Airplanes

[castor troy]

ORIGINAL: Big B

Interesting discussion (and I do fall into the 'US fighters used higher octane' camp.)

However, one thing I remember from 30+ years ago in my hot-rodding days, was that running higher octane fuel in a lower compression engine designed for lower octane fuel - actually hurt performance. As I recall you need higher compression to reap the benefits of higher octane fuels.

I readily admit that I have no experience with turbo/supercharged engines, however I do remember that if you go turbocharging or supercharging a stock lower compression engine - what ever gain you achieve will quickly destroy the bottom end of that engine because the crank, rods, rings, and bearings will not handle the boost....without seriously strengthening all of those components (not to mention modifying the oil pick-up, windage, and head-flow).

I may be all wet, but it seems to me that running significantly higher octane fuel without increasing compression is kinda worthless - and if you do increase compression - you MUST increase the robustness of the entire bottom end or it the engine will self-destruct quickly....so I'm not sure what good it would do to run 100+ octane avgass in a 90 octane designed engine?...it doesn't seem to make practical sense to my Neanderthal brain?
On the other hand, I may be completely wrong [:D]

ORIGINAL: Symon

ORIGINAL: JeffK
Interesting article about the other end of the spectrum, increasing the octane rating able to be used by USAAF/RAF fighteres in 1944-45

http://www.wwiiaircraftperformance.org/ ... -fuel.html

That’s an excellent summary article. The results certainly show significant improvement. I read it through several times, as well as the eleven others referenced within. The other articles tell the story of the months of iterative testing it took to get to those improved performance specs, and what had to be done to the engines in order to actually achieve those numbers.

Depending on the plane, MAP went from 52-56”, through the 64” range, and up to 70” in some cases. CAT saw a corresponding increase. It required changes to injection (#12 to #13 ports in most cases), changes to mixture control, changes to ducting for cooling (sometimes a new cooling system), changes to turbo speeds, with consequent changes to lo/hi blower transitions, Woof !!

A real eye-opener was the practical testing done on the early P-38s. Allison had a hard spec on the engine, 45C CAT and *maybe* 55C at 5-min WEP: exceed it and the engine turns into slag. But practical tests ran CAT to 85C without blowing it up. Pressure is Temperature, so higher T allows higher P, and HP can go up. That’s why the apocryphal stories of P-38 mechanics tuning their planes into monsters.

They were true but they were true for squadrons here and there that had knowledgeable commanders and righteous mechanics. Your run-of-the-mill P-38 pilot shows up with his copy of The Book and squadron practice makes that the basis for flight profiles. Obviously, some can perform better and do so. Sounds exactly like Sakai and Genda. But it wasn’t the “uniform” paradigm.

But alas … we had captured enough wartime documentation to know exactly how to run the various Japanese engines, according to their own specifications, so that’s exactly how we tested them. It’s what one would expect in a wartime situation, when one wishes to know the “capability” of an enemy aircraft for the edification of it’s pilots.

So, if one reads the “text” of the US test reports, one can get an appreciation of the what’s and wherefores of the results, including the engine operational conditions.

dunno about the '40s but nowaday's engines don't care. We used to drive cars using 90 Octane fuel that isn't even available on most petrol stations nowadays. So we go with 95 Octane fuel. Now Shell is promoting to use 100 Octane fuel (which is just horrible more expensive), saying it would get you more performance out of your crappy car and being better for it anyway, whatever that means. There also has been 98 Octane fuel as long as leaded fuel was allowed which then vanished and if you had a car using that you had to get 95 Octane fuel and fill in a litre of lead substitute.

[Symon]

ORIGINAL: John 3rd
I'm go regardless of things.

John: I will need you to also work the additional ZERO variants we've created for RA.

You did get the RA files I sent--correct?

Yep, got them. Suddenly dawned on me, when reading this, that you guys have some different airplanes. Oops. Have to do a sanity check with your airplane file.

Okey dokey, then. JWE

[Symon]

@ Castor Troy, and @ BigB,
Yeah, everything you guys said. The "octane" rating of a fuel is just a measure of its anti-detonant properties. Fuel, is just "fuel" and its specific heat depends on the blend of specific cracking temperature fractions. 87, 90, 100 "octane' fuel has the same specific heat/ml. They just have different anti-detonant properties. "Octane" is just the ratio of the octane molecule to the heptane molecule. Octane requires a few more KCal/Mole to "burn" than heptane, but the energy release is insignificantly different.

