alfredbmor

Happens all the time at the flying field, some guys stick only with wood and others with the rest of the propellers. I have tried both and I like the wood performance, I do not know how it works in a comparative proportion with the rest.
Any Ideas?

David Cutler

Wood is light, so has lower inertia, so the engine spools up quickly, and it doesn't distort as much as plastic so keeps its aerodynamic efficiency at higher revs.

-David C.

cyclops2

Wood is gooder when the prop hits your hand.

It is the ONLY material that MIGHT break on a hand.

Children should ONLY start and fly with wood.

stunner

better. (cough, cough)

BMatthews

Yeah, wood will break but only after doing a goodly woodly amount of damage to whatever it hits. I've got the scars to prove it. Beginners should just learn to keep their fingers out of the prop disc and use smaller engines to minimize the damage.

From an AERODYNAMICS standpoint (it's the aerodynamics forum after all ) wood is often stiffer and lighter but the airfoils typically used are far from efficient. But if you look at the higher end speed model wood props you'll see just what is actually possible. But your generic Zingers and similar are easily outperformed by APC plastic props just due to the poor and draggy airfoils.

But oddly enough the difference isn't as much as one may think. A buddy and I static thrust tested a bucket full of props in our early electric days. The coarse club like shapes of the Zingers were about 15%'ish less efficient than the equivalent APC. So they drew about the same current for 15% less thrust or needed 15% more current for the same thrust.

When thinned down to APC'ish thickness and shapes the wood performed within a couple of % of the performance of the APC's.

Johnnie Red

Hi guys
The best props for operation but not Best Value for money are the Carbon fibre 3W.
BMattwews is also right.
Cheers
Johnnie

Jim Thomerson

I know less about props than I used to. My mistake was trying a number of different props on a particular engine-airplane combination. The prop I expected to be best from flying similar combinations was useless. The best prop is a carbon fiber, then wood, then plastic, then an APC. Usually I find APC props to be the best, but not in this case.

Incidentally, I paid $35 for the carbon prop at auction some four years ago. It has several hundred flights on it and is like new. No problem with value for money on that one.

fredsedno

Haven`t been flying long,but crashing often.
Have come to the conclusion that neither have much of a survival rate[good for the engine?]however,when flying tri gear off grass the wooden props develope nicks& splinters quite soon, depending on height of the grass.

BMatthews

When you get right down to it with a glow engine you need a prop that is not only efficient on it's own but also lets the engine work at it's best power RPM and that generates it's thrust in the proper range for the model it's mounted to. So just because a prop works well for one engine on one place doesn't mean that same engine and prop is optimized for a different style of plane.

And I found that I really noticed this when you're running underpowered, by today's standards, with a lowly 4 stroke on a heavy model. The prop choice between even differing styles of the same size and pitch even made a noticable difference.

nekked_man_2000

If you go to the AMA digital archives and type in Propeller you will find several articles on modifying and even making wooden propellers. I've used this info to modify some Zingers with verry good results. The basic idea is to figure out what pitch and diameter will give you the performance you want then work on it until you get the engine in the proper rpm range....that's oversimplified, but that's basically how it works. One example, I started with a 12X5 on a .40, then thinned it and removed a lot of the wood, sharpened the LE and TE and balanced it, this gave me a couple hundred rpm over the unmodified version. then I clipped a quarter in. at a time until I finally came up with about an 11.5 X 5, then you have to re-thin the tips and rebalance....which may increase your rpms again.
This gave me performance on par with the 11X5 APC I was running, but the engine would rev a lot faster because of the lower mass of the wooden prop. Next I'm going to make some of my own from scratch, but I need to practice a little more with my bandsaw.

One thing I've learned, is that making scimatar shapes, sweeping the tips...etc., doesn't make a difference that I can notice! All that seams to matter is blade area, diameter, and pitch. They even give you some ideas to check the pitch so you can compare different brands and even the pitch of one blade verses the other, you might be surprised.

I originally read this topic thinking you wanted to know what kind of wood to use for a prop, thought maybe I found someone else interested in prop making. Ocassionaly I notice I think Dave Robelen(sp.) in the MA magazine mentions making his own props for electrics, and I know some the free flight guys do...but now I'm blathering...

