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TXFlyGuy

Well Known Member
Looking for an electric control, constant speed, 4 blade, 88" paddle prop.

Contacted MT, they do not build an electric prop in this size. Any ideas?
 
Check with Whirlwind (in Ohio) - they do have a four-blade they use on their Mustangs, but I don't know the size.
 
Myron:

Unless you are going for Ground Looks do not go with the 4 blade prop.
Why?
1 - Too expensive.
2 - Not supported and many airports if you need maintenance away from the home field.
3 - NOT efficient. Basic rule: A 3 blade is about 1/3 less efficient than 2 blade and a 4 blade is 1/2 as efficient than a 2 blade. Now, these numbers are way off due to ALL the variables but! The one huge factor is that each blade follows in the wake of the preceding blade. And with a 2 blade prop the proceeding blade is 180 Deg away from the first. In a 3 blade it is 120 deg away and in a 4 blade it is ONLY 90 Deg away. TOO much disturbed air. AND at the same time the pitch of a 3 blade is less than that of a 2 blade AND a 4 blade is even LESS pitch than a 3 blade and WAY- WAY - WAY less pitch than a 2 blade.
RULE: Speed is PITCH. Vertical Speed is RPM. A 4 blade has neither. NOT in our usable engines.

Barry
 
Barry_Barry said:
Myron:

Unless you are going for Ground Looks do not go with the 4 blade prop.
Why?
1 - Too expensive.
2 - Not supported and many airports if you need maintenance away from the home field.
3 - NOT efficient. Basic rule: A 3 blade is about 1/3 less efficient than 2 blade and a 4 blade is 1/2 as efficient than a 2 blade. Now, these numbers are way off due to ALL the variables but! The one huge factor is that each blade follows in the wake of the preceding blade. And with a 2 blade prop the proceeding blade is 180 Deg away from the first. In a 3 blade it is 120 deg away and in a 4 blade it is ONLY 90 Deg away. TOO much disturbed air. AND at the same time the pitch of a 3 blade is less than that of a 2 blade AND a 4 blade is even LESS pitch than a 3 blade and WAY- WAY - WAY less pitch than a 2 blade.
RULE: Speed is PITCH. Vertical Speed is RPM. A 4 blade has neither. NOT in our usable engines.

Barry
Click to expand...

I always thought a big, slow turning 4 blade prop was a good design. P-51's and many other planes have 4 blade props. Your argument is interesting, however.
 
Barry_Barry said:
Myron:
The one huge factor is that each blade follows in the wake of the preceding blade. And with a 2 blade prop the proceeding blade is 180 Deg away from the first. In a 3 blade it is 120 deg away and in a 4 blade it is ONLY 90 Deg away. TOO much disturbed air. AND at the same time the pitch of a 3 blade is less than that of a 2 blade AND a 4 blade is even LESS pitch than a 3 blade and WAY- WAY - WAY less pitch than a 2 blade.
RULE: Speed is PITCH. Vertical Speed is RPM. A 4 blade has neither. NOT in our usable engines.

Barry
Click to expand...

Paul Lipps would be rolling in his grave right now if anything in the above statements were true. In fact it is so wrong that there would be no way for forward flight to occur if each blade flew in disturbed air. One of the fastest biplanes at Reno is running his prop design which is a four blade. They lose efficiency if the root of the blades do not produce lift, and if you add more blades that do the same you lose efficiency but that changes with correct airfoils down to the spinner.
 
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Two blades are a way more efficient. Four bladed or more are used on higher powered engines in order to transfer the horse power and to keep the prop noise down on modern turbo props. The old war birds with multi blades did not have the room to swing long enough props to get the power transferred.
 
Barry_Barry said:
Myron:

Unless you are going for Ground Looks do not go with the 4 blade prop.
Why?
1 - Too expensive.
2 - Not supported and many airports if you need maintenance away from the home field.
3 - NOT efficient. Basic rule: A 3 blade is about 1/3 less efficient than 2 blade and a 4 blade is 1/2 as efficient than a 2 blade. Now, these numbers are way off due to ALL the variables but! The one huge factor is that each blade follows in the wake of the preceding blade. And with a 2 blade prop the proceeding blade is 180 Deg away from the first. In a 3 blade it is 120 deg away and in a 4 blade it is ONLY 90 Deg away. TOO much disturbed air. AND at the same time the pitch of a 3 blade is less than that of a 2 blade AND a 4 blade is even LESS pitch than a 3 blade and WAY- WAY - WAY less pitch than a 2 blade.
RULE: Speed is PITCH. Vertical Speed is RPM. A 4 blade has neither. NOT in our usable engines.

Barry
Click to expand...

This is not being used on a Lycoming or RV.

Point 3 here, nonsense. There is no polite way to put this. Let's take just one data point here, one of Craig Catto's 3 blade props. It is pretty clear that they are as fast or faster than almost any commonly used 2 blade on RVs. Clearly with the forward motion of the aircraft, the air coming off the blades describes a helical path. Pitch on a 2 or 3 or 4 blade will be similar for a similar advance ratio.

The last rule- more nonsense. You can't have forward speed or vertical speed without pitch and rpm to create thrust.

Believe it or not, there are RVs and other light aircraft flying with 4 blade props and automotive engines. They work just fine.
 
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