I resemble that remark.

Still have my good ass props.

Mike C.

If you assume the engine is uniformly efficient at all power settings.

Alas, they are not.

Fly at high altitude means best L/D airspeed is at higher power, and the engine slightly more efficient.

But one has to use fuel to climb, which negates the effect to some degree.

The 421C case shows how close the results are sometimes.

Mike C.

That is an effect, but the throttle partially closed dominates. The turbo is making upper deck pressure, but then the piston is sucking against the throttle plate, basically a big vacuum pump and that eats power from the process.

There's no way to operate wide open at low altitude and be in the power range for low speed flight unless your airplane is ridiculously under powered (like, say, pre WWI airplanes were).

One reason diesel engines are so good at part power efficiency is that they don't have any intake obstruction. The diesel simply injects less fuel for partial power, and doesn't spend any power on sucking air. This is why diesel is preferred for something like an electric generator that often runs well below max power.


To be more precise, pick an altitude where wide open throttle works, which is typically not down low.

Mike C.

That is an effect, but the throttle partially closed dominates. The turbo is making upper deck pressure, but then the piston is sucking against the throttle plate, basically a big vacuum pump and that eats power from the process.

There's no way to operate wide open at low altitude and be in the power range for low speed flight unless your airplane is ridiculously under powered (like, say, pre WWI airplanes were).

One reason diesel engines are so good at part power efficiency is that they don't have any intake obstruction. The diesel simply injects less fuel for partial power, and doesn't spend any power on sucking air. This is why diesel is preferred for something like an electric generator that often runs well below max power.


To be more precise, pick an altitude where wide open throttle works, which is typically not down low.

Mike C.

For those who want to look, I've uploaded the sales brochures Mike was referencing. They can all be downloaded (individual files) here:

http://www.mu-2aopa.com/Documents/SalesLit/marquise.pdf
http://www.mu-2aopa.com/Documents/Sales ... itaire.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2f.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2g.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2j.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2k.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2l.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2m.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2n.pdf
http://www.mu-2aopa.com/Documents/SalesLit/mu2p.pdf

I still disagree with Mike drawing conclusions from these as they are Sales Brochures and not performance charts, but I do believe that Mitsubishi probably (and this is an assumption) used similar assumptions for their estimates. What's confusing is some talk about Max Range with reserves, etc. and Max Endurance Range (which is takeoff, climb to most efficient altitude and run until tanks are dry, zero wind, etc.). Both are theoretical numbers that likely would not be reached in the real world. While I can't prove it, I think the "with reserves numbers" are based on the standard NBAA metric used for aircraft comparisons these days (or some variant of it), meaning a takeoff from sea level airport, unrestricted climb to most efficient altitude, ISA day, no wind, X number of pax, full fuel, 30 min reserve, etc.

Irregardless, the attached documents are pretty interesting if you want to know more about one MU-2 over another as they talk about what the planes came with, etc.

Reece's made up sheet has even less pedigree, so surely you won't trust it, either, then, given it has so many demonstrable errors and inconsistencies.

Mike C.

One more time: not at part throttle.

http://www.mechadyne-int.com/vva-refere ... -si-engine

This situation causes throttled SI engines to exhibit very poor efficiency under part load conditions compared to their efficiency under full load operation.

If slowing down to get closer to best L/D speed down low requires closing the throttle some, engine efficiency will be harmed regardless of LOP. That is just the nature of restricting intake air flow and has nothing to do with mixture.

The most efficient cruising setup would be the lowest altitude where LOP and wide open throttle results in flying at best L/D speed. That is when the engine is doing the best it can and the airframe is doing the best it can.

Typically, this is a high altitude because the lowest engine power you can reliably get at WOT is not that low. It will be closer to the max ceiling of the airplane than sea level.

Mike C.

OK, I think this is my favorite image... Talk about dated!

Some operators favor these "power by the hour" programs.

I elected to not do this. I figure the chance my 1000 hour engine get all the way to 5000 overhaul is slim, and then the engine program vendor has banked all that money that doesn't go to use.

As time goes by, the price of the program goes up, so there's no real economic balance in place to prevent fleecing of the owners. If they raise the price to $100/hr/side, what do you do? If you stop paying, you lost the banked value prepaid for the next overhaul. If you keep paying, your costs went up higher than if you didn't have the program.

Also, these program usually have a minimum hours per year requirement, typically about 100 hours. If you fly less (not uncommon for owner operators), they charge you for the minimum hours.


I find this aspect disagreeable.

My engines are due HSI/OH in 2500/5000 hours. If I put them on the program but otherwise do NOTHING differently, no change at all in operating or maintenance, suddenly the engines are good for 3500/7000 hours.

Now why is the engine airworthy for so many more hours just because I send money in the mail? How does the engine know that?

Shows me that Honeywell is withholding engine life as a revenue enhancement trick. As soon as it is something THEY have to pay for, suddenly the engine can be flown longer.

Also shows me the engine is really a 7000 hour engine. Some airline users of TPE331 can go 9000 hours between overhauls as well. Premature overhaul of a TPE331 engine just do to "normal" wear out is basically unheard of, there is always some unusual cause when it happens.


For absolutely the best up time, you can use rental engines. Exchanging one of your engines for a rental is a 2 hour job. The airplane was designed with this in mind.

Mike C.

Regarding the $100k props - they have mostly been put on 4 bladed props that had been overhauled past limits (sort of) due to an AD. Long story, but some people were facing an $80k purchase of new blades for old props and in that scenario the no-AD MT prop made sense.

Totally agreed. I think that two things are big factors on the economic decision on if it makes sense (I'll ignore the performance factors, no AD factor, etc.):

• If the plane is a business expense owned by a business and the new props can be written off the books as a capital expense.
• If you have props that are old and likely requiring replacement of all blades, etc.

In these cases, the expense of the props can make some sense. I had a great discussion about this with Mike Laver regarding my plane last November. He was the one who came out and said what I was thinking -- it didn't make sense for me unless I had a lot of cash to spend and wanted to do the upgrade, but even then it would probably make more sense to apply that money to a glass panel.

Which model Lear?

Have any of you flown an MU2 with the MT props so that you are able to provide a comparision of noise level in the cabin?







Totally agreed. I think that two things are big factors on the economic decision on if it makes sense (I'll ignore the performance factors, no AD factor, etc.):

• If the plane is a business expense owned by a business and the new props can be written off the books as a capital expense.
• If you have props that are old and likely requiring replacement of all blades, etc.

In these cases, the expense of the props can make some sense. I had a great discussion about this with Mike Laver regarding my plane last November. He was the one who came out and said what I was thinking -- it didn't make sense for me unless I had a lot of cash to spend and wanted to do the upgrade, but even then it would probably make more sense to apply that money to a glass panel.

OK, I think this is my favorite image... Talk about dated!

Yeah, no kidding! That guy is obviously being sexually harassed![/quote]


Unless she is that guy's wife. In that case, the pilot may be in an uncomfortable or hostile work environment.....