Supercharger vs. Turbocharger

wmaxt · Oct 11, 2005

FLYBOYJ said:
Marshall_Stack said:

All,

I am amazed at how much you guys know about aircraft engines. I'm not a mechanic of any sorts but just an enthusiast. Is there any books or websites that anyone can recommend that explains the internal workings of aircraft engines (both in-line and radial)? Some thing along the lines of "aircraft engines for dummies".

I have learned a lot so far from your entries. I just want something that puts it all together for the apprentice.

Click to expand...

This site is geard for someone who is learning to work in the aircraft industry....

http://www.aerolearn.com/

There's tons of sites on line and if you live close to a local general aviation airport, you could usually find aircraft meachnic's text books there. There is a book written by a guy named "Treager" that has technical infomation about every type of engine you could imagine, including rocket motors...

Thats cool! It's also probanly closer to what he wants to know.

wmaxt

GregP · Oct 11, 2005

There is no reason why botha supercharger and turbocharger cannot be used together. Whether or not they WERE is another question.

The P-38 had some turbocharger issues as well as another issue. It had the worst heater of any ETO fighter.

During the war, the Army sent Tony Levier over to England to demonstrate the P-38. He did. One of the pilots watching said, "I'd like to see this hot shot do that same airshow after 4 hours at 30,000 feet!"

Anyway, we seem to forget that early high-performance engines did NOT have computers. Their control was analog and real time manual to a large degree. The mixture on the P-38 and the boost were not really optimized for ETO conditions, and were problematic to a degree.

Once sorted out, the P-38 was superb, especially the J and L models, which were as good as any single engine fighter. Plus, their armament was on the centerline.

FLYBOYJ · Oct 11, 2005

GregP said:
During the war, the Army sent Tony Levier over to England to demonstrate the P-38. He did. One of the pilots watching said, "I'd like to see this hot shot do that same airshow after 4 hours at 30,000 feet!"

Tony LeVier's purpose in Europe centered around engine out procedures and fuel management - He did duck the issue of cockpit heating....

I knew Tony LeVier - I think he probably could of done that airshow after 5 hours at 35,000 feet!

Parmigiano · Oct 11, 2005

Maybe a bit off-topic, but Volkswagen has put in production a Golf coupling a mech supercharger+turbocharger engine : 1.4 liter and 170 HP!
Also I read on a car magazine of a small English company who sells a kit for water-methanol injection, it was installed on an Alfa 147: a bit of patience and they will start to produce cars with some Hispano and MG too!

wmaxt · Oct 12, 2005

Some info on the Allison.

It did have a normal, single stage supercharger and in some later models an axilurary second stage (F-82)

Crank is reversed for the left hand engine.

Cam timing
Ignition Mags were run by the cams - intake 28deg BTDC,M exaust 34deg BTDC this means the exaust is lit to maximise turbo efficency and those flames from the turdo with a rich start.

Intake cam: opens early and closes late. 110deg overlap
Exaust cam: opens early and closes late. 138deg overlap
Valves open 0.533" which is mild for an engine this size to minimize float under extended RPM/ Boost.

I have the numbers but will give you the site rather than put them here.

What the numbers indicate is that the lift and overlap are moderate but radical enough to require the high idle to prevent 8 stroking (with to much overlap the power pulses will fire after 8 strokes rather than a normal 4 causing a lope in the power pulses, which would destroy the crank, driveshaft and driveshaft with a prop on it).

Allison Specs for the H/J P-38
--Hp------rpm---alt---in/Hg
2,300 - 3,000 - SL - 90 - With water injection

This list doesn't show the L model but the above indicates that 64" and 1725hp is certainly ok for limited periods.

The website: http://www.unlimitedexcitement.com/Miss US/Allison V1710 Engine.htm

wmaxt

Lunatic · Oct 14, 2005

Most WWII fighters (especially later models) used two supercharger stages (or a turbo and a supercharger stage). This was necessary to achieve the desired levels of boost. If a boost system needs to generate 4:1 compression (for example) using a single stage as opposed to two stages each at 2:1 it will generate something like 16 times the internal stresses because of the much higher rotational velocities required, or it will have to be several times larger than the combine two-stage superchager/turbocharger system.

Water-methenol injection systems are available (or at least they were) for cars. However, my experiance with these units is that while they do allow higher power levels w/o detonation they are also very hard on your rings and seals, even using 1% top-oil in the mixture. This is not a consideration for a fighter engine which is expected to survive perhaps 50 flight hours max, but on your car...

=S=

Lunatic

wmaxt · Oct 14, 2005

Lunatic said:
Most WWII fighters (especially later models) used two supercharger stages (or a turbo and a supercharger stage). This was necessary to achieve the desired levels of boost. If a boost system needs to generate 4:1 compression (for example) using a single stage as opposed to two stages each at 2:1 it will generate something like 16 times the internal stresses because of the much higher rotational velocities required, or it will have to be several times larger than the combine two-stage superchager/turbocharger system.

=S=

Lunatic

Yes, it's often missed because they are integral with the rear engine/accessory drives. It's more important with the low (relatively) RPM range of these engines.

wmaxt

hartmann · Oct 26, 2005

Hello to all, at last I can return to write.
Not only two stage superchargers but also three stage and two speed as the great engine Jumo 213 F, which was disposed with MW 50 injection, or one model of the Nakajima Homare (but this engine was of relative poor quality at high altitudes).
In my honest opinion , I agree with coupling Super and turbochargers.

schwarzpanzer · Mar 18, 2006

Thought I'd drag this up again, as a lot of people seem to wish to know the info contained within?

Twitch · Mar 18, 2006

I'm not certain for the puzzlement here. They have always been called turbo-superchargers. There is absolutely no advantage to NOT using a turbocharger and only using a supercharger. No wartime application of consequence didn't combine both devices for maximum power. It's just plaine stupid not to have a turbo.

wmaxt · Mar 18, 2006

Twitch said:
I'm not certain for the puzzlement here. They have always been called turbo-superchargers. There is absolutely no advantage to NOT using a turbocharger and only using a supercharger. No wartime application of consequence didn't combine both devices for maximum power. It's just plaine stupid not to have a turbo.

The issue is threefold
1, Complexity - The turbo adds an intercooler (most of the time), ducting, size (look at the P-47 designed around a turbo that would work at 30k) and a waste gate.
2, weight - The turbos added weight for the turbo, ducting and structure to accomodate the extra equipment.
3, Size - room to accomodate the extra equipment.

A second stage (all the turbocharged aircraft have at least 1 mechanical supercharger stage) is the addition of a compressor usualy around 10-12" dia and 6" thick with gearing and housing ~300lbs and a 12"-18" of space. The turbo in the P-47 looks to be about 30" deep to house both turbines and about 30" in Dia. The fusalage has been deepened from the engine to the turbo to accomodate an exaust duct, a fresh air duct and a pressure duct plus insulation for both the Pressure and exaust ducts. The fresh air duct is an ambient + ram air pressure requiring at least 18" of duct space. Pressure and exaust are probably in the 12" range with another 3" of insulation. Note these are very rough estimates on my part but with an understandind of airflow requirements.

I like turbos to, sometimes its to much though.

wmaxt

schwarzpanzer · Mar 19, 2006

I suppose having a turbo on a ground attack plane would make a needlessely big, heavy, clumsy target.

For high-alt bombers, I'd say a turbo was near vital, unless it reduced the back-pressure too much on turbo-compound engines?

2, weight - The turbos added weight for the turbo, ducting and structure to accomodate the extra equipment.

They also necessitate heat-resistant construction on the turbine side (cast iron), whereas the blower can be all-aluminium.

BTW: Can anyone give an estimate of the minimum amount of boost needed for high-alt engines?

Was there a succesful Naturally Aspirated engine used in a WW2 Fighter/Fighter-Bomber?

At speeds that WW2 fighters could achieve, Ram-Air Supercharging would also have been very beneficial. I think it actually was implemented on some WW2 plane IIRC?

- The Mosquito seems to use it?

Also, what about Pulse-Tuning Supercharging?
- I guess it was, as the Meteor derivative seemed to be - but I thought aero engines only ran @ speeds like 3,000 rpm?

Twitch · Mar 19, 2006

By 1943 the writing was totally on the wall. Ceilings were the key to having advantage in bouncing enemy planes and there is no good reason technologically why a 1944-era fighter interceptor would NOT have a turbo-supercharger. Weight and bulk is not a valid concern if we look at the way fighters wer headed at this time- larger in every country.

Dogfighting-type fighters were so over by 1944 if they ever truly existed in WW2. There was no appreciable advantage to having a stunt plane when energy fighting ruled the day. And high altitude performance became paramount in not only getting above the enemy but in doing so in a way that meant you'd have a superior performing aircraft. Hanging on a prop at 34,000 feet meant nothing if your foe could wheel, swoop and maneuver with total control against you.

It's just a totally moot point to say aircraft didn't need turbocharger set ups for superior performance at any altitude if we look at history. Ram air was a simple functioning feature on most aircraft. Turbochargers put out power at all altitudes since they produce it free from the exhaust gases which are obviously always flowing.

Supercharger vs. Turbocharger

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wmaxt

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GregP

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hartmann

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