Warbird Information Exchange

I decided to make this a new subject and let the other topic stand on it's own. Vlado you wrote

800 to 1000 hour TBO for the Merlin is not too uncommon.
However, the 'other' motors seldom appears at 99% of public viewing events. These owners will confide that motor issues prevent appearances. Their TBOs may be high, but their reliability is a concern. (And that is reliability in todays enviroment - not sure of how to judge reliability in the 1940s.)

[ My Merlin gets 300 to 500 hours till TBO. It is flown mostly at high power for airshow flight demos - akro & Heritage. I know the trade-off of high power vs. TBO, and thus make my choice to be flown a certain way. Additionally, my ability to appear at aerial events is very high, 14 to 20 events per summer, due to capable and realistic maintainability. Parts and services are very readily available and operate on a modern aircraft AOG basis.]

I would love to see more Allison powered aircraft at the shows I attend. They are attached to wonderfully historic airframes, regardless of their originallity, rebuilt, restored, recreated, replicated, what-ever aspects.

My 2 cents,
VL

So this brought me to a few questions. This is not intended to begin a debate on the engine builders out there! This is simply intended to get an education from the operator perspective about the current state of the engine pool.

First, Vlado you say you running higher power and shortening the TBO. Are you running the engines at anywhere close to the war time settings? What has been your lead indicator that an overhaul is due, or has it varied?

Second, any other operators who can give the same info on the lead indicators an overhaul is due for the Merlins that are "not run hard"? Are we seeing some consistency across the fleet or is there a wide variation?

Third, Vlado stated reliablity is the issue for the Allison versus TBO. Is there any good feel for the issues that are plaguing reliablity? Also, what are the operators of Allisons finding for real TBO's?

Thanks for any factual data that is forwarded to this thread!

Dave

I can tell you from personal experience, when Vlado says he runs high power setting for the Heritage flights, he means it. I have cleaned off exhaust stains that almost reached the tail, unless he is flying with a A-10, then the stains hardly get past the stacks.......

_________________
Matt Gunsch, A&P, IA, Warbird maint and restorations
Jack, You have Debauched my sloth !!!!!!
We tried voting with the Ballot box, When do we start voting from the Ammo box, and am I allowed only one vote ?
Check out the Ercoupe Discussion Group on facebook

Oh boy, the A-10 guys are gonna kill me!
VL

Aw man...Vlado...I am not trying to put you on the spot....

In a serious discussion...

Thanks Matt for the confirmation that the Heritage flights are not easy on the engines...

Again, for anyone involved in the day to day operations, as a serious consideration, I again submit the above questions. This has no bearing on who built the engine, just on the real tangible education for those of us who love to see these machines...

Dave

Like any other engine, the Merlin will give you plenty of signs that it is getting tired. Low compressions, higher oil consumption, etc. The current overhaul shops have set recommended TBO's (and they are as many as there are shops) based on inspection and observations at teardown of wear patterns establishing " the point" where continued operation could lead to an increased chance of failure or excessive abuse to the innards of the engine. This "window" is supposed to provide the best life expectancy with minimum wear of internal parts.

Allisons simply make metal when they are due for overhaul......

Seriously, they show similar wear rate vs time in service. As I have not had any experience with Allisons other than cleaning plugs, changing Mags and engine change after massive failure I can not tell you what the times for best overhaul window is.

The same is true of any engine I imagine.

_________________
Expert:
Ex: Former.
Spurt: A drip under pressure.

Sorry I didn't reply sooner.......3 computers & ALL on the fritz this week.


Generally, talking to the WW2 veteran Mustang maintainers, they said their Merlins would get 100 to 150 hours till pulled for overhaul. And this was if the airframe survived combat operations. Airframe wise, P-51B/Cs were on the ETO scene for about 12 to 14 months, when replaced by P-51Ds, that finished the remainder of the war for another 12 months of service approx. During that time, the pilots would most commonly see a 'dogfight' or 'strafe' maybe once out of 5 to 10 missions. Of the vast numbers of Mustang pilots in Europe (or Pacific), only very-very few racked up scores to become Aces. All the preceeding says that most Merlin operations were at normal pwer profiles: full power takeoffs @ 61", climbs at 40 to 50" depending on the flight profile, long cruising at 36". Thus the 'average' combat Merlin was not very severely stressed and yet they ran 100 to 150 hours TBO. (FYI: Just a few weeks ago, I met a 9th AF crew chief, who followed his bird from England to France, 2 weeks after D-day; that's what I like about this job!!]

Now today, the common Merlin may/will get around 800 hours till TBO. It may require a top overhaul along the way - valves, etc. Since, most Mustang owners fly their bird very conservatively. These guys often need an overhaul due to hardening (leaking) gaskets & hoses or plain corrosion (on the crank, rods, etc.) due to low activity. These would be "calendar timed out" motors.

Other operators who fly a more aggressive airshow profile, would naturally need overhauls at a shorter interval. As a writer before had said, the reasons to pull a motor are highly variable. Some reasons are low compression, leaking oil from the sides, loose valve guides, high oil consumption, oil samples showing increasing metal,carbon values, etc. Sometimes they are pulled because of 'being-on-the-safe-side'; all might be running well - but since the motor is often flown at low altitudes, hot conditions and high power settings, it may be a safe plan to overhaul at some point. Airshow flights may involve erratic power changes while flying formation with dissimilar aircraft, high power for 30 minutes at low altitude, and very short flight segments. These constantly changing power demands all contibute to reduced TBO. [FYI: I had heard that oil companies in northern Canada used Meteor (merlin) motors to run their generators; I heard they would run at constant RPM for weeks - getting overhauls in the 10,000++ hour range - anyone know about this?]

Hope that answers your question,
VL