combatpigg

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The 2009 nontest will have at least 1 pusher nonentered, so you guys can breathe a sigh of relief now. Someone has to do it.

I've had some plastic laying around and decided to carve a prop out of it. I carved one a few years back out of maple and it did push the plane pretty well.

I started out with a 1/2" wide and 3/8" tall blank. Scribe diagonal lines on the ends to mark the underside of each blade. The jigsaw did a good job of hogging out with a free hand and a close eye, the final work was done with a course file. The topside of each blade was done with a rotary file in a die grinder, then brought into a higher degree of righteousness with a hand file.

To get the blades scraped down to perfection, a regular old Xacto is used to scrape those blades. Keep focused on the airfoil and symmetry. A ran the prop at 25,000 on the die grinder, it ran smooth and the blades tracked, so I didn't waste my time goofing it up on the balancer. It puts out good thrust and looks to be about a 4.5x4, but I'm just guessing at the pitch. The pitch could actually be a bit more. The AP / Norvel / TD in the photo turns it about 19,500 set slightly rich. If I had a stronger cooling fan in the garage, I would have run it up some more, but might as well R&D in the air.

ProBroJoe

Too cool CP! (I wish I had that kind of focus, desire, and motivation.) So, do you think that the die grinder just tops out at 25K or do ya think that it was loaded down to that? Weird how it produced as reasonable RPM for that prop size...

Now I'm not sure if I want to make a Norvel powered die grinder or a die grinder powered pusher!


-Joe

combatpigg

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PBJ, it only took an hour to get the prop "runnable". The die grinder did start to lug a little, but it's been through Hell....including a couple sets of Chevy heads. Compared side by side with APC's 4.2x4, this prop isn't as good. It doesn't have the helical pitch, it's just a straight shot from the hub to the tips. It flew the plane pretty good today, though.....but it's pretty much as much prop as this engine can handle. I bolted on a Grish 5x3 cut down to 4 inches and it flew the plane better, caused less heat and made the needle setting wider.
It doesn't take much to make a 4-6 inch prop and it is wonderful to see your "handy work" in action. A good tinkerer's experience

nekked_man_2000

just curious, why not do the helical pitch, and carve it to a true pitch? It's not that difficult to lay out a prop blank. For me, I like doing the prop blank so I can experiment, a little less pitch, little more pitch...and I know what I'm working with. Once you get the initial pattern for the blank, then you can just thin it a little bit or add a little thickness to it to make the changes...then you have a baseline to work from..Just curious. I got in the prop carving thing with an article in RCM I think for an .020 sized plane and he carved his own props because you only had pretty much one prop for that motor. I know on my little .049's just a little difference can go a loooooong way, and a couple hundred rpm in one direction or the other can mean a spectacular flying plane or a dog. But, you have powerful engines and so it may not be as much of a problem. I had an ace simple messerschmitt with a "product" engine on it and if you missed the setting by just a little it was almost unflyable, just a couple hundred rpm's.

Austin

combatpigg

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Hi Austin. Well, for starters, I don't know how to layout and shape a helical prop. I did some snooping around and only found rubberband freeflight info and old time scale prop info. The pusher prop I made out of maple a few years ago ended up with a twist but I don't remember how that happened. That prop worked real good, it was so light and pretty stiff.
This would be a nice skill to master, that's for sure.

nekked_man_2000

yeah, I've done internet searches for that too, very little information. If you are an AMA member in the member section search the archives. There is a very good article (actually a 2 part article) in the archives on making your own pylon props by Hal Debolt. Very good information, another couple of articles on just basic prop carving...and I think recently, within the last year, there was a short article by Dave Robelen (I think) showing the basic layout process...it's pretty much the same as what you are finding on the net just more detailed...the stuff I found on the net doesn't really have enough information to be useful. The article by Hal Debolt is a good read even if you're not going to make a prop, I used it and another article to learn how to make the unusable/useless wooden props that are available at the hobby shop work for me as well as APC props. So, for instance when I couldn't find a 12X4 APC, I modified a 12X4 Zinger and made huge improvements, bonus was it was lighter than the APC props and my little .40 could transition faster in 3D stuff. If I wasn't in the process of a move I'd locate said articles and e-mail them to you...but I'd hate to tell you I'm going to do it then it takes me 3 months.