Austin

da Rock

Yeah, there are others out here who modify props.

My experience matches some of yours. For example, it's very interesting to check the pitch of both blades on the same prop. Amazing actually.

I used to mess around with pitch, but have found that more effort than effect. And a synthetic prop that's out of pitch side to side is just lost money.

Diameter is another story. My experience is that diameter tuning is very effective and takes almost no time to do. Gotta mention right here that I'm not racing any more and don't do any contest flying any more, so don't feel the need for perfecting a prop beyond the large gains I've gotten with diameter changes. And I've found that changing pitch between the ones available stock isn't worth the effort. But the range of diameters available is way too gross. A change of a quarter inch diameter is sometimes obvious. A change of one inch pitch sometimes isn't.

But I do use wood almost exclusively. Used glass on combat engines and racing but never bothered for anything else.

davidfee

Not entirely true... you can re-pitch most plastic and composite props.

da Rock

Yes, you certainly can.
But, a synthetic prop that's out of pitch side to side is often a waste of time to correct. It takes more time than it's worth to me because since most synthetics are so thin, it almost always fails to result in a usable prop. Adding pitch to one side while removing pitch from the other usually results in requiring appreciably more planform area than simply changing pitch equally on the two sides. And the planform area lost is often different side to side. Depitching often moves the LE back. Pitching often moves the TE forward. As you work to match the pitch side to side, you wind up moving the span axis of each. Granted that each side's planform should move in the same direction, but not always. And the cambers of most plastics is often so hard to index that it's simply not worth the effort. At least for me.

The changes needed would seem to be insignificant and I couldn't prove otherwise. But what I could see were props that often didn't track the same on the engine when running. And when I couldn't figure out what I'd done to cause that, and more importantly how to not cause it, I decided it was more effort than it was worth. And flying proved to me that the effect wasn't worth it.

We've got fine enough pitch differences available in our prop sizes. We don't have fine enough diameter differences. Personal observation has led me to spend almost no time dinking with pitch. I can buy what I need easily. But very often the difference in diameter that will make a telling effect isn't available. It's a shame we don't have "half inch" props.

When glass props first hit the market, some were sold as semi-blanks. The buyer had to work it into a usable fan. The most effort was to shape and match the planform. And you had to keep an eye on relating that planform to where the camber and thickness was along the blank. I guess that effort back then has developed a lazy attitude in me concerning synthetics nowadays.

da Rock

BTW, a discussion of repitching should include mention of something............

It's not exactly easy to use most pitch gauges accurately. The measurements are of rather small differences. And there is a difficulty in accurately indexing the prop being measured. If you don't have the prop square in the tool, the pitch measurement can be affected significantly. Most pitch gauges don't come with any means of insuring the prop is at right angles to the measuring indexer. It's quite easy to measure one side of the prop at a slight angle that differs from the angle you measure the other side of the prop. It's worthwhile to make some type of fixture that helps you insure that each blade is measured in the same orientation.

And THEN you also have to keep in mind that the prop hub should be firmly grounded. It has a very small diameter and any flash or trash under one side of it will screw your efforts bigtime.

I've had two fairly expensive gauges that looked to be well made. Neither of them had any way to hold the blades square nor to insure that the hub was flat to the surface. Granted, that was an operator's problem, but my point is that it's a very important consideration to getting true measurements. One gauge actually did mention the two problems. The other came with no instructions at all.

da Rock

BTW, as long as the primary discussion topic of this thread is the differences between wood and others..............

I've found it to suit me better to deal with wood because I do mess around with my props to match them better to the individual aircraft, and wood does that for me better. Wood's airfoils are usually thicker. It's not possible to deal with some props that're so very thin there's nothing to work with. It's use it or not with them. With wood, I can almost always work out a usable "new" prop.

