technical question

I got question. about supercharger model in DCS.

for exaplme when i fly p-51 and from some reasons i lost my engine i have no power but engine spins not jammed do i have any benefit from backing up throttle to zero while gliding.

Becouse as i understand that, supercharger even when engine is not firing with throttle advanced full forward will create max boost for given engine rpm. So in that case glidign with thorttle at max glide range should be reduced becouse engine's supercharger wil suck energy from plane to create that boost so it should be mandatory in the case of engine lost pilot should cut throttle imidietly am i right and if i am right does DCS have this thing modeled

supercharge can suck out 100-200HP from engien crank shaft

I don't think it has anything to do with supercharger. Whenever you lose your engine it's better either with the prop stuck or windmilling to set rpm to full, which is the lowest actual pitch you can achieve as there's no prop feathering, and that to prevent windmilling precisely which rises the drag and shortens your glide time. Just use best glide IAS to the ground and that's all you can do. Who cares if you're even more dead because the supercharger or not :lol:.

I don't believe supercharger is working at all with no engine running, no matter what you do with the throttle. So as you wish.

S!

I don't think it has anything to do with supercharger. Whenever you lose your engine it's better either with the prop stuck or windmilling to set rpm to full, which is the lowest actual pitch you can achieve as there's no prop feathering, and that to prevent windmilling precisely which rises the drag and shortens your glide time. Just use best glide IAS to the ground and that's all you can do. Who cares if you're even more dead because the supercharger or not :lol:.

 

 

I don't believe supercharger is working at all with no engine running, no matter what you do with the throttle. So as you wish.

 

 

 

S!

when ever crank shaft is moving with sufficient speed spuercharger is working at least in gear driven solution like in merlin engines

Whenever you lose your engine it's better either with the prop stuck

You will do nothing in that case, because of oil pressure lost witch means inability to control propeller pitch..

windmilling to set rpm to full

if you want fly as long as possible in that case, do NOT do it that way...

If engine is windmilling, the way how to achieve the best glide flight distance is to set LOW propeller RPM, full backward propeller lever - the highest possible propeller pitch.

Higher propeller pitch means lower drag for forward plane movement. And higher drag for propeller rotating...

when engine is without power and only windmilling

decreasing propeller pitch (high RPM) - increase total drag - shorter flight distance

increasing propeller pitch (low RPM) - decrease total drag - longer flight distance

when ever crank shaft is moving with sufficient speed spuercharger is working at least in gear driven solution like in merlin engines

You will do nothing in that case, because of oil pressure lost witch means inability to control propeller pitch...

if you want fly as long as possible in that case, do NOT do it that way...

 

If engine is windmilling, the way how to achieve the best glide flight distance is to set LOW propeller RPM, full backward propeller lever - the highest possible propeller pitch.

Higher propeller pitch means lower drag for forward plane movement. And higher drag for propeller rotating...

 

when engine is without power and only windmilling

decreasing propeller pitch (high RPM) - increase total drag - shorter flight distance

increasing propeller pitch (low RPM) - decrease total drag - longer flight distance

S!

wait wait engine is till running even at low speeds so you wil have oil pressure still and the spuercharger will spin enough unles you deep below 1500 rpm in that case neither prop pitch will do anything

As far as i know prop in p-51 is spring loaded so spring will decerease pitch if rpm drop so at very low speeds probably neaither throttle and prop hnadle do anything significant

but i am asking about engine fail at for example 300mph at this speed prop gavernor will keep 3000 rpm even without engine power so in that case prop fulll back but what about throtttle i think throttle full back too, so you cut off air going to supercharger and another thing you preventing air to be inducted into cylinders so engine will spin with less input force

Just going to drop this tidbit: If you want to get the best glide angle, slide the prop pitch control fully aft. My guess is that the blades just knife through the air, instead of punching through it. If your propeller is wind milling, you may still have some hydraulic pressure for the blades to change pitch.

That's the only knowledge I can drop here. Sorry

whne engine is out propeler starts acting like a source of power. there is never easy corelation in rl

pitch of the propeler is not set by soem abstraction but only by specyfic rules set via control unit gavernor designed by men. So everythin will change pitch of the plane not only prop handle even turning off electric stuff will make engine crank easier so gavernor will set higher pitch on prop. but this is minor staff but supercharger can suck a lot of HP from the engine,

unless make that supercharger will work with least ammount power required = lowest rpm and lowest air flow. So you can avoid unnececary extra 100hp drained from your energy

First of all, you have to reduce rpm to min using the prop governor. Then, actually, reducing throttle can help a bit, you can even test the effect. Ctrl-Y bar can shows XY coordinates of your plane, so you can measure the path very accurately. Try to glide from 1500 m starting getting the best gliding speed (AS FAR AS i REMEBER IT IS ABOUT 175 MPH) to 1000 m and maintain it till you touch the ground.