Austin

GrahamC

neat prop! CP you having way too much fun!

Carving props can be fun rewarding, especially if you need something special and can't find one off the shelf. There have been several good articles in many of the model magazines in years past. Unfortunately the modern publishing industry sees no place for this sort of article in today's magazines.

As a start, for some good information you might want to check out:

AMA magazine May 1976 for Jim Wade's article on his Eagle I - a 1/2a proto racer, some good details on making 1/2a props.

AMA magazine June 1978 for Hal deBolt's article titled How to make High Performance props Part I
AMA magazine July 1978 for Hal deBolt's article titled How to make High Performance props part II

AMA magazine May 1977 for Hal deBolt's article titled Better Props for Formula 1

AMA magazine May 1983 in Gene Hempel's Control Line Speed column for Jerry Rautio's discussion on propeller design Part 1
AMA magazine July 1983 in Gene Hempel's Control Line Speed column for Jerry Rautio's discussion on propeller design conclusion

The last two references are more in depth that most will ever want to know.

It's been at least 20 years since I last carved a 1/2-a prop. I have some hard maple blocks set aside for whenever the urge strikes and I have been toying with the idea of setting up a TD 049 with a clockwise crank for a nostalgia 1/2a speed job and I would need a suitable prop.

cheers, Graham near Ottawa Canada

combatpigg

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Thanks guys! I'll check out those links. The problem with trying to draw layout lines on this plastic is finding a fine line marker that leaves a visible mark.
I cut a lower pitch prop out tonight and used an autobody style disc sander to make short work of roughing it out. This time the blank is 1/4" high x 1/2"wide and 5" long. It looks about the same as a 3 pitch. This prop really puts out some thrust, the engine revs it well into the 20,000 range, sounds happy.

combatpigg

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Tonight I "broke ground" and began the nontest plane.
So as usual, there will be no time spent drawing plans until AFTER the plane proves to deserve being drawn.
The heart of these sheet wing planes is the contest grade balsa to make the wing nice and light. If you try to build one with normal grade wood, it wont fly as well. This is SIG wood that I'm using, each sheet costs about as much as a pack of cigarettes.

One of the photos shows the complete array of tools and materials to get the wing to that stage. It's just a flat bottom airfoil, the top side is planed and sanded to a nice smooth shape with the high point at about the 30% chord line.

Another photo shows a fully prepped elevon with a greased 2-56 torque rod that has been fiberglassed to the flap with 1.5 pound cloth and medium CA.

The last photo shows the hinged elevon right after inbedding the "axle" portion of the torque rod in a mixture of 5 minute epoxy and micro-balloons.

These planes can very easily end up tail heavy, so I will do what I can to position the engine forward and leave room up front for the battery.

combatpigg

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Man! This sucker's going to be done pretty soon!

Just wrap it in packing tape and go fly......

MJD

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What is that on the corner of the bench in the background?

MJD

combatpigg

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That's the wing off the original SWR pusher, with a "field mod" taped to the fin.
I always make the fins too small.....big fins look dorky to me. [:'(] Amazing how little change it takes [sometimes] to get them on track.

combatpigg

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OK, just have to build the lower hatch and strengthen the fins and all the carpentry is done.
The canopy was found at a hobby shop, probably for a RTF model. It said "1/2A" to me, but it's taken a few years to work it into a plane.

RocketRob

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Hey CP,

Lookin good - might be tough to beat, I imagine there are a few to reconsider their entrys?
Whats that between the servos and the rx? Looks like a reject from Pike's Market? I know it's your tank/bladder but do tell the story, please. A fiberglass case for the bladder?

combatpigg

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Howdy Rob...hows your ME-163 nontest plane coming? Now wouldn't that be cool?

