Supercharger vs. Turbocharger

[syscom3]

Didnt the P38's in the ETO have wastegates that froze up from the cold? Something about the turbochargers would be stuck on full boost and it would ruin the engines (if it didnt fail right out).

[Marshall_Stack]

Here is a excerpt from Gabreski when his P-47 was shot up by a Luftwaffe pilot...

"I looked at my airspeed indicator and I still had plenty of airspeed, but my RPM started coming down and my manifold pressure started coming up. So the thought again occurred to me that, "Well, it must be the turbine supercharger and not the engine."

Wouldn't manifold pressure go down if the turbocharger was damaged?

[DaveB.inVa]

Maybe, maybe not. If the wastegate closed boost could go way up.

The whole P-38 turbos having trouble in Europe is a hard call. I personally think the damage didnt occur in the air, it occured on the ground. The location of the turbos on top of the boom really didnt protect the turbos and their components from the exceptionally wet European weather.

Youve got to consider that B-17's and B-24's in Europe didn't have these problems and their turbos were under the wing, protecting them from the rain.

At least thats my take on it.

The P-61C was equipped with turbos whereas the A and B were not. I dont know of any stories though about the P-61 not catching Bettys. A Betty wasnt turboed and only had a single stage supercharger if I remember correctly. I do know P-61s could catch fast B-29's but the story Im referencing happened below 15000'. Its a pretty good story: http://www.flightjournal.com/article...at/splash1.asp

[wmaxt]

Originally Posted by DaveB.inVa

Maybe, maybe not. If the wastegate closed boost could go way up.

The whole P-38 turbos having trouble in Europe is a hard call. I personally think the damage didnt occur in the air, it occured on the ground. The location of the turbos on top of the boom really didnt protect the turbos and their components from the exceptionally wet European weather.

Youve got to consider that B-17's and B-24's in Europe didn't have these problems and their turbos were under the wing, protecting them from the rain.

At least thats my take on it.

The P-61C was equipped with turbos whereas the A and B were not. I dont know of any stories though about the P-61 not catching Bettys. A Betty wasnt turboed and only had a single stage supercharger if I remember correctly. I do know P-61s could catch fast B-29's but the story Im referencing happened below 15000'. Its a pretty good story: http://www.flightjournal.com/article...at/splash1.asp

Yep, when closed they could start blowing things open from intercoolers to head gaskets.

The early P-38 intercoolers had several problems they were originaly sized for an 1,100hp engine so extended boost at 1,300+hp did warp leading edges. Holes shot into the intercoolers were bad news and hard to repair.

Wastegates did freeze at altitude, at -60 even lubricants freeze and the engines were run at 2,600rpm, fine pitch, and 35in/hg boost resulting in cold exaust, turbos and cockpits. In the Aleutions they ran 42/45in, coarser pitch and 1,700/1,800rpm resulting in fewer problems and warmer cockpits (still not enough but they could see out).

The air path on the P-38 was exhaust to turbo and out, Intake air was outside (small airhorns under wing) air to turbo to intercooler to carb. NO mechanical supercharger was used. I have also seen the engine setup for the P-38 and it did not include a mech supercharger.

I'll ask about the supercharger in the B-29 and I'm not sure about the others. Below 30,000ft the use of both is not weight or power efficent, and I have not ever read about the two being used together until after the war and the advent of the B-36.

I'm willing to be educated du you have some references?

The P-61C was equiped with turbos to add greater altitude ability.

wmaxt

[Marshall_Stack]

I don't have my P-61 book with me, but here is an excerpt from the web...

The shortcomings of Northrop's P-61B were no secret. Its performance above 25,000 ft (7620 m) was questionable..

I wouldn't think that Bettys could fly higher than P-61s. Maybe at times they couldn't climb fast enough to reach them.

[wmaxt]

Originally Posted by Marshall_Stack

Wouldn't manifold pressure go down if the turbocharger was damaged?

Depends if the slugs hit the turbo and did damage yes, if it hit ducting but within the pressure limits of the waste gate then no. If the waste gate was damaged open yes until the waste gate valve was overcome but if the wastegate was damaged closed it could go way up, to the capacity of the turbo anyway.

wmaxt

[DaveB.inVa]

The B-29 did in fact have two General Electric B-11 turbos in parallel feeding an engine mounted gear driven single speed supercharger. When used both were used simultaneously, there was no option to cut out one turbo as on the B-36. An engine driven supercharger was also present on the B-17 and B-24 in addition to the turbos. The supercharger is usually after the carburetor or injection system and serves as a way to mix the fuel/air. One of the big problems with early R-3350s was their magnesium supercharger case. This was the gear driven unit, not the turbos.

