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PT6A Versus TPE-331  
User currently offlineAllisonTP From United States of America, joined Sep 2001, 13 posts, RR: 0
Posted (12 years 5 months 4 weeks 17 hours ago) and read 14723 times:

Hi everyone,
I have a couple of questions I hope some of you could shine some light on for me. I already know the technical aspects (PT6 has a free power turbine, TPE-331 is a single shaft yadda yadda yadda) but I am confused about the actual operation of these engines.

Are either of these more prone to hot starts than the other? When the PT6 is started, N1 gas generator is being spooled but the power turbine is going very slow, seems as though it would be pretty easy to cook the buckets.

In the 331 all you have is N1, which would look like it would be much more difficult to start because of the loading from the PTO and the prop. Does the prop on the 331 have to be set to a fine pitch on shut down to aid in the next start up?

And finally, during flight how much more complicated is it managing the 331 for proper power settings and prop RPM since it is lacking the independent control of the power turbine.

I would also love hear any experiences with these engines pilots and mechanics views alike.


Thanks a bunch  Smile

16 replies: All unread, jump to last
 
User currently offlineL-188 From United States of America, joined Jul 1999, 29790 posts, RR: 58
Reply 1, posted (12 years 5 months 4 weeks 16 hours ago) and read 14689 times:

I am surprise Trots hasn't responed to this.....It should be good reading.


OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
User currently offlineTwotterwrench From , joined Dec 1969, posts, RR:
Reply 2, posted (12 years 5 months 4 weeks 14 hours ago) and read 14689 times:

Ahhh...my favorite topic. Alas, I must go to bed, but I shall shatter the illusion that Garrett makes a good engine tomorrow...promise.

User currently offlineL-188 From United States of America, joined Jul 1999, 29790 posts, RR: 58
Reply 3, posted (12 years 5 months 4 weeks 14 hours ago) and read 14683 times:

Going to bed..... Sad

Your public is disapointed



OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 4, posted (12 years 5 months 4 weeks 6 hours ago) and read 14678 times:

It's all about Fords and Chevy’s.

You are correct, The 331 is a very difficult engine to start as the whole rotating group is directly coupled to the gearbox. Weak batteries and cold ambient temperatures are the worst enemy.

The 331 is very compact with the exhaust duct at the rear of the engine. The PT-6 rather long with exhaust ducts at the front of the engine.

I believe these are some of the features that Aircraft designers considered when selecting a power plant.

Cessna experimented with both on the Conquest. Beechcraft tried it on one model, B100? Fairchild flew one Metro III with Prat's, rumor has that it was a ploy to get Garrett to lower the prices of their engines. However, I've been told that Operators at that time wouldn't accept a re-engined Metro due to extra cost in parts, and training.

Which engine is better? Considering technological advances made by both mfg's. The TPE-331. When Garrett and then Allied Signal owned the 331 many improvements were made to the 331.

This process was enhanced because of the Metro Operators Technical Committee, (MOTC). A network of Metro/Merlin Operators that have been meeting once a year since the mid 70's to press Fairchild and Garrett, now (Honeywell) to improve their support.

Having been in a position for several years at having access to costs and comparing both engines cost per flight hour over a multitude of TBO periods, The Garrett wins.

As for the Mechanic working hands on with both types, the PT-6 wins.

As for product support from either Honeywell or P&W of Canada, they both suck!!!!!!!!!!!!


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 5, posted (12 years 5 months 4 weeks 5 hours ago) and read 14678 times:

From my perspective as a pilot with a couple of thousand hours sitting between both types of engines I have developed a definate preference for the Garrett.

Like everything else in aviation, engine chice is a matter of tradeoffs. They have both evolved into very reliable engines, but they both also have their own strengths and weaknesses.

If speed and altitude performance are what you're looking for the the TPE-331 is tough to beat. It's more fuel efficient at the higher altitudes and (in most installations) you get a significant amout of bonus "tail-pipe thrust" - about 75 h.p. or so from each engine. The down side is that they do tend to require a bit more maintenance. That's really neither "here nor there" since it's all worked into the operating budget.

