Propellers for Idiots

One of the advantages listed for converting to the 3 blade Black Mac prop was:
"Sex appeal"
Haven't you noticed how the women just run up to the 3 blade props and give them a big hug? Too bad they don't do the same for the pilot.
I did not see a reduction in speed with the 3 blade at least not measurable. The sound is more mellow which I like.
 
Of course, the decision will be based upon desired performance and the best balance of power you can get, but this issue is a lot like selecting the prop for a boat.. a lot of factors here.. pitch, diameter, available power, RPMS desired, etc.
If you keep the same pitch on a prop, and switch from a 2-blade to 3-blade, you will turn less RPMS, given only a certain amount of power available.. Reason being? time how long it takes to cut a slice of cheese twice, versus three times.. then try to cut the cheese 3 times in the amount it takes to cut two slices.. See? more effort required.. if you only have enough "effort" available, you have to change how "thin" (pitch) the knife is.. (analogous to camber/pitch vs drag, etc.)
A prop with more blades can accelerate faster, although there is a limit applied with only so much power.. plus theres more drag.. hence, takeoff performance being improved with 3-4 blade props.. Its a big balancing act when applied properly.. but I dont think i would want a 3 blade with anything less that 300-350 hp..
 
I'm surprised that nobody has posted one of these, in keeping with the title of the thread
0511-0810-1304-1527_Cartoon_of_a_Boy_Wearing_a_Beanie_Hat_with_a_Propeller_clipart_image.jpg
 
I have one of those 3 blade props. When I purchased I was told the previous owner was inverted and scraped the ground, :hairraise: Hence, the 3 blades are bent at the tips. They seem to work as I am able to take off.......:D

I do not notice any sound difference from a regular 3 blade prop.
 
Does anyone have the 411 on what the difference is between a "standard" propeller and a scimitar type? Does the scimitar give you even more speed at the cost of climb perfomance??
 
Capt.Crash'n'Burn said:
Does anyone have the 411 on what the difference is between a "standard" propeller and a scimitar type? Does the scimitar give you even more speed at the cost of climb perfomance??
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The sweep on the leading edge of the scimitar blade is the defining characteristic. It gives the propeller airfoil the same advantages that a swept wing does for high speed aircraft.

This sweep helps reduce drag/increase efficiency.

Why would it cost climb performance? Particularly in a constant speed prop..
 
gkainz said:
I'm surprised that nobody has posted one of these, in keeping with the title of the thread
0511-0810-1304-1527_Cartoon_of_a_Boy_Wearing_a_Beanie_Hat_with_a_Propeller_clipart_image.jpg
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gprellwitz said:
We were waiting for Scott to do it! :)
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I was finally getting a round tuit (see pic below) this morning and was reviewing the thread to see if it had been done before.

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tonycondon said:
yes plus with fewer blades each blade encounters cleaner air
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These newer fancier prop design with the curved blades seem to us the more blades are better approach. Id there something about the blade design that helps them to avoid this general limitation of cleaner air that we see with standard prop blades?

This is the type of NASA efficient prop design I am thinking of.

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They seem to think more is better but I can also see that there is much more disturb air as you said. I wonder if there is something about the blade design that disturbs the air in a manner that is less random?
 

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gkainz said:
On the Hawkeye upgrade pictured above, the 6 8 (doh) blade scimitar upgrade was selected for takeoff performance improvement as the aircraft weight continued to increase with added equipment. The B model in the first photo could deck launch without catapult, lose an engine and still climb away at max gross, IIRC (albeit very slowly). I haven't heard/read what performance the new props restored, nor am I sure about how much max gross weight has increased, but it was significant, I understand.
In this plane's mission, cruise and/or top speed are not important factors; takeoff performance and time on station are.
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The big difference between the E2B and the E2D was the D has the AE2100 engine, which can develop 11,000 horse power, the 4 blade Hamilton Standard prop could not absorb that much energy.

Props must be designed to absorb the engine horse power at an RPM that does not allow the tips to exceed the speed of sound.

the AE 2100 runs the prop at 1020 +or- 2 RPM, controlled by the PCU on the back of the reduction gearbox.

the C-130s also have this engine/prop setup.
 
Doggtyred said:
The sweep on the leading edge of the scimitar blade is the defining characteristic. It gives the propeller airfoil the same advantages that a swept wing does for high speed aircraft.

This sweep helps reduce drag/increase efficiency.

Why would it cost climb performance? Particularly in a constant speed prop..
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Then why aren't scimitar props more common? Do straight blades have other advantages?
 
flyingcheesehead said:
I think the scimitar prop designs are relatively new, and the cost of certifying STC's has led to slow adoption in older designs.
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That whole issue can be problematic. Take, for example, the Hartzell Q-tip propellers. I have no idea if they're any better or not, but the only planes that have them as far as I can tell are the RAM and Colemill conversions that were certified with them. I don't know of any factory planes that do.

