Got the following email from an occasional reader in the UK that I feel unfit to service:
My question: Broadly, in most propeller driven aircraft, what would happen if a pilot took off at full power (or even WEP in a warbird) and remained at full power throughout climbout and for the entirety of the flight?
The expert I’m trying to convince otherwise is the owner and designer of an online flight simulation (very successful one too: www.hitechcreations.com) modeling WW2 warbirds. Now, I’m no expert myself but I do know engines and what *should* happen is, as the temp increases, the engine will start to tick and whine, followed by a ringing sound as the piston rings start to melt, then a condition known in engineering as power fade due to overheat….ending in a loud bang and prop no go round anymore.
Every pilots manual for every warbird I’ve ever read clearly states time limits to how long an engine should be run at max power.
Am I wrong here? I mean, of course, airspeed, altitude, ambient temp, cooling system damage, etc, would all have an effect on the situation, but under normal conditions and level flight…..can a old warbird’s engine be run at full military power forever? If I’m talking out of my backside here please tell me, and if not…..can you give me some pointers to use in my discussion that might make an old dog see things differently?
Swoop, RAF Regiment (retired)
I’m not the go-to guy on radial engined fighters (alas!), but the piston-engine Cardinal I fly on the occasional weekend is rated for max continuous power throughout its flight envelope. At higher altitudes in the non-turbo’d Cardinal, manifold pressure is more limited by air density than throttle position. In that aircraft at least, heat management seems to have more to do with the shape of the cowling than the power demand.
Most of the more competitive World War II fighters I believe had at least a supercharger if not a turbocharger and I imagine the answer will be “it varies,” for the war bird set depending upon the aircraft and powerplant combination.
We’ve got some experienced round engine operators running about the place.
What say you?
Of course it varied with the engine, but for the Packard Merlin V-1650-7 in the P-51 Mustang:
Max MP/RPM – War Emergency Power, 67″/3000 (5 minute limit);
Military Power, 61″/3000 rpm (I don’t know the time limit);
Max. Continuous, 46″/2700 rpm.
I have a copy of the Pilot’s Manual for the F4U, and as I recall, the War Emergency Power setting was only to be used for a few minutes. Flying inverted for more than 5 seconds was also not reccomended, or the fuel would not flow into the carb.
Scott, IIRC the F4U had an War Emer water-injected Power Setting. Had to push the throttle thru/break a small restraining wire to do so–so it must have been of limited duration–probably a one-time deal after which engine had to be changed out after you got back–IF you got back.
More like, until you refilled the water-methanol tank.
Well, my point is Brad, that if you ever found yourself in a situation that required War Emer Power, the situation, plus the pucker factor alone would probably cause one to run the engine well past limits making sure one escaped–throttling back to save the engine after water ran out would probably be the LAST thing on a guys mind unless a long, long way from good-guy terr. and clearly out of danger.
F4Us indeed had water injection. Ike Kepford of VF-17 used it in a well-documented case to outrun a couple of Zeros on him near Rabaul. AD-1s also had it later on. Requires a practical rebuild of the engine after use though.
JackSprat: Old Ike personally polished the leading edges with shoe polish for greater airspeed, IIRC–he credited that as well as the water injection (and luck–not to mention his skill) with giving him the edge. He was on the deck and feinted a turn one way, went the other and nearside zero’s wing-tip hit the water attempting to turn inside and cartwheeled. Offside zero was too far out of position once the turn was made…
It does depend on the exact engine of course but in general full “military power” was limited for a set period of time due to cooling considerations. I’ve read accounts of combat where those restrictions were ignored during a dogfight to save the pilots rear but I suspect the limits were somewhat conservative to account for the various other factors that effected operating temperatures as well.
I suspect the best thing would be to get a hold of a copy of the actual operating manual of the fighter being modeled as well as the engine to properly simulate it. Not as far fetched as it might seem as you can find almost anything on ebay these days.
I agree on the WEP statements. I know that some WWII aircraft achieved WEP power boost by injecting something (water-alcohol, etc) into the engine, of which there was a finite quantity. Cooling considerations limited other engines.
On military power, I think some of the more well known engines were rated to around 30 minutes, maybe less. Again, cooling and engine wear were the main concerns.
Here’s a question Lex might be able to answer. Is it possible to run a modern afterburning turbofan in full ‘burner for the duration of a flight? Obviously not on final, but could you theoretically take off in full burner and stay there for the limited number of minutes that fuel would last? If discussing the F404 is finger breaking territory, perhaps a slightly older engine, like a 2nd/3rd generation turbojet?
