Value of a three blade prop?

hewilson · #1 07-12-03, 02:00 PM

If it isn't already obvious, this question will really cement my neophyte status.

Exactly what is the benefit of a three blade prop? Intuitively it would seem that you are biting more air with each rotation but what exactly does this translate to? I would think it might mean any or all of:

1) higher speed at same power setting
2) better rate of climb
3) better DA performance
4) better high altitude performance
5) better engine out performance

I'm sure there are plenty of guys here who know the answer to this one. Thanks for any input you might have.

WebMaster · #2 07-12-03, 04:43 PM

Herb has the 3 bladed conversion on his skymaster.
The normal advantages are smoother operation, typically greater acceleration, and faster climb. However, it is also typically slower at cruise. Mooney changed from 3 bladed to 2 bladed, on one of their models to increase cruise speed.

RRossner · #3 07-12-03, 11:47 PM

We at Tule River Aero Ind are installing a set of the STC'd MT composite props on a Customers P337. I'll advise as soon as the verdic is in on the pros/cons.

I'm told to expect less vibration, less noise, better climb, but less speed at cruise.

Rick Rossner
VP, Sales
Tule River Aero-Industries

Mitch Taylor · #4 07-13-03, 01:23 PM

with propellors, fewer blades is better. If you could figure out how to do it, a single blade would be the best. In racing boats, they use a surface piercing setup where the prop shaft is even with the surface, and only one blade is in the water at a time.

Mitch

hewilson · #5 07-14-03, 08:43 PM

So is the reduced cruise speed due to increased drag then?

I've heard that the most "efficient" prop is the one with the fewest blades but efficient how? Though it may be efficient, is it the most "effective." Effective gets the job done best. Efficient gets it done with the fewest resources or at lowest cost. In props does this mean that two blades maximizes thrust while minimizing drag? In other words, any increased thrust from the third blade is more than offset by the drag?

Rick, I'd be interested in hearing more on how your customer(s) likes the three blade.

Thanks for the replies guys. I'm due to solo this week so I'm getting closer to my dream of owning a Skymaster. It helps to be informed when you finally get the point when you can actually pull the trigger.

Hugh Wilson

Bob Cook · #6 07-14-03, 10:37 PM

Hugh

Each application is different and each aircraft/hp responds differently.

In theory you obtain more "bite" with three blades at lower speeds. Efficiency is based on the pitch ie. 72 meaning one revolution the blade will move forward 72 inches. The difference in free air is the slippage thus the efficiency.

In the case of the MG blades being composite their is a considerable weight savings. With the harzell on the super skymaster there is a weight gain.

Since the skymaster is not a particularily efficient bird, the difference between a two and three bladed prop is probably not seen, however, in the case of the mooney there is a considerable difference.

In the case of the IO360 the MG props will give you a reduction in weight and possibly an increase in cost of maintance when FOD occurs. (MHO). This is the only 3 bladed prop certified for the 360.

I'll stick with aluminum and a file...... <G>

Bob

Kevin McDole · #7 07-15-03, 07:09 AM

Hugh,

I don't know the science behind it, but you will notice that higher horsepower engines seem to have more prop blades. The Malibu/Mirage is the only plane I can think of that has >300HP with only two blades.

I assume that you can only bite so much air per blade (i.e. increasing the angle of attack further results in an aerodynamic stall) - and therefore to get the advantage of the higher horsepower, you need more blades to bite the air. Another choice appears to be simply increasing the size of the blades (check out typical warbirds), but then ground clearance becomes an issue.

I've heard that one way to pass the much stricter European noise limits is to use a smaller diameter prop with more blades. The tips of the prop are aerodynamically going the fastest and create much of the noise. By reducing the diameter you can slow down the tip speed - and the resulting loss of thrust is replaced with an additional blade.

hewilson · #8 07-19-03, 04:31 PM

This is a great web site. I learn a lot here. Thanks for all the info. guys.

