Single Blade props

[mccoy40]

As I recall, Speed planes in the past used to use a one blade prop.

With the number of props I have with only one good - what are the pros and cons of using one blade with a couterwieght versus the two blade prop?

I don't know about the rest of you but I've got PLENTY repeat PLENTY of messed up two blade props that I could convert

[RknRusty]

I think for speed planes, one blade gets cleaner air since it doesn't follow in the wake of the other blade preceding it. I don't know if that allows them to use a significantly higher pitch or not. I'm interested to see what others have to say.

Rusty

[Randy Ryan]

As I recall, Speed planes in the past used to use a one blade prop.

With the number of props I have with only one good - what are the pros and cons of using one blade with a couterwieght versus the two blade prop?

I don't know about the rest of you but I've got PLENTY repeat PLENTY of messed up two blade props that I could convert

First, safety. What ever you do make sure any counterweight engages the crankshaft.

Second, effectiveness. Not sure what you intend to do with these but my humble opinion is that they would not be much good as stunt props.

Third, balance. Misunderstood condition of single blade C'balanced props is that simply static balancing is not sufficient. A 2 bladed prop loads the crankshaft longitudinally, each blade pulling the same theoretical amount therefore placing no angular load on the crankshaft. A single blade prop will both load the crankshaft longitudinally but apply a bending moment as well not having a blade opposite to balance that loading. On rubber powered models with single blade props the counterweight is placed aft of the prop hub as a means of reducing that bending moment. This offset moves the swinging mass aft creating an opposing bending moment cancelling the blade induced moment. Now at the speed of an engine driven prop you would probably see or feel little difference in balance with the prop simply statically balances, but in flight the offset dynamic load will be applied to the motor mounts and airframe, sort of a gyrating load at the same frequency as the piston which could cause failures you would not normally see using 2, 3 or 4 bladed props.

[Randy Ryan]

I think for speed planes, one blade gets cleaner air since it doesn't follow in the wake of the other blade preceding it. I don't know if that allows them to use a significantly higher pitch or not. I'm interested to see what others have to say.

Rusty

Not sure about the speed props, but many rubber flyers preferred them because there is no opposing pitch of the opposite blade. Prop blades are never the same pitch side to side, simple manufacturing or fabrication error.

[Larry Renger]

A single blade prop is supposed tp have extra diameter to keep the blade area and engine rpm the same. As a result, the swept area is much greater.

You might run into ground clearance issues!

[Howard Rush]

As I remember, fewer blades are more efficient for model airplane props.  I don't remember whether it's because the fewer the blades, the higher the Reynolds number on the blade, or something else.  You can easily check on JavaProp or with Adkins's and Liebeck's paper.  I never used a one-blade prop for combat because of the destruction that would result when that blade broke.  For stunt, efficiency is probably not the biggest concern.  Folks lean toward more than two blades and burn the fuel or get batteries that make up for the efficiency loss.  

If you have this surfeit of props because you tend to break props, buying new props will by far be cheaper than replacing everything you break when your engine takes off with only the counterweight after you break the single blade off.  

[bob whitney]

once u get past about an 8 in prop (which would be a 4 in half) the counterweight gets very heavy and will change the balance  of the plane . i had an F2A 15 speed plane jump the dolly and brake the blade,  the plane was in piece's before we could get to it . usable RPM would probobly go up past what a stunt engine  wants to run  the 15 turns between 32,000 and 40,000 RPM with the one blade prop

[mccoy40]

Guys
Thanks for the input . I was originally looking at this as a way to re-use busted props - where one blade is fine and the second is damaged. The counter wieght idea came when I was looking at an old speed plane in a old british modelling magazine.

Busted props come in waves - sometimes I am good for a whole season on the same prop, other times I bust props like no ones business.

If I head off to our clubs flying field Props are ok -if I fly from the local high school baseball diamond i tend to break more props - it's a rougher field

[john e. holliday]

Broken props make for good home made trophies.   Best use is mixing epoxy and paint.   They can be sanded to different shapes for filets also.

