BeechTalk - BT - The verdict is in.....MU-2

Username Protected · **Posted:** 08 Oct 2022, 20:01

Your list needs some correcting:)

P-180
MU2
Pc12
441
Commander
Metro

Username Protected · **Posted:** 08 Oct 2022, 20:36

Username Protected wrote:

How about the Merlin, which could barely carry crew with full fuel, and some of which had/needed water injection or RATO for EFATO.

I used to joke about it, but in the Merlin IVa/Metro II I could fly a 1000NM flight and use my departure airport as an alternate. You had to have the larger 4342# tanks (not sure why I remember that number after 20 years). The 35XX# tanks were a little more limiting.

The 441 is about the only airplane that could compete with it for range.

Username Protected · **Posted:** 09 Oct 2022, 00:55

Username Protected wrote:

I hope you’re right. But if you can’t accurately assess the health of the NTS system on the ground and you rarely test it in the air (since that’s the only apparent way to 100% check its functionality), then you’re basically having to assume you’re taking off each time with the NTS system not working. Especially if you haven’t “flight” tested the NTS system in the last couple flights, then I don’t know how you can fee comfortable about the NTS pre-takeoff check knowing it’s not 100% accurate. Maybe you just have to take off knowing that if you lose an engine before like 150kts you chop both throttles and land straight ahead. Because from what folks have said on here previously that losing an engine right after takeoff when you’re not cleaned up and fast is basically uncontrollable of the NTS system isn’t working. What am I missing in my assessment?

The NTS test (on Mu2 at least) is 2 pronged.

First is using the electric oil pump to validate the feather valve oil passage and verify this by changes in oil pressure reading at the Beta light pressure switch.

Second is literally watching the mechanical NTS CAM sense, react and report the actual “NT”- provided by the starter, same as a windmilling prop would.

I always do both of these tests on every single start, every one of us does I hope.

It will work.

Username Protected · **Posted:** 10 Oct 2022, 12:08

Username Protected wrote:

my turboprop rankings (wish list) puts mostly the Garrett powered airplanes out in front for their efficiency and high TBO. Being a mechanical engineer I see the common reference of “built like a tank” to be a negative, although most use it as a term of endearment.

It’s a negative because in aero overbuilding means you weren’t good enough to design and build it in an optimal manner (or you were but strangely chose not to). Experience shows many pilots and laymen are confused by this.

So I don't own an MU-2 but I researched them (and 441s) heavily before I ended up with a 501SP.

You are assuming that there is a single balance when it comes to under/over built. It depends on what you want to optimize. Performance? Go light. It will have great performance at the cost of longevity. The 441 is a fast and efficient airplane. However, they aren't aging well. There are weak points around the doors and also the wings themselves are showing stress waves in the skin. I don't think Cessna beefed up the 421 structure enough to handle the much higher power of the 441 engines.

If you want to optimize longevity and reliability, you will end up with a heavier/stronger structure. It's not "overbuilt" it's just built with a different goal in mind.

When it comes to a machine that is carrying myself and my family around in hostile environments, "built like a tank" is a term of endearment. I'll take a few knot penalty in cruise for peace of mind.

Username Protected · **Posted:** 10 Oct 2022, 12:15

Username Protected wrote:

While having an overbuilt airplane has some benefits, it also suffers from a performance perspective due to that.
Tanks don’t fly.

A good aerostructure is just as strong (heavy) as it needs to be plus margin. No more, lest you leave performance on the table.

“as strong as it needs to be” includes operating in your hostile environment

Username Protected · **Posted:** 10 Oct 2022, 13:44

Username Protected wrote:

Any knucklehead can overbuild an airplane. It’s expensive and more labor intensive, so most knuckleheads don’t. Conservative designers can also fall into the trap.

While having an overbuilt airplane has some benefits, it also suffers from a performance perspective due to that.
Tanks don’t fly.

A good aerostructure is just as strong (heavy) as it needs to be plus margin. No more, lest you leave performance on the table.

Aluminum is an interesting metal it will fail at any stress if you have enough load cycle unlike ferrous metals that generally have a limit below which it will never fail. so when you design an aluminum structure you make a compromise between weight and life.

look at the spars and other aircraft aluminum structures that are failing as the aircraft get older. the MU2 appears to have been built to last a long time so it will be heavier but you will be able to fly it for a long time before you need to replace anything.

make it light and it will perhaps carry more load but it will not last near as long. another example is there are aluminum helicopter blades that you throw away at 1000 hours no matter how good they look.