Depends on the engine. One of my TPS classmates worked out how to launch in a T-38, leave the pattern, head smartly for the approach end of the runway…and land at BINGO fuel after 0.3 hours. In A/B all the way. Never flew it…he would up flying something that does something similar, but with a deadstick landing.
I don’t know about WWII fighters but I have been flying skydivers with 2 cessna 182’s 2 c-206’s and a DeHavilland Beaver for over twenty years and here’s how we fly them. With the Cessnas we use fullpower and full RPM all the way, from takeoof to 11,000 feet then reduce power to let the jumpers out and decend. With the Beaver (round engine 450 hp) I used full power on takeoff then reduced power for the initial climb but was back up to full throttle by 6000 feet. I suspect that if I flew the Beaver like I flew the Cessnas I would have gone through cylinders like popcorn. Not on every flight but a lot. By the way i never had to overhaul a Cessna engine before TBO using that method.
Finally a skydiver driver shows up after all these years! D-7400 here.
Lots of real world data at this link RE: WWII aircraft, ranging from manufacturers publications to military flight test and combat reports. It isnt organized very well but there’s enough there to keep a sim enthusiest busy for days.
http://www.wwiiaircraftperformance.org/
Hope this helps.
Some of those engines could be seriously overboosted at low level in cold weather. I recollect a tale from my powerplant instructor of a Corsair popping a jug on takeoff during a Korean War winter alert launch.
Also (working from nearly 30 year memory here) some like the Aircobra had a transmission shifted by the pilot that engaged different levels of supercharger depending on the altitude.
A normally aspiratedengine cannot, by definition be overboosted. You can run it at balls to the wall all day as long as you have the temps/detonation under control and until you run out of fuel or oil. A supercharged engine is a very different animal. For example the max power on the R-1820 in the T-28 and others is either 51.5 or 52.5″ Map depending on -76 or -86 engine and 2700 RPM at sea level. Max continuous (all day as long as you have fuel and oil)is 45″/2500. Normal climb is 36″/2400.Again, the key is keeping temps/detonation under control. Also at full throttle, the carb has a power enrichment feature which adds fuel to cool the mixture thus preventing (hopefully) detonation. The mistake of the uninformed, but well-intentioned of not going full throttle on take off, is that the enrichment is activated by throttle position and failure to hit the detent by using less than full throttle can actually cause higher temps and engine destroying detonation.
The water/alcohol injected engines have a limited duration and when it’s gone, it’s gone. ON the R-2800 that I flew in the C-123, If I recall correctly, it was about 5 minutes max and if you didn’t turn off the switch before retarding the throttles, the engines would die momentarily, which would get your attention real quik. Only happened to me once and I never forgot it.
Detonation is the killer of engines and, in my humble, age addled and second glass of wine for the evening opinion,running the engine on the firewall stops indefinitely would only hasten the inevitable destruction of the engine by oil starvation and/or fuel starvation, but most likely, melting of the pistons. In any case negating any perceived benefit other than running for a brief period to survive an immediate threat,as it was designed for.
I Believe there is a sea story posted somewhere here about a Hornet which ingested part of the catapult track on launch and would only stay airborne in full burner. Came around and trapped – maybe Lex can point to it. A great story.
This story is around the web – one unpunctuated version here: http://www.aircraftresourcecenter.com/Stories1/001-100/0003_F-18/story0003.htm
This copy of the Operating Limitations from an airline’s DC-3 manual includes power settings for the engines (P&W R-1830 Twin Row Radial):
http://pcmuseum.tripod.com/dc3/dc3operatinglimitations.pdf
Corsair I-IV (F4U) Pilot’s Notes at: http://www.vfa-41.net/pgm-download_media.php?name=corsairpilotsnotes.pdf (3.3Mb) has some good ‘5 minute only at full or emergency or combat power’ tips.
My dad hired on with Pan Am in Fairbanks in winter of ‘48. His first job was filling the ADI (anti-detonate injection) reservoirs on DC-4’s that would stop over for fuel on the way to ?(Japan I think). Up and out the door at 0330 to ride his bicycle to the field in time for the 0400 flight. Sounds like he could have used some alcohol too.
There’s a really nice guy named John Deakin who is the perfect one to ask. Writes a column (or did at least) called Pelican’s Perch for avweb.com. I’d research his contact info but I’m writing this on a phone….google him.
Fascinating guy. Flew for air america and is a DE for types in round engine transports C-46 iirc
There’s a really nice guy named John Deakin who is the perfect one to ask. Writes a column (or did at least) called Pelican’s Perch for avweb.com. I’d research his contact info but I’m writing this on a phone….google him.
Fascinating guy. Flew for air america and is a DE for types in round engine transports C-46 iirc
Thanks for the input so far gents.
So….basically, what the general concensus is saying is that is really depends on the engine in question. Some can, some can’t.
As for water – methanol injection, it’s mainly Luftwaffe aircraft like the 109 and 190 that used it and, unfortunately, the sim doesn’t model that either. Which is surprising given how much else it does simulate.
The guy in question is an absolute expert on the dynamics and physics of flight, I cannot stress this enough, the game models all kinds of things your average flight sim gamer has never heard of and doesn’t even realise is being modelled, like P-factor, spiraling prop wash, ground effect….honestly, you wanna see some of the technical discussions on flight envelopes that go on in the forums over at Aces High (see link above), it’s all waaaaay over my head.
The curious thing is there are sooooo many actual pilots who fly in this game (off the top of my head – an Eagle pilot, a Top Gun instructor, most of the pilots of Air Canada and more retired military types than you can shake a stick at. Oh and an 90 year old ex-Lancaster tail gunner called Stamper) and yet no-one seems to have mentioned this ever.
Now my argument is about the behaviour of players in the online world he’s created, what happens right now is every sod and his dog takes off at full (military) power, transits to the combat area at full power, dogfights (or whatever) at full power and, sometimes, RTBs at full power. Well what I’d like is for the sim to be even more complicated than it already is and give people a reason NOT to fly with the throttle against the stop all the time (WEP is on a toggle via a button push, not from the throttle position). I like complicated, I like having lots to think about, I don’t like easy mode.
The sim models fuel consumption very accurately, following most aircraft’s max cruise power settings etc. The on board clipboard even includes an E6B with all power settings (max cruise, normal, military, etc) for every aircraft available in the game (all 70+) displayed. However, fuel consumption is rarely an issue unless it’s a special event (think historical recreation) so generally no-one bothers to slow down.
So, one more question. Is my vague description of the events leading up to a detonation purely due to overheat more or less accurate?
Swoop, I know that sim. Indeed, it models pretty much everything save what you’ve brought up here. Tell your guy my buddy Blue says hello and keeps reminding me I need to get back into this.
Your assessment of what happens in a full-power situation is correct for an air-cooled motor, though normally the cylinders stay fairly decent and it’s high cylinder head and valve temps that lead to the detonation problem. Also, high oil temps can break down lubricity properties but that is generally a concern for the crank and rods rather than the pistons and rings.
There is a design trade-off here your friend will understand. In a liquid-cooled motor we can take the horsepower rating, convert to BTU, then determine a radiator needed to vent that heat into the atmosphere. Water is our working fluid, and the amount of air flow through that radiator can be properly designed. The P-51 Mustang and its ventral radiator that actually contributed some minor thrust to the aircraft is probably the seminal example of this. As power settings were reduced flaps could be moved to reduce the drag from the radiator inlet, so you had the best of cooling and aerodynamics.
Now let’s look at a Corsair. Air-cooled, so we have cowl flaps to move around. Also liquid cooled via oil, so we have those wing-root radiators for cooling the oil too. At maximum power we’d need huge amounts of open motor for airflow to cool the cylinder heads and cylinders, plus the oil cooling radiators interfering with our wanting to go fast. So, we design a nice cowl and put some flaps on the back to restrict airflow, now at low power we’ve better aerodynamics but less air over the cylinders and heads. The oil coolers can take a lot of heat out of the motor, but only where oil is spraying at, typically the valve stems and most bearing surfaces. It’s not as much help as you might think. We need air to keep that motor cool enough, and passing air over the motor introduces drag which is what we’re making horsepower to overcome anyway.
So the design trade-off is assume you need to shed 2000hp worth of heat all the time and have no cowling, or assume you need to shed 1500hp of heat all the time and make a more aerodynamic cowling that, at 2000hp, won’t shed all the heat. Given combat only lasts a few minutes and most of your time is spent at cruise sipping gas and trying to find the enemy or a place to land, it makes sense to keep the aircraft more slippery and hence not only faster but also more fuel-efficient, then add some water or methanol injection to help control detonation at high power loads. Generally speaking, if the motor holds together for 5 minutes at full power it’s gotten you through the fight and you can throttle back to head home, both sides low enough on fuel neither is going to be chasing the other. At that point you want a slippery cowling placing as little drag on the aircraft as possible.
