indoorff

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Hey everyone

While not strictly a 1/2a question, I have noticed this effect on 1/2a nylon props too - I have been running up an engine with a Grish 9x12 racing propeller (presumably nylon), and at certain RPM's the blade tips will start tracing anything but a perfect circle (the prop disc becomes very 'wobbly'). The prop is perfectly balanced. Is this normal? Need I worry about fatigue and eventual shedding of a blade in flight?

Thanks for your help,

Chris

combatpigg

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Around here, Grish props are know as WHITE TRASH. What in the world would you be running a 9x12 prop on, with one of these rubbery wonders?

calmat

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Hey glad you brought this up. I have sometimes noticed this same scary thing with certain props. I always stay behind the prop line when i see this happening. Never had a prop fail when this is happening but i think it must be caused by props that are pretty flexable. Never see it with ridged prop blades. Wonder if it ever happens in flight ??? LOU

combatpigg

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Used to run GRISH yellow bladed 8x6s on FOX combat motors. The yellow blades made it easier for the neurosurgeons to pick the prop material out of your body when a blade let loose. These props performed fairly well, and at rest, they looked like a set of floppy bunny rabbit ears. You could stuff a plane at 80 or 90 mph, and pull the whole works out of the ground with the blades still intact.

indoorff

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CP - seeing what it would do on an OS .46. Like I said, not exactly 1/2A! Get a pitch speed of about 120mph.

LOU- It is certainly scary to see a prop doing that. I made sure there was nothing in the prop line, and wore eye protection!

So is this normal for a grish prop then?

Chris

Larry Driskill

I have used white Grish 5X3s on .049s quite a bit in CL 1/2A Combat.

But they were not as magic as the Cox Black 5X3s, especially if you cut the Cox to 4&1/4 to 4&1/2.

Both would survive the "event" Pigg mentioned and so we used them even when they might not be as efficient as a proper, glass/carbon prop.

Years ago. . . on Fox .36x engines I used the yellow Grich 8X8s. 8 inches of pitch on a CL Combat plane goes quite nicely, thank you, even on an engine that is turning only in the teens.

But they did fatique. We used to boil them in water for 15 or 20 minutes to keep them from shedding blades. 'Worked great.

If I needed 12 inches of pitch on a .40+ these days I would visit the APC site.

indoorff

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Thanks for the tips guys.

I have been flying a well boiled top flite nylon prop on a .25 combat model, and despite countless propstrikes, it has survived everything. It even went straight into the ground at full throttle, dug itself in to the field up to the wings leading edge, and the prop was STILL ok!!

Larry - Are all Grish props safe to boil? I don't know for sure if it is nylon or something similar. It says on the box not to oven cure the prop or a foul smell and decomposition will result. This is different than boiling though I think.

Flew the plane this evening and the prop held together.

Chris

Larry Driskill

I'm not sure about boiling some of the current ones, especially the ones that have a softer feel to them.

AndyW

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Grish props, I'm told, are made of polyester and not nylon. This apparently means that they're not as susceptible to drying out and becoming brittle over time. The white Grish props are pure polyester and the black have a glass fill. Yes, the whites are flexible as heck. The blacks are stiffer but still flexible enough so that they don't break as easily as the Cox greys,,, the best props ever made, in my opinion. I've used the black for many, many years, pushing the 6 X 3 to 25K on a pipe and never had a problem.

Anyway, do try a black in your favourite size. You may be pleasantly surprised. The only caveat is that some batches come out a little rough around the edges. But a little 600 grit takes care of that. You have to balance ANY prop anyway.

No, don't boil the Grish,,, no need.

Jim Thomerson

Guys used to run black Grish props, maybe 8 x 6's, on fast combat airplanes. At the end of the flight the prop would be about 7 inches long with fuzzy tips.

indoorff

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Thanks for the info Andy. The props I was asking about where off-white, so they must be the polyester then.

