Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on July 30, 2003, 03:15:55 PM
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I have a question about the use of higher grades of fuel in relation to American Aircraft.
Does the use of higher grade fuel create higher HP?
I believe it does because this would raise allowable MAP and there by increase output BHP.
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Originally posted by F4UDOA
I have a question about the use of higher grades of fuel in relation to American Aircraft.
Does the use of higher grade fuel create higher HP?
I believe it does because this would raise allowable MAP and there by increase output BHP.
Higher octane doesn't raise power by itself, but it does increase allowable MAP which does increase power.
Here are a couple of formulas you may find useful.
Convert octane rating to PN
2800 / (128 - octane rating) = PN
2800 / (128 - 96) = 87.5
MAP rating with changes in PN
((old MAP - 7) * new PN/old PN) + 7 = new MAP
((60 - 7) * 150/130) + 7
53 * 1.15 + 7 = 68.15 in Hg
PSI boost > Inches Hg
(Psi * 2.04) + 29.92
(15 * 2.04) + 29.92
30.6 + 29.92 = 60.52 in Hg
Greg Shaw
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No. 87 octane burns just as good as 100. However, 100 octane can be compressed more without detonating (known as "knocking" and like in diesel engines) allowing for higher boost levels. Running an engine on higher octane fuel does not give it more HP, you would have to modify the engine (increase turbo/blower charge and fuel injection) to make the engine produce more HP. It would be correct to say that higher octane fuel will allow the engine to produce more HP by increasing boost pressure.
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so if a engine is modify to X octane
and then i degrade the octane
will the emgine loose power?
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The fuel would detonate (self combust due to the heat from the compression in the cylinder) this would damage the engine if boost is not reduced quickly. Potentially the engine could explode.
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More importantly, and I think this is what GScholz is trying to say, is that it will pre-detonate.
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Well not explode but continuous self-detonation of the fuel will broke up the bearings and in some cases gaskets too.
I've seen a piston from aircooled Deutz engine which over heated and begun to detonate 'cause of that.
Pistons looked like a rat had been eating them, cylinder head gaskets (copper rings in separate cylinders) lost their shape, oil (high grade synthetic, not some cheap mineral oil) turned to black stuff which was looking like toffee... that was the end of that engine.
I had one of the pistons as an ash tray thought I haven't seen it in years, guess someone thought it looked cool or something... :D
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Oh it will explode if the pre-detonation (thanks Furious) is very bad (like if you run a 150 octane engine on 87 octane at full boost) and the engine is running high rpms. It would tear itself apart.
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Originally posted by Staga
I had one of the pistons as an ash tray thought I haven't seen it in years, guess someone thought it looked cool or something... :D
I use a 155mm artillery shellcasing. It stands on the floor and it takes quite a while between times I need to empty it. :D
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You can always use higher octance of fuel, never lower than it's supposed too.
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I have another question then.
In your opinion are these HP ratings from 115/145 or 100/130 fuel?
These engine ratings are from the same engine. PW-R2800-18W from the F4U-4
(http://mywebpages.comcast.net/markw4/F4U4hp.jpg)
(http://mywebpages.comcast.net/markw4/enginecal.jpg)
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Are you asking if the first page or the second page (or both) is using 100 octane fuel?
The second page in the bottom right corner states that the Fuel Grade is 100/130, AN-F-28.
The first page looks like the Notes page from one "Standard Flight Characteristics" pdf docs off the Naval Aviation History site ( http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf )
And if you look a few pages before in the "Fuel & Oil" section (page right after the 3 view diagrams) that it states that the fuel grade is 115/145 and fuel spec is AN-F-48
Does that help?
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I have nooooo idea. Can't even begin to figure out the math involved in finding that out.
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Verm,
That is exactly my point.
You are right that is the NAVAIR F4U-4 doc and the second one is from the flight manual. Point being they both have the same HP curve.
My point is that the flight test done in the NAVAIR doc was not done with 115/140 fuel.
Another way to show that is the speed of that F4U at sea level is identical to that shown in the AH charts. If the MAP were higher then the speed would be higher at sea level as well.
By that I mean the sea level speed in AH is 376MPH combat. The speed in the PDF is 374MPH.
So the test where the F4U is supposed to be overboosted it is actually slower than the standard boost while climbing 1K per minute better. Something doesn't add up.
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Originally posted by GScholz
I use a 155mm artillery shellcasing. It stands on the floor and it takes quite a while between times I need to empty it. :D
Bloody good idea! Think I will get one myself! Thanks, GS.
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Hi F4UDOA,
>You are right that is the NAVAIR F4U-4 doc and the second one is from the flight manual. Point being they both have the same HP curve.
Note that the maximum power setting specified in the curve as well as on the manual page is "take-off/military" of about 2100 HP. The maximum power setting mentioned is "WEP" though, which obviously is going to be more than 2100 HP.
As you can calculate from the Standard Aircraft Characteristics data, the top performance graph (curve 1) was based on around 2600 HP. (At 2100 HP, climb rate would be about 3800 fpm.)
The 2600 HP figure would match the 2650 HP quoted in the XF4U-4 comparison report quite nicely (2650 HP @ 70" Hg at sea level).