Since the conversions were certified with the props, people are bound to keep them. A friend of mine recently had to get them on his T310R when he got the RAM engines. He's not thrilled with them, and I can't say that I would be, either.
 
Ted DuPuis said:
That whole issue can be problematic. Take, for example, the Hartzell Q-tip propellers. I have no idea if they're any better or not, but the only planes that have them as far as I can tell are the RAM and Colemill conversions that were certified with them. I don't know of any factory planes that do.

Since the conversions were certified with the props, people are bound to keep them. A friend of mine recently had to get them on his T310R when he got the RAM engines. He's not thrilled with them, and I can't say that I would be, either.
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I think Ted brings up some very good points...

When a company gets a conversion certified it locks the owner of that conversion to those EXACT components. Since there is no way of altering that set up to prove or disprove the claims of increased performance the conversion lives on with no way to challange its claims. And....

If you need replacement parts you will pay dearly for them as the production numbers are so low. :eek::cryin:

Ya pays your money and takes your chances.....

IMHO

Ben.
 
flyingcheesehead said:
I think the scimitar prop designs are relatively new, and the cost of certifying STC's has led to slow adoption in older designs.
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What about in the homebuilt/experimental market??

You'd think by now that somemone would've used their Lancair 360 to demonstrate the difference between the 2 designs. :-/
 
Capt.Crash'n'Burn said:
Then why aren't scimitar props more common? Do straight blades have other advantages?
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I can see where there may be structural issues with a bent blade that you don't find with a straight blade. "centrifugal force" (yes, I know it's a pseudo force) will try to straighten the blades.
 
Capt. Geoffrey Thorpe said:
I can see where there may be structural issues with a bent blade that you don't find with a straight blade. "centrifugal force" (yes, I know it's a pseudo force) will try to straighten the blades.
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Then why make the 2 different blade styles? isn't one better in some ways and the other better in different ways?
 
Capt. Geoffrey Thorpe said:
I can see where there may be structural issues with a bent blade that you don't find with a straight blade. "centrifugal force" (yes, I know it's a pseudo force) will try to straighten the blades.
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I think the issue is getting confused here between Scimitar and Q-tip props - Ted brought up the Q-tips after my hypothesis on certification, while the question was about scimitar props, which are "straight" in that they don't bend, they just have a curved leading edge.

For those who want to know what the **** we're talking about -

Q-tip prop (well, just the tip):
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Scimitar prop:
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The end of the Q-tip prop is bent roughly 90º and functions somewhat like a winglet does.

The scimitar prop has a curved leading edge, so that the leading edge sweep is increased at the parts of the prop that travel faster.
 

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^^^ thanks for the clarification.

I'm still not understanding the advantages/disadvantages of each style though.
 
Capt.Crash'n'Burn said:
^^^ thanks for the clarification.

I'm still not understanding the advantages/disadvantages of each style though.
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I can't speak to the disadvantages

My limited understanding is that the q-tip prop tip acts like winglets in that air from the high pressure side of the blade (think bottom of a wing) doesn't flow as easily to the low pressure side; less energy is wasted in a tip vortex.

The scimatar propeller shap acts like a swept wing in those parts of the propeller blade moving at high speed through the air (near the tips).

I'm just summarizing other posts in this thread.
 
flyingcheesehead said:
I think the issue is getting confused here between Scimitar and Q-tip props - Ted brought up the Q-tips after my hypothesis on certification, while the question was about scimitar props, which are "straight" in that they don't bend, they just have a curved leading edge.

[snip]
The scimitar prop has a curved leading edge, so that the leading edge sweep is increased at the parts of the prop that travel faster.
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I've seen props that have a lot more "bend". There is a photo earlier in this thread.

But as for why one over the other - probably some chief engineer likes one style and another chief engineer likes the other.

At least that's how it works in the auto industry.
 
Capt. Geoffrey Thorpe said:
I've seen props that have a lot more "bend". There is a photo earlier in this thread.

But as for why one over the other - probably some chief engineer likes one style and another chief engineer likes the other.

At least that's how it works in the auto industry.
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So in other words, you'd have to ask an engineer at Hartzel to get an answer?
 
What would be really interesting is to see if a combination Q-tip scimitar prop would be more efficient.
 
Capt. Geoffrey Thorpe said:
And, depending on who you ask, you will get different answers :wink2:

Engineering is all about tradeoffs and compromises (and doing what the boss asks for).
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Yes, and the scimitar vs straight props are making 2 different types of comprimises, that SHOULD result in 2 different performing props.

It would be nice to see where someone did a side by side comparison.
 
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