jetranger-RCU

My Feedback: (1)

Have been testing this on the bench over one hour running time so far so good. Replaced screw with bolt with shank loctited in . Prop 7-3 folding from Hobby Lobby. Prop rated 16K , motor runs about 12K. Running 15% fuel three gaskets under head to keep power and compresion down. How safe is it, I wear safty glasses when running, taking no chances. Would be great in glider no weight from motor or batteries. Throttle response very smooth. I tilt motor down a little to start. Blades just loose enough to fold no more. With well broken in engine takes only a few flips to start. What do you think?

SoarNeck

I think that's a little irresponsible. Those props aren't rated for use in internal combustion engines (says so in the instructions), and they can't take the hammering of the combustion stroke of an engine.

Please stop before you hurt yourself or someone else WHEN a blade breaks loose.

BMatthews

First off I'm inclined to agree with Soarneck but without seeing how meaty the hub is I'll reserve judgement. If the prop is rated for 16000 rpm that's a helluva load already and I can't see the Norvel spinning it much over the 12 thou you state is going to cause a problem.

BUT......it's the side loads you put on the hinge points during starting that would bother me. That's quite a bit of levering for something that wasn't intended to take much load at all in that way. Especially if the engine gets flooded and bites back during a flip.

If you're electric starting it that would be a different story. And if you're not then you should be. Otherwise I do agree that you're setting yourself up for a bad accident.

A better option would be to get good quality carbon fiber hotliner prop. Those are meant to handle enough power that you could get away with this and no worries. But unless the hub is quite meaty I'd still use the electric starter to avoid the back bite side load damage to the hubs and hinges.

jetranger-RCU

My Feedback: (1)

I can see your reason for safety thats why I only run it on the bench in the yard for testing . Once started I walk away and let it run . Like I said this is only testing to see if it can be done. Hobby Lobby sells alu hubs and spinners which I am testing also, they do run better. Also note the props are not spining at max RPM. They turn between 10-12K on a good day for 7-3 and 6-3, they are rated for 16k . With out testing how do you know it wont work . I've got just over 21/2 hours running thats at full power and every thing is still good no cracks or problems, and I do use a starter most of the time, other than that I use a finger guard the one Ace sold.

SoarNeck

The thing that you folks aren't seeing is that these props aren't designed for the impact loads that a compression stroke gives. Fatigue cracks aren't likely to be visible to the unaided eye.

Just compare an APC standard prop to an E-series prop...same loading factor, same RPM range, but MUCH less meat at the point where the blade joins the hub. Folders are even worse from this perspective.

Plus, I guarantee that if there was ever an incident, your AMA/MAAC insurance carrier would come after you for negligence. "Electric only" is there for a reason.

BMatthews

Soarneck, I would certainly agree with you about the combustion shocks if it was anything bigger than an 061 size engine. But operating it at these revs and with the relatively weak shock loads you get from a 1/2 A engine there may be no problem at all. And it's not like the prop is ONLY designed for the motor forces. The average user is going to face plant the hub and blade roots many a time during the life of the unit. Mostly catching it on landing but occasionally hitting the sod while spinning. If it can survive those loads then it should be fine for an 061. At least he's using safety glasses and appreciates what he's doing. And while I'm not saying that the makers only put those notices on the packages for the good of their health you must realize that there is NO recognized authourity that rates this stuff. I and many others use cut downed and well thinned wood props on 1/2A texaco engines but they are only turning 6 or 7 thousand rpms. By rights all those that do this are in the same boat but it's an accepted practice done with a respect for the limited rpms and forces involved. I hear what you're saying and agree in principle but in this case I think Jetranger is testing properley and has a good deal of respect for what he's doing from how he's writing this up.

How about a compromise? Jet, you've put a fair number of runs on it so far I gather.... If you keep checking the hubs for signs of stress (whitish looking lines or zones especcially around the hinge pin holes) after each run and don't use it around people in close proximity then I think we can give it the seal of approval. In this I agree in principle with Soarneck. Be safe and step well away from any others when running this combo up. And it wouldn't hurt to keep those safety glasses on until the model is launched and well away from you as well. I'd stop the finger flipping altogether. Every time it bumps hard and doesn't flip over that's like hitting the blade with a mallet between your finger and the hub. What about adapting a COX like starter spring to the engine? That way you don't need the electric starter and you don't stress the blades. I suspect that finger starting is the hardest punishment you're giving the blades. If the blades last a full season then I'd buy new ones and you know you're good for the next season "just in case".

And finally there's always the 7x3 FAI free flight power folders. Carbon blades in a stocky aluminium hub and rated for over 30,000 rpm from a screaming Nelson. Don't know where to find them but they are beautiful to see. Doug Galbreath perhaps?

jetranger-RCU

My Feedback: (1)

There is no way to use a spring starter because of the back plate on the spinner. After each 15 minutes of running I take the prop apart coat all the plastic with water base markers black, then wipe off and look under a magnifing glass for any cracks that the marker flowed into, none so far. The alu. spinners use alu. hub and carbon fiber props with 3mm bolts. With the extra gaskets now up to four theres very little compresion. If the plastic holds up thats great, but the alu. and carbon is the way to go for safer operation Time and testing will tell, I'lll try to get that 30K set up you spoke of. Also beside the safty glasses I wear a full face safety shield, don't need a blade in the neck. I will post again after more testing

BMatthews

How about putting a couple of saw teeth into the spinner backplate? Sort of like the setup the COX engines used for a few years with that starter ring.

jetranger-RCU

My Feedback: (1)

I do not think it will work the spinner has a alu. insert in the plastic back plate to mount on the shaft. It may weaken the plastic. And the alu. spinners cost around $25 i would hate to chop it up. The electric starter works good . I made one from a 05 motor Master Airscrew prop adaptor for electric, I trimed off the flange the prop sets against and slipped on a piece of tubing for the cone and run off a 7 cell pack.

BMatthews

I've got a starter......... somewhere (haven't seen it for years)........ that's made the same way but with a custom made alu cup (helps to have your own metal lathe ). You're right, they DO work super. Used it back when I was flying a Tee Dee powered pylon racer type model. It was bladder fueled and I didn't fancy holding that darn tubing pinched off while dealing with a stubborn Tee Dee. With the electric it never failed to start within a second or two.

Keep us informed about how the prop works out.

jtech

Hello Jetranger,

This is abit off the topic, but I'm interested knowing the fuel consumption of your engine. Do you know the rate of fuel it consumes at full bore? How about half throttle?? Have you had much experience with this engine; is it reliable? How much fuel to break it in? My son and I are entering a marathon contest and we are looking for a power plant to design an airplane around.

jetranger-RCU

My Feedback: (1)

Yes the engine is very good I have four and all run alike. As far as fuel I'm only guessing about 10 min on one ounce tank I could be wrong , I have never timed it . On the bench I run a 10 flat tank and just time for 15 minutes then stop. Refuel cool engine and start again. If you do not need a throttle have you looked at Cox's Texaco 049 I have one it spins a 7-3 to 8-4 prop and runs a long time, it's not a power house so I don't know how much weight it can pull. You mite be better off with a OS 10 has power and good fuel run. You mite be better asking this question in the 1/2A section those guys are running all kinds and could have a better answer hope this helps