Chris

AndyW

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Geeez,,, [X(]

NorfolkSouthern

I absolutely agree with Andy. I used to run C/L models, and ran my engine at top end. It was a .15 O.S. adapted for control line use. Not only did the Grish Tornado prop make the model look better (APCs, in my opinion, are the UGLIEST things I ever saw), it made the model more controlable, and kept the speed consistant (at least in my opinion anyway), a big plus for Goodyear racers. My machine was a Sig Buster, and it looked sharp in the red coloration and white prop with black tips. I would not mind trying more for RC use if they're still available.

NorfolkSouthern

AndyW

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NorfolkSouthern,

Yes, imagine,,, a prop that looks like it and also does what it's supposed to do. [8D]

You CAN still get them and it's quite easy from here: http://www.grishproducts.com/

They've got a great variety of sizes in pullers, pushers, tractors, three blade, two blade, white, black, silver,,,,

The great thing about the Grish folks is that you don't need a credit card or Paypal. Just order online and they will send you a confirmation by email. Yes, you have to do a simple registration. But, here's the rub. Then they ship to you and send along the bill. You get the goodies FIRST and then you send them payment. What a great bunch of folks the Grish's are. I hear that they're a small, family owned business. Good old Yankee ingenuity and entrepreneurship. [&:]

Discussion on the merits of prop brands can be seen here. http://www.rcuniverse.com/forum/m_24...Ctaipan/tm.htm

The 8 X 4s were run on a dieselized .074. With the 6 X 3s, I found the Grish turning much faster than the Cox. In most cases however, the in air performance was the same and in SOME cases the Cox, even though turning slower, is superior. That's dynamic thrust, not static RPM.

max-nix

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Indoorff
The Grish 9x12 racing prop is made of Delrin, a plastic that is quite superior to nylon in most applications.

"Today, Delrin® is a mainstay of DuPont's engineering polymers line and is widely acclaimed as a lightweight but durable low wear, low friction plastic for electronic office equipment, advanced conveyor technology, and automotive applications."

It certainly is a beautifully crafted prop. What engine are you using this prop on? I never found a good aplication for it.

The original line of Grish Press-wood props were some of the most efficent props ever made, and came in an amazing number of diameter and pitch selections. Engine power output progressed until it surpassed the durability of the materias they were made of, I could never understand why Grish did not replace the nylon line of props with delrin, perhaps it would require a new set of expensive molds?
I had a yellow nylon 8X8, (one of my favorites), shed a blade while I was testing my rat race engine mounted in a magnesium Harters pan
and it broke the pan across the hold down screw holes! (14,000 RPM)[>:]

combatpigg

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In the 1/2A sizes that I did static thrust testing with, Grish white props under performed their peers in every size. The only brand that Grish out did was Zingali. I have always looked at their 5x3 and 6x3 white props as last ditch ways to get some more time out of a tired engine. I have not tested their firmer blade series,[Tempest? Typhoon, Hurricane?] I am waiting for a shipment of pushers right now.

indoorff

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max-nix - thanks for the info. Being delrin, I don't suppose they will get as brittle as the nylon ones with age? It is indeed a nicely made prop, even to look at. I was just experimenting with it actually, I tried it on a OS .46 FX. It spun it pretty well, but the plane I had the engine in was too draggy to take advantage of the lower static thrust.

Chris

AndyW

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Combat,

Wish I had a way of testing for static thrust. Have you tried the Grish black Magnum Tornado series? Clones of the white but glass filled and much stiffer. Also, how about Cox 6 X 3 compared to any others?

On my Low Stik, I had been flying the grey Cox 6 X 3 and one day broke it on a dead stick into tall grass. My only other 6 X 3 was a rubber ducky. Yes, it flexed and wobbled all over at full bore but in the air it surprised me. It almost felt better with a bit more thrust.

