How are you supposed to fly the MiG-15bis at super high altitudes?

[IcedVenom]

A lot of missions I try to fly the MiG-15bis with end up spawning me at very high altitudes and speeds in order to intercept Sabres, however as soon as I attempt to do anything whatsoever I immediately lose control and plummet to very low alt until I'm able to regain control. Is there anything I'm supposed to do in this scenario? I understand MiG-15bis doesn't operate well at high alts, but why would these missions spawn me up so high? How am I supposed to intercept bombers at high alts when I lose control when I do anything in high alts? Any help would be much appreciated. 

[lmp]

On 12/28/2021 at 10:00 PM, IcedVenom said:

I understand MiG-15bis doesn't operate well at high alts, but why would these missions spawn me up so high?

Because that's where the bombers flew. Flying high gives you a much better range and - as you noticed - makes you difficult to intercept. So that's what the B-29s did. The MiG-15 was built to deal with this threat and so high altitude intercepts were the bread and butter of MiG-15 pilots. Take off, make best climb into the stratosphere and catch the guy before he gets away or you run out of fuel. Just like BFM or making carrier traps it requires thought, practice and knowing your aircraft well.

On 12/28/2021 at 10:00 PM, IcedVenom said:

How am I supposed to intercept bombers at high alts when I lose control when I do anything in high alts? Any help would be much appreciated. 

I encourage you to get familiar with chapters 8 and 9 of the flight manual as well as the concept of "coffin corner":

https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics)

There are several things that work against you at high altitudes. Firstly, your engine can generate (significantly) less thrust in thin air. You cannot maintain airspeed in turns or recover it as well as down low.

Secondly, there is the "coffin corner".

when it comes to airspeed, your low limit is 300km/h indicated (citing the manual):

Quote

 

The minimum control speed at which the control surfaces retain sufficient
effectiveness is 300 km/h at altitudes above 12000 m.

The minimum speed for level flight and maneuvering, except takeoff and
landing, is set for the aircraft at IAS 300 km/h.

 

Your high limit is officially Mach 1:

Quote

Maximum Mach number (M): 1.0

but really, you'll be experiencing serious controllability issues much earlier:

Quote

 

At airspeeds exceeding Mach 0.86 - 0.87, the following particulars are
exhibited:
a) opposite roll response to pedal input (for example right pedal
input leading to left roll);
b) slight reduction of stick force in straight flight;
c) increase of stick force required to attain a unit of load (G);
d) uncommanded roll.

(...)

The elevators maintain effectiveness throughout the Mach number envelope up to Mach 0.92.

At Mach > 0.92, aileron effectiveness greatly reduces. At low angles of attack
(1.5°), ailerons effectiveness is practically zero in the Mach 0.96 - 0.98 speed
range.

 

Notice how your low limit is expressed in kilometers indicated and your high limit is a Mach number (true airspeed). As you get higher a given indicated air speed corresponds to a higher true airspeed/Mach number. If my online calculator hasn't lied to me, at sea level 300km/h indicated corresponds to Mach 0.25, while Mach 0.86 (so the Mach number where controllability starts to suffer) is 1050km/h. That's a difference of 750km/h to play with. And you get plenty of engine power to boot. At 15500m 300km/h is now Mach 0.7, while your upper limit of Mach 0.86 corresponds to 378km/h. That's less than 80km/h of difference! In other words, at 15500m you are almost stalling and at the same time almost out of control because of being too fast. And you can barely maintain that speed because your engine is at its limit.

The good news is, the Sabres aren't much better. They can go a little faster without losing control but their engines are weaker and their ceiling should be lower (it was IRL, I haven't done any extensive testing in DCS).

So what can you do at or close to the ceiling? Now I'm no expert, but here's what I do:
- Keep your airspeed indicators in your scan at all time. Pay attention to both your indicated and your true airspeeds.
- Forget about aggressive maneuvers, particularly in the vertical. Lazy turns and shallow dives and climbs only.
- Practice identifying overspeeds early and getting out of them. Read the manual, practice how your ailerons, rudder and elevators react at high Mach numbers. You probably will end up messing up and overspeeding from time to time, but if you can catch it early, you can often correct the problem without a huge loss of altitude.
- Pay attention to your fuel state. In order to climb to the service ceiling and stay there you will need to be flying at full throttle. You really won't have much time before you have to turn back.

