pushing the throttle how much?

[Speedy]

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.

Or, in the case of the VP Navy....all three lines form a really small envelope. Just fly straight and level, baby.....

[agent86]

Reno racers are pumping manifold pressures that were never dreamed of in WWII .i have some pics of a Merlin engine that was sawed in half by the explosion.God I love watching engines being run to the limit and beyond. Backfires really suck at these pressures

[famvburg]

The problem I recall was with smaller Lycomings & especially Continentals in the early - mid '70s during the transition from 100/130 to 100LL. The lower lead content in 100LL wasn't lubing the valves as well as the 100/130 was, IIRC, 100LL has only about 25% of the lead that 100/130 had, & people were having valves sticking every time they turned around. In later years, new valves were made using different metals that pretty much eliminated the sticking problems. I don't know if the bigger engines had that problem tho.

Lead is some bad-ass nasty stuff. But I have never seen any reliable data that suggests that lead is/was a lubricant in anyway.

Fair cop! I'm no chemist / engineer Glenn, so I put the lube in quotes. However this is a reference to my understanding of the point, the bit related to my previous point being highlighted, but a rider specific about lubrication coming after as well - the latter not my original thought, I should add. Lubrication may not be the best/correct term, but it does get used in this context. Better explanations welcome!

But leaded petrol had even more benefits. As it burns, tetraethyl lead turns into a tan-coloured layer of lead oxide, which covers the valves and the combustion chamber. The valves hit hard against the valve seats several thousand times each minute. The lead oxide acts as a cushioning agent, and protects the valve and the valve seats. The lead oxide is also a lubricating agent. This reduces wear in the valve guides, as the valves slide inside them.

If you start running your old leaded engine on unleaded petrol, the lead oxide quickly wears away. Damage begins, but only if your engine was made with "soft" metallurgy, and only in high-temperature areas - exhaust valves, exhaust valve guides and exhaust valve seats.

http://abc.com.au/science/k2/trek/4wd/lead2.htm

[shrike]

The problem I recall was with smaller Lycomings & especially Continentals in the early - mid '70s during the transition from 100/130 to 100LL. The lower lead content in 100LL wasn't lubing the valves as well as the 100/130 was, IIRC, 100LL has only about 25% of the lead that 100/130 had, & people were having valves sticking every time they turned around. In later years, new valves were made using different metals that pretty much eliminated the sticking problems. I don't know if the bigger engines had that problem tho.

Actually it's come full circle. They were originally designed for unleaded 73 octane and had to switch metallurgy and clearances to deal with the addition of lead starting in the late 30's/early 40's causing accelerated valve guide wear. (Franklin issued a service bulletin about it in 1941) finally going to large diameter stems (on Lycoming) and nickle based guides. With the switch to 100LL you get accelerated valve wear again. The 'cure' being to return to the old bronze guides where applicable, acceptable, eligible and available.

You'd be seeing a switch to completely unleaded fuels, except that the FAA regulatory climate is even chillier than the EPA's

[RobC]

There is only one answer to your original question: WFO!

[whistlingdeath77]

i can see where blowing an engine would be really expensive. pushing a 60 year old aircraft is risky.

[Nathan]

hello,


Everyone here is more knowledgeable about this subject then I. But I think I can say with confidence that the performance seen at Reno is a lot different then that of air combat during ww2. IMHO, the warbirds at Reno are "souped up" warbirds. Much like when people take a 32 ford, cut it down and make it into a hot rod.


I always thought you had to be at full power/throttle on take off for warbirds. Is that not so?

[cwmc]

There is a big difference in engine types on this thread and not all of them are very comparative.

Engines that are not supercharged probably won't have any issues going to unleaded from 80 octane. Old Lyc's, Continental and Franklin opposed engines seem to need less lead than what's available at the pump, that is 100LL. Sticking valves from not enough heat to disperse the leads beneficial by products make Marvel Mystery Oil necessary on some types.

Early, smaller supercharged engines like Wright 975's and Wasp Jr's and Wasp's run just fine on car gas and won't need much to run well on unleaded either. Perhaps they will need to go back to the old books and use 36 in hg for 5 minutes instead of max continuous as it is with 100LL.

With 1820's, 2600's, 2800's, 3350's and 4360's there are some real factors at work that will make these engines problematical. As I understand large engines from the standpoint of a transport pilot, max power and wear are synonamous with take off. The engines are run up to max manifold pressure and rpm, the airspeed is low, and cooling air through the cowling is at it's most critical. The cylinder head temps are at their maximum, and the lead in the fuel is cooking off and coating the exhaust valves with it's protective chemicals. The engine is set up to have an over rich mixture at this throttle setting, so the manufacturers found these settings to be best for making sure the exhaust valves and cylinder heads stay within an acceptable temperature until a certain time limit. By this time the airplane was accelerated to an airspeed where the gear and flaps were retracted and the engine could have it's power reduced to another hp level that wasn't so potentially destructive.

My experience was freight so loaded airplanes needed the power required. In the DC-3 we used power less than maximum if necessary to weight but never less than a certain manifold pressure, say 42 in hg. Low temps and low elevations with low weights made for an easy operation, usually. LAX in the spring mornings with 3000 lbs of payload were easy and so in my experience there was no problems. I'm sure that we have all read stories of fire bombers have needed all that was available out of their old recips.
B-25 experience, that was always rather light, but we often flew from short fields and used 40 in hg for normal take offs and 44 in hg for short fields or heavy loads. When giving rides with a plane full of pax we probably only weighed a fraction of the military gross weight, but it was noticeable from the normal weight and made a full power TO a better bet as we got cleaned up and to climb speed in less time. Especially important with the bombers as they do not attain VMC until long after liftoff.

With fighters with radials and inline V's I would think that there will be power adjustments and issues with cylinder temperatures for high load operations during take off as a result of the removal of lead from the fuel. These airplanes have the best power to weight ratio's and should be the least affected operationally. Their performance will be affected, no doubt as the power available will be reduced.

Lead's anti-knock properties, from what I understand, can be mimicked by proper refining of the gasoline, to a point. Once the fuel is decided upon, there will be a period of experimentation along with engineering calculations about what should be expected. Once that is done the engines should run OK, but at reduced power.

One man's opinion of course. I'm only a flight engineer and pilot, not a real engineer!

Chris...