Just MT Propeller

[Tom Martin]

Jim
Are the blades in the aerobatic MT rocket prop differenet than the blades in the standard version? I know that they default to the coarse pitch but are the blades themselves different. Thanks

[RVjim]

Originally Posted by Tom Martin

Jim
Are the blades in the aerobatic MT rocket prop differenet than the blades in the standard version? I know that they default to the coarse pitch but are the blades themselves different. Thanks

Hi Tom,

Yes and No.

The two Rocket propellers you are asking about are the standard 3 blade MTV-9-B/198-52 and the counterweighted 3 blade MTV-9-B-C/C198-52 propeller.

Aerodynamically, they are identical.

From the propeller model numbers you can see the the propeller diameter and blade design are the same.

However, the blade drive pin on the blade is in a different location for the "standard" blade than the location for the blade drive pin in the counterweighted blade.

This is because increased oil pressure from the governor is always pushing the piston forward in the hub. As the oil pressure increases,
1.) The standard blade starts at a fine pitch and is rotated to a coarse pitch.
2.) The counterweighted blade starts at a coarse pitch and is rotated to a fine pitch.

Bottom line, internally, only the propeller hub and a few of less expensive parts could be used if you wanted to convert a standard blade propeller to a counterweighted propeller.

Regards,
Jim Ayers

[RVjim]

For the MTV-15-B/183-402 Aluminum 2 blade 72" diameter MT Propeller, the minimum propeller diameter is 68".

For a propeller that has had a propeller strike, each of the aluminum blades from a 72" diameter can be trimmed by up to 2" (68" diameter), and still be serviceable.
There is a required inspection of the propeller hub. Normally, the propeller hub is simply overhauled and returned to service.
This is because the bearings and bearing races are usually the only items damaged in the propeller hub due to a blade strike.

For the MTV-12-B/183-59b "Natural Composite" 3 blade 72" diameter MT Propeller:

THe blade length is 1/2 the propeller diameter minus 3". So for a 72" diameter propeller, the blade length is 36" minus 3", or 33".
Up to 15% of the "Natural Composite" blade tip can be replaced by a factory overhaul of the blades.
The 72" diameter propeller can be reduced to about a 62 1/8" diameter, and the blades can still be overhauled back to be a 72" diameter propeller.
It normally takes about two weeks for the MT Propeller factory in Germany to overhaul the blades.
There is no life limit on the "Natural Composite" blades. There is no limit to the number of times that they can be overhauled.
Normally, the stainless steel leading edge is replaced and the blades are repainted.
Again, the propeller hub is inspected and overhauled for return to service. Any internal damage is normally limited to the bearing races and bearings.

Since Lycoming requires a tear down inspection of their engine, after a propeller strike, the propeller can usually be returned in about he same time as the engine is reinstalled. Assuming they are both started at the same time.
It does take about 4 weeks to replace the spinner, if this is damaged. (Been there, done that. Obviously, the blades weren't usable in this instance.)

Regards,
Jim Ayers

[RVjim]

I am in the process of building a Harmon Rocket II type aircraft. I plan to use this aircraft for higher altitude cross country trips, in addition to the other normal uses.
The 4 blade propeller theoretically has the best efficiency for this upper VFR altitude flight use.

MT Propeller designed a 4 blade propeller for my engine and aircraft. It has been flown on a F-1 rocket that normally had the 3 blade MT propeller. I was informed that the 4 blade propeller was 2 knots slower a 4,000'. A little less than I expected for this low altitude. Also, the 4 blade propeller seemed to perform better than a 3 blade propeller above 9,000'. (Unfortunately, there are no numbers available.)
Apparently, the performance cross over between a 3 blade and the 4 blade is a little lower than I expected. (It probably helps that the 4 blade propeller efficiency is 0.3% better than the 3 blade propeller.)

I have a customer, Bud, with a Lycoming 360 engine in his single aircraft. (Piranha) His son bought a 3 blade MT Propeller for his HR2. And Bud's aircraft is just a little faster than his son's HR2.
Bud felt he needed to replace his original 2 blade with a 3 blade MT Propeller. However, he wanted too still be a little faster than his son's HR2.
Bud really likes how smooth the 3 blade propeller operates. (Although there were apparently some issues with the original 2 blade propeller.)
And Bud's aircraft is still a little faster than his son's HR2.
(I still am amazed at the reported 120 mph stall speed of the Piranha.)

