CFAN is owned by GE and is the company devoted to those blades. Whether GE got the technology from CFAN or vice-versa.........I can't say.

All I’d like to add is never confuse the application of materials used in piston driven aircraft propellers with the blades of a turbojet/fan engines. They are two totally different applications with two totally different requirements.

There is a hell of a lot more involved than cost.
Flex requirements. Vibration absorption/transfer. Gyroscopic issues. Power input/removal rates. Crankshaft power impulses. Torque/Leverage issues…..

__________________
1980 300D - Veggie Burner !

I think titanium would be perfect for a piston driven aircraft propeller. It would flex quite a bit less than the aluminum, but that could be designed into the pitch. The weight is comparable to aluminum, so the gyroscopic issues are minimized. It's much stronger than aluminum so that it can take significantly more power and the crankshft power impulses wouldn't bother it.

I don't see any detriment to titanium for a piston driven propeller other than cost and the fact that it's more than you need to get the job done.

Early work in carbon fiber fan blades was done by GE back in the '80's with the Unducted Fan Engine.

http://www.airspacemag.com/history-of-flight/16044907.html

I have to fly this evening, so no time to get deep into this.
Maybe Shelby will later, as she has a rather boring HD tonight.

You are for the most part correct, if you’re talking about an application such as a large transport aircraft where power is run-up and set with only minor adjustments throughout the flight. But for an application such as an aerobatic aircraft, many of the reasons you feel titanium would be the right material, are actually why it would be wrong. As for all the aircraft in between… well, there is certainly the issue of cost involved. But there are also many factors involved where having the ultimate in rigidity, light weight and strength is a bad thing.

Don’t stay focused only on the issues related to how the motor will affect the propeller, but focus also on how the propeller and its properties affect the motor. Also – How the flight of the aircraft can affect the propeller, and how that in turn affects the motor.

__________________
1980 300D - Veggie Burner !

I'd need to look it up, but IIRC, the density of Ti is very close to the density of Al. Therefore, the engine won't know whether the propeller is titanium or aluminum.

I'm listening for any other variable that might affect the engine...........the increased strength and stiffness won't..........

Sorry, but:

Like hell it wont !!

There’s a good reason why the best all around propellers are neither aluminum or titanium, but wood/composite.

Stiff/ridged is a bad thing. Just ask Piper and their Malibu issues with cracked supercharger housings. It was all caused by vibration issues from stiff aluminum propellers. To go to an even stiffer titanium propeller…. Ouch.

Aluminum and Titanium both support harmonic vibration. This is why so many propeller driven aircraft have propeller RPM restrictions (And I don’t mean the max, or red-line.). Many (if not most) failures of gyro instruments, motor mounts, engine cowlings, radio systems…. can all be traced back to the propeller and the vibrations it can not absorb and thus sends back through the engine.

Aluminum and Titanium would both exhibit typical tip fatigue failure issues. Where the aluminum props often show erosion in this respect, I might think (you're more into this than I) that the titanium may crack. “Propeller” and “Crack” are two words we don’t like to hear used together.

As far as the gyroscopic issues. Light and short are everything. The lighter and shorter the blades are, the fewer precession issues have to be dealt with, including their affects on the motor. I don’t think aluminum nor titanium are light enough to be made as short as a composite blade with the same available thrust. This is why all the serious aerobatic aircraft run MT (or some other make) composite blade propellers. And trust me, “cost” is no issue there.


- Shelby

__________________
1980 300D - Veggie Burner !

This brings me to something I saw the other day on TV regarding boat propellers.

Maybe Hatt can jump in here.

A guy was talking about all these bass boats running around with pretty stainless steal props. He though that was nuts.

Being a boat that runs around in logs, stumps, and rocky waters, it made no sense not to have a more forgiving propeller.
He stated that bass boat operators would be better off with aluminum props (and a spare) that would bend (absorb) a hard strike, as compared to ridged stainless steal that transmits the strike right up the shaft to the pricey motor parts. Made sense to me. But then, I’m not a bass boat driver.
Not sure how the “sheer-pin” I’ve heard they have on the shaft comes into play here. Maybe that’s what the SS prop runners are counting on.



- Shelby

__________________
1980 300D - Veggie Burner !

Most, if not all metal boat props have a shear pin or a rubber hub or both. The rubber hub flexes to absorb small impacts and slips to absorb larger ones.

Another company, Comprop I think, makes cheaper plastic props designed to shear off with impact. Obviously losing a blade is not so much a problem in the water but I can imagine that the vibration would be pretty awesome spinning at 5000 RPM!

Most of the lakes around here are shallow and I hit bottom all the time. Aluminum props get pretty beat up but the stainless prop I have on one of the outboards is solid. It never bends or chips and I'd probably have to hit something metal or cement/rock to do any damage to it.

A friend of mine is building an airplane from scratch and I believe his engine/gearbox to prop incorporates a harmonic balancer and some kind of flex drive on the composite prop IIRC.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Yep, you could be right about harmonic vibrations. But, "stiffness" may be desirable or it may not be desirable depending on the frequency of the vibration and the operating frequency.

Traditionally, the stiffer the component, the higher the first order vibration frequency. If this can be well above the operating speed, the stiffer material wins.

It might be the situation, due to the shape of the propeller, that the operating range is between the first and second critical frequencies............and titanium might shift this point to an undesirable location.

In summary, titanium by itself is not an automatic reject for a propeller. It would depend on the harmonics of the material, if present, and the operating speed with respect to those harmonics.

Aluminum is more forgiving and will protect the driveline somewhat on a serious hit.

However, stainless is more durable for those operators that will hit some sand on occasion. The stainless is relatively tolerant of sand and the driveline is not harmed by a hit in sand.

So, it's strictly an operator choice. Take the more expensive stainless and don't hit any rocks..........or choose the cheaper and more forgiving aluminum

Makes good sense to me. As well as KarTeks post and the rubber mount.

Thanks for the lesson.

The only experience I have with powerboats and propellers is J & DJs Tige’ VE-24. It’s a V-Dive Inboard (I think that’s what they call it.) with a brass prop. We hit a log one time and hardly bent the tip of one of the three blades. But wow, what a vibration that made. I thought the whole shaft was going to rip out.

From what I recall, those brass props aren’t fun to buy or have fixed either. Luckily they keep a spare onboard and some funky looking puller that’s required.

- Shelby

__________________
1980 300D - Veggie Burner !

I touched down the starboard prop on one of the ferries just briefly..........in sand...........on a Saturday afternoon (weekends are the heaviest).

It folded the very tip on one of the four blades. The wheel is all brass..........very soft..........and it takes nothing to damage it.

Hauling the 75' boat in the middle of the parking lot on Sunday morning and changing the 34" wheel was definitely not what the mechanic wanted to do that morning. But, by noon, the boat was back in the water for the Sunday afternoon rush hour (actually 5 hours stretching from 4:00 to 9:00).

I think I recall him saying something about their props being soft as well, so as not to damage the shaft, bearings or seals.

Wow. 75’ with 34” props. I think I’ll stick with the easer to operate, helicopter.

As I recall, we were back in the water within about 20 minutes. But that prop is more like 12” or so.

- S

__________________
1980 300D - Veggie Burner !

I can drink till I can't see...........let go of the controls..........and the ferry will just continue straight ahead...........if I pull the power back to idle...........the ferry just stops and sits there...........I can pour more drinks...........

..........how'd that work for you in a helicopter............??

..........easier to operate............I think not.............