How do I achieve max speed?

[USARStarkey]

So in speed runs a 26000 feet i am able to get to about 430mph. I am using 67inch MP, 3000rpms. At 30000ft using a bot assigned to maintain a even higher speed and hold its alt, I got to 434mph. At 20k, I got to 402mph with a bot, and 410 on my own. This is not nearly fast enough. So what am I doing wrong?

 

P-51 speed vs altitude

 

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_Level.jpg

 

 

 

P-51 Bot Tests, which are rather consistant with both the real thing and my bot tests. Which makes me think Im making some kind of mistake.

http://i.imgur.com/EIzfhUw.gif

 

 

 

 

ED test results at 61 inches (I was at 67)

 

http://forums.eagle.ru/showpost.php?p=1577405&postcount=7

 

Incidentally, I have no issue overtaking the 190D at the same alt, with the bot told to fly straight and at the higher than realistic speed.

So do i need to open a radiator or something?

Edited April 14, 2014 by USARStarkey

[USARStarkey]

OK, so there is a bug or something going on here. Maybe. I cant seem to get to Max RAM air power. critical alt for ram air according to manual is 28000. 26000 if you go by ww2 flight testing. Regardless, I cant seem to get these value at any altitude over 24000ft. I get 61 to 63 at alts above this. am i doing something wrong?

[hitman]

Critical altitude for ram air is different from critical altitude for the supercharger. Its the supercharger that causes the upper manifold pressure to skyrocket like that. I am a bit confused though, the critical altitude for a supercharged engine like the merlin is about 26k, so it should read 14psi or 1 bar.

[USARStarkey]

Whatever the issue, I cannot achieve the rated power of 67in MP at the rate altitude of 26000. Or 28000 like in the manual. I have to go down to 24000 to get 67in. Fastest Speed Ive gotten to was 434 at 30k which is consistent for a bot at 61 inches.

[hitman]

Try emergency power? Press e to break the wires on the throttle.

[USARStarkey]

Ive got emergency power. that is the problem it doesnt work

[hitman]

Did you try retarding the throttle before you hit it? I never use it, perhaps you have to advance the throttle to get emergency power...

[USARStarkey]

Yeah Ive got the throttle full forward. Full rpm. but it only hits 60-62 mp.

[hitman]

Well, dont expect to match the AI pilot in performance, if that is what you are ultimately trying to do. Almost all pilots have flaws in the way they handle their aircraft, but the AI handles their aircraft beyond perfectly. Personally, I think you should feel lucky to even get your aircraft that fast at those altitudes.

 

Chances are also good that its the cold altitude that is restricting the flow into your manifold, with ice buildup choking the carb. What is the humidity? Altitude density? Dew point? Is the area you are flying in currently a low or a high pressure area? What about ambient air temperatures? All of these have a dramatic effect on carb performance, especially at altitude. You will see the best performance out of cold, dry air than you will any other type of atmospheric condition.

[USARStarkey]

Its set to default conditions, I figured those would be most conducive to performance. I get your point about the AI, but the AI for whatever reason, doesn't use WEP. Around 20k for example, The AI P-51 only gets to 406mph at 61inches, I can break about 416. I should be getting 420ish, but I guess I cant fly straight enough. My complaint though is at 26k and up where I should be approaching or even exceeding 440mph. Ill mess with the weather and see what happens. Ill try to change humidity or something then.

[hitman]

Try a cold day, but try to keep it above -30c at altitude. Anything lower than that is taking a big chance the fuel to freeze, and Im not even sure if thats modelled. Play a little with the carb heat as well. Dont keep it on, just keep it on for a few seconds to melt any ice in the intake and close it to see if any MAP is gained.

Edited April 16, 2014 by hitman

[USARStarkey]

No Dice. I am becoming increasingly convinced this is a bug of some sort. Wish we could get a dev to look at it

[gavagai]

Its set to default conditions, I figured those would be most conducive to performance. I get your point about the AI, but the AI for whatever reason, doesn't use WEP. Around 20k for example, The AI P-51 only gets to 406mph at 61inches, I can break about 416. I should be getting 420ish, but I guess I cant fly straight enough. My complaint though is at 26k and up where I should be approaching or even exceeding 440mph. Ill mess with the weather and see what happens. Ill try to change humidity or something then.

 

Don't you think you're cherry picking the very best measured airspeeds for the P-51D?

 

A good rule of thumb for flight model discussions is that if the difference is less than 5%, then you don't argue it. 434mph is less than 2% off from 440mph. A good flight model is the core of a good flight simulation. Let's save our passion for stuff that really matters.

[USARStarkey]

No I am not. The 434 was at 30k or 6000 higher than expected. I provided two speeds because i was NOT cherry picking. 430mph at 26000 was never a reported speed. Furthermore, the issue is more with the fact that I cannot achieve max power. The speeds I am achieving are exactly what was achieved at military power in the Mustang according to the tests. Not war emergency, which I cannot seem to attain at either the RL or Game specified altitudes. If I could actually achieve WEP, and then got to 435 or 445 or whatever....then we wouldn't have an issue. You quoted only part of this thread, did you actually read the rest? If not, Ill reiterate: This is about power achieved more than it is speed attained.

