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Max reachable manifold pressure without turbosupercharger.


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Shouldn't P-47 be able to reach 52'' manifold takeoff power with throttle alone? Our P-47 reaches maximum of 46'' - 47'' at near-sea level altitude with "default" DCS weather conditions (29.92 in Hg, something like +15 deg. C, no wind). Is this correctly modeled? And should it lose manifold pressure with increase in altitude as fast as it does now? Shouldn't regular geared supercharger provide enough boost to climb to 7000 ft at 42'' manifold?

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I was led to believe the same after reading various documents and watching various 1940's training videos, but apparently it's not possible to go above 46~47" with throttle alone and that's correct for our specific P-47. 

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I haven't seen in any of p-47 manuals, statement that 52" is achievable by throttle alone.

This is the first point.

Second point is that this  way is beneficial for engine power output, since supercharger is geared to lower MP, while in high speed SL flight you can keep full throttle and not exceeding 52".  

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2 hours ago, Nealius said:

Manuals also don't specifically state you cannot achieve 52" with throttle alone, which is probably the source of all the confusion.

It depends, if P-47 was used in trainer scenario, max take off power was 40" for 91grade fuel, then throttle alone was sufficient. 

Like i said earlier, P-47 does not have any kind of automatic boost control like in P-51, this mean that max MP will change despite that throttle is set to max.

In p-51 you open throttle too 100% and engine uses 1st and second stage supercharger, but throttle valve isn't opened 100%, automatic boost regulator will open it to get 61".

In case of P-47 you can boost much higher then 52' allowed for take off.

This is case for late D models at least.

This is from B and C model where throttle and boost lever didn't have interconnection.

You can read that using turbine allow for shorter take off this is the ultimate proof that throttle alone cant get 52".

This is how i do it in DCS p-47, i have found boost lever spot for 52" and at take off i move throttle to 100" since i have boost lever pre set for 52" i get 52"

2jE532R.png


Edited by grafspee

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But did the trainer scenario manual specifically state to use throttle alone for 40"? My point is that the confusion arises from a lack of specific wording. 

 

I thought I linked the last discussion on this, but the link was missing from my earlier reply. I'll drop it here for reference.

 


Edited by Nealius

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18 minutes ago, Nealius said:

But did the trainer scenario manual specifically state to use throttle alone for 40"? My point is that the confusion arises from a lack of specific wording. 

 

I thought I linked the last discussion on this, but the link was missing from my earlier reply. I'll drop it here for reference.

 

 

It does not matter, with boost or w/o, 40" is max take off power for 91 GRADE.

There is no point to provide this information.

Lets say that throttle alone gives max MP of 46" at SL

What about airfield with elevation 600ft ? Above statement wont be true anymore. At 600ft Throttle alone will not give 46" anymore, it will get less so you will have to use turbocharger to get to 46" 


Edited by grafspee

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My point is that the confusion arises from a lack of specific wording.

 

Since my point hasn't gotten across. Excluding one version of Chuck's guides, none of our documentation says what is or is not possible with throttle only versus with throttle+boost. This is further confused by the well-known videos by Greg where he explains the geared supercharger and boost lever, inadvertently implying that one can get 52" without boost on takeoff. 


Edited by Nealius

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43 minutes ago, Nealius said:

My point is that the confusion arises from a lack of specific wording.

 

Since my point hasn't gotten across. Excluding one version of Chuck's guides, none of our documentation says what is or is not possible with throttle only versus with throttle+boost. This is further confused by the well-known videos by Greg where he explains the geared supercharger and boost lever, inadvertently implying that one can get 52" without boost on takeoff. 

 

Manual says that for shorter take off boost is required and you still has doubts about that ? 

So he is implying that 52" is available at every possible airfield elevation ?? I don't know from where did they took that data. 

In all manuals i come across boost is required for max permissible take off.

chuck's guide is not manual for me. same as Greg's videos.

 

Anyway Greg's video about it, is very confusing, because  in one instance he says that throttle alone gives 52" and in next sentence says that turbo can be used for take off, why when 52" is achievable with throttle alone and this is max what you can draw from this engine for take off. This wasn't confusing for you i can see.

I went through B C D manuals and in all of them turbocharger is used for take off. 


Edited by grafspee

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What I got from manuals and 1943 introduction video for P-47 is: boost is optional for all takeoffs, majority of takeoffs are performed without turbosupercharger, and takeoff MP is 52''. From this I assumed that this MP can be achieved without boost. With turbo this setting can be reached easily at high elevation fields too. And I also assumed that P-47 can climb to 7000 ft without applying boost, and DCS one requires turbo to maintain 42'' as soon as 4000 ft. Also, I was flying A2A Simulations P-47 for a long time and got some "habits" and preconceptions about plane's operation, which did not "dissipate" for three years since I have moved from FSX to DCS. So, my questions are based on assumptions made from lack of definite info in manuals basically. I just want to know if DCS P-47D works as the real one made in 1940s, and I can start to learn stuff and form new habits without relearning it later when flight model or system operation gets updated.

