Turbosupercharger Use: 7000ft? 12000 ft? 3500 ft?

[Scotch75]

Many thanks for the info. With heavier loads or shorter runways, will it still be beneficial to use the supercharger for take-off (even with water injection too), or is it a cost/benefit ratio thing? Does the supercharger take too much HP out of the engine for take-offs?

Cheers!


Sent from my SM-G998B using Tapatalk

[Nealius]

That's a good question on shorter takeoffs. I've found that the turbosupercharger doesn't kick in until I'm already halfway down the runway. 

[SloppyDog]

17 hours ago, Caldera said:

From what I can gather the turbo (supercharger) on the P-47 was huge.   First off, with allot of rotating mass it would not spool instantly.  This "turbo lag" is what I see when I close the waste gate and direct engine exhaust gas to the turbo vice dumping it to atmosphere.  Second off, for efficiency, the turbine casing for the turbo would be large.  

Have you ever seen these? These are from the National Museum of WW II Aviation in Colorado Springs, CO. This site gives a good explanation how the system works. https://lynceans.org/all-posts/the-complexity-of-a-ww-ii-p-47-thunderbolts-powerplant/

Basically, the entire body of the P-47 is a housing to the supercharger and intercooler system.  People talk about pressures, but volume of air is also very important. Just look at the size of those pipes. It is a lot of air moving around.

[Caldera]

16 hours ago, grafspee said:

Any use turbocharger w/o throttle being wide open, evoke increased air inlet temp and increased back pressure which both reduce power output of the engine, which can reach 300hp.

Very true.

 

I am mildly curious and it would be fun to be able to quantify the actual pressures and temperatures.  Like knowing the actual pressure and temperature values at the compressor(s) outlet vice just the MP (effected by engine RPM and throttle plate position) as well as the intercooler inlet and outlet temperatures.  One could calculate allot from between those lines. 

But in reality, no importance to flying the P-47...

Caldera

Edited June 2, 2023 by Caldera

[Caldera]

1 hour ago, SloppyDog said:

Basically, the entire body of the P-47 is a housing to the supercharger and intercooler system.  People talk about pressures, but volume of air is also very important. Just look at the size of those pipes. It is a lot of air moving around.

Yep!

 

Basically RPM x Displacement, it is allot of air flow.

Thanks for the pictures!

Caldera

[grafspee]

16 hours ago, Scotch75 said:

Many thanks for the info. With heavier loads or shorter runways, will it still be beneficial to use the supercharger for take-off (even with water injection too), or is it a cost/benefit ratio thing? Does the supercharger take too much HP out of the engine for take-offs?

Cheers!


Sent from my SM-G998B using Tapatalk
 

Supercharger in P-47 is geared very low, so with supercharger alone you can pull about 46 inch for take off and this is below max take off power.

And supercharger in this case is thing which is very important because it provides engine with instantaneous smooth power, where power from turbo comes with significant lag  and for take off condition this is not good.

 

 

[Bozon]

I have not found any real vice to linking the boost & throttle. Probably eats a little more fuel.

The thing is, for max MP you need to add boost at any altitude, thus by linking the handles I get the same full power range. Now, it may be more efficient to get intermediate power by maximizing throttle and minimizing boost, but it is still the same power - I just burn more fuel.

So, unless you really need to extend your range, there is little harm in linking the levers. Every time I don’t, I end up destroying the engine… 3 separate levers are just to many for me…

[grafspee]

24 minutes ago, Bozon said:

I have not found any real vice to linking the boost & throttle. Probably eats a little more fuel.

The thing is, for max MP you need to add boost at any altitude, thus by linking the handles I get the same full power range. Now, it may be more efficient to get intermediate power by maximizing throttle and minimizing boost, but it is still the same power - I just burn more fuel.

So, unless you really need to extend your range, there is little harm in linking the levers. Every time I don’t, I end up destroying the engine… 3 separate levers are just to many for me…

Not it isn't while operating at partially open throttle to achieve same MAP turbocharger needs to reach higher compression ratio = higher turbo rpm = higher back pressure + higher carb air reduce output power of the engine. Statement that same rpm and same MAP gives same power avilable for prop is false. Ussing linked throttle and boost lever make flying easier but to achieve max performance you need to split throttle and boost lever.