I've also found that some plastics seem to have "cosmetic" tips. They're either so thin an airfoil or have so flat a working AOA that cutting their diameter does almost nothing to their effective diameter. Cutting the diameter a half inch often does nothing to the way they perform. Cut another quarter of an inch and they go sour. Trim yet another quarter and they're lots worse. I've had the impression that they need some non-working tip shape or somesuch. What it is exactly I got no clue. But I don't bother nowadays because I don't know a predictable technique.

Charlie P.

I believe it is done to reduce the tip vorticies, mostly in the interest of noise reduction. Seems I read that somewhere in the past.

nekked_man_2000

It reduces a lot of drag. Generally when I rework a wooden prop I shave the tips down to paper thin, the tips don't do much but make drag and not a lot of thrust. That's the reason for the little angle on the tips of APC and TF power props, and yes it reduces noise to boot. The idea for me is to make the propeller easier for the engine to turn. When you cut the tips off of plastic props, especially APC types, the new tip you have is significantly larger and thicker than the original tip. You have to sand the tip back to a point for it to work, and that is a royal pain! MA props are a little easier, but less efficient to begin with. Also the area around the hub creates lots of drag, on a 12 inch prop the actual real pitch probably doesn't start for 1.5" out from the center, that area is just a transition area between the hub and the pitch of the prop, and it can make a lot of drag...anything you do to reduce drag on the crankshaft, without hurting the area of the prop that does the work (so to speak) is just free power. About all I do with plastic props is carefully remove the molding flash, and balance.

On the other topic of one blade with different pitch than the other, you can sand the back side of the hub, or even shim it with aluminum tape. Think about it like this, if you put a shim on the LE side of the blade with less pitch it will angle the prop in such a way as to add pitch to the low pitch side while reducing pitch on the blade with more pitch...usually it takes very little sanding or shimming because you are splitting the difference. Shimming doesn't work very well on wooden props because the wood compresses.

And yes, some people like virtually no pitch at the tip, again to reduce drag. I've found some people who actually add pitch to the tip, I can't think of a good reason for that, but I'm willing to listen to theories. Seems like it might even induce stalling at a high AOA in exteme cases, and might cause the blade to flex from excess drag and lift at the thinnest part of the prop...I've never tried it.

Austin

And just for the record, my favorite props are the old TF Super M series...but of course they don't make them anymore.

HighPlains

My Feedback: (1)

Reworking wood props is an art. It's also a lot of work if you are starting with a Zinger, when this is what you are trying for. Rev-Up props were the most refined wood prop ever produced for glow engines.

nekked_man_2000

Yep, do they still make rev-up props, I forgot about those, and I can't find them at the hobby shop anymore.
Zingers probably don't save a whole lot of time compared to making one from scratch, I liked how thin the blades were on the old TF super M's, but I've had absolute zero use for the 2 or 3 TF power point props. And for one reason or another, I don't think I've ever tried one of the Master Airscrew wooden props.

HighPlains

My Feedback: (1)

Rev-Up's were first produced around 1948 or 1949 and were in production until the 1990's by Chris Machin and his wife at Progress Manufacturing.

DHG

My Feedback: (7)

I'll give you $25 for that 11 x 5 in the photo. One of the things on my long list of things to do is to pull a mold off me precious thinned/smoothed/pitched-up-tips Rev-Up 9 x 7-1/2 wide-blade and make some CF or glass copies of it. Nothing else works as well for sport flying with a hot .40. The 11 x 5 cut down to about 10.5 x 4.5 would be great for 3D work.

I know, you hate 3D ... forget I said anything about that.

HighPlains

My Feedback: (1)

I don't hate 3D, just flying picnic ware.

HighPlains

My Feedback: (1)

I might have another prop sizes in Rev-Up you would want to mold D. I only have a few hundred left.

nekked_man_2000

My brain started working after my last pos and I remembered I could do an internet search. Found a post that said John Brodak had bought the tooling for the rev-up props, if true I wonder if he will ever produce them.

Austin

HighPlains

My Feedback: (1)

He got none of the tooling. He did buy at the auction all the remaining stock for about 25 cents per prop. You can buy them from him for around $3 to $5 a prop. But his selection is very limited, lots of oddball sizes. Try finding a 10-6.