Gear keeps collapsing?

[JG-1_Vogel]

A month or two ago I was nailing landings in the '21 fine with no problems, now either I'm just rusty or have LN tweaked the stress tolerance of the rear gear? I land at 290/300kph and no matter how gently I touch the runway one of my rear undercarrage always collapses. Is it just me?

[xxJohnxx]

A month or two ago I was nailing landings in the '21 fine with no problems, now either I'm just rusty or have LN tweaked the stress tolerance of the rear gear? I land at 290/300kph and no matter how gently I touch the runway one of my rear undercarrage always collapses. Is it just me?

 

Maybe you can share a track? As long as landing within parameters (speed, sinkrate and especially weight) that normally doesn't happen to me.

[Hadwell]

firstly you'll want to make sure you don't cut your throttle until all 3 wheels are firmly on the ground, secondly you'll, wanna be going about 20-30 kph slower , third, you wanna hover your plane about half an inch from the ground, and decend the last half an inch with a decent rate of about 1/8th an inch per second, making sure as soon as the rear wheels touch you pull back on the stick and control the speed the front tire touches the ground, you don't want the weight of the plane transferring to the front wheel.

 

also the less fuel you have, the easier it is to land, best to wait till the low fuel warning light comes on if you want to be sure of an easy landing, but you only have enough fuel for a couple tries(if that) at that point.

Edited February 17, 2015 by Hadwell

[MiG21bisFishbedL]

I find sinkrate to be the most important factor. Never exceed about 3m/s in vertical speed during your descent and, as Hadwell said, NEVER chop the throttle. You land with power and, usually, a pretty significant amount.

[JG-1_Vogel]

So, touchdown at roughly 250-270kph? Will have another go and see how I fare.

[Auger73]

also the less fuel you have, the easier it is to land, best to wait till the low fuel warning light comes on if you want to be sure of an easy landing, but you only have enough fuel for a couple tries(if that) at that point.

 

I had the same problem the OP had, and landing with too much fuel was my biggest problem (not that I can't improve my technique).

 

Per the manual, you should start your approach at around 700L of fuel remaining in a clean configuration. Fuel limits with external stores are detailed in the manual.

 

Since you can't dump fuel in the 21, you may want use the (2nd) afterburner at low altitude to chew through fuel if you think you will have too much when you start your landing approach.

[JG-1_Vogel]

Now if you got a crosswind at all, don't bother trying to land, just eject, it's alot less sketchy.

 

:megalol: I don't think the crew chief would agree with that assessment! :pilotfly:

[mytai01]

my most successful landings are with an approach speed locked at 400kph pretty much all the way to touch down. Of course, I have learned to very very gently kiss the runway. With that kind of speed it reduces the AOA and I can stop without popping the chute if the runway is long enough.

Edited March 10, 2015 by mytai01

[panzerd18]

You have to land with approach power on. Flying it all the way onto the runway instead of pulling the power off over the threshold. The moment you pull the power off, the Mig drops like a rock and is probably why its hurting the gear as the sink rate is too much.

[malcheus]

I'm having the same issue, have been trying a lot for the last week.

Thanks for the advice in this thread, will try again, and maybe post a track if it fails agian.

 

edit: so one added question: do you always dump all your payload before landing?

seems a bit wasteful, but it does also save some landing weight...

Edited March 22, 2015 by malcheus

[malcheus]

So here's a track, I tried starting with low amount of fuel,

still I eithe ruin my gear or bounce most of the time when trying to land.

landing attempts.trk

[Cruiser18]

So here's a track, I tried starting with low amount of fuel,

still I eithe ruin my gear or bounce most of the time when trying to land.

 

Watched the track. You have to work on your flaring (pithing up the nose before contact). Especially the first attempt, you pretty much just pound right into the runway and bump right off again. The second time it's better, but your descent rate is still some +6 m/s. Ideally you'd like to flare in a way that leaves you with a descent rate of 1-2 m/s before you touch the runway.

[malcheus]

Watched the track. You have to work on your flaring (pithing up the nose before contact). Especially the first attempt, you pretty much just pound right into the runway and bump right off again. The second time it's better, but your descent rate is still some +6 m/s. Ideally you'd like to flare in a way that leaves you with a descent rate of 1-2 m/s before you touch the runway.

 

Thank you for the advice!

How many degrees should I (approximately) point the nose up?

 

Normally I use a lot more flare, but I noticed the mig21 has this fin like structure under the rear, and I'm always a bit scared of scraping it against the runway.

[Cruiser18]

Thank you for the advice!

How many degrees should I (approximately) point the nose up?

 

Normally I use a lot more flare, but I noticed the mig21 has this fin like structure under the rear, and I'm always a bit scared of scraping it against the runway.

 

The amount of degrees depends on how much you need to correct. ;)

 

I've never had a case where my ass hit the tarmac before my wheels, so don't be a afraid to flare as needed when putting it down.

 

I recorded two small tracks where I land. I'm a bit out of shape, but I manage to get down without any major problems. I usually land with the RSBN landing system glideslope on, so this was a new for me as well. XD

LandingDemo01.trk

LandingDemo02.trk

[Art-J]

Normally I use a lot more flare, but I noticed the mig21 has this fin like structure under the rear, and I'm always a bit scared of scraping it against the runway.

 

Rightfully so, because I've scraped a few of these myself in my early days with MiG :D. That however, was always the problem of approach speed being too low (hence the angle of attack being too high).

 

If You stick to recommended approach and vertical speeds You can still flare and land just fine, even with heavy fuel load and some ordnance aboard.