Look at this picture of the cutaway R-3350. The engine mounted supercharger impeller is clearly visible in the blue section. This was the way the R-3350 was and you couldnt get it any other way.
http://www.enginehistory.org/G&jJBro...way%20view.JPG

Here is an R-1820 (from a B-17) cutaway. Note the internal supercharger.
http://www.enginehistory.org/G&jJBro...%20cutaway.JPG

Its a little harder to see but heres a cutaway from an R-1830 (B-24) Follow the induction path on the right and youll find the supercharger impeller. http://www.enginehistory.org/G&jJBro...ice%20view.JPG

In fact FIFI doesnt have turbos, it only runs on the internal mechanical supercharger.

http://rwebs.net/dispatch/output.asp?ArticleID=7

Also about the P-38. The Allisons on it were much the same and did indeed have an engine mounted supercharger in addition to the turbos. I had this discussion with someone else another time. They insisted the P-38 had no internal supercharger. I have been to see Glacier Girl a few times in Middlesboro Ky and met a bunch of nice people. I emailed Bob Cardin, part of the Glacier Girl crew. Here is my email and his reply.

Dave:

I am curious are the Allisons on Glacier Girl equipped with a single stage supercharger along with the turbocharger... or does it have a two stage supercharger in addition to the turbo? Ive been under the impression that all P-38's had a single stage supercharger plus the turbo. Thanks for any information you can provide.


Bob:

David, the Allison has a single stage engine driven supercharger. Only the P-38 has a turbo to go along with it (the supercharger).
Bob

There you go, short and sweet.

[schwarzpanzer]

A point worth mentioning on turbos is that (basically) the compressor (inlet) side needs to be kept as cool as possible whilst the turbine (exhaust) side should be kept warm. Heat should be shielded/dissipated between the two.

Obviosly some parts can fail at extremly cold/hot/differing temperatures.

The materials used nowdays are the same, but the designs and possibly construction certainly aren't. They also require absolute precision, doubt they had that in WW2?

Originally Posted by Marshall_Stack

Another Question - I have also read that the P-38's turbosupercharger had problems in the frigid air over Europe, but never had heard of any problems with any supercharged engines. What gives....?

Originally Posted by DaveB.inVa

The location of the turbos on top of the boom really didnt protect the turbos and their components from the exceptionally wet European weather.

You've got to consider that B-17's and B-24's in Europe didn't have these problems and their turbos were under the wing, protecting them from the rain.

Wet weather doesn't harm turbos except for cooling on the exhaust side, a cold exhaust/turbo would severly hamper performance. If the water iced up it would be even worse.

However if this happened on the intake side, performance would drastically improve!

With the long, unprotected headers these engines seem to have?
I'd think the former to be at least 1 major factor.

Originally Posted by wmaxt

air to turbo to intercooler to carb. NO mechanical supercharger was used.

Originally Posted by Marshall_Stack

The supercharger is usually after the carburetor or injection system and serves as a way to mix the fuel/air.

Well, there's a contradiction here, but apart from that:

The set-up wmaxt said is blow-through, Marshall's draw-through.

I expected the P38 draw through because of the its flame problem, blow-through is favoured for preventing that.

Originally Posted by Marshall_Stack

Wouldn't manifold pressure go down if the turbocharger was damaged?

If headers to the turbo were damaged, yes. aft of that it could maybe do that, but the wastegate problem seems more likely.

One of the big problems with early R-3350s was their magnesium supercharger case

I can believe it!

Cheers for the pics DaveB.inVa!

That crank-mounted R-1820 supercharger, what rpm would it spin at? It would have to be geared up from engine rpm surely? (like the one on the R-3350 pic appears to be?)

Unless it just served as a mixer?

[DaveB.inVa]

Im not particularly saying that the turbo on top of the boom was affected in flight from the elements. Im more concerned with the turbo thats being exposed while sitting on the ground. Having the turbos turned straight up while sitting in the rain and elements is my hypothesis for the P-38's problems in Europe.

