Throttle Quadrant Procedure Video

[Weegie]

I know many will be familiar with how it all works and many will already have found "Greg" on YouTube

 

But for new users of the module this might help

 

 

[Weegie]

Here is Pt 1, he has made 8 videos on the "Jug" and I recommend them all

 

However Pt 1 also goes into aircraft operation so I thought seeing it was referenced above I'd also post it here too

 

 

[PL_Harpoon]

I don't want to add to the confusion but...

 

First of all, Greg's source here is the manual for P-47N (https://www.avialogs.com/aircraft-r/republic/item/5090-aaf-51-127-4-pilot-training-manual-for-the-p-47n-thunderbolt p.25).

In fact, the P-47 Training manual states that you have to disconnect the turbo at start and at high altitudes to prevent the turbo from overspeeding (https://www.avialogs.com/aircraft-r/republic/item/5091-aaf-51-127-3-pilot-training-manual-for-the-p-47-thunderbolt p.13). Also, there is no mention of it in the P-47D-25 to -35 manual (https://www.avialogs.com/aircraft-r/republic/item/5089-an-01-65bc-1a-pilots-flight-operating-instructions-for-p-47d-25-26-27-28-30-and-35-airplanes).

But I think this is a minor issue.

 

The big problem is, I don't really get how advancing the throttle forward and then following it by the boost lever should give you 300 more Hp.

As I understand from the P-47N manual, the R-2800 has a supercharger impeller, directly connected to the engine that costs the engine 300 Hp. That means it is used all the time, whether you use the turbo or not.

So, if the supercharger is constantly drawing power from the engine, how adding more air later (as opposed to sooner with throttle and boost interconnected) could result in more power?

 

My understanding of this rule from the manual is this:

You're loosing the 300 Hp to the supercharger anyway, so use it to it's full potential before adding more strain to the engine by adding air from the turbo. It's purpose is to extend the lifetime of an engine, not give you more power.

Edited February 15, 2021 by PL_Harpoon

[grafspee]

2 hours ago, PL_Harpoon said:

I don't want to add to the confusion but...

 

First of all, Greg's source here is the manual for P-47N (https://www.avialogs.com/aircraft-r/republic/item/5090-aaf-51-127-4-pilot-training-manual-for-the-p-47n-thunderbolt p.25).

In fact, the P-47 Training manual states that you have to disconnect the turbo at start and at high altitudes to prevent the turbo from overspeeding (https://www.avialogs.com/aircraft-r/republic/item/5091-aaf-51-127-3-pilot-training-manual-for-the-p-47-thunderbolt p.13). Also, there is no mention of it in the P-47D-25 to -35 manual (https://www.avialogs.com/aircraft-r/republic/item/5089-an-01-65bc-1a-pilots-flight-operating-instructions-for-p-47d-25-26-27-28-30-and-35-airplanes).

But I think this is a minor issue.

 

The big problem is, I don't really get how advancing the throttle forward and then following it by the boost lever should give you 300 more Hp.

As I understand from the P-47N manual, the R-2800 has a supercharger impeller, directly connected to the engine that costs the engine 300 Hp. That means it is used all the time, whether you use the turbo or not.

So, if the supercharger is constantly drawing power from the engine, how adding more air later (as opposed to sooner with throttle and boost interconnected) could result in more power?

 

My understanding of this rule from the manual is this:

You're loosing the 300 Hp to the supercharger anyway, so use it to it's full potential before adding more strain to the engine by adding air from the turbo. It's purpose is to extend the lifetime of an engine, not give you more power.

 

It is not always 300hp, i would say that it is up to 300hp.

Whole reason behind this is this supercharger. Engine is limited to 52" at 2700rpm. You can get this power setting in 2 ways.

Open throttle to max then add boost by turbocharger, second is to connect boost lever with throttle.

Throttle is device which is able too cut off excessive pressure at supercharger inlet.

Turbocharger in P-47 is device which can increase inlet supercharger pressure.

Throttle is situated between Turbocharger and supercharger.

When you have throttle not open 100% it will cut off some of inlet pressure, so to achieve 52" with throttle and boost lever connected turbocharger will boost higher   to provide enough pressure at supercharger inlet despite throttle being partially closed, to give 52" of MP.

The difference is in increased manifold air temp and exhaust back pressure(edited).

When you open throttle first then add boost air temp will be lower. With lower manifold air temp or charge temp density is higher and you have aditional power. 

More you compress air, more you heat up air. So you want to compress air as low as possible and operating engine with throttle not open 100% and at the same time turbocharger is used, you experiencing excessive air inlet heat up by turbocharger.

In hot weather operations, in some cases use of turbocharger during take off may be forbidden, due to excessive carb temps.

In flight air inlet scoop  is compressing air as well. So you need to remember about it as well.

 

 

Edited February 15, 2021 by grafspee

[Weegie]

Agree with everything @grafspee states, the load the supercharger imposes isn't constant it will depend on its speed (a linear function of engine RPM) and the back pressure, how much that will vary.....................no idea, I'd need to look at curves.

