FM question

[Mako]

You are very far from the truth: Mach number is calculated using just TAS. That's why the high altitude flight has relatively LOW IAS values but high TAS and M values.

 

...

So, it's not a bug - it's just pure physics...

 

I did say that drag is very high and that is what prevents a large increase in speed when in a dive. I agree that the low acceleration seen in LOMAC is accurate.

 

I understand the relationship between TAS and M (more or less). My statement about TAS vs. IAS was in regard to a previous statement about reduced manuerverability at high altitudes. It is my understanding that the low air density (and thus, low IAS) is the source of the problem not "compression". Am I incorrect?

[GGTharos]

Mako, 350IAS is 'good manauvering' speed for just about any aircraft as far as rolling etc is concerned. The problem IS however that your mach is very high, and anything you do induces pretty high drag and possibly compression which causes the controls to be sluggish. The IAS ITSELF would indicate that your roll, for example (forget turning, turning is very dependent on TAS as well) should be at close to max performance at that speed, as an example.

 

Just another way to see that flying planes is complicated ;)

[Mako]

Oh geez..of course!

 

So complicated that my thinking starts going in circles. Or would that be vortices?

[Yo-Yo]

I did say that drag is very high and that is what prevents a large increase in speed when in a dive. I agree that the low acceleration seen in LOMAC is accurate.

 

I understand the relationship between TAS and M (more or less). My statement about TAS vs. IAS was in regard to a previous statement about reduced manuerverability at high altitudes. It is my understanding that the low air density (and thus, low IAS) is the source of the problem not "compression". Am I incorrect?

 

When the M number is higher than 0.8-0.9 all the aerodynamics characteristics of the plane changes. The redistribution of the pressure makes the plane more stable and that's why the controls must be more effective. The lift/drag and Lift vs AoA curves is changed dramatically as well and for example the plane at the IAS 350 kts at low alt (low M) is not the same as at the 14000 m at the same IAS (high M).

 

That's why the subsonic overpowered planes like Su-25 have IAS never-exceed speed and the Mach never-exceed number. The first restriction is for low alt and the second for high.

[Tracker]

Part of the problem here is the energy loss in pitching from FL350 to 90degrees nose down attitude. Keeping in mind that your MA is reduced for a lighter A/C, the loss may be rather significant and difficult to regain due to some reduced thrust at higher Alt. Use a 1/4 Split S manuevre and keep your G loading below 2 and I think you'll find your accleration factors are closer to what your looking for. Another thing you may want to consider in this manuevre is your actual negative Vertical Velocity. Assuming there is no glide component and a true 90 degree nose down attitude your instruments should be syncronized well. Thus your Mach Gauge and Altimeter will agree. Your VV gauge will max at 6k. To Calculate your true accleration factor your going to have to clock either altitude drop or mach increase. I think you'll find its not as sluggish as it looks.

 

As regards glide component of the F15, I think it glides very nicely pitched for ~200 to 220 knots. Best glide seems to kick in below 13,000' and actual attitude varies depending on loads. In a real A/C there will be a difference between Idle approach and actual flameout due to autorotation of the turbines but I havn't seen this in the model. In this sim I've glided a fuel empty F15 54nm from FL200 and a crosswind component of 15knts with plenty of energy to complete a 90 degree left turn into the wind and land at 160+. ;-)

 

Another brief comment also on thrust-to-weight ratios. The F16 has a 1.1:1 ratio where a 747 has 0.26:1. I don't have the F15 data in front of me, but this also plays a part in the acceleration factor.

 

Additionally, keep in mind that the physics behind thrust will occur even in a vacuum ( otherwise our space missions would all be one way, lol) but the reduction of thrust is actually do to a pressure loss in the combustion chambers where less oxygen is available.:cool: