Plane engines

[Luke Skywalker]

 I know a lot about TIE fighters, but my knoledge about WWII planes is limited, to say the least. Well, not so about planes but about engines.

I own several books about piston engined fighters, and after reading them I have to ask this thing:

How does a piston engine work?

Ok, I know, the engine moves a shaft and the propeller, linked with the shaft, spins. But beyond that my knowledge is nil.

What is a supercharger? what is a single stage supercharger? what is a (X) speed,(Y) stage supercharger?...

What is the difference between supercharger and turbosuperchargers?...

I get completely lost after reading things such as that a Dornier 217 version had two DB603 on the wings and one DB605 in the fuselage to feed the superchargers?...

Then we reach the next question...I understand that water and water-methanol injection make an engine run with increased power...what I dont understand is how does it work. Will an engine run smooth with the injection on until the plane runs out of booster?...

And another thing, what is the use of that little scoop the Bf109 has in the side of its engine?.

I know, are a lot of questions...but I know a lot about hyperdrives and ion propulsion systems, I had no piston engines in Tatooine to work with  

[chisel]

1) Suck, Squeeze, Bang, Blow  

2) Supercharger is an air compressor. X speed means it can be driven at multiple speeds (can shift gear ratios) y stage means there is multiple levels of compression. 1st stage, ambient air is compressed, 2nd stage the already compressed air is compressed again.

Turbosuperchargers are Exhaust driven, Superchargers are Mechanically driven.

Water injection is used as an antidetonant. Stops Fuel/air charge from igniting to soon/exploding instead of burning.
 
Engines can run with higher boost (intake air pressure higher) levels to get more power with water injection.

The Doober on the 109 is a Ramscoop. Precomresses the intake air a bit before it enters the supercharger.


Check this thread out from Days gone by:
 http://homepage.eircom.net/~frontacs/WBStored/Engines.html




[This message has been edited by chisel (edited 11-19-2000).]

[Luke Skywalker]

 

Originally posted by chisel:

2) Supercharger is an air compressor. X speed means it can be driven at multiple speeds (can shift gear ratios) y stage means there is multiple levels of compression. 1st stage, ambient air is compressed, 2nd stage the already compressed air is compressed again.

OK. I can understand the meaning of "stage", but I cant understand what does the speed mean. It can be driven at multiple speeds. Great...so...what?  

Sorry I'm a complete ignorant.

 

Turbosuperchargers are Exhaust driven, Superchargers are Mechanically driven.

Same as before  ...Lets see if I understand, a supercharger ,by mechanical means, compresses air and injects it into the engine so it can run at a higher output than possible with the air available at the moment. THat is good as you climb because the air is thinner as you climb. (I do understand that there is a "peak" where compressing more air does no good, am I wrong?).

But...what means that a turbosupercharger is "exhaust driven?"...

 

Engines can run with higher boost (intake air pressure higher) levels to get more power with water injection.

yes, but my question is that if you use a water injection system, can you use it until you run out of booster?...or is there any limit in the engine?.

I ask this because when I go up in a 109G10 in AH, I can run in WEP until the temperature gets high, but then, and if I let the engine cool, I can engage WEP again with no problems. I have read in my books that MW50 in 109s could be used for short periods, some 10 minutes or so, I figure that the same is aplicable to water injected engines as the R2800. But I dont find anywhere that if you let the engine "rest" between uses, you can use it again.

I also find quotes of a DB605 engine that at WEP gives a 1475hp output, and with MW50 injection 1800hp...

That leads me to think 2 things:
1-in AH the supply of methanol-water in german engines and the water in R2800 engined planes is infinite?...

2-in AH you cant run WEP independently than the booster?...because I am figuring here that AH's 109G10's engine running without WEP is giving 1475hp, right?. and with MW50 gives 1800hp right?.

So bassically you can run a 109G10 with WEP on ALL THE TIME, because the engine doesnt overheat?. Shouldnt the 109G10 have a WEP key and an independent booster key? (Same goes for american R2800 engined planes)

I know I ask too much   thanks for the answer, and I hope to understand the things I don't right now.

[Darth Vader]

In RL, the MW50 bottle had enough for 4x10 minute boosts.

