Scimatar Prop

[querk1a1]

Anyone ever considered experimenting with a 3, 4, 5, or 6 bladed scimatar prop? What about it being a constant speed prop? or a fixed pitch? Are there any advantages to having more than three blades? at least in our applications? I noticed there hasn't been much activity on this subject so I hope to start some discussion. If you read this post please post a reply and let me know what you think, even if its not long thanks

 

-Jonathan

Plans # 1052

[Marc Zeitlin]

Anyone ever considered experimenting with a 3, 4, 5, or 6 bladed scimatar prop?.... If you read this post please post a reply and let me know what you think, even if its not long thanks...

What is it you hope to achieve?

[querk1a1]

The hope is to see a perfomance gain like those seen when We ( the Air Force ) switched from the 4 bladed C-130 props to the six bladed curved props being used on the J models. "The propeller has a swept blade design, which provides rapid take off and climb performance together with low noise levels." I think that maybe with this type of prop and a delta hawk engine you could really push the envelope of what the Cozy do. I know Catto Props have a slight curve to them I am just feeling this out right now.

 

-Jonathan

[deronjthomas]

( the Air Force ) switched from the 4 bladed C-130 props to the six bladed curved props being used on the J models. "The propeller has a swept blade design, which provides rapid take off and climb performance

 

-Jonathan

This is true, but the blades where much longer, larger, and engine put out a lot more HP. If I’m not mistaken, the Hell Cat put out about 1600+ HP. I don't know if a 200hp engine will do. I do know that length of the blades will determine the number of blades you can put on a prop with out losing efficiency. Some one with an engineering degree should probably chime in here.

[querk1a1]

True the engines are better on the new C-130's but if thats a major factor in the scimatar prop saga I'll venture to say it....... I'm planning on a Delthawk, so there will be more power availible to the prop rather than being lost to PA, especially at altitude and curving the blades can mean they can be longer or spun at a higher speed due to tip speed be lowered if they are shorter than a "placebo prop" configuration, ( which I dont think will make that much difference in this platform regardless of power plant ). Has it been determined that three bladed props max out the effeciency vs. design/power graph?

-Jonathan

#1052

[Norm M]

Prop length on the Cozy is limited by the geometry associated with the rear gear and position of the prop. According to the theory behind props, the larger the number of blades, the poorer the efficiency. Most people are flying three bladed props because they are smoother. Plus they look nice.

 

I seem to remember a discussion about the flexibility of the blades that would be required for a scimitar prop to flex, and that this actually worked against you. But I could be worng about that.

 

-Norm

[Don Woodward]

Hi All

 

Just a question, How about 2 , 2 bladed props counter rotating, using a gear box to do this.???

[deronjthomas]

Hi All

 

Just a question, How about 2 , 2 bladed props counter rotating, using a gear box to do this.???

I don't know of anyone who has done this, but this guy http://www.infortel.com/cozy/ put in two Suzuki 1600cc water cooled 100HP each. With TWO 3-blade coaxial counter-rotating (independent) pusher.

[Kent]

Scimatar blades increases parasitic drag over a strait blade.  Reason:  When an airfoil is producing lift the air not only flow chordwise, it also starts to move outboard.  This causes the air to increase it's travel from LE to TE.  A swept forward blade is more efficient than strait or sweep back.  I have only seen the Germans experiment with this technology.  Their Hanza jet had forward sweep wings.  one of our X planes has forward sweep wings, I think it was the X-35, don't remember now.  I saw a German ultralight with a forward swept prop blades, fixed pitch.  This makes sense because it makes the air flowing over the foil pass across in the shortest path, less parasitic drag.  Also as you all know, high aspect ratio wings (lifting foils) are more efficient than mattress wings. That is why sailplanes have high aspect ration wings. 

 

Same with propeller blades but that gets to be a problem with prop blades because of mechanical reasons.  And for the prop blade the airspeed is different for every station along the blade.  Consequently of course, the twist in the blade has to be different for every station along the blade.

 

It would be nice if the twist could be made variable like the pitch (Bata) can be.  But that is not practical.  Of the three parameters that a prop has to acomodate, Bata or pitch, RPM and AofA (Angle of Attack) only two of the three can be made variable.  Twist is fixed.  

 

The reason I bring up twist is because when you crunch the numbers the numbers say that for all the variable rpms, the variable airspeeds, the variable angles of attack, it would be nice of you had control over the twist of each blade.  But so far we can't do that.

 

If we could train the termites, in wood blades, to hold hands and sway to the right tune then we could make a prop blade a little more efficient.

 

If anyone wants to crunch some numbers, write me an e-mail and I will give you some math formulas that will put a twist in your brain.

 

BTW as some of you know, we took the C-90 powered V-EZ to Kanab for the fly in.  We didn't wind any race.  We don't run our engine up in the 3K+ rpm zone.  But did anyone notice how short the takeoff run was?