Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Regurge on February 20, 2002, 03:57:04 PM
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Looking at the speed charts for F4Us (and F6F), they all have 3 peaks, as if they had 3-speed superchargers. But I believe they were 2 speed like many other planes (190A, spit, p51, etc), but these others only have 2 peaks. Why is that?
Also, anyone know why the Germans didnt fit a larger supercharger in the 190As, or change the gearing in the existing one to improve hi alt performance? It seems to have worked fine for Spits and P51s.
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The supercharger system in the F4U was a two stage system. At low altitude it could be operated as single stage single speed system (ie engine stage alone) if required manifold pressure was not very high (say less than 70") ie supercharger at "neutral" position. At higher altitude second stage (auxlirary stage) was needed for high manifold pressures and it was a two speed system ie "low " setting for lower altitudes and "high" setting for higher altitudes.
There were several BMW 801 developements with advanced superchargers (like four speed system or turbo versions) but these did not see large service or more than experimental stage of developement.
gripen
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Does this mean the F4U had a 2 stage/2 Speed supercharger and the 190 had a 2 stage/1 Speed supercharger?
Hooligan
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Well, correct way to say this should be something like:
The F4U had two stage supercharger system where engine stage was a single speed system and auxilary stage was a two speed system. And the engine could be operated with the engine stage supercharger alone so in practice there were "three speeds" available despite it was not a real three speed system like some Griffons or Jumos. Late F4Us had variable speed auxilary stage like some V-1710s.
The BMW 801 was a pure single stage two speed system.
gripen
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PW2800's had a two stage two speed supercharger (47's also had turbos) FW's had single stage two speed superchargers. The difference is large at higher alts.
Put simply... two stage is compressing the air twice...much like a home air compressor of two stage design. Two speed is much simpler. it involves nothing more than gearing and "shifting gears" to spin the supercharger faster to compress more air.
Two stage superchargers are very complex and the germans simply couldn't make em. Every country does some things better than others. American's made very good superchargers, ships and fighter planes . Germans made good incinerators.
lazs
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Thanks gripen, that makes alot more sense now.
What I was getting at with the 190 is that some Merlin engined rides had 2-speed/1-stage superchargers tuned for high alt and others tuned for low alt. Just wondering why that wasn't true for the 801s.
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I believe it was tried but the metals required to mass produce it were not available. Cant remember where I read that.
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The Germans had couple two stage systems (Jumo 213E and F, DB 603L and 605L) and also turbos (BMW 801TQ) in the production but these did not reach large service.
It should be also noted that basicly most WWII turbo systems were two stage systems ie engine stage was mechanical and auxilary stage was turbo . Also some single stage systems did pretty well at high altitude like the DB 605AS and D.
gripen
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The BMW801D-2 had a two speed supercharger; which is the powerplant we have on both the Fw 190A-5 and A-8.
Source: "KURT TANK: Focke Wulf's Designer and Test Pilot", by Wolfgang Wagner (Schiffer publishing).
Focke Wulf Fw 190 in Combat by Sir Alfred Price.
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Regurge, germans used a different system to increase hi alt performance. The 190A8 R4 had a GM-1 bottle instead the aux fuel tank. GM-1 was also used by 109 and Ta152.
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How can you see it on the Charts what they are? Can you?
The Jumo E-1 that the TA152 is suposed to use is 2 Stage 3 Speed engine, capeble (with GM1) of getting the TA152 up to 760 Km/h at 12,500 meters (41k). Since our AH charts have been choped off from 30k and up, we can't see it anymore, however, AH TA152 only does bout 460 at 35k, equal the the P51 B at the same alt in AH.
(TA152 slightly faster).
Think we might not have the 3:d gear on our engine.
Is every little extra step on the chart new place where the engine get a little kick?
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Found the old Chart of AH TA152.
http://www.hitechcreations.com/cgi-bin/charts.pl?vehicle=ta152h
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Hey this old chart, shows the TA152 way to slow.
Top Speed i think was around 472 mph, not the "Slow" 460 in the chart.
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Yes Naudet, why I show it :)
The new chart is the same only that HTC has cut it in half (almost).
Think HTC might have modelled the wrong engine for it.
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With the right engine, it would be better up High then it allready is, better climb and better speed.