 

If the engine isn't at it manifold pressure limit from the throttle alone, then adding any boost via the turbo will be doing a few things I think.

 

Caveat I have not looked into this in any real detail, but here's how I see it

 

The throttle will be doing what throttles do. Throttling is inefficient thermodynamically so it should be minimized, you don't want to throttle then raise boost via a second system.

Exhaust backpressure will be higher, the amount and how much it impinges on performance I don't know, but in general it should be minimized

Finally as stated already, compressing twice to obtain the same manifold pressure will result in higher charge temperatures. This is undesirable as the charge will then be compressed again in the cylinder. Taking the ideal case for the compression process, work required for compression increases with temperature, so I think the supercharger will absorb additional power as will the compression process inside the cylinders of the engine itself.

 

I don't have the motovation to go into this in the minutae and will probably get handed my "ass on a plate" by somebody who does or has sufficient interest, but that's how I see the system working. My limited experience with engines is telling me to open the throttle to max, when I cannot get the boost I want from it, then start to open the turbo.

 

That's of course ideal there may be occassions when other limitiations make that impossible or impractical, I haven't had any real time in the module or studied the Jug to know

[grafspee]

Yes, i forgot about exhaust back pressure, it will reduce engine power further as well. 

So conclusion is when you operate your P-47 with throttle not opened 100% and at the same time you are using boost from turbocharger, 

1st you give engine less air due to higher charger temp.

2nd you force engine to make more work to blow exhaust gases from cylinders.

Edited February 15, 2021 by grafspee

[PL_Harpoon]

I think I understand what you mean.

Correct me if I'm wrong:

You're moving the throttle forward first and if the engine doesn't reach desired MP you increase the boost until it does.

 

If the throttle and boost are interconnected:

The carb receives more air that is also hotter (from the active turbo) and then throttles it to maintain 52" of MP.

 

If the above is true using both methods you get the same amount of power (provided MP = power), just one method is more efficient that the other.

Also at some altitude you will reach a point where in order to get max available power you will need full throttle and full boost. In this case there shouldn't be any difference between using both methods.

 

 

[Weegie]

That's as I see it @PL_Harpoon exactly

 

If you raise boost via the Turbo then throttle, i.e.opening the turbo before the throttle is maxed out, I think you'll need more manifold pressure for a given value of power, due to the inefficiencies that method introduces.

 

Using the turbo when it's not strictly necessary at lower altitude will reduce the max power that's potentially available.

 

I think the idea of the linking mechanism was to make engine management easier when pilot workload was high, a dogfight is a good example.

 

Eventually in the late models as Gregg inidcates, Republic automated the system to prevent the power loss, they wouldn't have bothered to do this if it hadn't been a potential weak point in the design.

 

You could always try Greg's experiment to see how well it's modelled and what the losses are, I've been meaning to try it but not got around to it

 

 

[grafspee]

1 hour ago, PL_Harpoon said:

If the above is true using both methods you get the same amount of power (provided MP = power), just one method is more efficient that the other.

Also at some altitude you will reach a point where in order to get max available power you will need full throttle and full boost. In this case there shouldn't be any difference between using both methods.

 

 

No quite, The main thing is that both method differ in Power output.

You have same MP but method with throttle and boost lever disconnected gives more power, due to lower charge temp and lower exhaust back pressure.

Ofc when throttle and boost is full forward, fact that those are interconnected or not does not matter.

I think that main reason why this interconnector exist is to avoid, situation when pilot in order to reduce MP will pull back throttle forgetting about boost lever in max position, that would put extreme stress on engine

We can only imagine how high pressure would rise in side pipes between turbo and carb, or how would rise turbine temp, it would surely exceed operation parameters of the turbocharger.

Edited February 15, 2021 by grafspee

[PL_Harpoon]

Ok, just did a very quick test to see if all this is even relevant in DCS.

 

It's by far not conclusive, but it appears that it is.

At about 9k feet, first I tried to go as fast as possible with full throttle and enough boost to reach 52".

The fastest I got was 344 mph (TAS).

Then I tried the same with throttle and boost interconnected and I got no more that 340 mph.

 

So it's definitely not 300 Hp but it seems the difference is there.

 

Here's the recording (Tacview).

DCS-P-47 power test.acmi

Edited February 15, 2021 by PL_Harpoon

[grafspee]

Take note that in top speed testes, small increase in speed require quite a lot of  power increase. Probably 4mph is not worth 300hp but this is hard to judge how much exactly.

 

 

Edited February 15, 2021 by grafspee

[Barrett_g]

On 2/15/2021 at 8:55 AM, grafspee said:

Take note that in top speed testes, small increase in speed require quite a lot of  power increase. Probably 4mph is not worth 300hp but this is hard to judge how much exactly.

 

 

 

^^^ THIS!!!  Look at drag racing.  At the higher end of drag racing it can take 100-150 hp just to go a tenth of a second faster!

[grafspee]

Drag is acceleration test, not top speed test.

You get 4 mph faster on final line and you get tenth of the second better time.

Edited February 19, 2021 by grafspee