My throttle isn't giving full MP: Curves problem?

[Nealius]

My Warthog throttle, when maxed, is not giving me maximum MP.

 

-prop pitch full

-boost off

-full throttle

-OAT 20C

-Elev 110' MSL

-QNH 29.29

 

On the takeoff run I'm only getting 45~46" MP instead of the 52" I should be getting according to manuals. Do I need to set a curve to get full throttle range?

[grafspee]

one thing you are doing wrong, you need to connect boost lever with throttle.

Supercharger in the engine wont give you full 52" take off power, but in very hot weather you may need to disconnect boost and take off with throttle only.

[Mud]

I thought boost was not used generally for take-offs.

[grafspee]

5 minutes ago, Mud said:

I thought boost was not used generally for take-offs.

Maybe it wasn't but to obtain full take off power you need boost.

This is from Flight operating instructions P-47D -25 to -35

 

Edited January 11, 2021 by grafspee

[Mud]

Thanks grafspee! 

[Nealius]

This is really confusing. I've gone through two original USAAF manuals, Chuck's Guide, Greg's Airplanes and Automobiles lectures, and nothing makes sense. I see everything from "boost is needed on takeoff" to "boost is optional on takeoff" to "boost should be off on takeoff." I do not see anything explicitly stating that 52" is impossible without boost, nor do I see anything explicitly stating boost is required for 52". I only see "boost is needed at alitutudes where throttle cannot give desired MP," which implies that boost may not be required to reach 52" (desired MP) on takeoff.

 

Why is this so inconsistent, ambiguous, and confusing? 

Edited January 12, 2021 by Nealius

[PL_Harpoon]

The required setting may have (and probably did) changed with different variants of the aircraft.

Also look for the primary sources. Greg's videos, Chuck's Guides and most likely even DCS manual are based on the original manuals.

As grafspee has shown in the original manual for the specific variants we have in DCS you're supposed to connect throttle and boost levers prior to takeoff.

 

 

[Nealius]

Chuck's guide uses one of the original USAAF manuals I referenced, and the guide says Boost OFF for takeoff, throttle up to 52" MP. 

[grafspee]

R-2800 has single speed single stage supercharger, If you look at planes which use this engine or similar one for example R-2000 they all have about 46" at full throttle.

Manual do not say it because you can take off w/o boost lever if you want. But this does not mean that you will get 52" with throttle alone while taking off.

But as you gain speed throttle alone will give you even more then 52" so boost depends how fast you fly.

Manual did not say how much you get from throttle because boost depends on airfield elevation and ambient pressure.

Edited January 12, 2021 by grafspee

[grafspee]

I take off in other way. I open throttle to max then i grab boost lever and add boost as required

[grafspee]

Let assume that throttle would give 52 at SL standard atm. You would stll complain that you get 53 boost because ambient pressure would be higher, or you would get 50 inch at elevated airfield

[grafspee]

2 hours ago, Nealius said:

Chuck's guide uses one of the original USAAF manuals I referenced, and the guide says Boost OFF for takeoff, throttle up to 52" MP. 

I want to see it in that manual i would not believe because someone have said so. I posted screen from manual intended for D -25 through -35 . It says that for take off you need boost.

This one from manual for B,C,D

 

Edited January 12, 2021 by grafspee

[Nealius]

That ambiguity is precisely why I got confused. The engine settings section of that manual shows takeoff as 52” not specified as “shortest run.” Therefore it’s rational to assume 52” is standard takeoff. Then the takeoff checklist says boost is required to “obtain shortest run.” Shortest run != standard. Since Greg’s channel claims a 300hp advantage when advancing boost after throttle at the same MP, I thus rationally assumed that boost would give better power/acceleration at the same 52” as what I thought was the standard takeoff without boost. 
 

As for Chuck’s Guide, p.96-97 is where he says to turn boost off, with a throttle-only takeoff of 52”. I don’t know if he forgot to add the boost step, or if he got confused about boost usage for the same reasons I did. 

[grafspee]

22 minutes ago, Nealius said:

That ambiguity is precisely why I got confused. The engine settings section of that manual shows takeoff as 52” not specified as “shortest run.” Therefore it’s rational to assume 52” is standard takeoff. Then the takeoff checklist says boost is required to “obtain shortest run.” Shortest run != standard. Since Greg’s channel claims a 300hp advantage when advancing boost after throttle at the same MP, I thus rationally assumed that boost would give better power/acceleration at the same 52” as what I thought was the standard takeoff without boost. 
 

