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Suspension


Tango
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Hi,

 

The suspension needs a tweak - it seems it is not critically damped.

 

Example problem:

 

* During takeoff with medium load, the aircraft is initially OK.

 

* Approaching 300 kph, I pull back to rotate.

 

* As the nose rises and the aircraft becomes light on its wheels, the aircraft will start oscillating in roll between the left/right main landing gear

 

* This oscillation is quite high in period, and can be so bad that it makes it appear the aircraft is about to roll over and take out a wing (that is the feeling, anyway)

 

* Once the gear is clear of the ground, the aircraft can have some form of roll, up to 15 degrees!

 

Best regards,

Tango.

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  • 7 months later...

Good that the shock absorbers and suspension springs are probably going to be reworked by the MIG-21's devs, but what about the damn annoying tire blowouts on the MIG-21 as you want to takeoff and you reached almost 400km/h and although you have your nose gear up which would produce some lift on the wings and thus reduce the downforce on the tires, the main gear tires blow up like firecrackers. I was able to roll with more than 450km/h with a heavily loaded Su-25T (full fuel also), with all wheels in contact with the ground (nose gear as well) and with no flaps (so the wings produce very little lift) and the weight of the plane was high on the tires and still they didn't blow out, while the light MIG-21 with higher tire radius (that means a lower tire RPM and centrifugal G-force) and reduced weight on tires as the wings produce at least 0.8 of the weight as lift force and blow up. I don't know why this hasn't been fixed or why didn't anyone complain of this (I couldn't find any topic about it), because this shouldn't normally happen.

 

Here are some real facts why the MIG-21's tires shouldn't blow up EVEN if the whole weight of the plane remains on tires (no wing lift at all) if for any other aircraft this doesn't happen, so even more it shouldn't happen to the 21:

 

1. The main gear tires on the MIG-21 are quite high in radius as compared to those on Su-25, or A-10, or even F-15 (which also rolls at very high speeds with no blowouts that easily). Some might know that the tangential speed (the speed of the ground relative to the tire's geometric center) on a circle is the product between the tire radius and angular velocity (which can be translated to RPM), thus the higher the tire radius for the same given tangential speed (ground contact speed in our example) the lower the angular speed (RPM) and due to the fact that the centrifugal acceleration (can be translated to G-force) is equal to the square of the tangential speed divided by the tire radius, makes it simple to understand that also the G-forces will be lower because of a higher tire radius.

 

2. There is a known case of the HIGHEST touchdown speed ever done in the history of aviation and that was when an F-104 Starfighter pilot found himself in a problematic situation where he was forced to land the aircraft without flaps at a speed of more than 245knots (450+km/h) and so he did and notice that the tires weren't spinning at the moment of contact which created a heavy wear and heated them up, the tire radius is much lower on the 104 (so the tire RPM and G forces are greater) and not forget the contact momentum (mass x speed (vertical speed)) that the tires had to endure at contact and still didn't blow.

 

Please guys, revise the tire blowout limits, because already this 100% rigid suspension is causing problems at landing and takeoff making the plane bounce in roll angles when the main gear is in contact with the ground and the landing gear itself is very sensitive and you must land very gently (vertical speed as low as possible) not to have the left or right main gear bent and needing repairs.

 

Thank you, have a good day!


Edited by Maverick Su-35S

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model fanatic!

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The MiG-21's tires are rated to a maximum of 370kmh. (First result in the manual, searching for 'tires'.) You should be off the ground by 350kmh, even overloaded.

 

There's much more to tire wear than size. If the MiG's tires are thin-walled (as you might want on an interceptor if you're trying to shave weight wherever possible), the simple heating from rolling friction could be enough to pop them. The Su-25T and F-15 are bad examples; both have much more modern tires, I'd expect. The F-104's typical landing speed was about 315kmh, but flapless landings (a reasonable emergency case) could happen at up to 450kmh, so it makes sense that its tires would be able to take that.

 

A light, empty, flapless MiG-21 lands at about 350kmh, IIRC.


Edited by Fishbreath

Black Shark, Harrier, and Hornet pilot

Many Words - Serial Fiction | Ka-50 Employment Guide | Ka-50 Avionics Cheat Sheet | Multiplayer Shooting Range Mission

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The MiG-21's tires are rated to a maximum of 370kmh. (First result in the manual, searching for 'tires'.) You should be off the ground by 350kmh, even overloaded.

 

There's much more to tire wear than size. If the MiG's tires are thin-walled (as you might want on an interceptor if you're trying to shave weight wherever possible), the simple heating from rolling friction could be enough to pop them...

 

Hi "Fishbreath"!

 

 

Sorry I didn't RTFM first, so now I feel a bit of shame! It only seemed too obvious that something is wrong when I've made the high difference comparison, but I take your word now and understand that maybe they were such sensitive indeed and blow up that easily.

 

It's a bit of a challenge to be a 21 driver when you don't watch the true airspeed (because if you have a good tailwind, you can blow them up looking only at the indicated airspeed) while rolling on the tarmac.

 

Thanks bud!

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model fanatic!

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Sure thing—there's so much to know about the MiG, it's hard to keep track of it all even if you've read the manual a dozen times, and there are so many things that make me say, "That can't possibly be how it is for real!"

 

It does seem like it's not a lot of safety margin, but the MiG's landing gear seem to be relatively unforgiving anyway, compared to heavier fighters like the Flanker and the Eagle. I guess it's just down to priorities in the design.

Black Shark, Harrier, and Hornet pilot

Many Words - Serial Fiction | Ka-50 Employment Guide | Ka-50 Avionics Cheat Sheet | Multiplayer Shooting Range Mission

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