[Derek Moran]

Which shoulder angel are you, MM?
Derek

[EddyR]

I conected two broken props. A 12" and a 9" and mounted it on my Pampa stunt plane at Huntersville one year. At least 8-10 people asked me how it worked. I changed it befor I flew and several told me later it seemed OK but sounded funny. I put the 12"-9"back on after I flew. Most thought I had used it.
Ed

[Jeff Traxler]

Are the props wood? Did you ever think about gluing two broken props together? End grain butt joint with plywood caps on both sides.

MM

    ASSNINE Idea!!!!!Death is iminent.What size do you use???I fly E and have BOXES of props I can send ya.An endgrain butt joint is the WEAKEST gluejoint possible.Even with theply plates you are GOING TO GET HURT.If you would like to continue seeing sunsets,grandkids,BABES don't be a MotorMoron.Get yourself some NEW props.

[Lauri Malila]

Hi

Yves Fernandez used 1-blade props in F2B some years ago. I think they were about 14" in diameter. I launched his model many times and didn't feel that my life was in great danger. I will try to find some pictures. L

[Jeff Traxler]

I'd rather send someone a prop or 2 than see them loose an eye.........or worse.Yes,I'll do it for free.A couple,not the whole box!!!!

[EddyR]

Gene Matine use to build beautiful 3 blade wood props. He used them on a FSR/45. Gene had the first 20 point plane at the NATS

[ryancompetition]

We run single blade props exclusively in F2A due to the fact that at the tip velocities we see one blade would be running in the other blade's wake.

Something to consider is that if you ever happen to damage the propeller on a single blade it is instantly out of balance and will result in catastrophic failure.

[George]

Cuts your chances of breaking a prop on landing in half.   

George

[RknRusty]

We run single blade props exclusively in F2A due to the fact that at the tip velocities we see one blade would be running in the other blade's wake....

What about pitch, do you run higher pitch with one blade, or not? I can imagine an argument for either answer, since for a given pitch, a single blade is able to grab more clean air, but then the load on the engine is  probably higher than two blades.
Rusty

[Randy Cuberly]

Cuts your chances of breaking a prop on landing in half.   

George

Haven't you ever heard of Murphy's law of prop rotation...the prop will always stop with one blade toward the ground...number of blades notwithstanding

Besides most props are broken on take off when it's spinning! 

Randy Cuberly

[Lauri Malila]

We run single blade props exclusively in F2A..

This one is competitive with 2 blades

Well, not exactly F2A but funny anyway. L

[ryancompetition]

"What about pitch, do you run higher pitch with one blade, or not?"

We don't run equivalent props with two blades in the event so really can't answer your question. My guess if I were to go from a two bladed prop to a single blade would be to look at my desired airspeed/rpm target and then set pitch to that. Many good calculators out there and experts to help. Afterwards, I'd look into diameters/area for load/preheating but this is probably something a person could spend an eternity on.

I know Willoughby/Oge ran a single blade on their goodyear for racing so maybe contacting Bob would be a good start since he could provide info on what his single blade dimensions are in comparison to say an equivalent G3 prop.

I think for a specific stunt application, as mentioned by others the ground clearance would become an issue very quickly. I'd love to see someone make it work though even if just for entertainment.

[Joe Just]

Todd, please check you PM.
Joe

[Howard Rush]

I'd love to see someone make it work though even if just for entertainment.

The entertainment would come when the blade breaks.  I'd enjoy seeing that, too. 

[Mike Lauerman]

Randy Ryan, I never thought to consider the thrust of the one blade inciting bending of the crank...but was always leery of that weight parting ways with the blade.

DGT!  (damn good thread!)

[Mike Keville]

Never had any experience with 1-blade props in CL, but I can remember an interesting time in Free Flight - specifically, the Coupe d' Hiver event (today F1G).  This was back in the '70s...the days of stick 'n' tissue...when the BOM rule was still in effect, and before today's mega-buck 'bought' designs.