As for Chuck’s Guide, p.96-97 is where he says to turn boost off, with a throttle-only takeoff of 52”. I don’t know if he forgot to add the boost step, or if he got confused about boost usage for the same reasons I did. 

There is no such a thing like standard take off boost for P-47, 52" is just maximum Take off power.

To obtain max power for take off you would need to do as fallows

After you line up with run way, push boost lever to position which will give you 52" with throttle open full. Where this spot is exactly it should be marked if not you just need to test it by yourself.

Then open throttle fully and you have your "300hp" back, ofc you need to watch MP and retard throttle if MP starts rising up

[PL_Harpoon]

3 hours ago, Nealius said:

That ambiguity is precisely why I got confused. The engine settings section of that manual shows takeoff as 52” not specified as “shortest run.” Therefore it’s rational to assume 52” is standard takeoff. Then the takeoff checklist says boost is required to “obtain shortest run.” Shortest run != standard. Since Greg’s channel claims a 300hp advantage when advancing boost after throttle at the same MP, I thus rationally assumed that boost would give better power/acceleration at the same 52” as what I thought was the standard takeoff without boost. 
 

As for Chuck’s Guide, p.96-97 is where he says to turn boost off, with a throttle-only takeoff of 52”. I don’t know if he forgot to add the boost step, or if he got confused about boost usage for the same reasons I did. 

Well, this is straight from Chuck's guide, p97:

 

[grafspee]

23 minutes ago, PL_Harpoon said:

Well, this is straight from Chuck's guide, p97:

 

Last part about water injection is taken from P-47N manual. I could not find anything about it in manuals for P-47 prior N variants

[Yo-Yo]

It is impossible to get 52" at start without turbo if the levers are disconnected and turbo is off. For interconnected levers to have 52" turbo lever is adjusted for ram pressure at the climb speed.

[Nealius]

Straight from Chuck’s guide, latest revision date. Since no one believes me. 

 

Edited January 13, 2021 by Nealius

[Art-J]

It's not like we don't believe you, but Chuck uses the same DCS manual and available real manuals to compile data for his guides, so:

a) the guide won't bring anything new to the table;

b) looks like he got confused / mistaken as well.

 

P.S. keep in mind Greg's video about throttle quadrant handling (if that's the one you referred to) is based on data from early P-47 manual and applies to planes using 91 octane fuel. It's not 100% valid for later, 100+ octane machines.

[grafspee]

7 hours ago, Yo-Yo said:

It is impossible to get 52" at start without turbo if the levers are disconnected and turbo is off. For interconnected levers to have 52" turbo lever is adjusted for ram pressure at the climb speed.

you can get even more, said that earlier.

But for take off, could be possible if there would be an airfield located 2km below SL  

[grafspee]

7 hours ago, Nealius said:

Straight from Chuck’s guide, latest revision date. Since no one believes me. 

 

 

 

 

Limits for 91 grade

I found this part, which was edited by this DCS guide

From  point 15, Almost copy pasted

Unfortunately guide creator mixed all in to one adding some stuff as well.

because in no single manual, i can see that author giving this 52" MP by only throttle.

I can see only warnings to not exceed 52.

Just take flight instruction manual or manual and just read that. 

 

Edited January 13, 2021 by grafspee

[grafspee]

1 hour ago, Art-J said:

P.S. keep in mind Greg's video about throttle quadrant handling (if that's the one you referred to) is based on data from early P-47 manual and applies to planes using 91 octane fuel. It's not 100% valid for later, 100+ octane machines.

As far as i know that P-47 was designed from start to use 100 grade fuel, but as Manual mention, p-47 works just fine with 91 grade which was used in training apparently very often.

Just with lower power limits.

[grafspee]

Digging through manual i found another info about throttle to MP relation

[Tiger-II]

52" is WITH boost (war power takeoff).

 

45" or so is max power WITHOUT boost (normal takeoff).

 

For an empty takeoff, 40" is recommended until rudder becomes effective, then use 46" or so.