[niklas]

Luke:
Stage means how many compressors you have, like chisel explained.
Speed means at which RPM the "propeller" of the supercharger is rotating, basically.
Look: At sealevel the DB605A producec 1475HP at 1,42ata. air Pressure is around 1,0ata. (?) compresseion ratio is minimum 1:1.42 in this simple example.
in ~18k feet the pressuere of the air is only 0,5ata. Now your supercharger must compress the air minimum with a ratio of 1:2,82 to get 1,42ata in your engine.
Of course you can compress also at sealvel the air with a ratio of 1:2,82, and afterwards reduce it with valves to 1,42ata but this would be a waste of energy. So different speeds allow you to run your compressor with maximum efficiency in different altitudes.
The DB605 had btw a regulation for the speed of the supercharger. The speed changed smoothly between 0-6km altitude. So you canīt say that it was a "single" speed supercharger, it run in every altitude at a different optimum speed.

the force to compress the air comes in a supercharger mechanically from the engine. The supercharger is connected to the crankshaft, where also the propeller gets itīs force from at the end.
in A turbocharger (you should know this from car engines) the exhaust gases drive a turbine, and at the other end of the turbine is the compresser "propeller". Becuase the pressure of the surrounding air becomes less and less with more altiude, the exhaust gases can stream out better and better. Thatīs one of the reasons why turbocharger engines have excellent high altitude performance usually.

I think every engine, where you used water-injection, and which cooled down again to "normal" temperatures, can use extra power again- when it has still some liquid in the tank.

WEP for german engines is usually called "Not- und Startleistung" (takeoff and emergency power), correct. MW50 is called "Sondernotleistung" (special emergency power)

It would really be interesting to know how much power is given to  the G10. The latest 605D were able to produce 2000HP near ground. The 605ASCM 1800HP. When i look at the speed of the G10 Iīd say 2000HP, when i look at the climbrate 1800HP.
When itīs a real 605-D-2 engine then 100% without wep should be 1435HP for takeoff.

niklas

[This message has been edited by niklas (edited 11-19-2000).]

[chisel]

Multispeed Supercharger
At low altitude the air doesnt need to be compressed as much so you can spin it slower requiring less energy.

As you go up in altitude you have to spin it faster to compress the air to the same level.


Turbocharger has a Turbine in the Exhaust pipe that drives the compressor. Uses the energy of exhaust gasses to drive it which would otherwise be wasted.

WEP on the 109 should be usable for 10min bursts with 5min for cooling in between. I think they carried enough for 45min use total.

Dont know about R2800's in the F4u but for some reason I thought it was a 1 shot deal on them.
 
Dont fly AH anymore. Dont know which DB605 they modeled. Do the MAP guages read accuratley now?

[juzz]

Supercharger speeds. Here is the A6M5b Zekes speed chart. It had a 2 speed supercharger.
   

The 1st gear speed is optimised to produce full pressure at 10,000ft. Below 10,000ft the engine has to be run under full throttle to avoid over-pressuring the engine. From s/l to 10,000ft the Zekes Sakae 21 engine maintains 1100HP. Above 10,000ft, the thinner air leads to a loss of power as the supercharger cannot maintain full pressure any longer at the 1st gear speed.

Then at about 14,000ft, the supercharger gear is moved into the 2nd speed, which gives 980HP from there until the 2nd gears optimum height of 20,000ft.

Basically, a supercharger or turbochargers job is to maintain sea level air density for the engine when it is in the thinner air at higher altitudes. But usually the charger over-boosts the engine to levels above sea level density in order to gain more power by feeding it more air.

A superchargers compressor is driven directly via gears by the engines crankshaft, while a turbocharger uses a turbine driven by the pressure of the expanding exhaust gases to power its compressor.


Concerning injection systems and WEP in AH.

For example, the F4U-1D.
War Emergency Power(water injection): 60 inches MAP, for 5 minutes duration. This is correctly modelled if you use the WEP key in AH.
Military Power: 53 inches MAP, for 5 minutes duration. In AH, you can run this power setting forever.  

The other problem is that in RL the water supply for WEP could eventually run out if you kept using it. In AH it is effectively infinite. For example: The Fw 190D-9 could use MW 50 for 10 minutes at a time, and it had enough MW 50 liquid to last for 40 minutes of continuous use, ie: 4 full uses of "WEP" if you let the engine cool in between.

I think the Me 109G-10 in AH uses a DB 605DB or DC engine with MW 50, which would output 1430 or 1370HP at 100% throttle, and 1800 or 2000HP with WEP(MW 50).