The PT-6's have a better reputation, but from what I've seen as a pilot it's overstated at best and undeserved at worst. They do require less maintenance and would make better choices for installations where maintenance availability is a factor and speed and altitude performance isn't as critical. The fuel specifics on the PT-6's aren't nearly as good as on the TPE-331's.

Bottom line is you'll tend to see Garretts on high-performance aircraft like MU-2's, Conquest II's, Metro's, Cheyenne IV's etc. and PT-6's on lower performance aircraft like Twin Otters, Cheyennes, King Airs, and the various single engine turboprops. Each engine has it's place.

Jetguy



User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 6, posted (12 years 5 months 3 weeks 6 days 22 hours ago) and read 14640 times:

>>>Each engine has it's place.

Yes, but the proper place of the garrett is generating 400 cycles in the tail of a 757...


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 7, posted (12 years 5 months 3 weeks 6 days 21 hours ago) and read 14633 times:

Aaron...
Come on now, you don't really mean it. Am I to believe that if someone offered you the going rate to fly their Conquest II that you'd turn it down because "the proper place of the garrett is generating 400 cycles in the tail of a 757." All you're telling me is that you don't have much experience with either powerplant.

Jetguy


User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 8, posted (12 years 5 months 3 weeks 6 days 20 hours ago) and read 14625 times:

no, I'd turn it down because I have a slightly better job.

Actually, I do have a sincere question regarding 331 installations, why is the MU-2 installation so much more abhorrently loud than any other tp? Is it the inlet design or the engine they are equipped with. I know were equipped with several variants; It just seems that every mu-2 installation is louder than any other 331 application.


aaron


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 9, posted (12 years 5 months 3 weeks 6 days 19 hours ago) and read 14635 times:

You're right, but I have no idea why. We used to call the Garretts "Converters" since they converted Jet A into noise. There was also the "Garrett Salute" given by all who happened to be standing nearby as you taxied past. The salute was accomplished by placing the index finger of the right hand into your right ear and the index finger of your left hand... Well, you get the point.

As I remember, they said that the noise was generated by the "inlet" compressor - but I don't really know for sure. If that were true then wouldn't all TPE-331 installations have the same noise level? The MU-2 Marquise model that I flew was really loud on the outside, but the interior noise levels were exceptionally quite. I had the same experience with both the Turbo Commander and Conquest II. Go figure.

So much for the "esthetics" of the engine. Operationally, the -10's on the MU-2 were pretty simple. They were flat-rated from around 1000 eshp to 717 eshp, so you seldom had to worry about temp limits - you'd always "torque out" until you were up around FL200. (Forgive me if I'm off a bit with these numbers, I'm quoting these figures from memory and it's been nearly 15 years since I flew a MU-2 Marquise.)

As far as performance goes, perhaps the closest direct competitor to the Marquise was the King Air 200. The Garrett powered MU-2 had a 10% larger cabin; was 10% faster; and burned 10% less fuel than the PT-6 powered King Air.

Like I said, both engines have their place. I understand that the Garrett does make a pretty good APU. (We've got one in the tail of our Gulfstream.) I've also heard that the PT-6 makes a heck of an oilfield pump - just rig it to run on natural gas and they say that they will run forever. Personally, I like airplanes that fly fast and high and if you're trying to do it in a turboprop then the Garrett's the only way to go. If you're out in the bush then I'd want something with PT-6's.

Jetguy


User currently offlineAJ From Australia, joined Nov 1999, 2386 posts, RR: 24
Reply 10, posted (12 years 5 months 3 weeks 6 days 18 hours ago) and read 14630 times:

I've flown both the Mu-2B-30 and the B200 Super King Air, apples and oranges (loved them both).
The Hiroshima Screamer made all that noise due to attenuation of gearbox noise in the intake. Once at high power/speed the noise was 'swallowed' by the engine, making overflight noise less than a PT6.


User currently offlineDalmd88 From United States of America, joined Jul 2000, 2533 posts, RR: 14
Reply 11, posted (12 years 5 months 3 weeks 6 days 17 hours ago) and read 14621 times:

During the 331 shutdown the prop is held in reverse to set the Start Locks. They hold the blades at 0 degrees if I remember. The piston that engages the locks tends to wear over time and the prop will jump the lock on start giving a hung on hot start. Hot starts are real easy to achieve. Just lay your thumb on the start button and hold. This over rides the start computer and dumps fuel at the nozzels. That little EGT needle starts to rise real fast when you do this. I always hated doing manual starts.

