Thanks for the info Jason. I am reading everything I can right now on the TPE331 engines. Really looking forward to taking it up to cruise altitude to see what it can do! It's in the shop right now for a few minor squawks and the pre-buy.

Not quite. The history is that the four bladed props had an issue with cracks in the hub due to a harmonic of the ground idle rpm. The fix that was implemented (via AD) required replacing the hub with a newly engineered hub, changing the idle rpm speed and then a recurrent inspection every 5 years or 3,000 hours.

Every four blade out there has the new hubs and adjusted rpm. Since then, there has not been a SINGLE crack found. Bottom Line, the fix worked. To date, Hartzell has resisted canceling the AD because they have the ongoing inspection revenue stream (no incentive to cancel). Furthermore, if you send your prop to Hartzell for the inspection, they will overhaul the prop and grind down the blades...they refuse to simply do the inspection required by the AD.

The inspection can be done at other prop shops and costs about 1,800. In addition, based on the lack of cracks and now over 20 years of data, two years ago we got the FAA to approve an AMOC to the AD which extends the inspection interval to 7 years (none of these planes are hitting 3,000 hours in five years anyway, some aren't even hitting 1,000). Those 7 year inspections are in the process of taking place now (first ones got inspected about six months ago. We are collecting the engineering data from the inspections and (assuming they show what everyone expects -- no cracks) are going back to the FAA with a request to cancel the AD. The principal inspector responsible for the AD is amenable to doing so but needs hard engineering data to support such an action.

Bottom line is that some will tell you the four blades cost more than three blades and that is true. If nothing else, it is a propellor you are maintaining and overhauling (on whatever interval applies to you - remember pt 91 you don't technically have to ovehaul but I personally don't think that is a particularly wise idea) which has one more blade than a 3 blade. However, the four blade planes are significantly quieter (at least inside the plane!).

Some folks with four blade planes are simply swapping them out for the five blade composite MT propellors which are pretty darn cool, but a significant chunk of money (upwards of $90K).

Bottom line is that there are simply so many variables and factors into the various models and what meets and individual buyer's needs that I don't think the fact it is a four blade vs. three blade would be a deciding factor. For example, if you want a Marquise or Solitaire (the last models built), you have to get a four blade because the -10 engine planes were not built with three blade props. What do you get for that (in addition to a four blade prop)?
-10 engines (more power and more power higher)
- more fuel (expanded fuel tanks compared to earlier models -- about 45 min more fuel onboard
- more soundproofing built into the cabin
- more advanced autopilot in most cases (all but the earliest Marquise and Solitaire models had the Sperry SPZ-500 autopilot vice the Bendix M-4D).
- quieter interior (soundproofing plus slower rotating prop (4 vs 3 blade))
- newer plane, probably lower total time, higher resale value

Again, it is a complex issue but I don't know of anyone who bought a 3 blade over a 4 just because of that. Generally there were other factors that drove their decision.

Hartzell, it's like you are dealing with the mafia.

Where?

I would be extremely surprised if you can get a set of 4 blade props AD compliant for that.


There is some debate about this because at the same time they changed to 4 blade props, they also significantly changed the sound proofing around the cabin, so it is hard to assign the quietness of the later models to the props just by themselves.

The added weight of the 4 bladed prop and sound proofing came to almost 200 pounds, a pretty significant weight hit.


I have 3 blade and -10 engines, by STC.


Only applies to the Solitaire and Marquise. The P and N models, with 4 blade, have the same fuel as prior models.

37 gallons does not get you 45 minutes more cruise, that would be cruising at 49 GPH. At best, it is 30 minutes.

Since the 4 blade prop is aerodynamically less efficient, some of that extra fuel is used to compensate for that, so range is not significantly increased.


Yes, from the factory, but it came with a significant increase in empty weight. There is a sound proofng kit you can apply to the earlier airplanes that weighs less than the factory system.


1980 and later models had SPZ500.

The things you get with the 4 blade airplanes that are negatives:
- less useful load
- glass windshield with very high replacement cost
- oil cooler deice boots which break all the time and cost money to replace
- AD mandated prop "inspection"
- slightly less performance, slightly less efficiency


I did. I wanted the most efficient, fastest, most economical MU2. That meant -10 equipped 3 blade airplane, specifically the M model.

Mike C.

Dave, you kicked the hornets nest.




It's worse than the mafia. It's like dealing with Honeywell.

Minor niggle, but I suspect it's 1981 and later models. I have a 1980 model that has the M4D, though mine was built in December 1979 (sold as a 1980 model Solitaire). Not sure which s/n made the cutover to SPZ500, mine is s/n 419, so sometime after that.

Hartzell is belzebub. The amount of stuff they get away with and how they treat their customers is mind boggling. This is not the thread for that, but buyers beware, especially on niche airframes with a minority.

Adam,

You're right. I've had some discussions with folks at Hartzell and they are good people and I found them pleasant, but when it comes to having them do work on a prop, they are quite pricey. No question you get good work and service, but you are paying a premium for that work.