Try jammed engine, prop at min rpm, at max rpm and min rpm with open throttle.

jammed engine is the worst scenario prop blades are at lowest pitch and prop is not spining so in that case prop is absorbing the most ammount of energy.

im asking only about scenarion when airspeed is still enough to keep 3000 rpm and i am asking does throttle position change ammount of force to keep engine spning at 3000rpm or not

i think that best glide for p-51 is 150mph

i just tested that haha its here :P at around 200mph then i hit full throttle engien starts loosing rpm that mean that engine spins harder then i cut throttle back engien spins up again mean that engien spins much easier

thanks ED. this is just awsome

If you increase the RPMs the supercharger might increase your manifold pressure but since there is no combustion that doesn't matter. Think about it - you're trying to use the drive shaft to power your supercharger, and then use your supercharger to power your drive shaft. P-51 is amazing, but it isn't *quite* a perpetual motion machine.

If you decrease RPMs you'll get a noticeably better glide slope.

If you're going fast enough to get 3000 RPMs then you should set full decrease and you'll bleed speed more slowly. Maintain lvl flight until you slow down to the best glide speed, around 150-175 depending on weight and if you have pylons or not (obviously drop your stores).

If you care about going max distance, that is. If not, just point at the ground and find a good place to land :)

If you increase the RPMs the supercharger might increase your manifold pressure but since there is no combustion that doesn't matter. Think about it - you're trying to use the drive shaft to power your supercharger, and then use your supercharger to power your drive shaft. P-51 is amazing, but it isn't *quite* a perpetual motion machine.

If you decrease RPMs you'll get a noticeably better glide slope.

If you're going fast enough to get 3000 RPMs then you should set full decrease and you'll bleed speed more slowly. Maintain lvl flight until you slow down to the best glide speed, around 150-175 depending on weight and if you have pylons or not (obviously drop your stores).

If you care about going max distance, that is. If not, just point at the ground and find a good place to land :)

i was talking about throttle position not rpm of the engine. i was talking about need of cuting throttle to 0 this helps avoid aditional drag via removing vast compression work from engine. and this is actualy modeled in the DCS now so i am happy

you can see rpm drop while gliding while you move throttle form 0 to max this indicate that engine take more power from prop so rpm starts drop but afte a couple seconds rpm go bac to normal becouse gavernor is adjusting pitch to maintian set rpm. so movinf throttle to 0 will exted your glide even more even turning off gun heater or generator would help in this regard too. But i dont know if this modeled in the game i will check it soon but rpm change may be not visible

So tell me if I understand what you're saying:

1 If you set the aircraft to full decrease, then the aircraft will maintain the lowest constant RPMs that it is designed to. It will adjust prop pitch up or down (causing more or less drag) based on it's situation, as long as RPMs are constant. (I agree with this premise)

Then you seem to imply:

2 If you have the throttle open, then the ram air will pass over the internal supercharger's impeller, and because the supercharger is directly connected to the crankshaft, but the engine isn't generating any mechanical energy, this causes the ram air passing over the impeller to create resistance on the crankshaft and the aircraft will have to increase the prop pitch to maintain that lowest possible RPM setting (premise 1), which will slow you down.

3 But if you close the throttle there will be no air passing over the impeller and the crankshaft will be unimpeded and the prop pitch will be lower because the impeller isn't causing any resistance.

4 Therefore, glide with the throttle closed.

(correct me if I have misunderstood you)

Ok, I disagree with premises 2 and 3 (and therefore the conclusion) IN THEORY.

For example,

If you ram a bunch of air through a pipe into a manifold and then turn on a fan in the pipe at 33,000 RPM blowing into the manifold, then you are going to get a higher manifold pressure. But if you turn off that fan, but continue ramming air into the pipe, isn't the fan still going to spin in the same direction as when it was on? And, if the fan is connected to the crankshaft, doesn't that therefore mean that opening the throttle and letting the ram air through would cause the fan to HELP the spinning of the crankshaft and not hinder it?

Now, an impeller is a weird sideways fan that scoops air and stuffs it into the manifold, so that analogy might not be accurate. I'm not an engineer, so I couldn't say. Like I said, this is just a theory.

But after a brief test in DCS with my engine off, I couldn't discern any difference between the throttle being at full and throttle being closed. I also didn't see any difference when my high blower switched off.

I did, however, notice that setting RPMs to full decrease got me from 2300 fpm descent to about an 1800 fpm descent, which is way more than I expected. Also, messing with the RPMs definitely causes a good amount of torque that worbbles the plane all over the place.

I also noticed that when at full increase the MP was well above 45 at FT and when I was at full decrease and FT it was still at about 28MP while passing through 10,000 ft. At that altitude the atmospheric pressure should be more like 20 inches. This implies that even with the supercharger off and the RPMs set as low as they can go that the supercharger is still doing its thing, at least as modeled in DCS. Although I have to admit, I don't know what the pressure of just the ram air would be in the manifold. It might be 28 inches without the supercharger.

Anyways, interesting technical question.

