Japanman

Glad you persevered with this, Pigg.
If you wanted to get the heat down, perhaps you could taper the fuse more in the rear to allow more airflow over the engine?
It might also make little difference.

The noise from the prop is probably coming from it passing through the high and low pressure zones of the main wing. If you moved the peop back, it might get better, but I thought you Americans don nee no steenkin muffler?

Really cool and interesting plane.

J.M

combatpigg

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Nice to hear from you JM! Whatever became of that plane your friend built? Right now I don't remember what it was, but I DO remember it being the finest looking small model I've ever seen. Don't tell me it's a Hangar Queen.....kinda bugs me that I forgot what it was modeled after, [I better start taking more niacin].
Pushers......
Even with the steel thrust washer, you can see way more aluminum slurry being made than usual. Pushers are a strange attraction, once it gets out there a couple hundred feet, it just looks like any other plane. I guess the main attraction is being able to get away with flying an unnatural act in public

Japanman

As far as i know, it hasn't been flown yet. He told me it is a bit heavy: though i would have guessed to be about 14 oz- but it is a small plane.
It is a little tony: Someone posted the plans here a while ago.

A PTFE <teflon> washer may be what you need if it starts to be a problem: run it in place of the steel.

J.M

AndyW

My Feedback: (1)

I had a similar problem many years ago on a pusher delta and for me, the solution was the phenolic washers used on Cox TDs. The surface glaze rubs off a bit exposing some of the fabric. This holds oil to a degree and seemed to work well. My delta didn't survive long though, due to yaw instability. I made twin fins near the tips but they were too small. Anything bigger looked sort of overkill but in that case, TLAR wasn't. [:'(]

The solution to pusher prop problems, of course, is to run the engine in reverse and use stock props. This gives you many different props to chose from. A Cox crank has been installed into a Brodak/CS with much success. There's a source for reverse, TD cranks and I've got a couple on order. This could be used for pusher OR twin applications. Gotta love Cox, they did almost anything and everything in their long history. Sad to see them go.

combatpigg

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Well....the very rare and collectable 4.5x4 Cox Rubber pusher prop was in today's mail, thenks to Robert [BuildLight] from Crete Neb [isn't Socrates from Crete?]. Very weird looking prop, very undercambered and twisted. I made a washer out of aluminum to fill the front side of the prop hub so it would fit a Norvel drive washer. It really is a load for this .061, the needle was very narrow, but the engine seemed OK with it. The launch was dicey and the model was slow to accelerate. After each dive the engine would unload enough to put out decent speed, but the engine was really lugging in the climbs.
For the 2nd flight I twisted those rubber blades back to zero pitch and they rebounded to somewhat less than before [which is what I wanted]. This time the engine was much happier, the launch was almost what you would call real strong and the entire flight was almost good enough to make me forget that this plane has the engine on the wrong end.
For flight 3, I noticed that some of the original pitch returned and so I decided to heave the plane skyward instead of just pushing it like all the other successful launches. The end result was a stall and nose first crash that forced me to drizzle more CA into the front end. The next launch had the prop blades re-twisted and with just a gentle push the model launched very nicely once again. I guess unless your throwing motion is just perfect, hard throws don't work with pushers at all. The power to fly is either there at the prop, or it's not.
This plane would need to be smaller and lighter to be anything close to a "show stopper", right now it falls into that mediocre category...it does all the basic stuff, but that's all.
Maybe I could get the Washington State DMV to sponsor it?

Thanks again, Robert....if only this prop could talk? It's done more traveling in it's lifetime than some people I know.

build light

CP, after looking at these many times I came to the conclusion that the leading edge of the prop is on the side with the recess. Where you put spacer. I feel that you are running it backwards in the pusher configuration. This is the strangest feature of the prop IMHO. Look at it6 real close. I think its best performance would be in a tractor position and run in reverse (clockwise from the front) rotation.
With the high pitch I doubt one can get good revs in static runs.

As often as you do pushers, You might consider a catapult launch stooge. Otherwise some have had good luck with discus type launches but this requires some practice to do well I'm sure.

I am glad you had some fun with this weird prop! Don't give up on it just yet! Makes me feel good it got airtime at all.

Robert

DeviousDave

These props just beg for a little reshaping of the LE and tip..... You won't believe what a difference it makes on the other Cox props. I just did some playing with a reshaped .020 prop on the .010 and it was quite an improvement in speed. Picked up 1800rpm over the stock prop with a nice bump up in pitch. Will be testing more tomorrow with a reshaped .010 prop. It's difficult to get these as good as you want them to be as they are very thick as standard and end up being toothpick props when you are done and then they don't last.[]

Still, a few minutes with a sanding stick, Xacto, and set of calipers might really wake the airplane up.

combatpigg

My Feedback: (3)

...either that, or spending a few minutes with an Xacto carving and reshaping the airplane might work too.
To be fair to the plane, it should really be running a AME, not a AP/MIG/TD.
And the engine should be in front.
Now would be a good time to thrash on it, try things but I hate to mess with my one and only Cox prop too much.

combatpigg

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Robert, I'll run the prop turned around just to see how it does. Right now I've got the airfoil of the blades so that they scoop air to the rear. The blades have quite an arch.... like an undercambered airfoil.

johnvb-RCU

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Is one of these any good to you? Gray 5*3.5 3 blade pusher.

http://cgi.ebay.com.au/COX-049-Airpl...d=p3911.c0.m14

I have one on a PAW .55cc. Turns at about 11,500. Your .061 should do a lot better I would have thought.