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56 minutes ago, Aernov said:

What I got from manuals and 1943 introduction video for P-47 is: boost is optional for all takeoffs, majority of takeoffs are performed without turbosupercharger, and takeoff MP is 52''. From this I assumed that this MP can be achieved without boost. With turbo this setting can be reached easily at high elevation fields too. And I also assumed that P-47 can climb to 7000 ft without applying boost, and DCS one requires turbo to maintain 42'' as soon as 4000 ft. Also, I was flying A2A Simulations P-47 for a long time and got some "habits" and preconceptions about plane's operation, which did not "dissipate" for three years since I have moved from FSX to DCS. So, my questions are based on assumptions made from lack of definite info in manuals basically. I just want to know if DCS P-47D works as the real one made in 1940s, and I can start to learn stuff and form new habits without relearning it later when flight model or system operation gets updated.

I think in manual we wont find clear answer.

But from this manual it looks like p-47 need turbo to get 52" if not i don't see any logic in that part.

 

wOf1jMI.png

I check recently, it is as well impossible to get 52' from throttle alone in famous ww2 combat sim which name i cant type in but i think every one knows.

i checked couple YouTube videos with pilot cam, unfortunately, modern p-47 don't exceed 40" even at take off.

Looks like 40" is sufficient for take off, so it is logical that most of the take offs mentioned in manuale are used w/o turbo since 40" si good enough.

Later i found in P-47N manual that 35' is enough boost to lift off w/o external load. It also confirms that only heavy loaded P-47 would require turbo boost for take off.


Edited by grafspee

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This is from RL P-47 look at MP and rpm during engine run up /check, i can see 30" of MP and 2300rpm but our dcs version do 2000rpm at 30" is it different prop ore something else.

I wish to know which version exactly ED based of their simulation.

IujCoYd.jpeg


Edited by grafspee

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The P-47D N647D has perhaps different engine, it is not B-series but it looks like C-series from M and N models. So different RPMs and power settings.

(according to propeller reduction gear cover)

 

Some aviable reports, unfortunetely only for R-2800-21, show for 52 inHg turbo RPMs around 5000 at low altitude and low speed. 

Supercharger was the same for -21, -63 and -59.

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 I just tested it, and this is very suspicious for me since P-47 manual often mention to not draw more power to get speed up during take off roll, this indicate that it is possible to draw more then 52 from engine at take off.

So i tested it

I pushed throttle and boost lever to max.

Looks like i got 52" at lift off speed and i was not able to exceed 52" at take off roll, so i think it is time for ED to comment on that matter.

Looks like boost lever has no impact on MP until some airspeed is build up.

I remember talking about turbo lag but is this lag so massive at low speed ?


Edited by grafspee

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9 hours ago, grafspee said:

Manual says that for shorter take off boost is required and you still has doubts about that ? 

 

 

I'm not doubting the need for boost, I'm talking about the gaps and conflicting information in the manuals. Even the checklist you posted, which specifies short takeoff run and 52", says to use boost "as follows" implying technique, not necessity. Followed by "full on or previously determined setting" implying a range of settings would give 52". A "range of settings" includes off. Combine that with manuals saying to takeoff without boost and not giving a specific MP for that situation, it solidifies the erroneous implication that 52" could be possible without boost.

 

I'm not stating that we should get 52" without boost, I am stating that 1940's technical writing is a pile of steaming crap that is causing a lot of confusion here. I work in academia where such reasoning, logic, critical/skeptical thinking, and writing mechanics are hard-coded into my brain. I know it's an appeal to authority fallacy but it's the only way to explain why I see such confusion in these documents.


Edited by Nealius

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Here are some excerpts from P-47 manuals. It looks like 

 

1) boost was used to achieve 52"

2) mostly full on or slightly below

3) it was advanced where it needs to be before opening the throttle ( same procedure as in B-17Gs)

 

engine runup:

 

1.jpg

 

takeoff:

 

 

2.jpg

Look at the drawing:

 

3.jpg


Edited by Reflected
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Can we get the TO numbers for the manuals referenced? I'd like to add them to my collection. The only one I could easily find for free was "AAF Manual 50-5" which is missing the excerpts posted here.

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So i tested it even with throttle and boost full on you still getting 46" for take off.

So part in manual which says to not draw more power from engine to build up speed faster is pointless here, since MP no near 52 at take off.

yUkGfAF.png

how to exceed 52" at take off to work up speed faster then, looks by manual that it was possible.

I could not manage it.

Am i missing something here ?

I had impression that turbocharger will add couple MP at beginning of take off roll, but looks like it does nothing. MP starts increasing slightly when approaching 80mph and reaching 52" at 100mph.

Maybe this warning is for heavy loaded P-47s which require speed +120mph for lift off than you can possibly exceed 52" before lift off.


Edited by grafspee

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I have accidentally gone over 52" with boost on takeoff before, but only up to 53" and I immediately backed it off when I noticed. I'll test and see if I can reproduce that again. Fairly certain you should be able to exceed 52" in the sim.

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In other Pilot's notes same thing 45" throttle alone, for 52 turbo is needed.

uYqKYeS.png

 

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Max MP from throttle alone will still change with, altitude, SL pressure and in flight with air speed as well. It is not as simple as in P-51 for example where throttle full on give 61"

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10 hours ago, grafspee said:

Max MP from throttle alone will still change with, altitude, SL pressure and in flight with air speed as well. It is not as simple as in P-51 for example where throttle full on give 61"

 

Of course. But unless that is explained somewhere in the manual the average user like myself won't know that. I didn't learn it until this discussion came up a month or two ago. 


Edited by Nealius

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