Edited June 8, 2023 by grafspee

[Caldera]

Bozon,

I believe that is a primary point of discussion.  It would use more fuel to achieve less Hp vice as you say the making the same amount of Hp (under certain conditions).   I have to remind myself that MP does not equal Hp.  On the other hand I agree with you fully as I have locked the boost and throttle myself many times.  

But...

I guess learning to do it perfectly so that I am fully aware when I do it sloppy is my goal.  With a 109 on my six I have little problems with any of it.

 

I have not tested any of this by conducting my own speed or climb tests and I am simply going off of regurgitated  information.  However take for example, if you do the training mission for take off, the boost and throttle are locked by default.

The D model, from my understanding, had a regulator (of some sort) on the waste gate control.  I can be certain (from the simulation) that it does not manage boost pressure very well as I have to constantly adjust the boost lever vice moving the lever to a pressure setting and then having the regulator do all the work.  Possibly done that way intentionally to be able to achieve maximum performance. 

The N (M) model had a more advanced regulator and supposedly removed allot more burden on the pilot to micro manage boost.  I have no clue how it worked.  That all seems simple enough today by current standards and with all that it turns out to be the fastest allied fighter of WW2. 

Caldera

Edited June 8, 2023 by Caldera

[grafspee]

@Caldera Same rpm and MAP mean same fuel burn rate so plane will burn same amount of fuel regardless how this MAP is achieved, only power will suffer if boost and throttle are linked. So separate use of throttle and boost gains power over linked throttle/ boost lever, fuel burn rate will stay the same. This is what P-47 manual says. Power loss up to 300hp with throttle and boost linked.

Edited June 8, 2023 by grafspee

[Bozon]

3 hours ago, grafspee said:

Not it isn't while operating at partially open throttle to achieve same MAP turbocharger needs to reach higher compression ratio = higher turbo rpm = higher back pressure + higher carb air reduce output power of the engine. Statement that same rpm and same MAP gives same power avilable for prop is false. Ussing linked throttle and boost lever make flying easier but to achieve max performance you need to split throttle and boost lever.

 

By “same power” I mean same power at the prop (BHP at the prop axis, or same torque at given RPM), not same manifold pressure. With the levers linked I may need a higher MP to achieve the same actual power at the prop, hence more fuel consumption for given actual power. But since the max power is the same (both levers firewalled), I have the same range of power levels.

Since we do not have “power at the prop” gauge, you can think of this as climb-rate at a given air speed. I can achieve with linked levers any climb rate you will set with split levers - but I will burn more fuel doing it.

 

Edit:

You may be correct and achieve a higher effective power in cases of high altitude where I can reach the MP limit at less than firewalled throttle and boost.

Edited June 8, 2023 by Bozon

[grafspee]

21 minutes ago, Bozon said:

By “same power” I mean same power at the prop (BHP at the prop axis, or same torque at given RPM), not same manifold pressure. With the levers linked I may need a higher MP to achieve the same actual power at the prop, hence more fuel consumption for given actual power. But since the max power is the same (both levers firewalled), I have the same range of power levels.

Since we do not have “power at the prop” gauge, you can think of this as climb-rate at a given air speed. I can achieve with linked levers any climb rate you will set with split levers - but I will burn more fuel doing it.

 

Edit:

You may be correct and achieve a higher effective power in cases of high altitude where I can reach the MP limit at less than firewalled throttle and boost.

 

We don't have power gauge but we have MAP and rpm limit, and if you climb at climb power settings you can't go higher so if you use split throttle you get more power then with throttle linked. And if you fly with 64" at 2700rpm with throttle linked you get power output below that when used with throttle split. So there is no way for pilot to determine how much more MAP it needs to achieve same power for split throttle technique. 

Summarising split throttle gives more power then linked throttle, fuel consumption is the same since pilot sets power via MAP and rpm not power gauge. And power loss depends on power settings and conditions like alt and airspeed, so power loss may stretch between near 0 up to 300hp as manual states.

Edited June 8, 2023 by grafspee

[Hammer1-1]

people also need to take into account air density with regards to the weather. Rainy summer days will be vastly different from dry winter days, also depends on humidity as well...but not sure if humidity is even modeled yet.

[Bozon]

1 hour ago, grafspee said:

So there is no way for pilot to determine how much more MAP it needs to achieve same power for split throttle technique. 

Sure there is, this is why I gave the climbing example: you fly at the same airspeed and same climb rate = same effective power. The MAP will be different.