Had a fairly conventional design from someone's plans that performed, well, so-so.  Then I switched to a one-blade prop - a folder, of course - simply an airfoil'd length of 1/8" balsa wrapped around a large soda bottle at 15 degrees.

Same power - 6 strands of 1/4" Pirelli rubber - and suddenly the climb altitude seemed to nearly double.  The little thing reached amazing heights (and also managed to find some decent thermals - which quickly led to winning two major So. Cal. annual FF events).

Not sure what, if anything, this has to do with your original question - although I can assure you that a one-bladed prop definitely made my little 'Coupe' come alive!

[RknRusty]

Doc said it best. Use the broken props for mixing epoxy, stirring paint, spreading filler, etc or make toothpicks out of them. Better yet, toss them into the trash. Wood, nylon, carbon fiber, fiberglass, unobtainium, whatever.   Be safe, not sorry.

I glue the best looking ones, usually the woodys, back together and prop them in the panes of one of my shop windows as a decoration for those outside looking in. I write "Do NOT use" on the backside of the blades.
Rusty

[ryancompetition]

"The entertainment would come when the blade breaks.  I'd enjoy seeing that, too."

I had that happen at a team trials on a dolly accident, pretty much turned itself back into a kit.

Will said he's heard or seen of it happening during a flight. I think he described it as becoming "a cloud".
A stunt ship with a broken single blade prop running in-flight would be...uh...entertaining!

[George]

I conected two broken props. A 12" and a 9" and mounted it on my Pampa stunt plane at Huntersville one year. At least 8-10 people asked me how it worked. I changed it before I flew and several told me later it seemed OK but sounded funny. I put the 12"-9"back on after I flew. Most thought I had used it.
Ed

 
Now THAT is funny!

George

[bob whitney]

a one plade prop would probly take out a bushing in a hurry, bearing engines only

[Dan McEntee]

    A local guy here in our club had a blade come off a Master Airscrew prop that was on a Brodak .40 in a Fancherized Twister he had just built. He's a combat flyer of many years experience and had himself a good flying model until it threw the blade and it shook the nose off the airplane! I think he ended up with a good wing and tail, no damage to the engine, and a good story to tell. It was a new Master Airscrew prop also, I believe.
   Type at you later,
   Dan McEntee

[EddyR]

Bill Rich and I were at out practice field many years ago and he had a new plane with less than six flights on it. One blade came off and the ST/60 shook the nose off in one or two seconds. There was not a lot left of the body.   I have seen 1/2A motors run with one blade broken off. They run until the motor vibrates off with no damage to the motor
Ed

[john e. holliday]

Wait until you see a Class II Carrier plane shed a blade.   It was Clayton Dunham at St Louis way back when the Rossi was coming into the competition.  He said he was on third lap when the plane exploded, in his words.   Said pieces were everywhere.  I had a blade come apart on the engine test stand one day while testing a K&B 5.8.   Glad I was behind it when I advanced the throttle to full open.   The engine was on the ground next the house in a split second.   

[Steve Helmick]

Ol' Dad was stationed at Wright Field before WW2 and said that a couple of times they had inventors bring single-bladed props to them to test, claiming improved performance. None panned out, he said it was because they only really balanced at one rpm, not at all rpms used during a flight.

I know (just) enough about F2A to know that there are two major benefits...less prop damage on landing (no LG) and the pitch is adjusted simply with a tapered shim under the prop. In F1C, before the geared engines, most ran 2 blade folding props, to improve the glide and reduce/eliminate landing damage. Oddly, the blades had no forward stops, and relied on centrifugal force to keep the blades running "out there". When they went to geared engines, the (much bigger) props caused folding interferences with the wing/pylon and many went to 3 blade props to shorten the blades and reduce/eliminate the problem. FWIW, I tried a single bladed prop on an F1C model with a ST G.15. Didn't work worth a darn. Later, another F1C model with a Cox Conquest (tuned by our own Ron Young), with a 2 bladed prop. It crashed with much more velocity.    I decided that I didn't build fast enough to fly F1C.

Unlike Unkle Mikey, I've seen many single bladed OT rubber models fly very badly, with the nose of the model following an orbit as the propeller rotated...not very efficient. Most these were built and flown by pretty competent and experienced fliers, so I expect Mikey found a good prop/rubber combination that balanced well enough to stop a lot of that chit. I don't recall seeing anybody locally flying modern FF designs with single bladed props.   Steve

[Randy Cuberly]

Well since we're telling about broken prop experiences I'll add mine.  About 1986 or so when I still lived in Phoenix I built a stilletto...nice finish and very pretty.  It lasted only two flights.  On the second flight, off of a grass field the prop (or at least one side of it) contacted something a doggy had left in the flight path...yes that's right a dog turd...and it shed one blade cleanly at the spinner from the 12X5 wooden prop.  Before I could get it back on the ground the the fuselage disintegrated and the engine flew on about another 50 yards or so...thankfully no one was around and only the airplane suffered a fatality...vibration is a nasty destructive thing.  The ST46 sounded like it hit about 25,000 before the rod broke and trashed the piston cylinder and crankcase.  I still have the head as a token!
I built another Stilletto and still have it.  Great flying airplane.

Randy Cuberly

[Ted Fancher]

One of the experimentally prodigious Adamisin boys ran a single blade prop on a stunter at a Nats many moons ago.  I think it was Archie, but don't quote me.  It may have also been on his "tri-plane" stunter that sported both a conventional tail and a canard with  a (don't know what to call what would be called a flap on a wing or an elevator on a stab; a canardlevator??) movable surface working, of course, in the same direction as the flaps.  Although it didn't win the Nats, it appeared to fly just fine with both the spinning one blader and the "extra" pitch axis generator!

Given Big Art's penchant for launching the boys with the Adamisin .35S's so rich they were barely running (so the pilot had to "work" according to Denny A.) the diameter probably wasn't much of a consideration.  Seems like my memory's eyeball sees it as just half of a 10 or 11" X 6 pitch EW.

Ted

[Chris Wilson]

http://www.supercoolprops.com/articles/propdocf2a.php

"The aerodynamics of F2A propellers I covered in a previous issue. To recap briefly, F2A props turn such staggering RPM and speeds they must be single bladed, with high subsonic tip speeds. The tip airfoil sections must be very thin, preferably using a modern transonic cambered section such as ARA-D. Two blades cannot be used, as the chord is then too low to provide any degree of profile efficiency."

[mccoy40]

Wow - great thread.

Jeff thanks for the offer of the prop blades. I will pass for now - because I need a reason to go to the hobby shop (another interesting thread about my wife)

I never reuse broken or modify my prop blades. I once tried to make a four blade prop but the experience taught me that my efforts were better spent elsewhere. I never used that prop.

OOPS I do modify my props - somewhat - I check them for balance and balance them by either painting the light side or sanding a little of the back of the heavy side

What started the question was the fact that one day I went out to fly and it seemed like I broke a prop just about every flight. some were jusy minor damage but still not usable. I thought it was sad that 3-4 bucks of a broken blade was wasted.

BUT golfers go thru the same thing every time they lose a ball in the Water on the course. OH well.

[Randy Cuberly]

Wow - great thread.

Out take...
What started the question was the fact that one day I went out to fly and it seemed like I broke a prop just about every flight. some were jusy minor damage but still not usable. I thought it was sad that 3-4 bucks of a broken blade was wasted.

BUT golfers go thru the same thing every time they lose a ball in the Water on the course. OH well.

HHmmmm...Just wait till you start using $50 Carbon Three Blades.  That gives you the honest reason to cry...
I have a wall full of them over my work bench...most missing one or more blades...

Randy Cuberly

[Norm Faith Jr.]