Username Protected · **Posted:** 10 Oct 2022, 14:34

Username Protected wrote:

The 441 is a fast and efficient airplane. However, they aren't aging well. There are weak points around the doors and also the wings themselves are showing stress waves in the skin. I don't think Cessna beefed up the 421 structure enough to handle the much higher power of the 441 engines.

The 441 is a whole different airplane than the 421. I assume you meant the 425?

Username Protected · **Posted:** 10 Oct 2022, 14:38

Username Protected wrote:

Aluminum is an interesting metal it will fail at any stress if you have enough load cycle unlike ferrous metals that generally have a limit below which it will never fail. so when you design an aluminum structure you make a compromise between weight and life.

The stress fatigue curve for aluminum is such that relatively small reductions in stress result in dramatically higher cycle life. So it doesn't take much to make an effectively unlimited life aluminum part.

Quote:

the MU2 appears to have been built to last a long time so it will be heavier but you will be able to fly it for a long time before you need to replace anything.

Maybe.

A problem with an overbuilt airframe is that it might actually increase stress in certain points. The stiffer airframe concentrates the force in those areas. So "heavier" isn't always "longer life". It most often is, but that's a not a given generally.

The MU2 was designed in the slide rule era and has DNA for F-104 Starfighters (which Mitsubishi was building under license from Lockheed). In that era, you tended to have relatively large design margins which yielded a robust and long live structure, but at a weight penalty.

Mike C.

Username Protected · **Posted:** 10 Oct 2022, 15:27

Username Protected wrote:

The 441 is a fast and efficient airplane. However, they aren't aging well. There are weak points around the doors and also the wings themselves are showing stress waves in the skin. I don't think Cessna beefed up the 421 structure enough to handle the much higher power of the 441 engines.

The 441 is a whole different airplane than the 421. I assume you meant the 425?

Username Protected · **Posted:** 10 Oct 2022, 18:53

Username Protected wrote:

The 441 is a whole different airplane than the 421. I assume you meant the 425?

Hi Jason,

Yes, sorry. Got my lineage wrong. 421 -> 425, 404 -> 441.

Username Protected · **Posted:** 10 Oct 2022, 19:09

Hi Jason,

Yes, sorry. Got my lineage wrong. 421 -> 425, 404 -> 441.[/quote]

Actually, the 441 first flight was six months earlier than the 404.

There is a guy on the Facebook page that is giving some good history of the 425/441 recently. He's retired from the Engineering Department at Cessna and is giving some good history of the later Cessna 400 series fleets.. The six months that I mentioned above just came up the other day..[/quote]

Interesting. Got a link? I couldn't find it and not the way I remember from Cessna Engineering. Could maybe be talking about the 431 which was the cancelled piston predecessor of the 441. IIRC 431 prototype was made into 441 prototype.

Username Protected · **Posted:** 10 Oct 2022, 19:10

Hi Jason,

Yes, sorry. Got my lineage wrong. 421 -> 425, 404 -> 441.[/quote]

Actually, the 441 first flight was six months earlier than the 404.

There is a guy on the Facebook page that is giving some good history of the 425/441 recently. He's retired from the Engineering Department at Cessna and is giving some good history of the later Cessna 400 series fleets.. The six months that I mentioned above just came up the other day..[/quote]

Interesting. Got a link? I couldn't find it and not the way I remember from Cessna Engineering. Could maybe be talking about the 431 which was the cancelled piston predecessor of the 441. IIRC 431 prototype was made into 441 prototype.

Username Protected · **Posted:** 10 Oct 2022, 19:12

Didn't quote the previous post because it didn't work.

With respect to Facebook post stating 441 flying before the 404:

Interesting. Got a link? I couldn't find it and not the way I remember from Cessna Engineering. Could maybe be talking about the 431 which was the cancelled piston predecessor of the 441. IIRC 431 prototype was made into 441 prototype.

Username Protected · **Posted:** 10 Oct 2022, 19:44

It's this group... I don't believe you have to be a TCF member to join.

Attachment:

Screen Shot 2022-10-10 at 19.44.17.png

Username Protected · **Posted:** 10 Oct 2022, 22:01

A few years back I went through my 7500hr inspection (outer wings off, gear off, NDT/X-Ray for the lot, first time for the ‘74 plane). I was nervous. One bolt on a wing assy failed testing. Compare to my experience with our 4 King Airs being disassembled every 5 years and having lots of parts tossed, I was amazed. It is a “brick s**t house.” Going through turbulence, the Mits rocks and warbles a bit…the King Airs high-freq rattle and oil-can on the wing skins. It feels like I’m flying a small version of a heavy transport.