So you got gas and you burn it and the manifold heats up and the cylinder heads glow red hot and after a while, you don’t need compression and a spark to initiate the power cycle; engine heat (and a skoosh of compression) is enough to pre-detonate the fuel. So what to do?

Well, you increase the octane ratio and when that isn’t enough you add things like TEL, or bromines, or benzene/nitrile things, anything that won’t change specific heat, but will shift the detonation temp. Doing that lets you run a motor at a higher temp. That means a higher intake pressure (P ~ T). That means a higher engine RPM. That means a higher sustained power output. It’s basic P-chem, PV=NRT.

And then you get turbos and other such, but the basic physics and P-chem is the same. Fuel is fuel, and additives are just there to adjust things to account for heat (the big T). “Octane” ain’t power.

[Big B]

ORIGINAL: Symon

@ Castor Troy, and @ BigB,
Yeah, everything you guys said. The "octane" rating of a fuel is just a measure of its anti-detonant properties. Fuel, is just "fuel" and its specific heat depends on the blend of specific cracking temperature fractions. 87, 90, 100 "octane' fuel has the same specific heat/ml. They just have different anti-detonant properties. "Octane" is just the ratio of the octane molecule to the heptane molecule. Octane requires a few more KCal/Mole to "burn" than heptane, but the energy release is insignificantly different.

So you got gas and you burn it and the manifold heats up and the cylinder heads glow red hot and after a while, you don’t need compression and a spark to initiate the power cycle; engine heat (and a skoosh of compression) is enough to pre-detonate the fuel. So what to do?

Well, you increase the octane ratio and when that isn’t enough you add things like TEL, or bromines, or benzene/nitrile things, anything that won’t change specific heat, but will shift the detonation temp. Doing that lets you run a motor at a higher temp. That means a higher intake pressure (P ~ T). That means a higher engine RPM. That means a higher sustained power output. It’s basic P-chem, PV=NRT.

And then you get turbos and other such, but the basic physics and P-chem is the same. Fuel is fuel, and additives are just there to adjust things to account for heat (the big T). “Octane” ain’t power.

Right - so if you're not increasing compression - you don't need higher octane fuel, to burn cooler and forestall pre-detonation.

@ Castor: in the pre-computerized engine days, if you ran 104 octane premium gas in a low compression 87 octane rated engine - you would simply foul the plugs (along with paying too much for gas).

[PaxMondo]

ORIGINAL: Symon
@ Castor Troy, and @ BigB,
Yeah, everything you guys said. The "octane" rating of a fuel is just a measure of its anti-detonant properties. Fuel, is just "fuel" and its specific heat depends on the blend of specific cracking temperature fractions. 87, 90, 100 "octane' fuel has the same specific heat/ml.

OK, I'll agree with you here within the scope of the games abstractions. There are differences, alkanes in general will have slightly higher specific heat than equivalent alkenes due to their structures (which is in fact why they "burn" slower). Emphasis is very much on the slightly and as I say, within the abstractions that we are dealing it is an acceptable assumption.

I bring this up only because back in the 40's high octane was generally made by alkylation, not cracking. It the opposite process. So back in the 40's/50's you could use high octane gas as a safe solvent, just like paint thinner today. Today's gasoline is HIGH in benzene (amoung other known carcinogen's) as it is primarliy from a cracking process (generally FCC) and I don't even recommend standing within 'sniff' range when filling your auto.

The upshot is that back in the 40's higher octane fuel also had a little more specific heat. Today, higher octane may have the same, or even slightly lower. Again, within the abstraction of the game, this is all pretty much moot.

The real benefit that the allies gained with high octane fuel was they would avoid WEP. Logistically this is huge. Instead of having to have TWO or potentially THREE fuel sources for each aircraft, they only needed one.* That's a HUGE savings.