The question of course is: How much power did the R-2800-18W produce in operational service? If water injection was functional, I'd bet it was more than the 2100 HP associated with the 3800 fpm climb rate figure.
With regard to the octane questions: Using Greg's formula, on 145 rated fuel the R-2800-18W might draw a maximum of 60" Hg. From a graphical estimate from the engine calibration chart, I'd say that equates to about 2400 HP at sea level and 2200 HP at 15000 ft.
However, that's still far short of the "curve 1" performance as the 2400 HP drop off with altitude immediately, while curve 1 drops off only at 11000 ft. By another graphical estimate, I'd say 70" Hg in low blower would just do the trick of giving curve-1 equivalent power.
Regards,
Henning (HoHun)
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Note that the maximum power setting specified in the curve as well as on the manual page is "take-off/military" of about 2100 HP. The maximum power setting mentioned is "WEP" though, which obviously is going to be more than 2100 HP.
I agree. I actually think the normal power setting is more interesting than the mil power setting because I don't have a speed or climb curve for mil power in the NAVAIR doc. But take a look at the normal power climb curve. 2900FPM at sea level and 7.5minutes to 20K. This power setting is the same with or without 115/145 fuel. Point being the climb rate is very high.
As you can calculate from the Standard Aircraft Characteristics data, the top performance graph (curve 1) was based on around 2600 HP. (At 2100 HP, climb rate would be about 3800 fpm.)
How would you calculate that?
The 2600 HP figure would match the 2650 HP quoted in the XF4U-4 comparison report quite nicely (2650 HP @ 70" Hg at sea level).
That is exactly what I thought except I can't figure out why the top speed is the same when you have such a huge increase(200HP) in available HP.
I have two other F4U charts showing climb at 60" MAP with climbs of 4,000FPM to 4,400FPM at sea level. But they all show the same top speed as the NAVAIR chart.
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Originally posted by DiabloTX
Bloody good idea! Think I will get one myself! Thanks, GS.
You're welcome :)
You need to do two things though. First make a piece of metal that you can put the cigarette out on and bolt it to the inside of the shellcasing. Secondly, make a lid for the whole thing to avoid the ash smell. Works great!
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Hi F4UDOA,
>How would you calculate that?
If you've got performance curves for a given data point, you just have to assume a reasonable propeller efficiency and then can extrapolate the data for another point in the envelope.
>That is exactly what I thought except I can't figure out why the top speed is the same when you have such a huge increase(200HP) in available HP.
The two capped pylons seem to eat up 200 HP of shaft power at top speed. If the Aces High F4U-4 is faster at the same climb than the NAVAIR F4U-4, one might guess it doesn't have the pylons.
However, the inconsistency between Aces High and NAVAIR is bigger than that. The shape of the climb graph indeed looks more like 2400 HP graph, so the lower climb rate would suggest a heavier aircraft. With 2400 HP and no pylons, you'd get the same top speed as with 2600 HP and the pylons in place. Still, you'd need a 14000 lbs Corsair to get the climb rate at 2400 HP down to Aces High level is you're using the NAVAIR document as a basis, and this seems a bit much.
>I have two other F4U charts showing climb at 60" MAP with climbs of 4,000FPM to 4,400FPM at sea level. But they all show the same top speed as the NAVAIR chart.
60" Hg should be equivalent to the 2400 HP I mentioned, so these planes probably didn't have the pylons either.
Another consideration would be that the Aces High F4U-4 could have a different propeller than the NAVAIR F4U-4 that gives less climb power, but more top-speed power. (That would imply the Aces High F4U-4 has the pylons, too.) The difference might be a bit too large to explained this way, though.
The NAVAIR document gives the propeller as 6501A-0 - do you know of any other propeller types used with the F4U-4?
Regards,
Henning (HoHun)
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Originally posted by GScholz
You're welcome :)
You need to do two things though. First make a piece of metal that you can put the cigarette out on and bolt it to the inside of the shellcasing. Secondly, make a lid for the whole thing to avoid the ash smell. Works great!
Hey, you know what? This could be a great money maker. I am sure we could get some empty shells cheap, have them modified for tobacco usage, advertise them in Soldier of Fortune and Guns and Ammo magazine and make a fortune! I'm in. :p
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Originally posted by DiabloTX
Hey, you know what? This could be a great money maker. I am sure we could get some empty shells cheap, have them modified for tobacco usage, advertise them in Soldier of Fortune and Guns and Ammo magazine and make a fortune! I'm in. :p
LOL! I'll take 10% royalty thank you. ;)
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Originally posted by GScholz
LOL! I'll take 10% royalty thank you. ;)
Ummmm...10%??? DEAL!!!!!!!!!!!!!!! :D
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Deal!
Royalty means I get 10% of what you make. You do all the work, risktaking etc. ;)
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I have no problem with that, its just that it was YOUR idea! My father in law is a superb welder and my oldest brother just retired from the Army. 20 years+ at Ft. Bragg. Sure there are plenty of empty artillery shells laying arond there!! LOL!
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Hey, maby it's worth looking into. Let me know how it turns out. :)