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Cox Engine of The Month
December-2018
Dave P.'s

"RC Tee Dee 049"



PAST WINNERS
Speed Contest 2018
CEF Traveling Engine

Win This Engine!
The Traveling Prop
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World of Aviation

Three or Two Blade Propeller

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Three or Two Blade Propeller

Post  Iceberg on Tue Dec 04, 2018 6:56 am

Gentleman
I have used two and three blade props on .020.049 & .051. It's there any hard evidence to prove if the three blade pushes more air than a two blade.

I think almost the same?
Iceberg
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Re: Three or Two Blade Propeller

Post  Levent Suberk on Tue Dec 04, 2018 7:47 am

Three blade props give more thrust than two blade props, at least I know.
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Re: Three or Two Blade Propeller

Post  KariFS on Tue Dec 04, 2018 10:27 am

The more blades, the more of the crankshaft power can be transferred to air.

Look at the late model Spitfires (the fighter planes), more powerful engine => more blade surface area on the prop. To increase the blade area, one could make longer or wider blades (there is a maximum feasible blade width, generally more rpm => narrower blade) or increase the number of blades. So, when you have reached your maximum prop diameter (generally dictated by the blade tip speed or landing gear height), and still have engine power to spare, add blades Smile

An exception would be very high-rpm speed engines, where a single blade is sometimes used. Two or more blades would interfere each others’ air flow and reduce the speed. One blade always works in as calm air as possible.
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Re: Three or Two Blade Propeller

Post  rsv1cox on Tue Dec 04, 2018 6:09 pm

The WW2 F4U Corsair went from a 3 blade propeller to a 4 blade with the introduction of the F4U-4. Better performance and reducing the overall diameter helped landings and takeoffs. I have read that it allowed the landing gear to be reduced in length, but find no documentation to support this.

The F4U was the only piston powered fighter to down a MIG 15 Jet in Korea.





Happens to be one of my favorites.


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Re: Three or Two Blade Propeller

Post  Mark Boesen on Tue Dec 04, 2018 9:24 pm

Iceberg wrote:Gentleman
I have used two and three blade props on .020.049 & .051. It's there any hard evidence to prove if the three blade pushes more air than a two blade.

I think almost the same?
Iceberg

i'm not an aeronautical engineer, but i have 50 years of modeling experience and some common knowledge. I guess i'd start with a clarification of your question, a prop doesn't move a plane so much by pushing air, its does by the prop creating lift (forward) the plane goes along for the ride cause its attached. Multi blade props are designed primarily where diameter is an issue...and at this point i'll let the engineers jump in.
Most use two blade as its the most effective for cutting into the air, some speed props are only one blade.
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Re: Three or Two Blade Propeller

Post  GallopingGhostler on Tue Dec 04, 2018 10:10 pm

I'd think the practical assessment that more blades allows a smaller diameter prop is the reason for 3 or 4 blades (or more as in say, an unducted fan - remember the DC-9 study back in the late 1980's? Never gained traction because fuel prices that spiked dropped making it economically unappealing).

Thing about the 2 blade is that one can get a larger diameter to move the air past the fuselage. A smaller prop is more effective with a narrower streamlined fuselage.

It's why an ignition .60 of 80 years ago putting out 1/4 HP (i.e., Brown Jr., same HP as a modern plain bearing .15 cross scavenge (i.e., Enya .15-III TV) of the 1960's or .10 sport Schneurle, i.e., OS Max .10 FP RC) could move a 7 - 8 foot (2 meter) wingspan cabin or pylon aircraft through the air. Turning a 14 to 16 inch propeller at 7,000 RPM could move those behemoths. A .15 turning a 8 inch prop at 13,000 RPM or .10 Schneurle turning a 7 inch prop at 15,000 RPM would never cut it because those props don't churn enough air past the fuselage cross section.
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Re: Three or Two Blade Propeller

Post  rsv1cox on Wed Dec 05, 2018 7:14 am

Mark Boesen wrote:
Iceberg wrote:Gentleman
I have used two and three blade props on .020.049 & .051. It's there any hard evidence to prove if the three blade pushes more air than a two blade.

I think almost the same?
Iceberg

Most use two blade as its the most effective for cutting into the air, some speed props are only one blade.

Remember this one Mark?







