how much power needs a supercharger?

[niklas]

Anybody has some data? In first gear, near sealevel. 50hp? 100, 200?

thx
niklas

[Tails]

Um, could you clearify the question? I know a thing or two about superchargers and turbosuperchargers, so if I knew what you were asking exactly I could be of some help.

[funkedup]

I believe Niklas is looking for power at the supercharger drive shaft.  I had a library book with a chart showing this for a Merlin, but I'm now 2000 miles from that library.  I have another book that I will check for this info.  If I can't get it there I will look up the name of the library book, maybe someone can find a copy.

[Tails]

That I dont know. Sorry.

[Zigrat]

its significant. i know guys that are restoring a king cobra, they are taking out the supercharger since they will be running it at low altitude, obviously, and super charger just eats up power at low out since you cant use it or youd overboost the engine

[Regurge]

I can calculate it once I get home and scrounge up my old thermodynamics charts. I'm sure it's a significant amount.

I read somewhere about a German plane that had a fuselage engine used solely to drive a compressor for the 2 wing mounted engines (and for itself I presume).

[wells]

In the case of the R-2800, the difference in manifold pressures for the same power is 52" vs 54" (P-47 vs Corsair), so you're looking at about 75 hp there.  

In the P-39 with mechanical supercharger, 51" gives 1325 hp @ 3000 rpm and with the P-38, the same power is attained with 47", so a difference there of about 110 hp.

The P-38 and P-47 use exhaust driven turbo-superchargers, so there's no load on the engine.

[Regurge]

For a p51 merlin 1650c.i. running 61"@3000rpm I get 130hp. Accounting for losses in the compressor, plumbing etc. I'd figure true shaft input would around 160-200hp.

Wells, did you mean there's no load on the crankshaft with a turbo? Turbos will have more backpressure in the exhaust so they'll lose some power there, just not as much as ith a crank-driven supercharger.

<EDIT> caught a mistake and edited numbers

[ 10-10-2001: Message edited by: Regurge ]

[gripen]

Well, there is no simple answer for this question because there is many different supercharger systems and required MAP and FTH varies a lot.

The most simple case is the single speed single stage supercharger like in the plain V-1710 and in the some Merlins. For example the V-1710 with 6,44:1 supercharger gear used just about 50hp for the supercharger but over 200hp with 9,6:1 gear.

Then there were two speed systems, three speed systems, two stage systems, variable speed systems, combined single and two stage systems... Anyway it should be noted that AFAIK all turbo systems which reached service during WWII were combined two stage systems (first stage mechanical and second stage exhaust driven).

gripen

[ 10-10-2001: Message edited by: gripen ]

[Seeker]

Regurge, you're right, and I beleive it was either a hi-alt recon Ju88 or Ju188.

Superchargers come in different configurations - the one most people will be familiar with is the Rootes type, as commonly found in big block V8 auto engines, where two lobed paddles are driven off the engine to compress air into the intake.

However, most aero engines had centrifugal types whaer air is spun out from a centre intake point.

Also the drive mechanism it's self is important. The Merlin used a geared drive, where the drive ratio could be changed (hi boost, lo boost etc), whereas the 109 used a stepless system.

Lastly, turbochargers are also technicaly superchargers too.

[-lynx-]

Seeker - both types are used for the same purpose, to stuff more air/fuel mixture into the cyllinders. The difference is in the name. Superchargers are using direct drive from the engine to drive the compressor while turbos are using the exhaust gases driven turbine to do the same.

Superchargers are far better suited for aviation engines as you can use different gearing for different altitudes sacrificing some of the engine power to "squeese" more out of it in the end. The efficiency of a turbocharger will decrease with altitude as the engine power output goes down.

Turbos are by far more economical way to charge the engine - you are using otherwise "wasted" resource but due to their limitations they are hardly suitable for aviation...

 

[hitech]

The efficiency of a turbocharger will decrease with altitude as the engine power output goes down.  

You are forgeting the decrease in outlet
pressure here. Hence raising the eff of turpo chargers. But they still need to do more work as the air density decreases.

Turbo chargers typicly out perform super chargers at alt.

The 3 planes we have with turpo chargers are b17,p38 and p47. Take a look at there climb rates. The climb rate decreases less with alt Vs the Super Chargers.

Turpo Chargers are much better for avaition. There limitation is much more do to reliabality then there performance.

HiTech

[-lynx-]

Stand corrected - thanks HT for clearing this for me

[niklas]

thx for the replies so far.

What do you think: When you change the supercharger of a DB605AC to the larger supercharger of a 605D - can this justify the difference of 115hp (1550hp >1435hp) near sealevel?

niklas

[HoHun]

Hi Niklas,

It seems to me that you could have a look at the different Merlin engine variants for a reasonable comparison.

Regards,

Henning (HoHun)