Warbird Information Exchange

Depending where I look for information, I have been getting varying numbers in respect to power settings in the Harvard.

I was taught:

Emergency/periodic take-off - 36" 2250
Take Off - 32" 2250rpm
Climb/Aero - 28" 2000rpm
Cruise - 23"1750rpm @ 23gph

The RCAF Flight Manual (CAP 444) indicates
Take Off - 32" 2250 rpm (was 36", but they ammended to 32" in the 50's)
Climb/Aero - 28" 2000 rpm
Cruise 25" 1750 rpm (not to exceed 26")

NATA Pilot's Checklist
Take Off - 36" 2250 rpm
Climb 30" 2000rpm
High Speed: 32.5" 2000rpm
Cruise 25" 1850 rpm


Obviously the RCAF dropped the take-off power to 32" to limit engine wear (although I understand radials are healthier with higher manifold pressures on takeoff).

Does anyone have a chart indicating what the power setting maximums would be at each RPM (incrementally) for the 1340?

Does anyone have a Do Not Exceed for various power settings from USAF or North American?

According to my T-6D hanbook: (AN 01-60FFB-1)

First off, for truth in advertising, I have very little time in the T-6. However, I have spent a considerable amount of time lately reading just about everything I can get my hands on about operating the Six -- I'm hoping to spend a lot more time in it in the future.

You hit upon one of the challenging points for someone trying to learn to smartly operate this airframe: there is simply no one correct "book answer".

Here's what Skipper Hyle says about the differences in numbers between different operators of the T-6/SNJ/Harvard:


(source: http://www.warbirdalley.com/articles/T6-sf.htm)

So, bottom line: there is no "right" answer so far as military tech data goes.

The problem is even more complicated than that, though. According to Randy Sohn, many military procedures were designed for safety and ease of use rather than on long life for their engines. Remember, the military of the 1940s and 1950s had a huge maintenance infrastructure to work on engines. Plus, overhauls weren't a $25,000 out-of-pocket expense for the pilots!!

Here's what Sohn says with respect to RPM vs Manifold pressure:


(source: http://www.douglasdc3.com/sohn/3.htm)

So, what you read in a military manual MAY NOT BE what is most healthy for operating the engine. It may not be the best way to operate the engine to ensure long, reliable operating life. This is the crux of the reduced-power-takeoff discussion, too.

The idea behind a reduced power takeoff is that it supposedly limits the amount of strain on the engine during its most vulnerable point. Unfortunately, there may be unintended consequences to that reduced manifold pressure. Sohn addresses reduced power takeoffs here:
http://www.enginehistory.org/wbn/WBN11.pdf

It's even more complicated than THAT, though!! The warbird operating community doesn't even agree with itself on many of the things that Sohn says. If you ask 10 different pilots, owners, and maintainers of radial-powered airplanes, you'll probably get 3-4 different answers on what they do on their particular aircraft. The problem for a neophyte like me is that ALL of those 10 people are all very experienced and knowledgeable! Who do you believe??

Operating and caring for radials is becoming more of an art these days than a science. The goal of this art is to maximize safety in operation of the engine and maximize time between expensive overhauls.

So, good luck in trying to find a black-and-white answer to your question. The best you can do is take the military manuals as a starting point, and then get as many opinions as you can. Ultimately, you'll have to operate the airplane the way the owner wants it operated -- or, if you are the owner, you'll have to assess which of the experts you happen to agree with.

I'm very interested to see what the other WIX experts have to say on this topic. It's a great one to discuss.

I don't have much experience in the T-6/SNJ/Harvard series. But I have heard many different versions on how to fly the airplane, specifically on take-off and cruise power settings. One thing I note is that since there are so many of these aircraft flying, there is plenty of opportunity to do some field researach on what power settings people are using, and what their engine life is like. Another item is that there are places with 1340 powered aircraft in constant operation (Warbird Adventures, etc.) that would probably be good sources for data on how the engines perform over time with various power settings.

In my experience with the L-5, prior to actually transitioning to the airplane, I received a lot of advice. All of it was helpful- some to varying degrees of assistance. Relating this to the 1340 power plant- there are plenty of "hangar engineers" out there who may or may not have the requisite skills to interpret their engine's performance and then make recommendations on power settings. The varying times of operation, frequency of operation, and consistency of flight regimes are what is going to impact on the wear on the valve train, cylinder walls, and bearing surfaces in the engine. What one person experiences in 50 hours of operation in a year may not be what another detects in 200 hours of operation in a year.

That said, I don't see it as unreasonable for the NATA group to find some way to document what is going on out in the T-6 powerplant world, perhaps with a voluntary anonymous questionaire for data on annual results, cylinder replacement times, etc., possibly aimed at the engine rebuilders or maintenance personnel who work on the things. What would other people suggest for metrics that would be appropriate for such a study? Is this simpler or more complex than I am sketching? Is this a reasonable suggestion, or is it unrealistic?

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Someplace around here in a pile someplace I have what a Pratt and Whitney document for the 1340 that shows the recommended power settings. I can't lay my hands on it right now. I got it from the good folks at Covington.

If you are looking for a 'modern' opinion, I would follow what Covington says. They see more of these engines than anyone else, operated in a variety of environments.

I personal use the power settings from NATA for take off and climb, although I have experimented with other cruise settings that Paul Redlich and I had discussed at length years ago.