Regards,
Jim Ayers

[gmcjetpilot]

Originally Posted by Tom Martin

Jim Are the blades in the aerobatic MT rocket prop different than the blades in the standard version?

Aerobatic propellers have counterweights on the blades and use oil pressure to decrease pitch. Any momentary oil pressure loss (common with hard acro maneuvers) causes the engine to go to a high pitch and the engine slows down. Aerobatic propellers are heavier due to the counterweights. With standard props (pressure for high pitch) you can get the engine to Rev if you lose oil pressure. Not sure why Jim pushes the acro prop. We do acro but not Pitts/Extra acro. If you have done acro and lost oil pressure you do get a RPM surge, but not gentlemans RV acro. If you are doing wild ultimate acro maneuvers like a Lomcevak, yea, get a acro prop, but you are not doing Lomcevak in a RV or Rocket.

Some say its better for engine out guide even for a non hardcore Acro plane? May be? Course pitch would give less drag than fine pitch, which is what standard props go to when RPM/oil pressure drops. Is that really a reason to buy a prop on a single sport plane? Why by a light weight MT prop and add the weight back? Jim whats your reason for pushing Acro props on planes that really are not for aggressive acro (like the Rocket).

Originally Posted by RVjim

For the MTV-15-B/183-402 Aluminum 2 blade 72" diameter MT Propeller, the minimum propeller diameter is 68".

For a propeller that has had a propeller strike, each of the aluminum blades from a 72" diameter can be trimmed by up to 2" (68" diameter), and still be serviceable.

Jim has MT ever done Vibration surveys for Lycs with electronic ignition? If so do you have proof in writing. This question applies to both the metal and "natural composite' bladed props.

For the MTV-12-B/183-59b "Natural Composite" 3 blade 72" diameter MT Propeller:

THe blade length is 1/2 the propeller diameter minus 3". So for a 72" diameter propeller, the blade length is 36" minus 3", or 33". Up to 15% of the "Natural Composite" blade tip can be replaced by a factory overhaul of the blades.

It normally takes about two weeks for the MT Propeller factory in Germany to overhaul the blades.
There is no life limit on the "Natural Composite" blades. There is no limit to the number of times that they can be overhauled.

What does it cost? What is a full standard overhaul for both the metal two blade and wood/fiberglass three blade props. I assume shipping cost to Germany of a prop is not cheap? I heard the cost to OH a MT is almost as much as a new Hartzell? I doubt that but what is the real cost, with shipping, the full meal deal cost.

Why do you call the blade "natural composite"? Its WOOD right, wood wrapped in fiberglass. I don't know any material called natural composite.

Normally, the stainless steel leading edge is replaced and the blades are repainted.

How often do those leading edge erosion shield become de-laminated? I assume a repair means taking to prop off and shipping it, verses just blending the a nick out of a Hartzell with a file.

Originally Posted by RVjim

The 4 blade propeller theoretically has the best efficiency for this upper VFR altitude flight use.

MT Propeller designed a 4 blade propeller for my engine and aircraft. It has been flown on a F-1 rocket that normally had the 3 blade MT propeller. I was informed that the 4 blade propeller was 2 knots slower a 4,000'. A little less than I expected for this low altitude. Also, the 4 blade propeller seemed to perform better than a 3 blade propeller above 9,000'. (Unfortunately, there are no numbers available.)

Well I heard just going from a two bladed Hartzell to a three bladed MT causes loss of 6-9 mph, which seems to be shown over and over by independent sources. I also heard the Four blade was worse than the three blade by more than 2 kts. Van did one of these prop comparison fly-offs, and it showed the MT's where slower, significantly. It would be good to give the MT a fair shake. May be we should have another independent Prop Round-up, fly-off comparison with all the MT's verses other props.

[Tom Martin]

I guess if I am going to be quoted I should clarify why I wanted to know if there was a difference between the standard and aerobatic blade. I was curious to know whether there would be a top speed difference between the different versions. I have been in three races where my MT standard prop rocket was faster than some other aerobatic blade MT props. Jim answered that aerodynamically the blades are the same. The differences are all in the hub. Thus I would conclude that there should be no difference in speed between an aerobatic and standard MT prop. I have owned both versions and prefer the lighter weight standard prop.

