The -10 engine gets its power from two things, higher temperatures and more efficient turbine section extracting mechanical power from the hot gas. Both things increase the efficiency of the engine overall.

Because the -10 engine can allow the plane to fly higher and faster, it increases the efficiency of the airframe as well.

Those two factors make the -10 more efficient per mile than the -5.

Further, since you fly faster with the -10, you get an even larger benefit from the engine TBO since it took fewer engine hours to fly the miles.

Mike C.

The -10 engine gets its power from two things, higher temperatures and more efficient turbine section extracting mechanical power from the hot gas. Both things increase the efficiency of the engine overall.

Because the -10 engine can allow the plane to fly higher and faster, it increases the efficiency of the airframe as well.

Those two factors make the -10 more efficient per mile than the -5.

Further, since you fly faster with the -10, you get an even larger benefit from the engine TBO since it took fewer engine hours to fly the miles.

Mike C.

You should have kept the Piper Cub and not taken on the burden of all those expanded missions.

Mike C.

If you fly it long enough, yes.

Mike C.

Not for a private guy who flies 100 hrs a year. The fuel saving is real but not enough to offset the increase in purchase price.

If you fly it long enough, yes.

Mike C.

I admire your perseverance but it is a bit misplaced.

A -10 airplane in 5000 hours flies as far as the -5 airplane does in 5400 hours, so that blows you theory out of the water on a per mile basis even if the two engines cost the same otherwise.

But wait, there's more savings...

The HSI on the -5 is also about double the cost for EACH one. A typical -5 HSI will run you $70K, a -10 about $35K, typically. The ITT harness alone is major money on the -5.

The -5 required TWO HSI on the way to 5400 hours. The -10, only ONE.

The -5 required a gearbox inspection at 3600 hours to the tune of about $20K. The -10 has no gear box inspection.

So that's $160K for the -5, $30K for the -10, to do all the work between overhauls.

At OH, the -10 will generally be cheaper, too.

There's no way around it, the -5 costs more per mile to fly than the -10. The only downside to the -10 is the initial investment to get it.

Also, if you think the 5400 TBO plan is better, you can elect to do that to the -10, it is owner option. No owner I know of chooses that option.


The -10 metallurgy is different so the engine can take the higher heat with less damage. The first stage T wheel also has cooling passages that the -5 design does not have. The -10 also has replaceable first stage T wheel blade units, the -5 has a blisk first stage T wheel and anything bad with any blade rejects the entire blisk. The -10 has an entirely different combustor and nozzle setup that greatly reduces flame propagation to the first stage T wheel. And so on...

Mike C.

I admire your perseverance but it is a bit misplaced.

A -10 airplane in 5000 hours flies as far as the -5 airplane does in 5400 hours, so that blows you theory out of the water on a per mile basis even if the two engines cost the same otherwise.

But wait, there's more savings...

The HSI on the -5 is also about double the cost for EACH one. A typical -5 HSI will run you $70K, a -10 about $35K, typically. The ITT harness alone is major money on the -5.

The -5 required TWO HSI on the way to 5400 hours. The -10, only ONE.

The -5 required a gearbox inspection at 3600 hours to the tune of about $20K. The -10 has no gear box inspection.

So that's $160K for the -5, $30K for the -10, to do all the work between overhauls.

At OH, the -10 will generally be cheaper, too.

There's no way around it, the -5 costs more per mile to fly than the -10. The only downside to the -10 is the initial investment to get it.

Also, if you think the 5400 TBO plan is better, you can elect to do that to the -10, it is owner option. No owner I know of chooses that option.


The -10 metallurgy is different so the engine can take the higher heat with less damage. The first stage T wheel also has cooling passages that the -5 design does not have. The -10 also has replaceable first stage T wheel blade units, the -5 has a blisk first stage T wheel and anything bad with any blade rejects the entire blisk. The -10 has an entirely different combustor and nozzle setup that greatly reduces flame propagation to the first stage T wheel. And so on...

Mike C.

-

I believe those figures to be in error based on the MU2 owners I talk with. The -10 conversion is about $300K (maybe somewhat less than that, $275K/side if the props are compatible), the overhaul of an existing -10 is about $225K, maybe those got confused.


