Wood type for wood prop?

[BJC]

I have a sterba prop That is a little aggressive for my 0-200. I think it would be great for something in a 125 horsepower range. I have one hour on it. Put my Prince P tip back on. It is a beautiful propeller that I had made but but I lost some climb in the deal. Nothing against Ed Sterba at all. Excellent excellent price and very nice looking propeller.

Have you considered sending it back to Ed for some trimming?

BJC

 

[Doran Jaffas]

Have you considered sending it back to Ed for some trimming?

BJC

Already did once. Then I trimmed .75" off each blade and rebalanced it. The rpm came up and my top speed increased 7 mph but my climb decreased 300 fpm. The propeller did what was intended. I just chose climb over speed.

 

[Mike von S.]

I recently spoke with Aviator in the United Kingdom. He told me about Hercules Propellers. The performancy he is getting is pretty astounding. I've contacted them via email. I will keep you posted as to what I find out.

Hercules Propellers are well regarded in the Flitzer builders' community. Both Rupert Wasey, who runs Hercules, and his father Ian are engineers, and both have built their own Flitzers from scratch. The props and the aircraft (designed by Lynn Williams) look old school, but enjoy the advantages of modern engineering. Here's a nice pic of a Herc prop on a (VW-powered) Flitzer:

 

[Mike von S.]

Hercules Propellers are well regarded in the Flitzer builders' community. Both Rupert Wasey, who runs Hercules, and his father Ian are engineers, and both have built their own Flitzers from scratch. The props and the aircraft (designed by Lynn Williams) look old school, but enjoy the advantages of modern engineering. Here's a nice pic of a Herc prop on a (VW-powered) Flitzer:

I should also say I am a fan of Ed Sterba's props. Years ago he built a prop that I inherited with a Ron Herron designed "LittleWing" autogyro. Looks great and performed beautifully.

 

[raymondbird]

That is a nice looking prop. Where did you get the Hub?

Oh, it's a Sensenich ground adjustable airboat hub. Meant for composite blades of course so had to keep the weight down with Poplar. The shanks have many layers of glass sleeves

 

[speedracer]

I glued up prop blanks for Klaus Savier back when he was building props. He specified birch or maple, no fewer than 8 layers, and resorcinol glue, which is expensive. He had me glue up a blank using West System epoxy (105/206) for testing. He heated that blank to ? temperature in an oven. He pulled all the laminations apart with his hands. FYI, I'd clamp all the laminations to a perfectly flat 6' I-beam.

 

[meglin1]

Hello colleagues! Ukraine, Aviation University, Kharkiv. We have been engaged in propellers for more than 30 years. We use ash, beech, maple, oak for the manufacture of propellers. Recently, more often oak. We glue the outside with fiberglass, protect the leading edge with stainless steel. The main glue is epoxy resin.

 

[Appowner]

I glued up prop blanks for Klaus Savier back when he was building props. He specified birch or maple, no fewer than 8 layers, and resorcinol glue, which is expensive. He had me glue up a blank using West System epoxy (105/206) for testing. He heated that blank to ? temperature in an oven. He pulled all the laminations apart with his hands. FYI, I'd clamp all the laminations to a perfectly flat 6' I-beam.

Got this off Wikipedia:

"Although the greater ease of use and versatility of epoxy makes it much more popular, epoxy has poor UV resistance and in most structural applications has only a modest heat resistance, making it less than ideal for many outdoor uses. Resorcinol remains a suitable adhesive for exterior and marine use. Unlike epoxy, it is not gap-filling, so requires a higher standard of workmanship and joint fitting."

They also mention a relatively short shelf life of 2-3 years.

I have never used resorcinol when making RC Props years ago. Always a slow cure epoxy and clamps. But then, I never bake my props either. Might be interesting to see which experiences the most stress. A 20 inch RC prop at 9000 rpm or a full size doing 3000 rpm?

 

[Mike von S.]

