4 blade props cost too much.

Does anyone sell a reasonable price 4 blade prop?

All the 4 blade props seem to be priced about $40.00 each. Has anyone tried putting 2 single blade props on the same engine? Most crankshafts are too short for 2 props.

Gary....there are some 4 blade sport props around....and the cost is reasonable.

The expensive 4 blades are more than likely carbon firbe.....

I would wonder ehy you are desiring a 4 blade?

See Ya

Try Towerhobbies. They have APC 4 blade props at less than $10.

Just to make it easier, try this:

http://snipurl.com/9s3e

Sure seems that the pitches are too high for what we really need.

>
>Sure seems that the pitches are too high for what we really
>need.
You can re-pich it.

LAST EDITED ON Oct-14-04 AT 04:45 PM (CDT)
 
Gary,
I just had a long discussion with Cliff and Rico of J&M Hobby House in San Carlos, CA last night about this. I'm working on plans to a scale asymmetical model that has counter-rotating props in a push-pull engine configuration. I was thinking of not doing the counter-rotating of the props, but for the sake of appearances, I was thinking of affixing two two-blade props together to look like a counter-rotating props. I had thought of drilling two holes in the hubs and pegging the props with short lengths of 1/8" music wire as well as epoxying them in place. That's one idea. (I figured I'd make a jig using a 12 X 12 X .75" piece of plywood drilled at the center and at 90 degree angles to accept 1/4 lengths of music wire to align the props when conjoining them.) Others have used a cut and grove method to mate two props together to create a four bladed prop.

Another consideration is spinners. Cliff didn't know if Dave Brown can cut custom cuts in his aluminum spinners. Cliff is going to call in a week or so and let me know. CNC can do this at a cost of about $18.00 per custom cut. They will also sell un-cut spinners and one can make their own cuts. CNC has a computer cutter and a huge file on specific props by specific manufacturers and do superb cuts. Since I will have a spinner on the rear engine and this will be turning a pusher prop, I will need to have a spinner custom cut. I decided to forgoe the idea of conjoining props and will simply be using two blade props. It seems no one manufactures multi-bladed pusher props.

I prefer wooden props for safety reasons. I've been cut by wood, plastic, glass filled, and you-name it and believe me, I prefer to get whacked by a wood prop, which tends to break and doesn't cause as severe a cut as the others. Master Airscrew manufactures pusher, wooden props. Not that you will want to fly your model backwards. . . but I'm not familiar with your style. I hope this helps. For safety's sake, spend the 40 bucks if you plan on running the engine with the four bladed prop. I decided I wouldn't trust a conjoined prop turning on a modern high reving engine. If your making a static display model, then go for it.

Another way to think about the costs is to consider what you might be saving on a visit to the Emergency Room to have a blade removed from your chest or eye and have a finger reattached.

Not sure but I think bolting two two blade props together won't work too good because of the prop wash off the first prop or something.

How does a person decide which pitch and diameter is needed to replace a 2 blade prop on an engine. Lets suppose an engine is performing well with a 10x6 prop, correct speed, correct amount of torque. I would assume to maintain the same speed the 4 blade prop would need to be a 6 pitch like the 2 blade prop. But what about diameter?

Duke Fox advocated using two two-bladed props, mainly as a way to quiet the engine for RC. In fact, for awhile the sport motors came with somewhat longer than normal prop studs to accomodate this.

If I remember right, he recommended going a couple inches smaller in diameter and up a couple inches in pitch. Something like switching from and 11/6 on a forty to two 9/8's. Lot's of room to experiment here.

The smaller prop really can do wonders for noise. I switched from an 11/4 to a 10/4 3 blade on one plane. Now I can hear the LA 40 above the prop noise. It is much quieter- nearly electric quiet. The RC guys use the 130 figure- prop diameter in inches x rpm in thousands should be under 130. That keeps the prop tips well under the speed of sound. An 11/4 at 11,500 rpm gives 126.5, much higher than the 10 in. prop at 115, and noticeably louder.

Fortunately the 10/4 3 blade flys as well as the 11/4 two blade.

>Does anyone sell a reasonable price 4 blade prop?
>
>All the 4 blade props seem to be priced about $40.00 each.
>Has anyone tried putting 2 single blade props on the same
>engine? Most crankshafts are too short for 2 props.

Paul Smith

Two-blade props are no bargin, either.