I suspect that prop performance can reflect the SPEED (RPM) that the prop was designed for. For instance, it appears that APCs may be superior to others because they are designed to be most efficient at speed. When running diesel, you typically go to the next size up from glow and if it's an APC, you may not be driving it at the RPM that reflects its maximum efficiency. A prop has to "get on the step" so to speak.

WFO is a lot of fun but if you're flying sport aerobatics, I guess you need a compromise solution in prop selection.

combatpigg

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Andy, being little wings with a variety of airfoil shapes and planforms, doing prop comparisons to check efficiencies at different rpms would be the most complete type of study, but way too exhaustive for me to try. I was mainly testing thrust output of different 1/2A engines, using a handful of typical props. The prop test results were pretty consistant whether they were bolted onto a Babebee or a Fora. There were some minor inconsistencies.
Bolted to a 1/2A C/L Combat plane is a good way to see the difference, you can feel the line tension, clock your speed for a few laps, and see how quickly the plane gets pulled through loops. Plus this way is more fun than running engines on a test stand.

I think the rubbery props depitch themselves and the more power you give them, the more they flatten out. I am going to get the GRISH hard plastic props to try soon, with the idea to see how much blade thinning they can tolerate. If APC made 1/2A pushers, I wouldn't bother with Grish, but the old yellow Grish pushers were acceptable, so right now I am thankful that someone still makes 1/2A pusher props.

AndyW

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Combat,

If you get some Grish blacks, you'll note that the airfoil goes semi as it approaches the hub. Good for strength, maybe not good for aerodynamics. Try this. Take one and sand the airfoil flat bottom all the way to the hub. Then run both the stock and the modified one. I did this on a 7 X 3 on the .074 on glow and I picked up a free 500 rpm. One I did even goes very slightly undercambered. Still lots of strength, that one is an 8 X 4 on diesel.

If you have any Cox props, you'll see that that is the way the airfoil runs in their design.

combatpigg

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That's a good tip, the airfoil on these tiny props is very important. Getting rid of unwanted mass is even more important, in the area toward the tips. APCs are superior in many performance applications not just because of some high tech BS that they feed you, but because they have less mass at the business end of the prop blade. As far as the appearance argument goes, that one is totally lost on me....all props look pretty much the same at 30,000 rpm and at 200 feet out.

NorfolkSouthern

Maybe a part of the reason the Grish worked so well for me, was that I was using a bigger engine, a .15 on a Goodyear racer, which turned more slowly than on a combat model. It looks to me like those who choose an APC want speed more than anything, looks come secondary. And like Combat pointed out, the prop looks no different from any other at full RPM and 200 feet away. As for me, I have to look at that model every day because I don't have the closet space to put it in. I'm not after a racer, I want something that is both pleasant to look at, and offers good utility. The Grish met my needs perfectly, as it both performed well and made the model look more decent. The black tips on the white airfoil were also very helpful for safety: I could more easily see the tips while the engine was running. If I were operating a UAV for aerial photography, I would mandate one of these for liability reasons.

NorfolkSouthern

AndyW

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Combat,

When you get your Grish's, you may be pleased to find that the tips are not only nicely rounded but quite thin, better even than Cox. Plus, they give you some meat where it counts. I've thinned these out some but on a sport aerobat, it's hard to tell any difference. On a hot combat ship though,,,

Appearance can matter on a scale ship where half the fun is just looking at the thing. Think Piper Cub with an APC on the nose. [:@]

But geez, 30K rpm,,,, that's gotta sound awesome. Guess that's where the term WFO comes from. [X(]

NorfolkSouthern

I would look at the Cub with the APC and wonder who nosed it in with too much down elevator...

NorfolkSouthern

gcb

I'm glad to hear that Grish props are available again. They were out of production for awhile because the molds had worn out. I have enjoyed them since the old plasticote pressed wood days. I remember when the white nylons came out, then the yellow, etc.

The last ones I got were the ones that said to not boil them.

George