[RVjim]

Originally Posted by Tom Martin

I guess if I am going to be quoted I should clarify why I wanted to know if there was a difference between the standard and aerobatic blade. I was curious to know whether there would be a top speed difference between the different versions. I have been in three races where my MT standard prop rocket was faster than some other aerobatic blade MT props. Jim answered that aerodynamically the blades are the same. The differences are all in the hub. Thus I would conclude that there should be no difference in speed between an aerobatic and standard MT prop. I have owned both versions and prefer the lighter weight standard prop.

Hi Tom,

I guess I'm not the only one that resents being misquoted. :-)

Just as a clarification, the counterweights are mounted at the base of the blade hub. (There are two hubs on the MT Propeller, the propeller hub and the blade hub.)

The counterweights weigh around 4 pounds each. This is 12 pounds on the three blade propeller. There is a CG change with this weight increase.

There is also a 12 pounds different between the aluminum 2 blade propeller and the 3 blade propeller. When I do testing on my RV-6A with the extra 12 pounds of the Aluminum propeller on the front, I place 16 pounds in the baggage compartment to maintain the CG location, and burn off an extra 5 gallons of fuel before I start the test.

The counterweighted blade propeller could just be shifting the CG forward with a resultant increase in pitching moment, and additional elevator trim drag. Or it could just be the differences in the aircraft.

Regards,
Jim Ayers

[RVjim]

MT Propeller refers to the core of the propeller blade as "Natural Composite". They manufacture their own blade core from the selection of the Beechwood and Spruce to the completed blade.

The initial Beechwood and Spruce are dried to a 6% relative humitity. While most of the blade is Spruce, the blade hub is Beechwood.
These two materials are bonded together in a press, which causes the wood fibers to become impregnated with resin, like any other composite product.

Since this process starts with a natural fiber, you get a "Natural Composite" blade laminate that becomes the core for the MT Propeller.

The two layers of fiberglass are used as a moisture barrier to maintain the 6% relative humitity of the core.

Regards,
Jim Ayers

[DanH]

Hello Jim,
Does MT publish mass moment of inertia values for their propellers, in particular the MT7(?) as used on Eggenfellner Subaru packages? If so, can I get a copy?

[RVjim]

Originally Posted by DanH

Hello Jim,
Does MT publish mass moment of inertia values for their propellers, in particular the MT7(?) as used on Eggenfellner Subaru packages? If so, can I get a copy?

The first place to look for this type of information is www.mt-propeller.com

The following is information I remember that I may have just heard and not seen written down.

The polar moment of inertia of the 3 blade MT propeller is 40% of that for an Aluminum 2 blade propeller.

A feathered propeller has 7/8ths less drag than the same propeller in low pitch.

A counterweighted blade propeller with the loss of oil pressure has 5/8ths less drag than the same propeller at low pitch.

Zero G maneuvers are most likely to cause the loose of oil pressure to the governor and propeller. Even with an inverted oil system.

I had the opportunity to disassembly a 2 blade MT Propeller that had been flying off of rock strips in Iceland. (I was attended the MT Propeller certification class in Germany, at that time.) The stainless steel leading edges were badly dented on both blades. However, they were still serviceable and the propeller had only been sent in due to the required overhaul time. The blades were serviceable because there were no cracks in the stainless steel leading edge. Only dents.

The two layers of fiberglass on the ?Natural Composite? core are not a structural part of the blade assembly. However, this layer acts as a moisture barrier for the core, and this surface must be kept sealed. The Installation and Operation manual that comes with the propeller identifies typical repairs (and repair limits) that can be done.

A Velocity landing at Sun-N-Fun had to make a go-around, and in the process over rotated and trimmed ?? off of each blade. The blade tips were trimmed to equal lengths and sealed with 5 minute Epoxy. The owner was only cautioned to make certain when the propeller was overhauled that the original blade length was emphasized to the repair station when it was time to overhaul the propeller. That way he could get the overhauled propeller back with the original blade length.

Regards,
Jim Ayers