[This message has been edited by juzz (edited 11-19-2000).]

[juzz]

 

It would really be interesting to know how much power is given to the G10. The latest 605D were able to produce 2000HP near ground. The 605ASCM 1800HP. When i look at the speed of the G10 Iīd say 2000HP, when i look at the climbrate 1800HP.
When itīs a real 605-D-2 engine then 100% without wep should be 1435HP for takeoff.

Yeah, this is a confusing one.

Here's the numbers I have gotten from this website.

Engine: Max. output at 0m and at critical alt, climb output at 0m and at critical alt.

DB 605A-1: 1475HP and 1355HP@5.7km, 1310HP and 1250HP@5.8km
DB 605D: 1550HP and 1360HP@6.5km, 1300HP and 1250HP@6.5km
DB 605D-2: 1435HP and 1300HP@8.0km, 1240HP and 1150HP@8.0km
DB 605DB: 1850HP and 1600HP@6.0km, 1430HP and 1285@6.8km
DB 605DC: 2000HP and 1800HP@4.9km, 1370HP and 1285HP@6.8km

If you assume that the G-2 and G-10 have a similar drag condition, then look at their 0m speeds, with emergency and climb power respectively: ~340mph vs ~337mph.

To me that suggests the G-10 has the DB engine with 1430HP at 0m with climb power, compared to the G-2 with 1475HP from the A-1 at emergency.

But then like you say, it would need the 2000HP of the DC engine to reach it's K-4 like speed of 450mph with MW 50.

[Luke Skywalker]

Well now I understand a lot of things.

I have still some questions...for instance,seems to me that turbochargers are more efficient than Superchargers, given that they use residual energy (exhaust gases) that would be wasted otherwise.

Then why to put a supercharger instead of a turbocharger?...

Other question, as we all know, the Fw190 only got a good high altitude performance in its D version with an inline engine instead of the radial. That was because the BMW engine on the 190A lost power at altitude.

I suppose, then, that the supercharger in the BMW801 wasn't quite good, why?...

I think that maybe because radial engines are difficult to supercharge, but that seems odd, because one of the best high altitude planes of the WWII was the P47 with a radial engine.

So why didnt the germans put a supercharger optimiced for higher altitudes in the BMW801?. Seems to me a less problematic fix than to put a new engine in the airframe.

And about the booster systems...well I suspected that WEP was independent from the Booster, and that you could overheat the engine without the booster on. Seems that HTC should take a look into this?

And now that we talk about engine admission pressure...I see that Spitfire, P51, P38, Etc, show changes on the Manifold pressure gauge, and that they greatly change with the altitude.

But I have tested the 109s (All of them) and the Fw190A5 offline, and none of them show  changes in the manifold pressure gauge.

Is this normal?. After reading juzz's post I think it isnt (BTW juzz, great explanation, thanks!   )

[juzz]

Superchargers are somewhat easier to make I think, plus they take up less room. Look at the size of the planes with turbochargers: P-47, P-38, B-17, B-24... Also turbocharger impellors have to cope with very high rpms and temperatures in the exhaust pipe, requiring special alloys.

The Germans tried turbocharging on the Fw 190, but failed because they didn't have the metals available to do the job properly.

I think some(most?) of the MAP gauges still aren't working properly yet. Eg: The Spitfire IX  and Mustang display the same critical altitudes, but their engines were different. Mustang peaks at 12k and 25k, Spitfire should be at 15k and 28k I think.

Then there's the other planes that display no drop of MAP at all with altitude.

[Luke Skywalker]

 

Originally posted by juzz:

The Germans tried turbocharging on the Fw 190, but failed because they didn't have the metals available to do the job properly..

then why not use a different supercharger?..or it is an integral part of the engine itself?

[flakbait]

Actually, compression in the DB-605A was:

 

7.3 in the port cylinder bank, 7.5 in the starboard. So sayeth Squadron/Signal Pub.

------------------------
Flakbait
Delta 6's Flight School
Whattaya mean I can't kill em? Why the hell not?!
 

[niklas]

There was a BMW801 project running for a high altitude version.

At the end of the war BMW didnīt had the production capacity or the difficult situation didnīt allowed a production.


