pushing the throttle how much?

[Dan Jones]

in all the ww2 birds flying today. How far can the plane and engine be pushed before it's considered unsafe? In a corsair, can that still top 400mph in level flight or having the lack of high octain fuel not make the engines do what they used to in ww2? This question goes for all the fighters and bombers.

It's not about fuel. Remember these are aircraft for 'play' or commemoration, not fighting wars.

Few warbirds fly with the loadings or equipment that the would have done in their primary service. (There's an inverse ratio of 'activity' between the heavilly restored fully complete with original widgets warbirds, which are flown careful, and limited, by and large, against the stripped back, gunless hot-rod fun 'planes.)

Apart from at Reno, there's no good reason for pushing the airframe, engine (and pilot) as hard as they were in wartime, where there was a supply-chain to back up wastage, including, we remember here, of aircraft and crew.

No warbirds fly at wartime operational heights, with oxygen, for instance.

Sure, you can make more noise and speed with the aircraft by pushing the throttle; but your costs go rapidly up straightaway, and for Americans, Uncle Sam's not funding that this time. So there are a few who fly hard at times, but the majority don't.

Thanks to Reno, there are options for going as fast (low down) as W.W.II but the engine (and airframe) consumption rate reflects that. And don't forget that pushing the envelope cost lives back then; doing it now would increase the number of warbird accidents.

Muddy; Lead (euphemisms Ethyl, TEL, tetraethyllead) helped reduce 'knocking' and allowed greater power out of engines, and 'lubricated' things like valves to avoid the valve head leaving parts on the valve seat - all at the great cost of literally putting cumulative heavy metal poison into every man, woman and child on the planet.

I'm sure there are those here who can explain the lead fuel additives benefits better than I can, meanwhile if you'd like to see how amazingly we can screw something up on a global-effect level by believing a business when they tell us something's harmless, may I introduce Thomas Midgley Jr and the Ethyl Corp?

http://en.wikipedia.org/wiki/Thomas_Midgley,_Jr.

Just a few thoughts...

To be fair James, I think there's a little bit more to it than that. Where the power issue becomes critical for some airplanes is in the case of multi engine aircraft operating with an engine out. At high density altitudes I would expect that something like an A-26 or a B-25, or a drop tanked P-38 could easily become something of a marginal proposition due to the inability to pull max power from the good engine due to the poorer quality fuel. And lets not forget the working radial engined airplanes out there still like the DC-3, DC-4, DC-6, and C-46. Having an iced up C-46 with an engine out and a load in the back was never a great situation even on 115/145, but on 100LL... the boys are gonna earn their money. I know they say 100LL is the same as 100/130, but it isn't. It's a poor quality fuel that decomposes quite rapidly compared to the real stuff. I've seen 100LL that wouldn't run a -670 radial properly (5.1 to 1 compression ratio and designed for 73 octane).

Just my two cents.

Dan

[JDK]

To be fair James, I think there's a little bit more to it than that. Where the power issue becomes critical for some airplanes is in the case of multi engine aircraft operating with an engine out. At high density altitudes I would expect that something like an A-26 or a B-25, or a drop tanked P-38 could easily become something of a marginal proposition due to the inability to pull max power from the good engine due to the poorer quality fuel. And lets not forget the working radial engined airplanes out there still like the DC-3, DC-4, DC-6, and C-46. Having an iced up C-46 with an engine out and a load in the back was never a great situation even on 115/145, but on 100LL...

Hi Dan,
Fair comment; I was focussing on the single-engine egofighters and the max speed / max performance for 'show' rather than the multi-engine point (good one) or working types. I should know better than focussing just on show-bling.

[Dan Jones]

I'd be curious to know what the highest octane the Germans were able to get out of their wartime synthetic fuel program was, but it also likely contained the tetra ethyl lead additive. If the best we're able to do in the future is 92 or so unleaded, that'll likely be the end of a lot airplanes (not just warbirds).

Last edited by Dan Jones on Mon Jan 31, 2011 7:06 am, edited 1 time in total.

[tom d. friedman]

i'm fairly sure it wasn't 100 octane... except jet fuel which was kerosene based.

[Warbirdnerd]

John Beyl can't log in so he asked me to post this for him...

The answer to the original question is -yes- these vintage engines will run just fine at fully rated manifold pressures on the available 100LL fuel. As some have mentioned already, it was designed to be a direct replacement of the 100-130. In fact there have been long standing questions and discussions surrounding whether or not it actually is. I believe there is enough scientific data to suggest it is -in a laboratory setting- but real world performance dictates otherwise. Many operators and engine builders will go with richer jetting, retard the ignition timing, and in the instance of liquid cooled engines, run them several degrees cooler. All of these variables allow the engine to safely operate at the “Advertised” manifold pressures however, the trade off is the engines make less over all power.
There are plenty of high quality unleaded fuel alternatives on the market that would be very suitable from anti-knock performance perspective but they are expensive and do nothing for valve lubrication which is critical in engines without hardened valve seats. Most of the engines we’re dealing with here do not currently have hardened seats. Research has proven TEL’s lubricating effects on these surfaces. Brewing one’s own 100LL by adding tetra-ethyl lead is not an option since it is readily absorbed through the skin and is lethal to the touch in very small amounts.
James has it spot on. These old warriors fought their battles long ago and have nothing more to prove. The harder we push them the more parts we break. The more parts we break the sooner flying them will come to an end. I’d rather see a P-38 loafing around at cruise power than see one sitting on the ground collecting dust because there were no parts to make the engines airworthy. As much as I love racing in all forms, including Reno, I have serious heartburn about the destruction of irreplaceable vintage parts year after year.

