Unable to reach full throttle in F-15C using Warthog in Instant Action mission

[pengjn]

Day 1 of DCS for me! :) I've been looking fwd to this for a LONG time. Just finished building my rig with 4790K, GTX980 Ti and Thrustmaster Warthog - plus TrackIR obvs.

 

I'm struggling a bit. If I cold start then I have proper throttle control but if I go instant action then I can't get to 100% throttle nor burner. Clearly i'm doing something stupid but I know not what. Any advice?

[sobek]

Have you checked whether the instant action mission has a different realism setting than the cold start mission?

[Whistler_RIO]

ensure that the option described roughly as 'synchronize controls upon mission start' is enabled

[Sweep]

I'm sorry, I've got to ask the stupid question...Are you looking at the RPM gauge? It doesn't move over 96%.

 

I'm guessing 'no', but had to ask.

[pengjn]

I'm getting 96% RPM in both cold start and instant action. However, i get 40 (units?) fuel flow in cold start and 30 in instant action. What fuel flow should I see in full burner? If I do the Instant Action Aggressor mission then I'm down to 150 knots during my first turn after the merge and then i'm wallowing at the stall from there on into the fight. Either i'm not getting full power or i'm expecting way too much turn performance but I thought the F-15 could sustain a high rate of turn indefinitely due to high thrust available?

 

I've got 'Sync controls upon mission start' enabled and 'Use these options for all missions' enabled too.

 

Sorry for being such a noob. Literally day 1 :)

 

PS Also - i'm not totally convinced that i'm getting minimum power either - it takes all day to slow down from 300 knots to 200 knots at min power with the air brake open, in a shallow (5 degree) descent with throttles on the backstop. Confused! :S After engine start i'm seeing 66% at idle - sounds about rright?

Edited January 17, 2016 by pengjn

[mvsgas]

Fuel flow is Pounds per hour (PPH). Are you at the same altitude, speed? Is the ambient temp the same?

[pengjn]

Fuel flow is Pounds per hour (PPH). Are you at the same altitude, speed? Is the ambient temp the same?

 

I just did a cold start from Nellis and was getting 50 PPH (thousands presumably?!) at 3'000. At 24'000 in the instant action i'm getting 30. Does that sound right?

[mvsgas]

IIRC, PPH changes with altitude and other factors. RPM is the same in RL.

[pengjn]

Def something wrong - if I go to full throttle immediately i enter the Aggressor mission then i'm at the stall before i've managed to do a 180 turn at the merge - i must be doing something v stupid. I'll try adjusting the throttle with the keyboard to see if that shows it to be the HOTAS throttle config.

[mvsgas]

So in flight, the F100-PW-220, you can't say RPM is this and fuel flow is that (I do not think all of it is modeled in DCS). So, in flight, to know AB is working, you are just looking for nozzle opening ( no specific number), fuel flow increase ( no specific number) and noise and no faults indicated. That is the only thing as a pilot you have.

 

The higher you are the less capable the aircraft is to sustain turns generally speaking. To know if you have a problems, test both missions at same altitude/speed/load out and same environmental conditions.

[pengjn]

Makes sense. I'll give it a bash. Using the keyboard didn't seem to make a notable difference in terms of the fuel flow initially but then it was up to 50-60 and I was able to sustain 7-8g turns at 500kts at various altitudes so I must be doing something stupid somewhere.

[sobek]

It sounds like what you are missing is the influence of induced drag on continuous turn performance. You might want to check that out.

[pengjn]

I do love a bit of aerodynamics being a glider (sailplane) pilot as a hobby. I haven't found anything in a (very) brief google. Is the idea that if you start a high performance turn too slow then you end up burning more energy due to induced drag than if you start at a higher speed. Thinking about it that would make some sense - in gliding we load up water ballast to weigh the aircraft down to increase wing loading, thus reduce induced drag. I'm guessing that higher speed = more g = less induced drag????