Though I want a Skymaster ultimately, I need hours to get insurance so am looking at some interim a/c, most likely a C182. It's surprising how many have 3 bladed props.

hharney · #9 07-19-03, 08:13 PM

WELL HERE GOES, I AM ABOUT TO VENTURE INTO A SUBJECT THAT I HAVE HAD SOME PERSONAL EXPERIENCE WITH. (UNLIKE SOME OF THE OTHER DRIVERS OUT THERE THAT SEEM TO HAVE ALL THE ANSWERS) ON ANOTHER THOUGHT, WHEN YOU SPEND AS MUCH MONEY AND WAIT THE AMOUNT OF TIME I DID FOR A SET OF PROPS YOU BETTER LIKE THEM.

I HAVE INSTALLED A SET OF 3 BLADE MT (NOT MG <G>) PROPELLERS ON MY 1968 337. I HAVE BEEN ASSOCIATED WITH THIS PETICULAR AIRCRAFT SINCE 1977. I HAVE JUST OVER 2000 HOURS IN IT. AFTER I MADE THE HUGE DECISION TO BE THE SECOND 337 WITH THIS CONVERSION I REALLY WONDERED IF I MADE THE RIGHT CHOICE. AFTER FINALLY HAVING THEM INSTALLED THEY ARE GREAT. MUCH SMOOTHER ON THE RUNWAY AND IN THE AIR. MUCH QUIETER? MAYBE A LITTLE BUT IT IS DEFINETLY A DIFFERENT SOUND. CLIMB PERFORMANCE? YOU BET, I CONTINUE TO ENJOY THE CLIMB DIFFERENCE. MAYBE AROUND 2-300 FPM IN MOST CASES. SPEED, DID NOT SEEM TO EFFECT THE CRUISE PERFORMANCE ONE WAY OR THE OTHER. I DID GAIN 60 LBS USEFUL. AND AS JERRY TOLD ME THE ONLY TIME THEY LOOK BETTER THAN THE 2 BLADE IS WHEN ITS PARKED. THEY DO HAVE A COMPLETELY NEW SPINNER FRONT AND REAR THAT REALLY LOOK A LOT DIFFERENT. MORE MUSCLE LOOK.

I HAVE ALMOST 100 HOURS ON THEM SINCE JANUARY AND OTHER THAN A LITTLE MORE GREASE AROUND THE HUBS (WHICH MT IS LOOKING INTO) I HAVE NO REGRETS. WOULD I DO IT AGAIN? NOT SURE. IT REALLY TOOK A LONG TIME TO GET THEM. NOT SURE WHAT TO EXPECT AFTER 3 - 5 YEARS. (THEY DO HAVE A 6 YEAR TBO) ALL OVERHAULS ARE DONE IN FLORIDA AT THIS TIME. THEY HAVE A NICE STAINLESS STEEL LEADING EDGE THAT IS VERY REASONABLE TO REPLACE IF NEEDED.

ACCORDING TO MT THEY HAVE A LOT OF MALIBU CONVERSIONS WITH THEIR COMPOSITE PROP. REDUCED VIBRATION AND SMOOTHER OPERATION MAKES THEM BETTER FOR THE MALIBU.

BTW, THEY ARE ACTUALLY MADE OF BEECH WOOD.

rmorris · #10 12-20-15, 02:27 PM

Herb - you've had a lot of time now with the 3-bladed MT Props...would you do it again? any new pirep on them from what you originally posted?

All - I am flying fine, but props and governors getting long in tooth since last overhaul. Looking at overhaul of the original 2-blade McCauleys or replacing. pireps from anyone on other options of course are welcome.

on a related note - the rear engine is getting near TBO. Yes I could top overhaul it and extend, or full overhaul. or buy new same size. But thought I would get any pireps on other engine options than the TSIO-360

hharney · #11 12-20-15, 08:49 PM

Fifteen years with MT props and I would definitely do it again. In fact I just purchased another 3 blade MT for the Vans RV-8 that I am building. What a huge difference they make.

If you look at the engines available for your plane it's going to fit on one line. Unless you get some kind of field approval or purchase an STC that is already out there (there's only 1 that I can think of) you don't really have any choices. It comes down to how much time do you have? Nothing wrong with a good shop doing an overhaul but it will be grounded a lot longer than a factory exchange. I've done 2 factory reman's and both so far have been great.