Bob is very active in Council331, a group of TPE331 folks dedicated to supporting the TPE331 engine (which often means fighting Honeywell). I'm an adhoc member of that group, my main contribution was helping to get the AMOC for the FCU AD (saved TPE331 owners about $100M, including Commander owners), which was then subsequently incorporated into an AD revision recently.

Bob may be quoting you the base price if nothing wrong is found. On a -5, there will always be something wrong on an HSI. Ask Bob if he is willing to do an HSI for $50K fixed price no matter what. Then ask him if he is willing to do an HSI for $100K fixed price no matter what. He won't take that deal, either.

There was a time when Honeywell offered a fixed price HSI parts program for the -5, -6. I think it was $75K, no matter what the engine required. They lost money and the program stopped about 8 years ago. Now there is no cap.

I have not yet seen a -5 HSI come in at $50K. There is always a chance, I suppose. Good luck!

Mike C.

Another thing, how many -10's can one find mid- to hightime to hang on to the plane should one want to save a buck or two? Not so easy. -5's you can find at Walmart.

So much of this depends on how much time is left on the engines and how much flying you will do.

I have not shopped the used -5 market but I would imagine you could find some -5 with time left as an option to doing a overhaul.

The cost of overhauling 421 engines at 1600 hrs isn't cheap either.

There is always the scary unknown you can find on any airplane. The exposure increases from recip to TP to jet.

The 690 with -5 is a great value in the TP world.

Mike, did I read you right that there is no gearbox inspection on -10s? I have looked at a few planes where I was told the next HSI needed the gearbox too?

If the -10 is on the 1800/3600/5400 schedule, then it will get a gear box at 3600.

If the -10 is on the 2500/5000 schedule, then it doesn't.

If the -10 hasn't been overhauled or brought up to a certain SB level (which I think was defined about 20 years ago, so not particularly recent), then it can't be on the 2500/5000 schedule. Only the Solitaires and Marquises, which came -10 from the factory, would be in question here, all the conversion engines are eligible to my knowledge.

Even if the -10 could be on the 2500/5000 schedule, it is technically optional and an owner could select the 1800/3600/5400 schedule. I've never seen a case like that, but it is theoretically possible.

A TPE331 engine shop can review the records and tell you for sure.

Mike C.

Let's hear from Bob himself:

---cut---

From: Ciholas, Mike
Sent: Thursday, November 12, 2015 11:48 PM
To: Bob Hancock
Subject: HSI, OH costs these days

Bob,

I was curious what the typical HSI are for -5, -6 engines, and -10 engines like mine?

> -5-6= 80K
> -10=45 to 90K

Also, what are typical overhaul costs for -5, -6 and -10 engines?

> -5-6=180k to 210K
> -10=160K to 215K

When I mean "typical", I mean, say, 2/3rds of the folks get out for that price or less. There are obviously the outliers who end up much more.

> Above are real numbers.

---cut---

The -10 HSI costs were higher than I expected, which I think has to do with some of them being older -10s that aren't up to SB status (engines back from the mid 90s or earlier, meaning more conversion engines are likely to be at the low end since they have upgraded torque sensors and other expensive SBs done).

The -5, -6 HSI was about what I expected, I actually said $70K, $10K less than Bob.

So, for 5400 hours on -5, -6, we got $180K for two HSI and one gearbox.

For 5000 hour eligible -10, we got $45K for one HSI and no gear box.

Add in the overhauls for a full TBO cycle, we get:

-5, -6: 5400 hours, $390K, $72/hr.
-10: 5000 hours, $260K, $52/hr.

If you consider you flew the same miles for both TBO cycles due to the extra performance of the -10, then the effective cost of the -10 is 33% less than the cost per mile of the -5, -6. For a twin, you will save about $260K over that cycle in engine work, PLUS the plane flew 400 hours less air time which saves about $100K in airframe maintenance ($250/hr?), net savings is $360K. An extra $360K will buy a -10 equipped airplane over a -5 one, and you get much of that back on sale, so the money is not lost, just tied up.

Mike C.