 

 

 

Could you be any more patronizing dude? You just waltz in here and tell us to "save our passion for the stuff that really matters..." Geez...condescending much? I DO think that this matters. The upcoming aircraft were getting are very close to each other in top speed at critical altitude. 51-442 109-441 190-442. A slight error, much less one of 10MPH is a big deal when it is that close IMO. Especially when were talking about MP here, not just top speed.

Edited April 16, 2014 by USARStarkey

[hitman]

Just for sh1ts and giggles, what does the performance scales state that the manifold pressure should be at those altitudes? Max speed at 26k was 437kts, and anything higher in altitude than that you start to lose bhp to the prop. Not just loss in manifold pressure, but airflow over the props. The faster a prop spins, the less efficient it is. Air friction is inversely proportionate to altitude, and the prop would spin a little faster than it should. Perhaps you should increase the blade angle as well?

[USARStarkey]

I don't think you can manually adjust the prop pitch in the mustang since it has a constant speed propeller. Max Power at 26k was 67inches MP. The DCS manual places it even higher at 28000ft!

 

Here is what the manual states: War Emergency= 67inches MP @ 3000RPM @ 28,800ft @ High Blower/ Mixture set to Run/AR.

 

Alas though, I cant seem to make it hit 67 inches at any alt above 24,000ft, which is much closer to the WEP critical altitude for Non-Ram, of 23,200ft.

[hitman]

Its a variable pitch propeller, a Hamilton Standard. If anything, it has reduction gears as well to slow the prop down.

Edited April 16, 2014 by hitman

[USARStarkey]

Where is the pitch control. I mean, I know the plane can adjust pitch, but I thought that only the prop governor had control of it as a function of RPM/Power.

[hitman]

Its a hydromatic pitch control, and its located right next to the throttle. Its the black knob labeled propeller outboard the throttle. It should be full forward during takeoff, and at 2700 rpm at landing. The rest is just trim adjustments. I would assign that lever to an axis on your joystick. The pitch controls the rpm by increasing the angle of attack of the blades, which causes drag, which in turn will increase the load on the engine. You will see a manifold pressure drop proportionate to your propeller speed. So dont go overboard with it, because you can come close to feathering the props. Im not sure if they are full feathering, but the blade angle gets pretty steep on them blades.

Edited April 16, 2014 by hitman

[USARStarkey]

There is a black knob labeled "P", but that it RPM control. Is that what you mean? If so, the best power setting for speed or power in general is 3000rpm.

[hitman]

P for prop, and thats how the rpm is controlled. 3000rpm at sea level is not 3000rpm at 26k feet. Try trimming the rpm between 2800 - 2900 and test the results. Not going to guarantee you are going to see what you want, but it is a variable you want to explore.

[USARStarkey]

3000 rpm is 3000rpm. As soon as I decrease the rpm, the prop governor for the constant speed prop automatically increases he prop pitch to maximum obtainable and as a result, the MP drop.

[NoJoe]

Just in case you hadn't tried it, have you ruled out throttle calibration? Is your throttle actually at 100% in the sim?

 

I have a vague recollection of some posts by Yo-yo where he discusses why WEP is only able to give a MP boost at lower altitudes... I'll see if I can find it. Anyone else know what I'm talking about? It might have the answer to your questions, Starkey.

 

[EDIT] I think this is the thread I was thinking of. There's a bit of discussion later in the thread:

http://forums.eagle.ru/showthread.php?t=119654

 

See post #14, where Yo-Yo says:

THe engine will not give better performance HIGHER than 5000 ft! It is an obvious mistake in the manual.

The point is that if you have throttle full open all the way, the power will decrease as altitude increases.

 

MP regulator set to cut MP cutting the power at the certain altitude, i.e. the power increases a little from SL th this altitude, then goes along the same curve. The more MP we cut the less is SL power and the higher is the knee or the critical altitude.

Thus, increasing the MP cut level we can only increase low level power, though the power at the altitudes higher than the knee remain the same.

Edited April 17, 2014 by NoJoe

[hitman]

3000 rpm is 3000rpm. As soon as I decrease the rpm, the prop governor for the constant speed prop automatically increases he prop pitch to maximum obtainable and as a result, the MP drop.

....its not going to constantly stay at 3000rpm. Its going to stay at the rpm you adjust it to. Its only constant as it will stay at 3000rpm if you back off the throttle. It will also stay at 2700rpm if you back off the throttle. Adjust the pitch for optimum performance, dont know how much clearer I can make it.

Edited April 17, 2014 by hitman

[USARStarkey]

If I adjust the Propeller RPM to 2900 or 2800, the max MP drops even if I don't touch the throttle. It doesn't allow me to run 67 or even 61 inches at any RPM less than 3000 at that altitude. I'm not sure I understand what it is you want me to do.

 

To No Joe: I'm not sure what Yo-Yo is on about, but he is dead wrong that the engine wont give better performance higher than 5000ft. MP pressure was maintained by the engine in two stages, High and Low blower and could maintain the Max MP to much higher altitudes than 5000ft. Even DCS models this, as I can currently hold 67inches up to 24,000.

 

Here is the proof: