crispyspa

Hey guys, I have have a question. Has anyone really pushed the limits of an APC prop? I mean, are they good for faster than the rated RPM? I have a 14 cell set up on a 3 point hydro boat. Swordfish 300a ESC and a *laugh* Turnigy G160 290kv motor rated for *gulp* 10 cells. Kind of overvolting a bit.

I did test it and chickened out at a near full throttle pull at 12,800 RPM on an APC 16x10 two blade. I have no idea of the amps I pulled because the ESC I chose doesn't have data logging. The thrust calc I used put me in the 30lb range though. http://personal.osi.hu/fuzesisz/strc_eng/

Is that prop going to hold together @ 13,000+ ?

airraptor

My Feedback: (66)

Well APC lists the rpm limit of 11,875 rpm. So you are close but not sure how much more I would go. you can goto a 15" prop and have a max of 12,700. for that boat I would try a 15x12 and let it rip.

1QwkSport2.5r

He would be really pulling some amperage by going to that high of pitch... I believe his ESC is rated for 300A, but the motor is only rated for 10-11 cells anyway.

Kurt - how many Amps were you pulling when running that 16x10??

Jeff - do you know where he could get a Carbon Fiber 16x10 that'll handle the rpm better than a regular APC (fuel sport prop, not a thin electric)?

combatpigg

My Feedback: (3)

I had a 16 inch prop lose it's blades during a climb and it tore the engine loose from the firewall. It was only turning 9500 or so on the ground.

1QwkSport2.5r

What brand prop?

I know I'll be testing the waters with an APC 10" diameter prop sometime maybe early next year when I do the final pipe tuning on a 56LX. But the 56LX doesn't even compare to a brushless electric outrunner putting out close to 10hp.

speedracerntrixie

My Feedback: (29)

The prop is going to be subjected to less stress on an electric as opposed to an IC engine. We know that the APC 14" props will hold together at 11K on a 4 stroke. I would call that closer to the limits then what the OP is doing.

airraptor

My Feedback: (66)

CP prob using a MA prop or those old Kavan props that would come apart at 8000 rpm. I have ran many 16 APC props around 11,000 in the air not recommended by APC but they did hold. Also a Carbon prop can be had for about 400 dollars for the mold but don't copy any prop made out there with out the owners permission, IE don't be China.

A 16x10 and 15x12 are very close to the same load in not a a few more RPM to the 15x12 over the 16x10.

If you really want to try some rpm with it get it away from people and or try a wood prop also.

combatpigg

My Feedback: (3)

It happened about 20 years ago. It wasn't APC...might have been MAS. I just wanted to point out the action / reaction deal. I remember the throttle cable kept the engine from separating from the plane...so the CG was still OK enough to land it

airraptor

My Feedback: (66)

Yes a shed blade will wreck the front end of a plane for sure.

1QwkSport2.5r

I know a shedded blade can be bad news, no doubt. I was also asking not for the mould to make a prop, but merely if there's a carbon prop that big that would handle the rpm he's running at as a safety margin.

Wood props are a no-no on boats. When they hit the water at rpm they shatter. The OPs setup is on a 20lb airboat hydrofoil. He's already had it going 68mph or so.

mikes68charger

My Feedback: (34)

I used to run an APC 12X12 electric at 14k but it was useing a big 700 heli motor on 12s, I had no issues, but as you go bigger you get closer to the tips going sub sonic, there are caculators out there that help you measure tip speed. If you get the tips going to fast they can have issues.

If I was to turn one that fast it would have to be a nitro prop not a electric apc.

I like your power set up.....

1QwkSport2.5r

He is using a glow engine prop. We've ran our speedy airboats together several times and I've seen the boat the OP speaks of run a few times. It's quite impressive to see 20# of plywood flying at 60+mph on the water.

A 16" prop turning 13k has a tip speed of about 618mph or .8 mach. According to DuBro's RC Flight Source smartphone app anyway. It said "rpm too high". A 12" prop at 14k is 499mph tip speed/.7 Mach and "good rpm range". I've done a lot of looking online for a carbon prop manufacturer that has rotational speed limits for their props but I've come up short. APC lists figures for their carbon pylon props, but they're the small .40 pylon props.

1QwkSport2.5r

In case anyone wants to see a video of the boat and powering up the big prop, here it is. http://youtu.be/yvbcy4nNiXo

combatpigg

My Feedback: (3)

That's a lot of force pushing down on the front of the boat.
Is that an advantage..?