* AvGas, Methanol, Distilled Water. Methanol could be pre-mixed but it is hygroscopic and hard to store/maintain. Since the proportion is rather critical, it is generally mixed just prior to filling. At least that's what we did back in the "old days" of dirt track racing. Not sure how they handle it now ... but my old days would be far closer to the realities of 1942 than 2013 would be. [;)]

[Symon]

ORIGINAL: Big B
Right - so if you're not increasing compression - you don't need higher octane fuel, to burn cooler and forestall pre-detonation.

@ Castor: in the pre-computerized engine days, if you ran 104 octane premium gas in a low compression 87 octane rated engine - you would simply foul the plugs (along with paying too much for gas).

This is so true. I am become an avid Light Sport Aircraft enthusiast and am learning more about the generally available 87 and 91 "octane" fuels that I ever wanted to know. The Navy guys turned me on to a couple of "local" stations that have pumps for 92 grade, ethanol free, unleaded. Been using that in the Harley for almost a year. Am researching planes and engines (gonna buy one, soon) and find dire warnings about using Auto-gas, hidden away in the tech-specs. Exactly like PaxMondo suggests, ethanol content has caused many unplanned landings because of condensation fogging of the lines. The Navy guys told me to buy a good 5 gal jerrycan and when I fill up the bike (or the Jeep) fill up the can for the plane.

There's a very serious movement afoot to relabel airfield MOGAS and have refiners provide product that is safer for use, and forget the politically correct bull$hit. There's also a movement afoot to have a CAT gauge on the panel again. Many of the legitimate LSA manufacturers are rethinking their engine control monitoring techniques as a result.

I guess the only point to this is that gas ain't gas. There's this kind, there's that kind, and it all depends on the engine what kind works.

Ciao. JWE

[John 3rd]

John: Just got back from a quick family trip to KC. What is your status with this?

[PaxMondo]

ORIGINAL: Symon
I guess the only point to this is that gas ain't gas.

In a nutshell, YES. [:D]

And today much moreso than in the 40's due to all the EPA requirements, additives for FI, CA specific requirements, yaddi yaddi yaddi ....

[PaxMondo]

ORIGINAL: Symon
ethanol content has caused many unplanned landings because of condensation fogging of the lines.

Even the IJ knew for aviation you MUST have separate AVGAS and WEP tanks in the aircraft. You cannot mix these two in an aviation setting. These are injected separately, best if directly into the combustion chamber.

The partial pressures of the two liquids and their respective miscibility curves are very much dependent upon temp and pressure. Mix in advance of flight and your engine will stop and likely not restart without removing the cylinger heads. At the very least you will need to pull the spark plugs to dry the cylinders out. Not much fun at 20,000 ft and 40 miles down range of your airport.

[Symon]

ORIGINAL: John 3rd
John: Just got back from a quick family trip to KC. What is your status with this?

Jury duty. A horror show. Told them about Mom and they want Drs and Caregivers to file statements. Wrong !!! I thought I was being righteous and trying to get my sister Jennie to take Mom for a week, but circumstances got in the way. I said so and volunteered for a deferrment to the next term. But the system, here, is beyond Byzantine.

So I told them I would not be showing up and if they want to issue a warrant, that's their privilege. I'm a retired Cali Atty and have retained a local friend. to represent me. It would take him all of 20 minutes. And after he's done, I'm no longer eligible for the jury pool. A rather sad ending from my prospective, and certainly from Baldwin County's. But folks need to look at 'needs must', and not just their paperwork.

Might have to spend an hour in 'county'; there's no way in Hell I'm spending money for bail for this piece of ridiculousness. Golly, I'm getting all fired up again, like I used to. Woof !! This is gonna be fun. Being retired and doing what you want is pretty cool.

Ciao. John

[PaxMondo]

TDF!!!

[:D][:D][:D]

[&o][&o][&o]

[Symon]

Ok, still plugging away despite the mongrel bureaucrats nipping at my heels. Here’s a preview of IJN fighters, with USN planes for comparison. Notice several changes (in red).

Max Altitude is no longer “service ceiling”. It is an evaluation result somewhere between “combat” and “operational” ceilings. An altitude where a plane can actually do something.

Max Speed is more consistent. It is all given at Military power (max sustained power, at altitude, for at least 15 minutes). All the different kinds of WEPs are ignored, as being too different to allow for a consistent algorithm, as well as being individually limited as to time by injection fluid tank size and maintenance schedules.