Every other fighter or bomber with turbos had them underwing or under the belly (like the P-47). Here while on the ground they couldnt get as much exposure from the elements.

Im with you, a little moisture ingestation will surely up the power! This would be getting into ADI or water/meth injection.. but thats a whole nuther thread.

I don't know the supercharger ratios right off. I have seen them before but cant recall. I seem to remember values around 5 or 6 times crankshaft speed though.

The WPAFB site gives the R-2600 (on B-25's) having a low blower ratio of 7.06:1 and a high blower ratio of 10.06:1.

http://www.wpafb.af.mil/museum/engines/eng42a.htm

Here is an excellent page for some basic descriptions of the supercharger, turbo and PRT and combinations of them. I was looking for this last night but it got too late and I needed to study!

http://www.avweb.com/news/columns/182102-1.html

[Marshall_Stack]

DaveB.inVa,

Great article on superchargers and turbos-chargers!

Two more questions (I ask a lot of questions) -

1. The P-39 is always maligned of its lack of high altitude performance. The P-40, although not a high flier, doesn't get criticized as much even though they have the same engine. Is the P-39 worse at altitude (compared to the P-40) because of its smaller wings?

2. War Emergency Power. I thought at one time I read that if this feature is engaged the engine needs to be overhauled upon return to base. Is this true? It seems like many pilots often used this for more than defensive purposes.

[wmaxt]

Interesting info guys. I've never run across that info and I have seen several engine set-ups and cut aways without the single stage supercharger, oh well.

The cut away shows of the 38J/L shows the carb after the intercooler so from the turbo its blow through, ALL P-38 intake air was near the turbo from the air horn below the wing. I don't remember flames in the intercooler ducts but the heat was very hi at times and aluminum will buckle at low temps. Look at ths side wrinkles on a B-52 and those are just from heat generated at 600mph. However fuel in the exaust system would throw a flame into the air on a rich start even with a blow through and is unrelated to type of carb or intercooler or even location of carb or intercooler in the system.

The turbo wastegates froze at altitude on P-38s, by then the water from the ground should have been evaporated/blown out by the end of the climb. Thats not to say your theory is wrong either, the issues may have been related.

I will be doing some research too, like I said I'm willing to be educated.

Marshal, WEP power got some added limitation after the war in my P-51 TO-1 (1952) it lists several perameters for inspecting/overhaul:
1. overspeed 3,300rpm to 3,600 rpm inspection prior to further flight.
2. Over 3,600rpm overhaul period.
3. WEP is limited to 5 min to preserve engine life
I didn't find the WEP limit but one is in there. It also must be remembered that in the war life span for the whole plane was `~50 missions so such limitation were not always used.


wmaxt

[FLYBOYJ]

Originally Posted by Marshall_Stack

The P-39 is always maligned of its lack of high altitude performance. The P-40, although not a high flier, doesn't get criticized as much even though they have the same engine. Is the P-39 worse at altitude (compared to the P-40) because of its smaller wings?

Consider the whole package - Airframe, engine, and very important but sometimes neglected - propeller!!!

[schwarzpanzer]

Originally Posted by Marshall_Stack

2. War Emergency Power. I thought at one time I read that if this feature is engaged the engine needs to be overhauled upon return to base. Is this true? It seems like many pilots often used this for more than defensive purposes.

Hydro/Methanol (C-Stoff?) = no.

(NO2 Nitrous Oxide) = maybe.

- It may also mean overboost on a Supercharger.

[quote"wmaxt "]However fuel in the exaust system would throw a flame into the air on a rich start even with a blow through and is unrelated to type of carb or intercooler or even location of carb or intercooler in the system. [/quote]

True, in that case it might have something to do with the camshaft(s?) duration also?

Nice info DaveB.inVa It's nice to see how ground technology applies in the air.

[schwarzpanzer]

On 1st glance at that article, it doesn't mention pulse-tuning or RAM-air.

These increase Manifold absolute pressure to way beyond ambient pressure without forced-induction and are deliberately used in F1 cars, though can exist naturally.

I think the latter was deliberately used in a WW2 engine?

[BillytheKid]

Hello: Go to Google (imagines) type in P47 Thunderbolt, click,
second row on the left, is a picture of a cutaway P 47, click, then the
turbo setup.
I don't see any mechanical supercharger in there.
anybody see one?
Billy the Kid AGF