or for small angles, u close to Ft / Fn.
Fn is typically the normal (vertical) force exerted by the weight on the wheel in consideration.

  • Static friction: for a blocked wheel (or any material) when there is no slip at all. In our case with the brakes ON and infinitely strong. The wheel does not slip or skid or slide, does not roll.
  • Dynamic friction (I agree): when there is slippage. The wheel does not roll (brakes ON) but Ft is strong enough to have it slipping (sliding, skidding).
  • Rolling friction (I agree).
JSBSim is perfectly clear on these.
The measured static friction is generally greater that the dynamic one. Hence, the loss of braking efficiency if you block the wheels of your car.
Code: Select all
   <static_friction>  0.80 </static_friction>
   <dynamic_friction> 0.50 </dynamic_friction>
   <rolling_friction> 0.02 </rolling_friction>

are correct, at least a good start.


@TheEagle, mind that, the static (or/and?) dynamic friction are also against lateral skidding. If you decrease one or the other you will degrade the lateral stability when rolling on the the ground.
Last edited by dany93 on Tue Sep 21, 2021 5:46 pm, edited 3 times in total.
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Re: Cessna 210 "Centurion" family development topic

Postby dany93 » Tue Sep 21, 2021 10:29 am

S&J wrote in Tue Sep 21, 2021 9:38 am: <dynamic_friction> 0.05 </dynamic_friction>
On the ice?
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Re: Cessna 210 "Centurion" family development topic

Postby S&J » Tue Sep 21, 2021 10:52 am

Works for me
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Re: Cessna 210 "Centurion" family development topic

Postby TheEagle » Tue Sep 21, 2021 12:09 pm

dany93 wrote in Tue Sep 21, 2021 10:29 am:
S&J wrote in Tue Sep 21, 2021 9:38 am: <dynamic_friction> 0.05 </dynamic_friction>
On the ice?

:lol: :mrgreen: :lol:
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Re: Cessna 210 "Centurion" family development topic

Postby TheEagle » Tue Sep 21, 2021 12:11 pm

dany93 wrote in Tue Sep 21, 2021 10:26 am: @TheEagle, mind that, the static (or/and?) dynamic friction are also against lateral skidding. If you decrease one or the other you will degrade the lateral stability when rolling on the the ground.

You mean increasing one of these (or both), I also increase the risk of rolling over on a crabbed / crosswind landing ?
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Re: Cessna 210 "Centurion" family development topic

Postby dany93 » Tue Sep 21, 2021 1:07 pm

Yes. (although you cannot increase them much)
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Re: Cessna 210 "Centurion" family development topic

Postby TheEagle » Tue Sep 21, 2021 1:10 pm

dany93 wrote in Tue Sep 21, 2021 1:07 pm:Yes. (although you cannot increase them much)

You mean, they have a max. of 1 ?
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Re: Cessna 210 "Centurion" family development topic

Postby dany93 » Tue Sep 21, 2021 1:28 pm

In the code, I don't know. But in reality the friction coefficient of a tire on dry road is rarely above 1.
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