User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 12, posted (12 years 5 months 3 weeks 5 days 21 hours ago) and read 14598 times:

With Hartzell props on 331's ice will prevent the start locks from disengaging, as the locks are external on the hub. You can go speeds high and rock the power lever back and forth all day and they won't release.

One of the original questions was operational differences between the two. Essentially, once the prop condition has been set, either engine is single lever controlled by the power lever.


User currently offlineMiles_mechanic From Canada, joined Sep 2001, 136 posts, RR: 0
Reply 13, posted (12 years 5 months 3 weeks 5 days ago) and read 14581 times:

Hello everyone,
well the info that I am including is based on my experience working with my company for the past 4 years. I work as a mechanic and we operate Pratt & Whitney PT-6 engines on Turbo Beavers, Turbo Otters, Twin Otters, King Airs, and Beech 1900C and D. And TPE331 engines on a MU-2, C-441 Conquest, and BAe Jetstream 31.

From my experience the TPE331 engine that is computer controlled on our Conquest is a good engine, it is very easy to rig and doesn't give us any problems, I know the guys working on the MU-2 are not crazy about the installation of that engine, and they have had some problems with the engines on it over the past few years, but that could just be a fluke. As for the engines on the Jetstreams they are not computer controlled, so they have a whole bunch of control rods to operate the FCU and MFV, PPC, etc. Of the 8 engines we have on the Jetstreams we have never had more then 5 engines that were not loaners on the aircraft at one time since I have been working on them, from my experience we are always having to adjust the rigging on the aircraft, and in the summer the engines are always temping out so they only operate at between 10,000 and 17,000 ft as they can't get any higher, they require Water Methanol in the summer or they have no payload, these are comments from our pilots. I am assuming the reason for the bad performance and requirement to have water methanol is that British Aerospace just picked a underpowered version of this engine for this aircraft.
I love the Conquest as it will fly high and fast, but not the Jetstream.
I really can't say anything bad about our PT6 powered aircraft, other then yes it is a dirty installation with the exhaust at the front so you get exhaust all over the plane, and yes it does burn more fuel, but since our PT6 aircraft can get up to 25,000 ft, they end up burning the same amount of fuel as the Jetstream so there is no real savings there, and the PT6 equipped Beech 1900 flies at 290 Kts true from our pilots and the Jetstreams fly at 255 Kts true. The MU-2 it cruises around 260 and our Conquest with its upgrades flies at around 310 kts true.
The Beaver, Otter, and Twin Otter of course don't fly fast because they were not designed to fly fast, they are bush planes. But the King Air according to Raytheon website is no turtle, it is capable of flying at 295 Kts. true.
So from my position with the company I work for the engines in our Corporate aircraft the MU-2 and Conquest are good TPE 331 engines and are reliable, but the TPE331's in our Jetstreams are not.
The PT-6 engines have proven to be very reliable in the dead of winter in Western Canada, and also in the hot summer, on average of all these aircraft we operate the PT-6 engine is more reliable in our operation. Yes it costs more to buy, and to maintain it, but from my position as a mechanic, it has required a lot less maintenance.



User currently offlinePeterba69 From United States of America, joined Mar 2002, 70 posts, RR: 0
Reply 14, posted (12 years 5 months 3 weeks 4 days 5 hours ago) and read 14543 times:

Hello, I've been trying to locate a site for Honeywell's engine dept., and all I get is the avionics stuff. Any help appreciated. Peter

User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 15, posted (12 years 5 months 3 weeks 4 days ago) and read 14532 times:

They do, it's Honeywell e-engines, but it is password protected.

User currently offlineAllisonTP From United States of America, joined Sep 2001, 13 posts, RR: 0
Reply 16, posted (12 years 5 months 3 weeks 3 days 17 hours ago) and read 14523 times:

Thanks everyone, I appreciate your responses!

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