The 801J was ready to be tested in flights (Ju88D) in 1943 with a turbocharger. It had a critical altitude of 38k feet. Though it was never used for fighters, the Ju388 got it at the end of the war.

801 TM, TN , TQ1, TQ2, were all projects of the bmw801 as a high altitude engine, but never were build in serial production.

In 1944 they also had the bmw805 engine, later they changed it and used many parts of the 801 and called it bmw801TR. Critical altitude in 35k. Again they had no capacity AND the Jumo213 and DB603 engines were avaible, so there was no need for it.

I read something that a turbocharger is good for bomber, but has disadvantages for fighters. The LW trusted in supercharger, and they had GM1.

It is not easy to build a high altitude engine. The air heats up a lot in the compressor. The higher you fly, the more you must compress the air to fill the engine with always the same pressure, and the more the air heats up in the compressor.
In 20-25k you have to compress the air with a ratio of 5-7:1 to get maximum allowed pressure in your engine. When you donīt cool down the air after you compressed it, the gas mixture will explode uncontrolled in your engine, even with 150oct. fuel.
For example a Jumo213E in 30k feet, the compression of the air in the second stage and third speed of the charger heated the air up of 250°C. It had to be cooled down to 190°C before it streamed into the cylinder.

flakbait, 7.4/7.5 this is the compression in the cylinder. We talk about compression before the air sees the cylinder.

That the manifold pressure gauge doesnīt change in the 109 is imo an unfixed error since a long time.

That the spitfire9 seems to have a single stage engine in AH, or the second stage doesnīt produce a power loss is imo too an unfixed error since a long time (compare it to the P51 manifold pressure gauge and climbrate when you climb and pass 10-15k)

juzz this is an interesting source, but iīm wondering myself why the DC engine produce 1285HP @ 6,8km and 1140HP @ 6,0 km . Usually, when you fly with less manifold pressure(power), your rated altitude should raise and not fall.

According to my source (daimler benz sheet) a D2 was able to produce max. 1210HP@28k

I have only a problem with the climbrate when i compare it to other fighters (assuming 2000HP)
I mean mc205 same weight but 25% less power, only 10% less climbrate
N1k same power but 20% heavier only 10% less climbrate.

btw a small source i have says that a 109 with 605ASM engine reached 590kmh/366mph near ground when they calibrated the speed gauge.

niklas

[juzz]

 

juzz this is an interesting source, but iīm wondering myself why the DC engine produce 1285HP @ 6,8km and 1140HP @ 6,0 km . Usually, when you fly with less manifold pressure(power), your rated altitude should raise and not fall.

I'd think so too. I never noticed that on that table before, but it is similar for all the engines listed. Odd - or maybe the DB 605 series was like that for some reason? Loss of ram air effect from the lower cruising speeds maybe?

 

I have only a problem with the climbrate when i compare it to other fighters (assuming 2000HP)
I mean mc205 same weight but 25% less power, only 10% less climbrate
N1k same power but 20% heavier only 10% less climbrate.

Looking at the AH initial climb of the G-6 vs the G-10, both at climb power - suggests to me the G-10 has the 605DB engine.

[-lynx-]

Gents

When talking super/turbo charges keep in mind that it's not the air that is compressed but the air-fuel mixture. This is the reason for their very existence.

They were developed originally to boost the power output of car engines. The principle is dead simple: at 1 atmosphere the cylinder is sucking in 1 volume of mixture, at 1.5 atmospheres it's 1.5 times the mixture yielding roughly 1.5 times the power output from the same engine size.

Superchargers drew power from the engine itself - from this point of view turbochargers were way more efficient (utilizing the wasted energy of exhaust gases). However, the turbine runs at very high revs (ball bearings need to be of exceptional quality) and high temps - it is, after all, just a gas turbine, same as a turbojet engine.

On top of that there's a lag between you pushing the throttle forward and the full power kicking in as the turbocharger needs time to get to working revs to boost the power that is needed to boost the supercharger that is needed to boost... You get the picture With the engine driven supercharges the boost is almost instantaneous.

And the that all important in aviation question of weight - the turbos weight is much higher than that of  superchargers with comparable compression output.

As for the water injection - I've read somewhere that in many cases the water in question was sprayed on the cylinder heads to prevent their overheating when excessive man pressure was applied rather that directly in the cylinder but I maybe wrong .

------------------
lynx
13 Sqn RAF