[ShuRugal]

I do love a bit of aerodynamics being a glider (sailplane) pilot as a hobby. I haven't found anything in a (very) brief google. Is the idea that if you start a high performance turn too slow then you end up burning more energy due to induced drag than if you start at a higher speed. Thinking about it that would make some sense - in gliding we load up water ballast to weigh the aircraft down to increase wing loading, thus reduce induced drag. I'm guessing that higher speed = more g = less induced drag????

 

There are a couple things coming in to play here.

 

The first is airflow into the engines. The faster you are flying, the more air the engines can breath, thus the more power they can make. The saying goes "The faster you go, the faster you go faster" and its correlate is "The slower you go, the faster you go slower".

 

Second thing is something called "corner velocity". This is, in essence, the slowest airspeed at which you can pull maximum-Gs. Flying at this speed will give you the best possible instant and sustained turn rates. If I recall correctly, the F-15 corner speed is 350~450 Kts IAS, depending on load.

 

Flying faster also means a lower AoA needed for the same lift. Lower AoA == lower induced drag, which means flying faster == lower induced drag.

[SinusoidDelta]

I'm getting 96% RPM in both cold start and instant action. However, i get 40 (units?) fuel flow in cold start and 30 in instant action. What fuel flow should I see in full burner? If I do the Instant Action Aggressor mission then I'm down to 150 knots during my first turn after the merge and then i'm wallowing at the stall from there on into the fight. Either i'm not getting full power or i'm expecting way too much turn performance but I thought the F-15 could sustain a high rate of turn indefinitely due to high thrust available?

 

I've got 'Sync controls upon mission start' enabled and 'Use these options for all missions' enabled too.

 

Sorry for being such a noob. Literally day 1 :)

 

PS Also - i'm not totally convinced that i'm getting minimum power either - it takes all day to slow down from 300 knots to 200 knots at min power with the air brake open, in a shallow (5 degree) descent with throttles on the backstop. Confused! :S After engine start i'm seeing 66% at idle - sounds about rright?

 

Max throttle is correct at 96% RPM. Idle rpm is correct and should be 65%-66%, on the ground and in the air. IRL between mach 0.8-1.4 idle was increased to MIL 79-80% to avoid compressor stalls. The ground thrust at idle is low according to a few sources but that's another discussion.

 

I'm sure you know thrust isn't instantaneous and it will take time to get that speed back up. The F-15 is a slippery bird with a lot of mass, bring the nose up and it will decelerate quickly.

[mvsgas]

Confused! :S After engine start i'm seeing 66% at idle - sounds about rright?

Yep

[pengjn]

Max throttle is correct at 96% RPM. Idle rpm is correct and should be 65%-66%, on the ground and in the air. IRL between mach 0.8-1.4 idle was increased to MIL 79-80% to avoid compressor stalls. The ground thrust at idle is low according to a few sources but that's another discussion.

 

 

 

I'm sure you know thrust isn't instantaneous and it will take time to get that speed back up. The F-15 is a slippery bird with a lot of mass, bring the nose up and it will decelerate quickly.

 

 

Great info I'm starting to get my head around this. High altitude + low speed = low fuel flow rate due to lower volume of air entering the engines (lower speed and air density) plus lower drag. Low and fast is the opposite.

 

I hadn't thought about bleeding more energy at lower speed but I'll be sure to enter the merge with a lot more speed from now on.

 

Good point about reducing energy by pulling the nose up and I'll make sure I don't enter final approach with too much energy from now on and expect the air brake to magically fix my error.

 

This is all making good sense - I flew as a passenger in an English Electric Lightning ten years ago and that has somewhat similar performance to the F-15. I recall that it took a fair bit of time to accelerate into the supersonic regime and when we came into land the only way to slow it down was to crank in some decent g turns to get down to around 200-250 knots on the downwind. That's a long story in itself but if you're interested then check it out; Google "Pengelly Thunder City Lightning".

 

I'm impressed so far by how challenging (and i'm guessing accurate) the simulation is. It's going to be a great challenge to achieve some basic level of competence!!!!

 

 

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