Ralphbf

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Everything I've read says a 3 bladed prop is less effecent than a 2 bladed prop.

Except on this forum I've read that a 3 bladed prop works well.

Does anyone know at what rpm the 3 bladed prop work better?

How many people perfer the 3 over the 2 blade design?

To make matters more confusing, APC makes 4 bladed props for pattern planes.

What are your basic thought on the matter?


Ralph

Hobbsy

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Ralph, I use three blades exclusively and have come to the conclusion that at Diesel and fourstroke rpm there is no discernible loss of efficiency, plus, using a three blade of the same diameter and pitch is an excellent way to load a converted glow engine about right. This Maloney 125 turned a 15x8 at 7,200 rpm on gas and the 15x8 three blade at 7,050 as a Diesel.

dennis

My Feedback: (90)

Hobbsy,
If you can latch on to one of the tartan 1.37 singles with the ST 60 carb on it, at a good price, do so. You will have in your posession the finest made over built smoothest running ,in either direction as it's reed valved, motors in your collection. While we used 18 inch wood mostly, we also used the Graupner 16/8 3 blade and found that this was an ideal companion to the motor.
A dieselized Tartan single is about a s great as it gets unless you've had a twin set up as a diesel then your in a whole new world of power. You will never live long enough to wear it out.
Dennis

Seems like I always have to add something to these posts. The Tartan was used a lot on a 90 inch Road Runner, which is a real building job as Frank Gonzalus must have had access to a lot of very reasonably priced great wood. Plane weighed about 13.5 lbs and was flown extensively at a lot of fun flies in the late 80's into the 90's. I do know that Bob Davis has the only surviving footage of that plane flying and the sundancers and a whole bunch of other stuff that I shot for him back then. Shame that I don't have the stuff anymore . It would be fun to see the great old girls flying again. They gave me a lot of years of great service. None were ever wrecked but most wore out or got sold to make room for a new project. You know how that goes.
Dennis

Hobbsy

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Bob still has some Tartan heads, he found them when he was looking for a head for the Maloney. Thanks for that Dennis, I'll be watching for one.

Dan Vincent

Ralph,

For me, a three-blade prop is used when you have a fairly slow-revving engine. A couple of models that come to mind are fighter plane types with large engine and short landing gear, or a flying boat. In both instances a shorter prop arc is a benefit. A high wing pusher model can also keep the engine nacelle to fuselage measurement a little more compact.

The only time I would'nt use a multi-blade prop is if it were on a high-revving glo engine but they are usually more expensive.

Ralphbf

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Ok Dan, what are you calling "A fairly slow-revving engine".

What rpm range are we talking?

Dan Vincent

Ralph,

There is no hard & fast rule. I would say somewhere around 15,000 or less. It all depends on how much pitch and diameter, does the engine overheat or sound stressed. Those Large scale chainsaw size engines turn a lot slower so there is no problem at all.

The closest thing that comes to mind is a four blade boat prop will often cavitate (like a slipping clutch) while a two-blade will still get a bite. If you go to a boat race and see a boat make a quick turn and just sit there while the engine screams and the driver has to back off on the throttle to get it hooked up again.

There is so much experience here I can guarantee you someone has tried the combination you come up with.

Ralphbf

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Actually I'm working on 2 conversions.

1) Super Tigre 51 on a Sr. Kadet float plane.
It came with a tired K&B 61. I've never seen it in the air but thiught it would be a good combination.

2) Super Tigre 3250. I bought this with a plane in mind but the plane was sold out from under me.

I ran it last week with less that great results 22x10 APC prop

Hobbsy

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Dennis, my LHS thinks he has one of the Tartan singles NIB, he thinks it has a Walbro carb and Ignition. I'll know Monday.

dennis

My Feedback: (90)

Hobbsy, Thats not so good. It's the real expensive model that you will have to strip off the ignition equipment and the carb won't work at all. You'll have to buy the reedvalve plate that took the ST 60 carb and that could be a bit of trouble since Kline seems to be tho only source of parts for the motors in this country The only way to buy that motor is if it's really cheap and you can sell the surplus parts off to fund the parts you need. Of course I'll look and see what I have as I have a fairly large store of parts that I haven't looked at in quite awhile. I also have 5 of the singles 2 are Super tartans, yes there are 2 varieties of singles and 2 varieties of twins, atandard and super. The super has a larger head with taller fins and has an extra boost port[schnurle] and the diaphram carb. The standard has a head with smaller fins and the single has the ST60 carb on it's own reedvalve adaptor plate.
Be prepared to do a lot of running to break this motor in. It has 2 very large rings on it and they take some real time to seat. Fuel is absolutely NO NITRO to run these EVER. THE COMPRESSION RATIO IS 11:1 AND YOU CAN GET PREIGNITION REAL QUICK WITH AS LITTLE AS 2% NITRO unless you add head gaskets and who would want to do that. Oil never has to be more then 11% new and as little as 5% when broken in. The crank has massive bearings and the rod has roller bearings on top and bottom. Con rod has a bronze coating on it and the crankshaft is typical chainsaw type. Lots of special parts were available for these motors and I had a lot of special parts made too. As it is the motor is quite short in the nose so for anything other then a radial type plane you could have some problems getting a prop out of the plane. I had shaft extensions made,also quad reedvalve blocks and numerous other subtle changes to optimise the motor for higher output. Of course as a diesel I didn't have to do anything but break it in as a glow, about 10 gallons worth convert and enjoy. Oh Bob Davis made a special fuel for these tartans called amazingly Tartan mix. Ask Bob how much he likes the tartans converted. Then ask about a converted Tartan twin. It will blow a ST6000 to the weeds. and thats saying something as the ST can swing some staggering wood.