So, you know, some slip-stick operators made some assumptions and that’s what you’re given. Air-cooled motors have a lot of limitations, heat dispersal being the most limiting. In a lawn-mower the motor generates its own cooling breeze over the cylinder via fins on the flywheel, but that’s only a good solution for relatively steady power output levels. In motorcycles air cooling was certain to reduce available power by 20% just due to the excess heating — a motor that has to run at 20 degrees and 600 degrees is going to be less tight and less efficient than one that has to run at 20 degrees and 190 degrees just due to thermal expansion alone, let alone adjusting the mixture to compensate for the intake temperature and such.
On your jet engine question, the limiting factor again is heat. I suppose if you made your motor entirely of titanium you might be able to run at full power all day long at sea level. Problem is all that hot air from the motor is hitting the nozzle, which probably isn’t made of titanium, and needs to move a bit to change size as we go through different power settings. If it were a fixed size, like in our lawnmower example above or in the case of a rocket engine, we’d just cast a ceramic nozzle and let it take all the heat we want for a known amount of time. We can’t, so we make a variable nozzle and expect a certain amount of bleed air to be passed through it to cool things down, and expect it to not be subjected to afterburner heat levels for very long.
Speaking of heat, concrete on runways has a certain heat limitation as well, so even if you’re passing enough bleed air through your jets to keep the nozzles cool enough to function you might find yourself at run-up with a hole behind you after a few minutes, the concrete flaking and chunks being blown behind you. I’m told the Boeing 747 can only hold full power for about a minute on the runway for just this reason, I suspect the jet blast deflectors on a carrier have similar limits for time behind aircraft at full power settings.
– Max
D-7400, that’s a pretty low number XFORMED. you must be even older than me! D-11990
first owned canopy was a dyed surplus C-9…with suspension lines.
RW? We just looked at the pics in Parachutist and fell out of the Cessna 182 or 206 trying what we thought they were doing….:) First 3 way as Rick closed in at 3000′…so we…well…you know…initiated opening IAW BSRs if anyone asks.
It’s funny when different threads in ones life intersect…I spent many years running with that combat flight sim crowd, even to the point of joining the game biz for several years. The above mentioned F-15 driver is a bud and former virtual “squadron” mate of mine.
The thing to remember is the main arena in Ace High skews everyones perception. Opposing fields are practically a stone throws apart (actually a short tank drive for those so inclined). Each team can fly virtually any plane (late war stuff is somewhat restricted) so you end up with P-51 on P-51, etc. Most fights are below 10K as few bother climbing up to the nosebleed seats from rear area fields (unless you are flying a bomber). So fights are lower, matchups are not historic, and many of the great WW2 planes strengths aren’t obvious. The P-47 is a great example – in a historical event where fights are at 20K+ feet, it is a superstar. Down on the deck in the main arena, it is a grape.
AH does limit WEP use a bit, but there are no restrictions on max throttle as noted. This suits the arenas well, but does teach bad habits. Historical events are where it is at…I’ve had the great honor of “flying” with members of the Tuskegee airmen during one such event. I’ve lead a formation of B-17’s from the 303rd BG to the subpens at Kiel, Germany. Shot up, I managed to limp home escorted by a gaggle of “little friends” (P-51’s). I’ve felt the rush spotting a formation of B-17’s below our gruppe of FW-190A-8’s, with not an escorting allied fighter in sight. When we hit them, it was like a puppy getting smacked by a truck. I’ve bravely run away from incoming zeros over Henderson Field in my Iron Dog (P-39)…only to turn around and charge into another group of zeros chasing our B-25’s. Etc, etc. Good times.
Swoop, tell Hitech Smut says hello.
-CJ
heh, small world innit lads?
When I was a kid (circa 1968), I found a P-51 manual in the main county library in Fairfax, VA. Checked it out a couple of times and read it cover to cover. I seem to remember something about a wire that had to be broken to get WEP and a time limit like 5 min. I also remember a warning about a time limit for inverted flight, something about starving the oil pump.
A chum urged me to check out this post, great post, interesting read… keep up the good work!