1QwkSport2.5r

Yes. These 3-point designs will go airborne without that downforce. They're actually balanced quite bow-heavy as well.

MJD

My Feedback: (1)

If it is going to run 65-70mph, I am curious as to why so much pitch at those rpm? Seems to me more disc area (3 blades?) and about 8" pitch would do a better job of pulling a draggy boat faster than a 12-12 at 12k or so rpm. 12" pitch at 12k is a pitch speed way over 100mph - so the blades are running a high AoA all the time at the lower forward speed and may be wasting some energy. Or put another way, I think it would pull harder in the 60-80 speed range. Just a thought.

Man that thing has some hp!

1QwkSport2.5r

Well, we have to prop our airboats a bit differently than an airplane... Usually smaller diameter at least, sometimes less pitch depending on hull design. What would be normal for a 20lb airplane and comparable 7-10hp engine?

MJD

My Feedback: (1)

More disc area for sure - and the boat would benefit from the same I think.

Is diameter restriction the issue on the boats?

1QwkSport2.5r

In a way, it is restricted as the motor pylon/stand is in a fixed position height-wise. I'd have to ask crispy, but I don't know how much more diameter it could handle and conversely he's already over-powering the motor by 4 cells I believe. I'm not sure what's worse - over powering the motor by a bunch or spinning the prop 1k rpm above its safe limit. Hopefully crispy comes back with some better answers than I can provide.

Edit:
16" diameter prop is the biggest he can fit.

MJD

My Feedback: (1)

http://www.chiefaircraft.com/mej-16x10.html

Is this a better choice, I wonder?

They are hollow blade but that doesn't concern me as much as spinning the crap out of large injection molded molded props.

Joshy4u2

I once used a 12x12 prop on a 10s system for a prop jet I had and I turned it at 21,000 rpm. It was a Graupner prop that was rated for 14,000 so I was a full 50% over it's limit but it never gave me a problem at all. Just make sure it is completely undamaged, perfectly balanced and on a solid and straight shaft. Also, don't use the aluminum collets, use stainless steel. The kinetic energy in these prop blades is incredible at these speeds so my recommendation is don't push it up until you are at a safe distance from anything that could be impacted by an exploding prop. For me, that meant limiting the RPM to 12,000-14,000 except for 10-20 seconds per flight where I would switch flight modes, unlock max RPM and let her rip. It was a hell of a sound as she flew by and it really turned heads, but it requires serious respect to stay safe.

Josh

airraptor

My Feedback: (66)

Joshy what was your set up to turn a 12x12 prop at 21,000 rpm??

Since your limited to 16" you can use a 17" APC and cut it down to meet you dia. requirements. this will give you more load to the engine.

Joshy4u2

I used a Scorpion 700 size helicopter motor with a 540kv on a 10s setup. You can see a video of the plane itself here.

https://www.youtube.com/watch?v=xU-PJe84JK4

As I said, I limited it to 60% total power for all flight operations except high speed passes. Even at 60%, there was more then enough power for any flight operation or stunt. At full power though, it was awesome. It pulled about 5500 watts at about 150 amps. Flight time was about 3.5 minutes but it was exciting!!!!

Josh

MTK

If it's a prop for IC engines, it quite possibly will. Just to be safe, let me recommend you do what I do in similar situations. Buy some carbon braid material from McMaster Carr. A 1" size will be adequate. Cut a section about 4" long and laminate it directly to the well sanded apc prop hub with a good grade laminating epoxy. Then add a full length piece of the carbon sock. Usually I fashioned a set of plastic blade covers which are added after the assembly is done. 6 mil polyester works reasonably well and results in a pretty good finish. Taped on just to hold everything in until the vacuum bagging

Then I vacuum bag the whole assembly. I use a Food Saver for small jobs like my props or firewall laminations but any bagging will do. Let the thing cure for at least 24 hours. If you were careful with epoxy saturation and are careful sanding the prop shape with no cutting through, the prop should be almost balanced. Regardless, re-balancing is a must.

I make many of my larger gasoline props using electric woodies as blanks, so far up to 26". The end result is much lighter than a regular wood prop for up to 80cc engines and far more durable. In fact, if you don't feel comfortable working with the APC nylon, take an e-woodie of the size you want and laminate it as I described. The wood makes a terrific filler and the carbon cladding makes for a very tough, stiff, efficient due to the thin blades and light, true composite. Then you can brag to your racing buds that you fashioned it yourself....

Good luck