The one saving grace with respect to the 4 blade PROP AD is that the engineer as the Chicago FSDO who has cognizance over it is a very reasonable person and is data driven. We were told that we'd never get the 5 year inspection lifted because Hartzell replied to all requests for data with "it's a flight safety issue and we don't concur with lifting it." Pleasantly, the FSDO guy we worked with said the data we presented was reasonable and authorized the 2 year extension to a 7 year interval in under 30 days. He did tell us we would have to present additional data based on those 7 year intervals if we wanted to continue pursuing deleting the AD (or at least the recurring inspection requirement for all planes that have the new hub and changed idle rpm). I found his approach very reasonable and sound from an engineering perspective.

That said, some who have the money (or can write it all off as a business expense) have just chosen to eliminate the problem by going to the MT prop. Can't disagree with their approach, I'm just not prepared to drop $90K on two new props just to eliminate an inspection that runs every 7 years.

One thing that is tough to do is separate the cost of the AD inspection from an overhaul because most people choose to overhaul at the same time, whether at 5 years or 7. The general consensus is that the real issue for a lower time prop that hasn't gotten anywhere near 3,000 hours in 5 (or 7) years is corrosion. Moisture builds up in the hub and can be a long term issue. Note this is NOT unique to the 4 blade propellers or even the MU-2 or Garrett props. It is true of EVERY constant speed prop. The issue becomes that if you are going to pull the prop and open it up to inspect it and regrease it, why not do the overhaul at the same time.

So what is the big cost issue? Well, when Hartzell overhauls (remember, they don't just do the inspection -- they refuse to do that but other prop shops will), they grind the blades to balance them. The result is that eventually the blade has been ground down below limits so a blade which has thousands of hours of life on it (these are 10,000 hour blades) goes below limits and has to be replaced. So the overhaul/inspection has now turned into replacing at least one blade. Now say you replace just one blade...remember that new blade has full material on it so it will not necessarily match the blade opposite...so now the new blade has to be ground down to match an older blade (thus getting rid of good material and prematurely wearing the blade). So you get in this vicious cycle.

The cost of just doing the inspection is labor and some minor parts if the shop has the appropriate tooling (for example, some prop overhaul shops don't have the ability to do the hub tubes/pins and actually send the hubs out to another shop (Hartzell or someone else) vice doing it in house.

Bottom line is that (like an engine overhaul) there are options on who you have do it and how much is done. All of those can affect the total cost.

Actually, it's not just Hartzell - as part of the definition of "overhaul" the blades must be ground into the exact correct airfoil shape, so any shop complying with an "overhaul" must grind the blades. Hartzell ships the props new with somewhere around 3-4 overhauls worth of extra material. Work out when the AD came into effect, and much of the fleet has now done 3 or 4 overhauls (by definition).

As background, the scope of the inspection is nearly the same as the scope of an overhaul, with the exception of the blade thing, so most owners just say "well, might as well be an overhaul" since it costs roughly similar, then they get a "0 TSO" prop back. But the downside is about to be felt in a fleetwide manner over the next few years.

New blades are basically $5K. So you take a 5 year "overhaul" requirement that costs something like $9K per prop, and then suddenly add $20K per prop. Ouch.

So the 7 year thing is great if it buys a couple years to show the FAA guy enough data to eliminate the AD requirement. It'll save truckloads of money on props. Also, it's not a bad idea to just comply with the *inspection*, not say "just make it an overhaul".

Thanks Jon. As usual, you are correct and stated it better. Was trying to make clear that if you send it to Hartzell there is no option, even if you ask for just the inspection (no blade grinding) , you WILL get an overhaul and blade grinding. Other places are willing to do just the inspection (no grinding).

Minor niggle, but I suspect it's 1981 and later models.

SPZ500 started with Solitaire SN 430 (1980 model year was 415 to 435), Marquise SN 779 (1980 model year was 755 to 799). Marquise SN 748 and 758 were also modified to SPZ500.

Mike C.[/quote]

Go figure, mine's sn#429

Thanks David.

But what's worse, Hartzell forces their certified shops to overhaul them, even if they only need an inspection or an SB to comply. If they don't, the shop loses the right to be Hartzell certified. I had a very hard time finding a shop that would just comply with the SB.

You look at the FAA and Hartzell forces more SB's into AD's than any other aerospace company. Because it's free money for them. These AD's are not air safety mandated or due to accidents, they come from Hartzell alone. They lobby the FAA to change them to AD's.

If you make props, and every single hub or prop has an AD, you're either:

1. Very bad at what you do…

or

2. You've found an easy way to make money.

Or
3) your lawyers advise you to do this


They sound like a really pleasure to deal with....
:(

Adam,

For what it is worth, IJSC in Oklahoma City has a prop shop now. While they are an MU-2 service center and specialists, I would imagine they would not turn down other work as well (of course I have no connection with them, can't speak for them, etc.). I can tell you I spoke to Heath (their prop shop manager) in great depth about inspection vs. overhaul. He was absolutely able and willing to do the inspection. One thing he pointed out to me is that they (IJSC) have the very expensive tool necessary to reset/insert the tubes in the hub. Apparently you need to apply a ridiculous amount of pressure (20,000 lbs?) and most prop shops don't have the tool-- hence they send the hub to Hartzell and are dependent on Hartzell. He indicated IJSC is not the only shop, but one of very few, that can do all the work in house.

Next time your props are due, might be worth giving him a call and exploring your options...

As always, no recommendation or guarantee given, just passing on information from a conversation I had with the caveat that I have found the folks at IJSC to be (a) straight shooters, (b) knowledgeable, and (c) a reputation for quality work.