Also this one looks like a pusher but it could be just the photo is reversed:

http://cgi.ebay.com.au/COX-049-Airpl...d=p3911.c0.m14

build light

CP, if you have the blades so that they scoop air to the rear, you won't do better than that. The undercamber is pretty pronounced as you say.
Course I have heard claim that some planes fly better with the wing on backwards!

Robert

MJD

My Feedback: (1)

[:-] ?

Of course that is the way to run it. CP looks like he has it right. The prop is in the same orientation as if it were on the front, just moved back somewhat and the engine has been moved to the front of the prop.

MJD

DeviousDave

Lemme check my stock on these... I bought a few, but don't remember how many.

combatpigg

My Feedback: (3)

JVB, thanks for those links to props! I've run the 3 blade 5x3 on a Norvel .074 and it really did well pulling around a SWR. I think it would be a slight overload on a .049-.061 making the engine run below where it likes to run.

MJD, I had to look twice to make sure this one was on correct the first go around. I'm curious to see what a strong TD can do with this prop. I'm really not that big of a fan of pusher set ups, I just like the challenge of doing something different once in a while. It would never occur to me to go out and build some .40 sized monstrosity. .049 scale is just right for a place to let this type of creativity fester, ooze and drain out.

build light

Spinners being on topic for now I happened to find this jewel! I was not looking or thinking about a pusher prop spinner yet I ran smack into one!

CP, you gotta have one of these for Pusher Man! http://www.lightspeedengineering.com...es/Spinner.htm

Robert

AndyW

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It's a real pusher. The seller offers a supersized picture and the pitch and dia. are embosed on one of the blades in the correct configurqation.

combatpigg

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DD... thanks, but this prop that BL sent will do me just fine for the duration. Being rubber and in the back of the plane about the worst thing that could happen to the prop is to lose the whole plane with a fly-away.

BL, that is a wild looking spinner! The tear drop shape is what a lot of very fast models have from the back of the wing to the tail feathers now. In a way, the P-51 was a little bit tear dropped.

Today was for R&D...basically to see what the plane can do without for flyability. The wingtips and central fin were cut down in stages and flown a few flights at a time to draw conclusions. Where the plane is at right now is on the verge of not enough vertical area. I will glue some of the central fin back on. The tip fins added something to the way it flew, possibly making the plane smoother. They really aren't drag reducers at the speed this thing flies, maybe they would be at 200 mph, but not at 40.

The AP .061 wore out. The wrist pin boss in the piston has over 1/16" of slop. I've seen this before with AP. The last few I've bought didn't make it through a gallon of fuel before they wore out, maybe not even 1/2 gallon. That's it for me, they aren't that cheap any more, just garbage now.

So tonight I hogged out the engine mount and crammed a .074 in there. The "big block". It spins that Cox 4.5x4 the way it should be spun. I can't wait to try it out. It sounds like this plane will be doing 80-90 if it holds together

balsa brain

I hate to say it Mr. Pig, but it looks like you may have used your chainsaw to do the mods to your plane.

RocketRob

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Simply no substitution for cubic inches

AndyW

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Not a chain saw, that knife sitting on the magazine in the second picture. At the field, any tool will do in a pinch. Looks like something that's cleaned a lot of catfish or something.

combatpigg

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I butchered a 150 pound deer with that knife! I hit a chunk of steel in one wing tip and put a nice divot in the blade [&o]
That steel from Bangladesh might be soft, but it's easy to sharpen. For a survival knife, that's what you want, easy to sharpen. For balsa with fiberglass, I should have a razorsaw in the tool kit, but didn't.
Anyway, I ran this plane today and it was an improvement, but also a disappointment. The .074 turns the 4.5X4 25,000 still 4 cycling and unloads it nicely to maybe 27-28,000....but the speed is not there. Maybe 80 mph down wind. It just isn't as efficient as it should be. Even with the .074, the launches were not a sure thing, many launches the plane just didn't get enough speed soon enough to stay airborne and sat there in the grass with the engine still running....waiting for me to get to it and throw it again.
The "Pusher Man" has satisfied my need for uniqueness.
The engine isn't getting enough cooling, either. I could fix that, but it just isn't worth it. Time to move on.
I flew the Black Bat Outta Hell and the F-16 with Cyclon .061 power tonight, had a complete blast and forgot all about this "Volkswagonish" airplane.
For my money, in this application, pushers suck. [>:]!

johnvb-RCU

My Feedback: (1)

27-28000, revs per minute.... Potrzebie! That's going to make my little 32" canard pusher with all of a 1/2 cc diesel look a bit sick :-) If it does 20mph I'll be surprised

combatpigg

My Feedback: (3)

John, depending on how you design yours, you might get good efficiency from it and have it fly the way you like. The design I came up with is too boxy in the rear for a 4 inch speed prop to get a full gulp of air. I think a future design will have the rear firewall no wider than the engine. The elevon servos will have to sit one in front of the other to make room. I don't know how much that would effect throw geometry...but having a 4 inch prop hiding behind a 2 inch wide firewall is no good.

Remby

My Feedback: (3)

Got to say that C.P. is a builder, and one of the true 1/2a masters here at RCU. Great thread and project!
I have that Firebolt carnad pusher I built that had simulated jet engine inlets, I sealed them and let them channel the air into the engine compartment where it was needed. I was hoping the suction from the prop, and the pressure of forward motion would pump cooling for the engine at the rear. Cooling the engine is always troubling with pushers.
Great model and post C.P.!

Big Al-RCU

And THAT is a FACT!!
al