[Derbysieger]

firstly you'll want to make sure you don't cut your throttle until all 3 wheels are firmly on the ground

 

You can reduce throttle as soon as the main gear is on the ground.. Aero-braking is very effective in the MiG. I usually go to idle as soon as I have the main gear on the ground and keep the nose gear up for as long as possible. I'll post a track later.

 

Edit:

 

I attached two tracks flying RSBN and PRMG assisted approaches and landings (flying mostly visual though) starting south east of Maykop. Added light crosswind (~4m/s from the east) and a little turbulence (15m/s*0.1) to make it more interesting. If you only watch one track then I recommend the second one. I pretty much nailed my approach (glideslope&speed)

MiG-21_landingdemo1.trk

MiG-21_landingdemo2.trk

Edited March 23, 2015 by Derbysieger

[1.JaVA_Platypus]

About the "flare" before final touchdown, I don't look at the nose-up attitude at all. If your airspeed and flap/gear config is right, the exact nose-up attitude is not really all that important. You should be focusing on the VSI. It should read about 1 to 2 m/s.

 

Approach should be flown with about 400km/h. (it was somewhere in the manual) and around 5m/s on the VSI. (down that is :smilewink:) At this speed, you have sufficient vision of the runway. Do not stare at the ILS system too much. But watch your airspeed and sinkrate. Usually your engine RPM with full flaps and gear is somwhere between 80 and 90. Aim for touchdown about 100 or 200m before the threshold. Becaus if you flare, you won't be sinking all that much, but you still should be traveling down the runway with an indicated speed of about 350km/h. Flare to about 1 to 2 m/s. If done right, the time between flare and actual touchdown should be 2 to 3 seconds max. Wich is not a lot of time at all! So usually, it is better to look outside the window a bit to see if you are actually still going down.

 

Aerodynamic braking (keeping your nose up while traveling down the runway) works, but it is tricky because at some point, you MUST lower the nose, otherwise it will lower itself because of insufficient speed and it will bounce and potentially damage the nosegear. So to be safe, I gently lower the nose-gear and release the dragchute.

Edited March 23, 2015 by 1.JaVA_Platypus

[Derbysieger]

My procedure is usually like this:

 

• Gear down at 600km/h IAS, ~10-15km out
  
• First stage of flaps at 500km/h IAS
  
• Second stage of flaps at 380km/h IAS
  
• Maintain 340km/h - 360km/h throughout the final descent - not faster than 360km/h because at higher speeds (I think +380km/h) the BLC System disengages, roughly 5m/s descent rate
  
• Reduce descent to 1-2m/s, touchdown at 270km/h-290km/h IAS
  
• Throttle to idle, Airbrakes out, chute only if necessary (that last part is a personal thing but especially in crosswind situations the current implementation of the chute can really mess up your roll out))
  

[malcheus]

thanks again for all your advice, it's going a lot better now, indeed flaring more makes a big difference.

Only problem now is trying to touch down on the first quarter of the runway :music_whistling:

[1.JaVA_Platypus]

thanks again for all your advice, it's going a lot better now, indeed flaring more makes a big difference.

Only problem now is trying to touch down on the first quarter of the runway :music_whistling:

 

Yeah... I had the same problem. So, during the approach, you aim for 200 or 300m BEFORE the runway treshold. Something the PRMG approach won't allow. :pilotfly:

[Derbysieger]

Well the PRMG isn't supposed to guide you all the way down. IIRC if you can't see the runway when you're at ~100m AGL, ~2000m away from the runway (inner marker) you should go around. The PRMG gets very sensitive when you're getting close to the airport so that's when you should stop to fly by your instruments.

 

If you watch my tracks you can see that I treat the PRMG more as a suggestion because I'm flying a visual approach and only use the PRMG as a rough guideline. While I'm quite a bit above glide slope in the first track, in the second track I'm almost exactly on the PRMG glide slope up until I get close. Not because I flew that approach strictly by my instruments but because my initial setup for the approach was a lot better than in the first track.

[mytai01]

I don't even look at instruments or the angle of flare. I just concentrate on going straight down the middle and use my peripheral vision to judge the rate at which the runway edges are coming up at me. I make sure that I'm going about 400 kph in a shallow approach and leave the throttle alone till I touchdown. I've been able to land with any amount of fuel and ordnance.

[Derbysieger]

400km/h is too fast for the BLC System to be active so you definitely want to go slower than that to avoid running into a situation where you're ballooning up just before the runway when you finally slow down and it kicks in.

According to the manual it is active below 360km/h so that's the maximum speed I will fly during the final approach.

 

I am most comfortable around 340km/h and down to about 320km/h after the inner marker just before the flare.

[johnv2pt0]

Airspeeds for landing will vary based on how heavy the jet is. I'd recommend flying 8 deg AoA and using a power push of around 10% instead of flaring to arrest descent. No crunched gear or tail strikes.

 

Full fuel and stores hanging you'll probably be around 340 and empty around 300 or so. AoA is right in front of your face for a reason XD

[Golo]

Airspeeds for landing will vary based on how heavy the jet is. I'd recommend flying 8 deg AoA and using a power push of around 10% instead of flaring to arrest descent. No crunched gear or tail strikes.

 

Full fuel and stores hanging you'll probably be around 340 and empty around 300 or so. AoA is right in front of your face for a reason XD

 

Huh, realy?

--

There is a perfectly OK procedure for landing MiG-21 developed already and it is in manuals, I suggest you try to follow it. Works for me every time.

Why people try to make their own (out of limits) I dont get.