Got this off Wikipedia:

"Although the greater ease of use and versatility of epoxy makes it much more popular, epoxy has poor UV resistance and in most structural applications has only a modest heat resistance, making it less than ideal for many outdoor uses. Resorcinol remains a suitable adhesive for exterior and marine use. Unlike epoxy, it is not gap-filling, so requires a higher standard of workmanship and joint fitting."

They also mention a relatively short shelf life of 2-3 years.

I have never used resorcinol when making RC Props years ago. Always a slow cure epoxy and clamps. But then, I never bake my props either. Might be interesting to see which experiences the most stress. A 20 inch RC prop at 9000 rpm or a full size doing 3000 rpm?

If my math is correct, your 20" spinning 9000 rpm would have a tip speed of 0.7 Mach, which is comparable, at least in this one element of stress.

 

[TFF]

Epoxy for our coveted objects is usually not an issue.

You can make it not good, though. A black painted prop left a desert airport outside for five years might have issues. A certified prop has to be able to handle this abuse. If you make one prop, why not make a half dozen? You are in control of the nuances and can build to suit.

If it’s going to be abused, resorcinol is the best. It is the hardest to use also. Epoxy is easiest to use. Does the builder need help in the craftsmanship? Yes, well then epoxy is a good choice. No, resorcinol will not be a challenge. Is this an outside prop or will the plane be hangared? Like anything, it’s stacking the deck to help the situation. No reason an epoxy glued prop can’t last a thousand years. Lots of reasons a badly made prop can’t last a weekend.

 

[BJC]

There are many, many wood props flying on homebuilts and ultralights that are held together with Weldwood Plastic Resin. It has been discussed here before.


BJC

 

[raymondbird]

There are many, many wood props flying on homebuilts and ultralights that are held together with Weldwood Plastic Resin. It has been discussed here before.


BJC

What I used and what the Culver prop girl uses and she says there's never been a glue failure. BTW, she has some great prop making videos. Great looking lady too. Could watch her working all day.

 

[Appowner]

If my math is correct, your 20" spinning 9000 rpm would have a tip speed of 0.7 Mach, which is comparable, at least in this one element of stress.

Yep! I came up with a tip speed of 535 mph.

 

[BJC]

If my math is correct, your 20" spinning 9000 rpm would have a tip speed of 0.7 Mach, which is comparable, at least in this one element of stress.

Please help me get from tip speed (units of distance per time) to stress (units of force per area) in comparing different propellers.


BJC

 

[Mike von S.]

Please help me get from tip speed (units of distance per time) to stress (units of force per area) in comparing different propellers.


BJC

The stresses in a propeller of given proportions varies as the square of the tip speed.

 

[BJC]

The stresses in a propeller of given proportions varies as the square of the tip speed.

Suppose that you have two propellers of the same diameter, but different twist profiles. Are the “stresses” equal? Stresses where? Further, assume that the mass distributions are different. Are the “stresses” equal?

Thanks,


BJC

 

[Mike von S.]

Suppose that you have two propellers of the same diameter, but different twist profiles. Are the “stresses” equal? Stresses where? Further, assume that the mass distributions are different. Are the “stresses” equal?

Thanks,


BJC

BJC,
I'm not an engineer. I am sure you know far more about this stuff than I do. However, NACA TN-212 makes it clear (to me, anyway) that stresses in any prop relate to tip speed in a big way. Not to say there aren't myriad other factors.

 

[Mike von S.]

FWIW, here's the jig for gluing up my prop. The wood is maple. the bolts are 3/8" dia and the aluminum channel is 2" x 1" x 1/8. The table is flat, and the lower channel pieces are screwed to it. I intend to glue in stages: 3 boards at a time, twice, and then glue them together. 6 total at 5/8" @ = 3 3/4" hub thickness. This is only a dry run because I need a postal scale (on order) to measure the UF glue and water properly.

 

[BBerson]

NACA TN212. NACA_TN-212 - [PDF Document]

 

[Mike von S.]

Right. My note this morning was a direct quote.