Climb rate is again more consistent. It is a weighted average of initial climb rate and rates at the critical altitudes. Everyone is treated equally.

Maneuver is subject to a proprietary program of the Air Team. But, once again, consistency is paramount. Maneuver is subject to the standard engine performance specifications that generate Climb, Speed and Ceiling parameters. Must say (sorry, Ian, but it’s obvious by now) that Maneuver has a dependency on HP. You get a good plot of HP at Alt, you get a good number for comparative Maneuver.

You will see a lot of similarities with BigBs airplane data. Some departures, to be sure, but conceptually similar. You will also find the data working smoothly within the A2A combat algorithm. Despite what you may see on the main thread, A2A is a matrix of Speed, Climb, Maneuver, within the different bands. As planes approach unity, in the algorithm, pilot experience becomes paramount.

Ciao, JWE

[Dili]

You get a good plot of HP at Alt, you get a good number for comparative Maneuver.

Not true. There are several fighters that employed same engine and were very different at altitude. Example DB 605 engine and Bf-109, Fiat G55, Reggiane 2005, Macchi205. The Macchi with much less wing loading was lousy at altitude but great at medium,low level. They then increased the wing size to get it better. G.55 and Re.2005 were the better ones. All same engine.

[PaxMondo]

John,

Nice work here. Thanks for all your efforts.

[&o][&o][&o]

[LoBaron]

Wow JWE, you are moving along much faster than I thought. Number look interesting, although I do not have the skills to compare them to their r/l counterparts and what the A2A engine does with em.

That said, I at least partly agree with Dili.

The mvr value is, as you say, highly dependent on HP per alt. But equally important are airframe attributes, both for assigning the basic mvr value as well as how the performance curve looks at alt. The problem is that this value represents a pretty large ammount of variables all thrown together in a number.

P.S.: Did you consider looking at acceleration and divespeeds and the likes? For example Tbolts used a simple dive, or a split-s as an (at least in the PTO) unbeatable defensive move. Such specialities might influence mvr as well.

Or am I into too much detail for what you are aiming for?

[Symon]

Howdy, Baron.

There’s a ton of airframe attributes that go into it. If you look at the data, you can see that there’s many planes with identical engines that have very different performance parameters.

One can get good numbers at specific points. Once you get them they form a functional constant and one can use a plane’s power curve to ‘fill in the blanks’ or determine the shape of the roll-off. Makes it smoother, and more consistent, although calling it smoothness is kind of silly for stepped bands at 10k intervals.[;)]

Don’t forget, this is for calculating values useful to the game engine. Not quite the same as irl.[;)]

Ciao. JWE

[oldman45]

This may be out to lunch and not apply at all, but I have a neighbor that flew hellcats late in the war and swears that they would out turn zero's by using the engine torque, is that for real and should/would it apply here?

[LoBaron]

Yep, sorry JWE. I assumed from your post you factored in airframe specs for initial mvr and completely relied on the HP/alt for the alt band curve.

Was pretty stupid to assume the Babes team would not take such stuff into account. [:)]

[Symon]

We try, Baron, we try [8D]

Here's the IJAAF planes. Not all done, but mostly. Missing ones are the wierd exp stuff. Have to go to the crystal ball for that. The real witch is the Ki-100. The legitimate sources give reasonable specs for it, but they just don't quite jibe with Cd0 analysis given the planned engine HP. Think a lot of IJ wartime specs (faithfully reproduced by Francillon) were the product of what they had in hand at the time. And this was the time period of the T-42 Mod-2 fuel specifications. What could they have done with well built and well maintained engines using their everyday, ordinary, 1941-43 standard combat aviation fuel. The world wonders.

[Symon]

ORIGINAL: oldman45
This may be out to lunch and not apply at all, but I have a neighbor that flew hellcats late in the war and swears that they would out turn zero's by using the engine torque, is that for real and should/would it apply here?

Could be real, don't know. Doesn't matter anyway. The game algorithm is a mathematically driven evaluation of performance characteristics of devices characterized as "airplanes". Planes are planes. They are nothing but a data box with technical parameters defined "relative" to one another.

J