Im Just wondering if anybody knows what difference a 2 bladed prop will have compared to a 3 bladed prop on a ho (310)
cruise speed?
t/o distance?
interior noise?
thank-you kindly,
TM
Navajo (310) question
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duramaxguy
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PunkStarStudios
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Re: Navajo (310) question
Well.. I can tell you the theoretical and "gut reaction" difference (I've only flown a 3 blade Navajo).
The more blades are the less efficient they are (as there is more backwash for the following blade to cut through).
It would be quieter as the 3 blades would be generally shorter than a 2 blade. The noise is generated by the speed of the blade tip - so shorter diameter, lessor speed on the outside, less noise.
The more blades are the less efficient they are (as there is more backwash for the following blade to cut through).
It would be quieter as the 3 blades would be generally shorter than a 2 blade. The noise is generated by the speed of the blade tip - so shorter diameter, lessor speed on the outside, less noise.
Re: Navajo (310) question
I think it has 3 blades to clear the gravel!
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GoinNowhereFast
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Re: Navajo (310) question
I can give some generalizations:
3 blades is quieter [reason already covered]
2 blade is faster in cruise because there is less propellor blade area to spin through the air
2 blade will generally take off shorter because of a larger diameter
HOWEVER, 310hp is a lot of power to put through 2 propellor blades. The diameter required to hold back that power would likely cause the tips to go supersonic and just wastefully beat the air into unwanted noise. [Think Cessna 185 on floats]. I'd be willing to bet that a 3 blade prop will give the best performance for 310hp.
I'm not an aeronautical engineer, so don't take this as gospel.
3 blades is quieter [reason already covered]
2 blade is faster in cruise because there is less propellor blade area to spin through the air
2 blade will generally take off shorter because of a larger diameter
HOWEVER, 310hp is a lot of power to put through 2 propellor blades. The diameter required to hold back that power would likely cause the tips to go supersonic and just wastefully beat the air into unwanted noise. [Think Cessna 185 on floats]. I'd be willing to bet that a 3 blade prop will give the best performance for 310hp.
I'm not an aeronautical engineer, so don't take this as gospel.
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wallypilot
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Re: Navajo (310) question
I have flown both types, although it was a fair number of years ago now. Theoretically, what the above poster said is mostly right.
I definitely noticed better take off performance.
Cruise speed suffered, however with the 2 blades. While an above poster mentioned that cruise speed should be higher with the 2 blades due to reduced drag of the less surface area, in fact with greater forward speed, the 3 blades have more clean air to bite at then at low speeds during initial take off roll. I think the 3 blade props produce more thrust at higher forward speeds than the 2 blade. It was noticeable, maybe 5 knots difference. However, this may have been due to other factors, as every airplane is different.
If one was to go to a 4 blade, I believe that would then be enough to make cruise speed suffer. but the 3 blade is in fact a great cruise prop. The top of the curve, so to speak.
The cabin noise is not doubt higher with 2 blades. But not extremely.
2 blades will take more FOD damage on unpaved surfaces.
If anyone has different experiences, let's hear 'em. But that's what I noticed.
I definitely noticed better take off performance.
Cruise speed suffered, however with the 2 blades. While an above poster mentioned that cruise speed should be higher with the 2 blades due to reduced drag of the less surface area, in fact with greater forward speed, the 3 blades have more clean air to bite at then at low speeds during initial take off roll. I think the 3 blade props produce more thrust at higher forward speeds than the 2 blade. It was noticeable, maybe 5 knots difference. However, this may have been due to other factors, as every airplane is different.
If one was to go to a 4 blade, I believe that would then be enough to make cruise speed suffer. but the 3 blade is in fact a great cruise prop. The top of the curve, so to speak.
The cabin noise is not doubt higher with 2 blades. But not extremely.
2 blades will take more FOD damage on unpaved surfaces.
If anyone has different experiences, let's hear 'em. But that's what I noticed.
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oldncold
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Re: Navajo (310) question
One might consider engine out 2vs 3 blades . Say you have to feather an engine, in theory the 2 blade would have less frontal drag vs the 3blade. Even though the blades are feathered in both cases. Ergo potentially better single engine climb performance, all other things being equal. it may be insignificant 99%of the time until you have to depart a short strip on a warm day. but something none the less to consider. 
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Frank Gallagher
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Re: Navajo (310) question
Another factor to keep in mind is cost.
From my experience 3 blade props are actually cheaper compared to the 2 blade variety due to supply and demand. Most 310's have been phased to the three blade design and 2 blade parts can be hard to come by thus the 2 blade props can be more expensive. From what I've seen the price difference can be $10,000
From my experience 3 blade props are actually cheaper compared to the 2 blade variety due to supply and demand. Most 310's have been phased to the three blade design and 2 blade parts can be hard to come by thus the 2 blade props can be more expensive. From what I've seen the price difference can be $10,000
Re: Navajo (310) question
Manufacturers of 3 blade props want to sell them.
In general they get you out of the hole faster on takeoff. What the manufacturers try to do is make the blade more efficient and work in closer to the hub with newer 3 blade designs. The normal "penalty" of the third blade is made up for, by aerodynamic improvements in the blade shank or root area. What it usually looks like in newer 3 blades is a working "blade" that comes closer to the hub than the 40 yr old 2 blade it replaces. Often the old 2 blades had rather stumpy looking root areas, rather cylindrical, than blade like.
Three blades sound nice, look sexy, and often improve gravel clearance. They should cost more to overhaul as there are 3 of most things that used to be 2. See note above about older prop parts mind you.
In general they get you out of the hole faster on takeoff. What the manufacturers try to do is make the blade more efficient and work in closer to the hub with newer 3 blade designs. The normal "penalty" of the third blade is made up for, by aerodynamic improvements in the blade shank or root area. What it usually looks like in newer 3 blades is a working "blade" that comes closer to the hub than the 40 yr old 2 blade it replaces. Often the old 2 blades had rather stumpy looking root areas, rather cylindrical, than blade like.
Three blades sound nice, look sexy, and often improve gravel clearance. They should cost more to overhaul as there are 3 of most things that used to be 2. See note above about older prop parts mind you.