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I wonder why Fw used a "geared" supercharger when the 109 had the variable speed compressor, which seems at first glance to me more suitable.
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hah strato buffs... Ta 152 at 47K. yawn.
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Seeker, the blower speed on the DB engines was controlled by clutch slip. By definition this was an inefficient mechanism.
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Hi Funked,
>Seeker, the blower speed on the DB engines was controlled by clutch slip. By definition this was an inefficient mechanism.
On the other hand, fixed gearing required the throttle to be closed somewhat below full pressure altitude, which is inefficient, too.
Like everything in aviation, it was a compromise: Fixed gearing provided higher peak power, but fell off quickly if you left design altitude. Hydraulical clutches gave lower peak power, but maintained a high power output over a broader altitude band.
Regards,
Henning (HoHun)
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Of course Hohun. But mechanical engineers like robust and efficient mechanisms like gears more than clutches. Especially P&W engineers. And the BMW engineers learned to design radials by license production and reverse-engineering of P&W designs.
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Wilbus, I would have to do alot more checking around to be sure, but check out this chart, from the Ta152 book I've been referencing lately. Specifically look at the entries for the Ta152-H0, with the Jumo 213E. (note that this is not a C model, its the first run of the H models)
According to that chart, this aircrafts top speed at altitude with WEP(the number in parenthesis) is 742 km/hr at 10.7 km , which according to my calculations is exactly 461 mph at 35,105 ft.
If you also look at the WEP Sea Level speed of the H0 on the same chart you can compare the 580km/hr or 360 mph, to the HTC chart and see that it also closely matches.
Just some additional information, if you go back and look at the evidence, it appears that only 3 of the total 48 production aircraft were H1 models with the 470+ mph you reference, and the other 45 aircraft were H0 models which lacked MW50 and GM1 due to production difficulties. There was an excellent thread on this subject about a year ago, where NathBDP and myself discuss this issue in depth.
Just a quick guess on my part
http://www.vermin.net/fw190/translated-fwchart.jpg
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Check out the charts in your TA152 book Verm, the ones with curves. There are no for the H0 and H1 models there, there are only for the C models (shorter wings basicly) with different kind of engines, C with Jumo 213 has the same speed as our TA152 in AH. The TA152 C with DB engies seems to to be a beast at the deck but those engines hardly existed.
Will have to read up some more, but still think it's the wrong engine.
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Wilbus, Your right the performance curves your talking about do not have the H0 on those charts. But if you look at the table (which I provided a link) you will see the numbers for the H0 which matches the AH performance right on.
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But AH has got H-1.
Allso, the H1 had slightly longer wings then the H-0 + GM1 and MW50 boost wich gave it better high alt performance (GM1 specially). Think the Boosts might be a bit undermodelled and my guess is the our TA152 has got the Jumo 213 E engine and not the Jumo 213 E1 Engine as the TA152 H-1 had.
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Actually AH planes don't have any engines, just a bunch of code trying to simulate them. Sometimes this 'has' thing makes me smile a bit.
HT changes a couple numbers in the code and the 'Juno' engine starts to have a performance like a UFO.. lol.
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Hi Funked,
>But mechanical engineers like robust and efficient mechanisms like gears more than clutches.
Are you aware we're talking about a hydraulical clutch here? A hydraulical clutch resembles a turbine operated by hydraulic oil much more than the automotive slip clutch you seem to be thinking off. I don't see any reason to consider a hydraulical clutch anything else but robust and efficient. It's not like they were only used by German manufacturers - Allison and Wright are two US manufacturers who employed hydraulic clutches in their aviation engines, too. And if you talk about efficiency, remember that closing the throttle to avoid overboosting from a fixed-gear supercharger results in a decreased volumetric efficiency of the engine as well. Like everything in aviation, fixed-gear superchargers were a compromise.
Regards,
Henning (HoHun)
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Yeah I assumed it was a friction type clutch. Even with a fluid coupling, the mechanism is not as efficient as a gear train. I'm referring to the efficiency of the mechanism, not of the entire engine/supercharger system. Shaft power output divided by Shaft power input.
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Uhmm, Mrsid... that wasn't very clever. You know very well what I and others mean by it, AH doens't have any airplanes in the case either, right? To discuss like that is just plain silly. AH Has got planes, with modelled engines, weapons, armor etc.