[grafspee]

12 minutes ago, Bozon said:

Sure there is, this is why I gave the climbing example: you fly at the same airspeed and same climb rate = same effective power. The MAP will be different.

Yest you can do it, just for tests but it has no purpose other then testing if this power loss is modeled or not but even so at climb settings power loss will be much smaller then at max power and for max power you can't compensate with MAP so you are left with just less power and not with higher fuel consumption. With MAP and RPM you can establish climb power very quick and actual power on propeller crank isn't limiter at all and does not matter.

With Linked throttle you will climb slower because power setting for climb are combination of MAP and rpm and you can do it instantly and no need to carefully monitor climb rate which imho is near impossible to do it in P-47.

And in some cases difference could be very small.

It will reduce maximum range, with split throttle you will climb and fly faster so you can cover more range with same fuel.

Edited June 8, 2023 by grafspee

[Caldera]

I think a climb to altitude time would settle this for sure.  However, a level flight speed test at low altitude might be easier to perform.  Both tests using unlimited fuel and performed at the same RPM.

Just keep in mind that the pilot does not see the total boost pressure only the MP indicated on the cockpit dash.

Caldera

[grafspee]

47 minutes ago, Caldera said:

Just keep in mind that the pilot does not see the total boost pressure only the MP indicated on the cockpit dash.

Caldera

This is true when throttle isn't full open and turbo is in use, when throttle is wide open pilot see total boost.

[Art-J]

Some time ago I did try to compare level airspeed at 42" @ 2550 with levers split and connected, at 5k and 10k ft maybe? I don't remember now. There didn't seem to be any noticeable difference, but I admit it was a quick and half-as..ed test, so who knows if that power loss we're discussing here is simulated in DCS Jug at all or it isn't. More thorough and accurate testing would definitely be needed.

[grafspee]

@Art-J running engine at 42" and 2550rpm is something like 50% max power so power loss could be around 150hp tops, top speed difference will be quite small.

[henshao]

I see the # 300hp thrown around a lot with regard to the P-47's boost lever and I think this is a misinterpretation. The manual actually says the first stage mechanical supercharger costs the engine 300hp. This cost is whether the turbo is involved or not. Therefore let it pay do its job without further reducing power by increasing engine back pressure with the turbo.

The manual does not say Turbo = -300hp, such is a massive oversimplification

null

https://www.reddit.com/r/hoggit/comments/13kq9dg/p47d_boost_lever_mythbusting/

[grafspee]

On 10/10/2023 at 10:49 AM, henshao said:

I see the # 300hp thrown around a lot with regard to the P-47's boost lever and I think this is a misinterpretation. The manual actually says the first stage mechanical supercharger costs the engine 300hp. This cost is whether the turbo is involved or not. Therefore let it pay do its job without further reducing power by increasing engine back pressure with the turbo.

The manual does not say Turbo = -300hp, such is a massive oversimplification

null

https://www.reddit.com/r/hoggit/comments/13kq9dg/p47d_boost_lever_mythbusting/

It is as said above. At max rpm 2700 supercharger draw about 300hp from engine and supercharger compression is the same at certain rpm.

If you open throttle max w/o turbo and you obtain 45" MP you are using all your supercharger which sucks 300HP and in case when you open throttle and turbo boost, since turbocharger make initial boost so it does some work for supercharger but supercharger constant speed will boost even more so you have to throttle down supercharger inlet to level which at the supercharger output gives 45" and this reduce power of the engine due to couple factors, 

1. Increased inlet air temp which makes air less dense, air charger less dense = less power at the same boost

a. Throttle only situation 45" 

         Turbocharger inlet 30" -> Turbocharger outlet 30" -> throttle inlet 30" -> throttle outlet 30" (at this point air is not heated up) -> supercharger inlet 30" -> supercharger outlet 45" (air charge temp increased).

b. Throttle and turbocharger

        Turbocharger inlet 30" -> Turbocharger outlet 45" (air charger temp increased) -> throttle inlet 45" -> throttle outlet 30" (at this point air charger is heated by first charging stage ) -> supercharger inlet 30" -> supercharger outlet 45" (at this point air charge is heated by factor 2 by first and second charging stage).

I ignored ram air in this flow.

2. Increased back pressure which draws power down

Edited October 22, 2023 by grafspee