Airspeed and altitude, economic airspeeds and FM.

[illern]

Hi!

 

I have been testing the cruise speeds at different altitudes.

When I tried using the time keeping function it uses standard values for mach during the flight. It states it uses economical airspeed unless you set mach speed at an ingress point.

So as I understand we should be able to cruise at the economical airspeeds.

The manual states that this is the airspeeds at certain altitudes:

 

Economic airspeeds at altitude

Stored in the CK37 for fuel calculations

Altitude.....................Airspeed (Mach)

0 m (0 ft.)................ M 0.55

3000 m (10,000 ft.)..M 0.66

6000 m (20,000 ft)...M 0.76

9000 m (30,000)......M 0.86

10,000 m (33,000 ft.) M 0.9

 

I have done 2 tests, one with full armament and one empty.

For full I had 2 air to air missiles 24, KB pod, jammer pod and 2 RB05 missiles and an extra tank.

I started on NTTR at the southern most airport.

Set main altimiter to the airport QFE 992.0 and backup on QNH 1012, standard values from the mission.

 

Started and accelerated to speed and settled on different altitudes and let the speed drop on full military power to see what max cruise speed I could be able to sustain.

 

QFE alt...QNH alt...Mach full...Mach empty

700........860.........0,77..........0,87

3700......3940.......0,76..........0,88

6700......7250.......0,64..........0,86

9700......10820.....Not able to sustain cruise, stalled out.

10700....12080.....Not able to sustain cruise, stalled out.

 

When you get some altitude you can no longer cruise at economical speeds or cruise at all.

 

I think this must be a incorrect behaviour?

 

It´s tested with v2.2 alpha

 

/illern

[renhanxue]

No, that sounds correct. The distance economy numbers for 9000 and 10000 meters are only relevant to a clean aircraft. As per the SFI for the real aircraft, if you have a drop tank you can't maintain level flight at those altitudes without the afterburner. Depending on the loadout, best distance economy is usually somewhere around 7 km MSL.

 

If you want the details, go look at SFI fpl AJ 37 del 3, in particular the flight envelope graphs under the heading "planflykt" around page 80 in the PDF. There's altitude vs top speed graphs on the following pages as well.

[illern]

I was searching for tables like that in the AJS SFI but couldn´t find them.

According to the table for Planflykt with clean aircraft I should be able to sustain 0,7-0,9 Mach at 10000m.

In my test above I have a clean aircraft (column Max empty above) and it will stall out in level flight and max thrust without afterburner.

 

 

I started level flight at more than mach 1 and autopilot on. ("Höjd")

But still it slows down to a stall.

 

Other from that it looks like it is somewhere in the right numbers according to the SFI.

 

/illern