I might do it the old fashioned way, but for the last twenty plus years operating my SNJ here's what I do. A very important first point is getting the oil above 40c before you do anything. I keep the prop back until I can get the rpm to 800 keeping the oil pressure at or below 100psi. Once I'm at 800rpm and 100psi I push the prop forward and it takes it right to 1200rpm, bypassing that harmonic rpm range.

36"/2250rpm for takeoff. Always. I understand there's some valve thing in the carb that opens only at full throttle? I don't know. Rich??

climb: 30"/2000rpm

cruise: 26"/1850rpm. lean it till it barks a bit and then richen. that gives 30gph which helps my math-challenged brain in flight planning.

Be mindful of power reductions so as to not shock cool the engine.

Our last overhaul was done by the folks at Tulsa long ago -- mid 1990's -- and it's still running well with minimal oil consumption.

Jim

Like Randy I'm just a Harvard neophyte, but I've been instructed to follow the RCAF Manual settings.

Jim

Not that it matters, but when I flew, I pretty much operated the T-6 how Mr. Beasley has it listed there.

Gary

As a comparison to the various figures posted, the official Air Ministry Pilots Notes I have for the Harvard IIB (A.P.1691 2nd Editon) have the following engine limitations (in PSI of course!) :-

Max Take Off (5 Min Limit) - 2250 RPM/+3lbs (36.02 inHg)

Max Climb (Continuous) - 2200 RPM/+1.5lbs (32.97 inHg)

Max Cruising (Continuous) - 1925 RPM/-0.5lbs (28.90 inHg)

Max Weak (Continuous) - 1850 RPM/-2lbs (25.85 inHg)

Note that the inHg figures in brackets are straight conversions of the PSI figures.

Cheers

Paul

Power enrichment valve.

24 years in my SNJ-5 I used (see below) and ave. 28 GPH, but flight planned for 30 GPH. Safely fly 2 1/2 hours with about 1 hour still in the tanks. Each plane is different as to how much the tanks hold and how low the tail is. You can assume the you have about 100 gallons max (G's and Mk 4's hold 30 gal. more if they have the bladder tanks). Don't forget how much you use in the run-up, about 5 gallons. Jim is right about the warm-up to 40c.


NATA Pilot's Checklist
Take Off - 36" 2250 rpm
Climb 30" 2000rpm
High Speed: 32.5" 2000rpm
Cruise 25" 1850 rpm

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Interesting reading here. I love to learn through this stuff! Let's keep this thread going! Here's what my dad and I use for the '6...

Take off: 36 inches, 2250 rpm. No reduced-power take-offs for us! Say no to reciprocrating loads *see Randy Sohn's notes! One, that's what P&W says to do. Look in your dash one! Two, the radial engine inherently wants to throw itself apart. What stops that, is the combustion up in the top of the piston. That pressure up there keeps the recip loads in balance, and keeps the piston in straight. If the combustion pressure is weak, the piston may become cocked/crooked. If you don't have the ideal/pressure in there, that piston will crooked, and cause uneven piston wear, the rings, ect. With reduce-power takeoff, you don't have auto-enrichment, less fuel --> higher cylinder temps. Slower acceleration, less airflow to cool down. Use more runway, and that's bad juju to have runway behind you. If it's a reduced power, you'll have a slower climb, which keeps you closer to the ground, and when and if the engine quits, you're left option-less...

Cruise: We use 27inches and 1700 rpm or 28-1800. With proper leaning of peak (50-100 degrees rich of peak) have yielded us 23 to 25 gallons per hour. That gives us 155mph in a lighter T-6 Yay for low GPH!!!

When we are coming back into the pattern, we reduce power 3 inches at a time, for cooling purposes, so you don't shock cool the engine. On downwind, we are 20 inches-1800rpm, which gives us about 110 mph, which is safe for the Gear Speed and it's perfectly safe to get 10 degrees of flap. Turning base, we reduce to 18 inches, giving us 18-squared. (18in.-1800rpm) And then we can select full flaps, and we will be around 90 mph, and keep a relatively tight pattern. On short final, push the prop up (GUMP), so you won't get a prop surge. It sets you up for the availability for the need in a go-around. This also gives you less time being "under square" or in an underboosted condition, prop turning the engine, ect...

Hope this adds to our conversation!

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Dang......reading this thread sure makes me miss flying the ol' T-6.

(And before everyone freaks out, this picture was more "optical illusion" than dangerously low flying. The photographer is standing on a levee at the end of the runway, which puts him more or less eye level with me.)







Sorry y'all.......was just remenicing a little bit. Back to T-6 talk now....

Gary

I'm with Gary! Reading about flying the Six make's me miss it quite a bit!

In my relatively low time of 200hrs in T6's I was taught by the owner of the plane I was flying using the same numbers Jim and Stoney describe. He's owned and operated that T6 since the late 70's and virtually Zero problems with the good old Pratt. ( finding and knocking on wood currently).

Mike VBC

Well let me join the ex-T-6 pilots nostalgic club. I did a season last summer with a travelling ride-hauling outfit on the West coast where I racked up 500+ hours, and now I'm suffering from withdrawals. I have to settle for reliving my experiences by watching other companies' Youtube videos. Maybe someday someone will upload one of mine, wouldn't that be cool?

Anyone in Norcal with a 6 wanna go flying? I'll buy the gas and lunch...

Retroaviation, awesome looking machine... way to keep a yellow one that clean! I've heard that's not an easy task.