Bob
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Re: Three or Two Blade Propeller

Post  GallopingGhostler on Wed Dec 05, 2018 1:39 pm

You got a rare one there, Bob. Is prop original, or was it modified after purchase? Always found those 1 bladed's to be a bit of mystery, think it was because it was only found in speed circles. I guess it was the cutting edge of taking the best advantage of technology to gain an advantage over contest competition.
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Re: Three or Two Blade Propeller

Post  Mark Boesen on Wed Dec 05, 2018 3:28 pm

grrr....lol, yes, yes i do! I'm still looking for a least a tank!!
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Re: Three or Two Blade Propeller

Post  rsv1cox on Wed Dec 05, 2018 5:10 pm

Mark Boesen wrote:grrr....lol, yes, yes i do! I'm still looking for a least a tank!!

Smile Smile.......................

Still figuring out your new avatar.  Dukes guys rolling over the General??????  Guessing here, I never watched an episode.  

Prop came with the engine George. I dunno, Mark is the guy on these.

Bob
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Re: Three or Two Blade Propeller

Post  Iceberg on Wed Dec 05, 2018 5:15 pm

They must have vibrated with single blade? I had the occasional twin blade snap one side while running. It practically vibrated my plane in half??
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Re: Three or Two Blade Propeller

Post  GallopingGhostler on Wed Dec 05, 2018 6:11 pm

No, it is balanced, there is a lead counterweight on the non-blade side.
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Re: Three or Two Blade Propeller

Post  ticomareado on Wed Dec 05, 2018 6:34 pm

Single blade props are also especially useful in full size underpowered airplanes:

https://www.youtube.com/watch?v=fqiBb98o1D8 a 37 HP (over-rated by Continental engines) J-2 Cub
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RE:Two or three blade propeller

Post  66 Malibu on Wed Dec 05, 2018 6:44 pm

Just jogged my memory of a single blade set up that I got 10 or so years ago from a mouse racer in Texas.
It has a tear drop shaped brass hub that was also a counter weight to perfectly fit the orange KK LH race props.
The KK props were not cut through the screw hole but biased to the side of the lost blade.
The prop was perfectly balance even with the one blade radically shaved and narrowed.
I'm pretty sure due the quality and fitment to the KK orange props, it may have been a KK product.
Does anyone have info or recall such a thing ?
Sorry for no pic due to my ignorance.
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RE: Three 0r Two blade propeller

Post  66 Malibu on Wed Dec 05, 2018 7:01 pm

BTW, Here's a heads up from some info I got last week from a couple of LHS regarding propeller availability. Seems there may be difficulties in getting glow props.
Fortunately , I believe Bernie and Matt have access to new production Cox sizes, which is great since, otherwise, probably no actual Cox produced props have not been minted , in what, nearly 25 years now.
Buy accordingly may be a wise move now..
Sorry for the rambling but a bad cold has me not thinking right.
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Re: Three or Two Blade Propeller

Post  Mark Boesen on Wed Dec 05, 2018 10:20 pm

rsv1cox wrote:
Mark Boesen wrote:grrr....lol, yes, yes i do! I'm still looking for a least a tank!!

Smile Smile.......................

Still figuring out your new avatar.  Dukes guys rolling over the General??????  Guessing here, I never watched an episode.  

Prop came with the engine George.  I dunno,  Mark is the guy on these.  

Bob

The Duke boys always slid over the hood in a hurry to save Daisy or foil some evil plan, wasn't a big fan of show, but saw enough that the photo just cracks me up.
The prop didn't come with engine, but its period correct. I can't tell you if the prop is factory or somebody modified it, i'd lean toward the later as I don't see a market for speed props, but who knows, maybe Bill Mohrbacher does.
I believe the brass stunt tank can with the first run of 'Hobby' version.

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Re: Three or Two Blade Propeller

Post  ticomareado on Thu Dec 06, 2018 6:22 am

If you look closely at outward blade/pitch sculpting root at hub area of prop it strongly seems that it came out of factory as a single blade prop.
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Re: Three or Two Blade Propeller

Post  Iceberg on Thu Dec 06, 2018 6:27 am

Does the single blade design have a strong front gyro effect? That is holding the front of the plane rock steady due to centrical force? If so maybe interesting for maneuverability??
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Re: Three or Two Blade Propeller

Post  rsv1cox on Thu Dec 06, 2018 6:51 am

ticomareado wrote:If you look closely at outward blade/pitch sculpting root at hub area of prop it strongly seems that it came out of factory as a single blade prop.  

Good point Victor, there is no corresponding relief there.

Bob
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Re: Three or Two Blade Propeller

Post  Mark Boesen on Thu Dec 06, 2018 1:33 pm

Iceberg wrote:Does the single blade design have a strong front gyro effect? That is holding the front of the plane rock steady due to centrical force? If so maybe interesting for maneuverability??
Iceberg

The idea of the single blade was to help cut thru clean air (due to the higher RPM) gaining some efficiency, i.e. speed.
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Re: Three or Two Blade Propeller

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