Several years ago, I mentioned the use of a single blade propeller used ("Flying News" article, circa 1958, about an experimental use of this system) on a Super Marine racer to a "pilot, customer" of mine. BTW he held an engineering degree. He went on to inform me that I was full of...anyway you get the idea...and that from a "physics point" it was not practical.
I went on to tell him that we had been using this system on models for years. He was still skeptical. The "internet" was new, but some how I got a response from a curator of an aviation museum in the UK. He remembered reading he same article, but could not find it. He did send me some information that confirmed the use of single blade props. My customer? Well...let's say he doesn't bring the subject up much. 
'

[Lauri Malila]

I use a butt joint & slow epoxy, then cut a groove and fill it with some carbon. Quick & easy!

Lauri

[RknRusty]

I use a butt joint & slow epoxy, then cut a groove and fill it with some carbon. Quick & easy!

Lauri

Nice work. Is that made from 2-blade prop blades?
Rusty

[Igor Burger]

I would guees that it is made from single blade blades :- )))) ... no kidding, siple blades are done on purpose, not cut from finished prop

however I have seen also metal rings for connecting (Havran props used by Richie K.) ... unfortunatelly I have seen also prop dismounted in air ... I think carbon is better solution

[Lauri Malila]

Igor is right, they are made from 3 blades
I have also used dural rings, and Kevlar too but I think that carbon is best.
I have never had any problems with them, actually the other end of blade gets more abuse
But, I know that there are many ways to screw up if you don't know exactly what you are doing. For example, it's allways a surprise how much hard end grain maple impregnates high viscosity epoxy. If you join the parts before the impregnation has stopped it's not going to be strong enough.
I'm interested in making my props in carbon fiber but it's very difficult to have them in same weight as wooden ones. Maybe hollow blades, or balsa filled.. L

[Igor Burger]

Yes, there are many ways to do it wrong :- )))

that model lost blade by blade during flight ... it is several years ago, but I think it worked at high rpm even without all of them :- )))

I note that the prop washer was smaller then the ring, that could be also one of reasons

[Lauri Malila]

Of course it can be done from 2-blade props, that's the easiest source. My blades are cnc-cut by Yuriy so we can do it how we want. Sometimes I use individual blades, sometimes 2-blade props to start from.
Igor's case seems to be caused by the too small washer; it takes very little shear load to crack the wood like that.
I have found out that epoxy goes about 10mm deep into the wood, that is good for the compression strenght of hub. Also, before inserting the carbon in groove I make about a million pinholes to the bottom and sides of the groove. That's good for strenght as it creates a gradient layer between the hard carbon and softer wood.
Also, it's good to use a slightly elastic epoxy, like Loctite Hysol, or other slow epoxy with slightly "too" much hardener. L

[Lauri Malila]

Sure it's possible but is it really worth it? Also, I think that safety rules don't allow you to repair propellers, so we are in gray area with this..
Anyway, the grooves in my props are 2mm deep. L

[Lauri Malila]

Aha.
But you can change the pitch just by heating the root of blade & tweaking. L

[Keith Renecle]

Loren Nell in New Zealand has made a number of 3-bladers from XOAR wood props. He uses the method from Barry Robinson in the UK. The make a jig to align everything properly and cut a 3 mm groove in the hub for a plywood ring. Each blade then has 2 carbon rod pins that go through the hub and ring and it's all epoxied together. Many of Barry's props are in use and it seems to work well.

Keith R

[Norm Faith Jr.]

Several years ago, ( in a casual conversation with a professional pilot) I
brought up the subject of a"Super Marine Float Racer," (circa 1930's) that had
experimented with a single blade propeller. ( 1950's magazine article) I was
informed, by this pilot, in so many words, "to be delusional." The internet was
quite young then and there were not many aviation sites at the time. I did post
a request to one of the existing sites for information on the subject. I was
contacted by a gentleman living in the UK. He had seen the same subject that I
had read, as a boy. He worked as a curator in an aviation museum in the UK. He
could not find information on the Super Marine, But he did send me a copy of an
article that covered the attached photo. The article was published in a Pre-WWII
aviation magazine. My professional pilot friend? He never doubted a thing I've
told him since.
BTW: I told him that model airplanes had been using single blade propellers
"forever."
Norm

[Bruce Shipp]

they should work in scale...