So tell me if I understand what you're saying:

 

1 If you set the aircraft to full decrease, then the aircraft will maintain the lowest constant RPMs that it is designed to. It will adjust prop pitch up or down (causing more or less drag) based on it's situation, as long as RPMs are constant. (I agree with this premise)

 

Then you seem to imply:

 

2 If you have the throttle open, then the ram air will pass over the internal supercharger's impeller, and because the supercharger is directly connected to the crankshaft, but the engine isn't generating any mechanical energy, this causes the ram air passing over the impeller to create resistance on the crankshaft and the aircraft will have to increase the prop pitch to maintain that lowest possible RPM setting (premise 1), which will slow you down.

 

3 But if you close the throttle there will be no air passing over the impeller and the crankshaft will be unimpeded and the prop pitch will be lower because the impeller isn't causing any resistance.

 

4 Therefore, glide with the throttle closed.

 

(correct me if I have misunderstood you)

 

Ok, I disagree with premises 2 and 3 (and therefore the conclusion) IN THEORY.

 

For example,

If you ram a bunch of air through a pipe into a manifold and then turn on a fan in the pipe at 33,000 RPM blowing into the manifold, then you are going to get a higher manifold pressure. But if you turn off that fan, but continue ramming air into the pipe, isn't the fan still going to spin in the same direction as when it was on? And, if the fan is connected to the crankshaft, doesn't that therefore mean that opening the throttle and letting the ram air through would cause the fan to HELP the spinning of the crankshaft and not hinder it?

 

Now, an impeller is a weird sideways fan that scoops air and stuffs it into the manifold, so that analogy might not be accurate. I'm not an engineer, so I couldn't say. Like I said, this is just a theory.

 

But after a brief test in DCS with my engine off, I couldn't discern any difference between the throttle being at full and throttle being closed. I also didn't see any difference when my high blower switched off.

 

I did, however, notice that setting RPMs to full decrease got me from 2300 fpm descent to about an 1800 fpm descent, which is way more than I expected. Also, messing with the RPMs definitely causes a good amount of torque that worbbles the plane all over the place.

 

I also noticed that when at full increase the MP was well above 45 at FT and when I was at full decrease and FT it was still at about 28MP while passing through 10,000 ft. At that altitude the atmospheric pressure should be more like 20 inches. This implies that even with the supercharger off and the RPMs set as low as they can go that the supercharger is still doing its thing, at least as modeled in DCS. Although I have to admit, I don't know what the pressure of just the ram air would be in the manifold. It might be 28 inches without the supercharger.

 

Anyways, interesting technical question.

i dont know how you didnt notice rpm change while moving throttle from 0 to max while gliding with decent speed i did noticed it. when you cut air to supercharger it will not work so hard becouse it will provide very little boost and engine will not be forced to compress dence air.

test it at lower alt. above 10k ft first gear at 1600rpm wont give much boost

Basicly less difrence in air pressure between intake and supercherger discharge outlet less power required to sipin it. if some how air presusre woild drop to zero in intake impeler would spin without air drag ofc there is cost paid to create this low pressure but its lower then boosting full charge with throttle wide open

This 0 to max throttle impact on rpm is even more niticable while gliding at 3000rpm set

when you lower rpm to minimum in p-51 you actualy reducing power required to spin engine and becouse of it you extend glide range

if you want to spin something faster you need more power/force

Ah ok I see.

I recorded my test and looking back I can see that when I jammed the throttle forward the RPMs did go down to about 1590 and then went back up to 1600 which would imply the aircraft had to increase prop pitch to maintain those 1600 RPMs it likes.

I forgot that the supercharger is mechanically connected to the crankshaft with something like an 8:1 ratio, so of course the impeller is going to have an easier time spinning in a vacuum than in air. I was assuming the impeller and prop were separately in a neutral position but that putting air over the impeller could somehow transfer power to the prop lol.

I still can't discern any difference in my rate of descent because of it, but if your engine is out at high altitude and you have a ways to go, this is good to know.

Ah ok I see.

 

I recorded my test and looking back I can see that when I jammed the throttle forward the RPMs did go down to about 1590 and then went back up to 1600 which would imply the aircraft had to increase prop pitch to maintain those 1600 RPMs it likes.

 

I forgot that the supercharger is mechanically connected to the crankshaft with something like an 8:1 ratio, so of course the impeller is going to have an easier time spinning in a vacuum than in air. I was assuming the impeller and prop were separately in a neutral position but that putting air over the impeller could somehow transfer power to the prop lol.

 

I still can't discern any difference in my rate of descent because of it, but if your engine is out at high altitude and you have a ways to go, this is good to know.

actualy when you move throttle forward blade pitch has to decrease it need to show more area of blade to incoming air to spin engine up to 1600 and viceversa whne you cut off throttle

yeah difrence will be very tiny in decent at lowest rpm but its in the game so preaty in depth modeling imo

whne you try this throttle thing at higher rpm like 3000rpm the impact is much bigger

oh p-51 actualy has 2 superchargers one feed another one