Safe MP & RPM ratios?

i read somewhere on this forum that in p-51 between 61" and 67" there is no difrence in top speed at sea level.

for me looks like difrence is preaty big

i know it is p-51B this one is a little faster then D but still difrence should be similar in D version but it is still v1650-7 same as in p-51D

oh i found it its from DCS manual Now i dont quite understand that becouse between 61" vs 67" there 374mph vs 389mph at 5000ft what benefits dcs manual refering to i have no ide becouse for me 15mph faster is preaty good benefit from using WEP

In DCS, at sea level, you can get the extra speed from WEP by backing down the RPM to about 2700-2750 RPM. Also, if you manually control your coolant radiator, you can reduce some drag by closing it down a bit. You will need to watch the coolant temp closely to keep it from getting to hot.

With these setting, I can get the P51D to maintain 382 mph (332 knots), level flight at sea level.

In DCS, at sea level, you can get the extra speed from WEP by backing down the RPM to about 2700-2750 RPM. Also, if you manually control your coolant radiator, you can reduce some drag by closing it down a bit. You will need to watch the coolant temp closely to keep it from getting to hot.

 

With these setting, I can get the P51D to maintain 382 mph (332 knots), level flight at sea level.

while using wep 3000rpm is required so 2700 is out of question

most of the tests done on p-51 are with coolant/oil set to auto (auto should keep max allowable temps at high power settings)

how much faster at 2700 then at 3000rpm ??

wonder what is the reason behind it maby less throttling convering to more net power

Or programming inaccuracies?

In the real mustang, pitch is automatically controlled by mechanics of the system(exactly how, I do not know). Under power, pitch is suppose to increase as long as the engine can maintain the manifold pressure set by the throttle and the RPM set by the propellor control lever, at least until it hits the max pitch allowed.

This is not happening at sea level in DCS. The pitch is being restricted for an unknown reason at 3000 rpm. At lower RPM, higher pitch is allowed and pulls the aircraft to a faster speed.

Or programming inaccuracies?

 

In the real mustang, pitch is automatically controlled by mechanics of the system(exactly how, I do not know). Under power, pitch is suppose to increase as long as the engine can maintain the manifold pressure set by the throttle and the RPM set by the propellor control lever, at least until it hits the max pitch allowed.

 

This is not happening at sea level in DCS. The pitch is being restricted for an unknown reason at 3000 rpm. At lower RPM, higher pitch is allowed and pulls the aircraft to a faster speed.

prop at high pitch become less effective.

prop gavernor will adjust pitch to keep rpm set by pilot.

it is quite logical that pitch will be lower at higher rpm becouse pitch must be lowerd to let prop spin faster.

so for example when engien developing the same power the pitch will be lower at 3000rpm and higher at 2700 rpm it absolutly clear.

and max pitch of the blade is just extra range in pitch preventing overspeed while diving but at very high pitch prop thrust is reduced

and real mustangs racing at 3000rpm or if modified at 3250rpm or higher.

thats whjy you dont see prop plane crusing at 800kph at daily basis

for exmple flying at 2700 rpm with 20" 30" 40" at speed 200mph will give you certain pitch angles on prop higher MP higher pitch will be required to prevent engine rev faster then 2700

but situation will change while tha same power settigns will applied at speed 300mph you will see pitch increase across board compare tho the same power settings with lower speeds

i can assume that at lower rpm 2700 supercharger dont need to be throttled so much giving higher net power afterall but for me 67" at 2700 would be deadly for engine in short time

Have you seen the pitch angles of the prop of a racing Mustang? They are near if not at MAX angle at that RPM (3000-3250).

If the aircraft is capable of more speed, which according to the charts it should be, then the prop pitch should increase resulting in more speed. Increased drag will eventually limit speed increase.

ofc i saw but those engines are developing extreme ammount of power :) and more power bigger pitch simpla as that

oh pitch of the blade is only outcome of plane speed and engine power it in not thing which increase speed of the plane.

if at level flight pitch stop increasing that mean that engine dont have more steam to fly faster those pitch will not increase anymore

p-51 uses ram air and this will decrease power of engine at high speeds . reducing rpm will reduce overboost which have to be cut out and this could make net engine power higher at high speeds

i wonder if unramm air wil change anything in that case

im curious what yo-yo can say about it

Yes, but the concept is the same, More pitch at max MP and RPM will result in more speed. DCS is limiting the pitch for an unknown reason at max RPM. Thus the lower than expected top speed at sea level.

Yes, but the concept is the same, More pitch at max MP and RPM will result in more speed. DCS is limiting the pitch for an unknown reason at max RPM. Thus the lower than expected top speed at sea level.

more pitch at max MP and max rpm will result in rpm drop

plane speed depend directly on power avilable on prop shaft not based on pitch of prop blades

prop pitch is changed only to maintain rpm set by pilot thats it

and top speed at SL in p-51D is 368mph at 67"/3000 rpm

You are automatically assuming that more pitch will cause RPM to drop, and it will, eventually, once it meets the balance of drag vs thrust. Then the pitch will stabilize. Its at this point the max speed is at. Not at a lessor pitch value, but the max pitch that can be maintained at max MP and RPM.

You are automatically assuming that more pitch will cause RPM to drop, and it will, eventually, once it meets the balance of drag vs thrust. Then the pitch will stabilize. Its at this point the max speed is at. Not at a lessor pitch value, but the max pitch that can be maintained at max MP and RPM.

how do you know what is max pitch for p-51 prop at 67"/3000rpms at top level speed

this whole thing is wierd for me

i tested it it fly good 8kts faster :P 67"/2700 rpm

what happen when i go 2600 rpm

i jut flow 67' at 2700 for a good 20minutes no damage to engine.

i dont know why in p-51 manual in part about use of WEP they said like 20 times wep is allowed only at 3000rpm when in dcs you can run 67/2700 just fine probably with same engine fail chance

the only explanation for me is that engine at 2700 rpm and 67" actualy have more power than at 3000rpm but it is not allowed to run that high MP at low rpm acording to p-51 manual

I don't know WHAT value its at, but I do not that it is AT its max attainable pitch that maintains the RPM and MP. DCS will show you that pitch value in F2 view data tape, there, you can see the pitch increase slowly until the aircraft hits is top speed. Never does it decrease to a more efficient pitch angle, only increase.

I don't know WHAT value its at, but I do not that it is AT its max attainable pitch that maintains the RPM and MP. DCS will show you that pitch value in F2 view data tape, there, you can see the pitch increase slowly until the aircraft hits is top speed. Never does it decrease to a more efficient pitch angle, only increase.

its preaty clear why prop pitch is increasing while accelerating. dont know what is wierd about that

there is two ways to keep optimal AOA of the blade one is increase of prop rpm and another one is increase of prop blade pitch

since you cant increase rpm a lot than prop blade pitch is the way to go

faster you flying higher pitch will be required to keep rpm from going up

job of gavernor in p-51 is only one to maintain engine rpm set via handle in cocpit it has nothign to do with optimal pitch angle (whne p-51 hit tops speed any change in prop pich will result in rpm change there is no way that engine rpm will stay unchanged)

i tested unram air at 2700 and supercharger can get about 61" without ramair

so ram air gives benefit at 2700rpm so i think net power is higher at 2700rpm then at 3000 rpm

but in real life power setting 67" at 2700 would create engine fail in short ammount of time