[warbird1]

Some interesting information about the Allies' use of 100/150 fuel and specific's about it's performance increases:

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

[RareBear]

The high visibility orange and lime-green paints used on aircraft (Dayglo orange) had an extremely high lead content. Also very high in lead content was the yellow paint used for years on Navy ground support equipment. Found this out after having to dig up and dispose of a large amount of it in an environmental clean-up project.

Walt

[whistlingdeath77]

so when we go to airshows and see a corsair or a mustang, are they flying the aircraft maybe at 50-75% of what it's really capable of? I've seen some great mustang demos and it seemed like it was screaming thru the sky. I always wondered if he was really pushing that plane to see what it could really do. Great Answers so far guys!

[warbird1]

so when we go to airshows and see a corsair or a mustang, are they flying the aircraft maybe at 50-75% of what it's really capable of? I've seen some great mustang demos and it seemed like it was screaming thru the sky. I always wondered if he was really pushing that plane to see what it could really do. Great Answers so far guys!

I would venture to say that most warbirds are not pushed as hard as they could be at airshows. Why would you? It makes no sense to push either the G limits or engine limits just to "look cool" when 98% of the airshow public wouldn't know the difference anyway. Remember, these planes are very expensive! Engine overhauls on most large recips's cost anywhere from 70K to 150K on American engines. Rare axis types could possibly go into the millions.

If you really want to see a warbird tested at it's limits, there is only one place in the world for that - the Reno Air Races. I've seen numerous engines blown over the years and even saw a Mustang once pull 12G's on the race course! Here, you can see, hear and feel what "all-out" warbird performance is like.

[JDK]

If you haven't been to Reno, you haven't seen W.W.II era aircraft at full chat.

[Dave Hadfield]

In an airshow display, you'd normally plan to keep the power at Max Climb.

In the P-40 we can use 52" for take-off, but we generally use 45" (that's if you can actually get it that high before becoming airborne at our light loads), and the prop is governed to 3000 rpm (Allison V-1710-81A).

Then we bring it back to 35" and 2500 rpm for the max climb power setting (max continuous).

I plan an air display at 35" and 2500, or less, saving take-off power for emergencies or screw-ups.

The P-40N manual, USAAC, specifies 100 octane for these power settings, but LESS power (lower settings) for the 93 octane they used at that time in the training world in the continental US. (The high-octane stuff went to the battlefield.)

Having 100 or higher octane fuel was a real advantage over the Axis air forces.

Dave

[JohnTerrell]

It's a similar case from what I have read and seen, that in a Merlin-powered Mustang, pilots tend to use anywhere from 45-50-55-in MP - the original in-service manual will tell you to use 61-in MP, but that seems to be more than what is needed to get a Mustang quickly into the air, especially one that is not loaded for combat-use of course, thus there isn't need for it. In all other realms of flight - climb, cruise climb, and normal cruise - settings used are often times the same as what would have been used in the service, if not slightly lower to conserve fuel in cruise.

For display purposes, I have heard Mustang pilots use as much as 46-in MP & 2700 RPM in an acro performance, the same as max climb power, or 42in MP & 2500 RPM, or 40-in MP & 2400 RPM depending on the nature of the display, which is right around max continuous power.

[Speedy]

It's a similar case from what I have read and seen, that in a Merlin-powered Mustang, pilots tend to use anywhere from 45-50-55-in MP - the original in-service manual will tell you to use 61-in MP, but that seems to be more than what is needed to get a Mustang quickly into the air, especially one that is not loaded for combat-use of course, thus there isn't need for it. In all other realms of flight - climb, cruise climb, and normal cruise - settings used are often times the same as what would have been used in the service, if not slightly lower to conserve fuel in cruise.

For display purposes, I have heard Mustang pilots use as much as 46-in MP & 2700 RPM in an acro performance, the same as max climb power, or 42in MP & 2500 RPM, or 40-in MP & 2400 RPM depending on the nature of the display, which is right around max continuous power.

Sort of puts an exclamation point on the conversation when the Mustangs running up front at Reno are using 120 inches on the magneseum-doped VP racing fuel....and I've heard some up to 140 inches and 4200 rpm, though they didn't last very long.

[Randy Haskin]

so when we go to airshows and see a corsair or a mustang, are they flying the aircraft maybe at 50-75% of what it's really capable of?

Not even remotely.

The real trick to employing a fighter as a weapon -- which is what you do in a fighter: the flying part is simply the "administrative" stuff that gets you to and from the fight -- is operating right on the three edges of the flight envelope.

To the left is the max lift limit line...ergo, pull a little harder and the airplane will accelerated stall.

On top is the max load limit line...ergo, the G limit.

On the right is the Vmo/Mmo line...ergo, go faster and she'll come apart.

The way that a fighter is able to maneuver itself into a position of advantage against another aircraft means flying right up against those limits. It means squeaking out ounces of performance here and there in hopes of beating the other aircraft in turn rate, turn radius, energy sustainment, etc. The pilot's skill is in being able to consistently find those limits and comfortably operate there without exceeding those limits.

As many warbird operators have said here before, there are two big factors why they don't ever actually get near those limits in flying them today:

1. Don't need to. We're not in a furball with the Jerries. No reason to risk exceeding those limits just for the purposes of 'keeping 'em flying' and preserving history.

2. We don't really know where those limits are anymore. Between questionable WWII metallurgy, unknown corrosion or other damage to the construction materials, to the lack of knowledge about what types of 'damage' previous owners did to the aircraft, it's impossible to know where the actual edges of the flight envelope are anymore. Thus, since there's no reason to go there, there's a pretty good argument for staying away from even the ragged fringes.

[RickH]

We use full power on takeoff. I'm pretty sure we're getting all she's got !!