In the end, like everything in DCS, it comes down to practice. Practice efficient climbs to stratosphere altitudes, practice how the aircraft behaves at 8000m, 10000m, 12000m, 15000m. Shoot down some non-maneuvering targets first, then move on to maneuvering ones...

Good luck!

Edited January 5, 2022 by lmp
typos

[IcedVenom]

1 hour ago, lmp said:

Because that's where the bombers flew. Flying high gives you a much better range and - as you noticed - makes you difficult to intercept. So that's what the B-29s did. The MiG-15 was built to deal with this threat and so high altitude intercepts were the bread and butter of MiG-15 pilots. Take off, make best climb into the stratosphere and catch the guy before he gets away or you run out of fuel. Just like BFM or making carrier traps it requires thought, practice and knowing your aircraft well.

I encourage you to get familiar with chapters 8 and 9 of the flight manual as well as the concept of "coffin corner":

https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics)

There are several things that work against you at high altitudes. Firstly, your engine can generate (significantly) less thrust in thin air. You cannot maintain airspeed in turns or recover it as well as down low.

Secondly, there is the "coffin corner".

when it comes to airspeed, your low limit is 300km/h indicated (citing the manual):

Your high limit is officially Mach 1:

but really, you'll be experiencing serious controllability issues much earlier:

Notice how your low limit is expressed in kilometers indicated and your high limit is a Mach number (true airspeed). As you get higher a given indicated air speed corresponds to a higher true airspeed/Mach number. If my online calculator hasn't lied to me, at sea level 300km/h indicated corresponds to Mach 0.25, while Mach 0.86 (so the Mach number where controllability starts to suffer) is 1050km/h. That's a difference of 750km/h to play with. And you get plenty of engine power to boot. At 15500m 300km/h is now Mach 0.7, while your upper limit of Mach 0.86 corresponds to 378km/h. That's less than 80km/h of difference! In other words, at 15500m you are almost stalling and at the same time almost out of control because of being too fast. And you can barely maintain that speed because your engine is at its limit.

The good news is, the Sabres aren't much better. They can go a little faster without losing control but their engines are weaker and their ceiling should be lower (it was IRL, I haven't done any extensive testing in DCS).

So what can you do at or close to the ceiling? Now I'm no expert, but here's what I do:
- Keep your airspeed indicators in your scan at all time. Pay attention to both your indicated and your true airspeeds.
- Forget about aggressive maneuvers, particularly in the vertical. Lazy turns and shallow dives and climbs only.
- Practice identifying overspeeds early and getting out of them. Read the manual, practice how your ailerons, rudder and elevators react at high Mach numbers. You probably will end up messing up and overspeeding from time to time, but if you can catch it early, you can often correct the problem without a huge loss of altitude.
- Pay attention to your fuel state. In order to climb to the service ceiling and stay there you will need to be flying at full throttle. You really won't have much time before you have to turn back.

In the end, like everything in DCS, it comes down to practice. Practice efficient climbs to stratosphere altitudes, practice how the aircraft behaves at 8000m, 10000m, 12000m, 15000m. Shoot down some non-maneuvering targets first, then move on to maneuvering ones...

Good luck!

 

Wow, really informative answer. Thanks!

[Tiger-II]

If you have the right climb rate/speed your IAS should be slowly reducing while Mach number increases. As you climb, your vertical speed will reduce from a max of ~45 m/s between 0-5000 ft or so down to around 10-15 m/s at 30000 ft.

When you get to about Mach 0.80 you want to climb to maintain that all the way up to 50,000 ft (constant Mach climb). You may need to experiment as climb speed and max alt is weight-dependent. If IAS reaches ~500 kph then you need to pitch to maintain that instead (min indicated speed). If you're maintaining a constant IAS then as you climb Mach will slowly increase. Again, upon reaching around Mach 0.80 you want to switch to a constant Mach climb.

The typical "Mach transition altitude" is around 30000 ft +/- 5000 ft depending on the airspeed you started with and how well you managed your speed.

Max performing climbs is only something you can perfect with practice. I often fly lots of climb/descent profiles trying to minimize fuel burn and maximize the altitude I can fly at without burning too much fuel to maintain altitude.

If you're clean with just full internal fuel, you should be able to make 40000 ft. As you burn fuel you can climb higher.

Edited March 21, 2022 by Tiger-II