Low drag between 200kts to 400kts

Hi!

I have tested the new FM for the M2000 and I think there is an issue here that is present since the beginning and now feels worse with the update. Drag below 400 kts and above approx. 200 kts feels extremely low.

I have made very basic test flights with clean aircraft and around 80 percent fuel at approx. 10300kg. The test included idle power descents from 10000ft at steady speeds.

Results:

at 400 kts AOA 3 deg. glide ratio 7,8 (7,8nm horizontal distance for 1nm alt.)

at 300 kts AOA 5 deg. glide ratio 13,2

at 250 kts AoA 7 deg. glide ratio 14,9

at 200 kts AoA 10 deg. glide ratio 10,7

I find that the glide ratios at 300 and 250 kts are way over the values that I would expect from a delta wing fighter with high wing loading.

I have made some calculations with the equation for delta wing total drag (see attached pdf) where I used an aspect ratio of 3,02 (AR).

The end result was a lift to drag ratio of:

L/D= 5,44 at AoA 5deg at 300 kts Cd = 0,0373

L/D= 3,95 at AoA 7deg at 250 kts Cd = 0,0739

I don't expect this to be accurate calculation, but it shows the huge difference. (way over 10 vs below 6)

There is another (low quality unfortunately) pdf that shows Cd values in the same range that I have calculated.

I also did the same idle power descent test to the Belsimtek F-5 and the ED Su-27, and both resulted in glide ratios between 6 and 8 for the same speeds. I know that these are different aircrafts but not this different.

(14 vs 7) Mirage has basically half the drag presently in the simulator.

I also did a test flight where I turned the engine off at 1000 ft AGL at 300 kts to kill the idle thrust, and it took about 30 seconds to decelerate to 250 kts. I restarted the engine with quite a delay after this (around 220 maybe)

and I was still able to survive this with an altitude loss of around 500 feet close to stall speed. The time spent without thrust was way over 1 minute.

This seems quite wrong to me.

Don't get me wrong, I still like both the Mirage and the Harrier, but I think this problem should be adressed.

NACATN1468.pdf

Equations total drag.pdf

Also noticed this...I can fly in idle for minutes at level flight almost ground level. The new FM is A LOT better but guess it still need some fine tunning.

Mirage is hell of a glider right now :D

Monitoring. Nice finds if accurate.

I have tried the new version under 1.5.8 just now, and for me it feels great.

I measured the glide ratio now between 8,2 and 4,2 for same speed range as before. For me this seems realistic as well as the deceleration in staight and level flight. :)

Thank you very much for solving this issue!

I've noticed a few things.

- it's harder to take-off ( with the same load, there wasn't any problem to take-off over 140-150kn, now it's almost impossible )

- harder control during low speed (~200 kn )

- I've changed nothing so far but even at ground 'flaps' are still moving ( to big sentivity )

- Don't know why but my plane diving like Su-27 when it's not trimmed

Btw.: Most realistic is using Force Feedback or not?

I've noticed a few things.

 

- it's harder to take-off ( with the same load, there wasn't any problem to take-off over 140-150kn, now it's almost impossible )

- harder control during low speed (~200 kn )

- I've changed nothing so far but even at ground 'flaps' are still moving ( to big sentivity )

- Don't know why but my plane diving like Su-27 when it's not trimmed

With the "new" (more accurate) fly by wire modeling you need to trim the aircraft, especially at low speed. Use either the auto pilot to trim for you or use hat like Su 27.

If you look closely, you will see the the control surface moving during take off run before rotation:

Take off rotation speed, try:

- 130kt for full AA weapon load (4 missile + fuel tank)

- 160kt for heavy AG weapon load (2 Magic, 2 wing tank, 4 x Mk 82 on fuselage pylons)

To land trim on final at desired AoA (14°)

Finally, the real stick has no force feedback, only springs.