The bladder compartment here is a plastic golf club tube. It is about 1 1/8" I.D. The inflated diameter is important because the inflated bladder can't be squeezed by the compartment at all. If so it will give a false high pressure that upsets the needle setting. The bladder is black latex 1/8" thin wall found in the archery dept. It blows up to a thinner diameter than 1/8" fishing tackle tubing.
I wonder if the makers of this tubing know that guys have been using it for 60 years to go 100 mph?
I've found that having the bladder exit the compartment at a shallow angle is best so it doesn't accidentally pinch itself off. I've had running problems and found that it wasn't the engine or the setting, just dumb plumbing. So for now on the bladder will be inserted through a balsa block "45" at the far end of the compartment.
To glue in the balsa end caps, rough up the plastic tube with 60 grit and use medium CA.
pack any gaps with saw dust and CA.
I used 1 oz cloth here to re-enforce the end caps, but it's not crucial.
In the future, I will try a FG layup of a fuel cell. Use a golf tube [slitted lengthwise for a mold with a built in release. I'm not sure how much weight would be saved, but it's another opportunity to inhale more CA fumes [sm=tongue_smile.gif].

combatpigg

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I couldn't get used to the rabbit ears, no matter what I did they just got goofier looking.
My dog liked them, though.
Here's a less cartoonish look I hope. Not only that, but hopefully more functional.

kpriddle

I'm just curious, why exactly would one fin be more funtional than two?  Less drag?

KP

combatpigg

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KP, I hope 1 fin VS 2 fins on this plane wont mean much for aerodynamic function. The main issue is trying to keep the dead weight in the back of the plane to a minimum. If 1 fin does the job, then that's the way to go.....I think.
Every extra gram of weight in back will need to be counterbalanced with 3 grams of lead in the nose. I might find out after the model has been test flown that there was "room" in the design to have the 2nd fin. It might even prove to be needed for stability, but I'm going with TLAR engineering.
Scratch building is about a bunch of little decisions coming together, which is what makes it so fun.

kpriddle

Well, yes, of course the less weight the better.  Anywhere it can be taken off...go ahead.  In fact, I scrape any extra glue that I have left over on all joints on my Guillow's electric kits (maybe a little too far you think).

I now notice that the single fin you have is quite large so stability does not look like a problem.  It's all about decisions.  Decisions...decisions.

KP

combatpigg

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It's all wrapped up. Weighs 12 ozs, but there's 3/4 oz of lead stashed in the nose, so it's actually 12.75 RTF...for now. I might discover later that some of the lead isn't needed, but I might need more. Plugging the dimensions into the CG calculator is still a matter of intepretation of where some lines begin and where others end, plus the cockpit in front of the wing throws the calculations off.
Covering the plane with Towerkote added 1.2 ozs. I glassed the fuselage and had every intention to paint it, but chickened out at the last minute and did the whole plane with iron on except for the engine area. So, there's some unneeded glass and epoxy on it...maybe 1/2 oz worth.
I'll send it off rich on the first launch and cross my fingers.

ProBroJoe

Looks great CP! What is that, a one week build from concept to completion? Oh wait, it's not over 'til the fat lady (or Norvel in this case) sings!

I know I've said it before, but I'll say it again, I love how you don't let the details slow you down. Maybe that "lack of worry" comes from experience, but whatever the case may be, it's a good lesson for all!

Now you know, if you're not happy with the way the little Norvel performs, I think it wouldn't take a whole lot of work to graft in a 24mm rocket motor mount.... I think a launch on a F24 would really get your attention!

Anyway, cool stuff, Chuck, I always look forward to your posts (whichever forum they happen to be in)...

-Joe

RocketRob

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Hey CP,
Could you get the wing any thinner?

Looks great and the covering over the glass looks impressivly smooth!
Bravo!

combatpigg

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Joe, thanks for the vote of confidence.......however, tonight didn't go so well. The plane left my hand OK, showed early signs of being a little bit nose heavy...it took full up stick to get through the launch phase up to flying speed.
Once up to speed, the plane didn't feel right and I stuffed it at full speed [60 mph or so]. At first I wasn't sure what went wrong, this stuff happens kind of fast. Upon further review I found that the righthand stick on the transmitter is not centering quickly, plus it feels like it's got a bind going on. The radio is only about 15 years old, what a POS! This is the first TX failure I've ever had in 25 years.
The damage is "modular", even though it looks bad now, it'll be going again soon.

Mr Cox

Nice build, looks just right again, can't believe how fast you put these things together and they just keep comming... [sm=thumbup.gif]

combatpigg

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Thanks guys. This is my 3rd 1/2A pusher flying wing, the first 2 weren't real pretty...this one did turn out nice.......[if you go for the Karman Ghia look].

I taped the plane back together, checked the thrust angle, control throws, CG and set it up with a Spektrum PFer radio [with the funky 90 degree antannae]. The biggest flaw I could find besides a crooked nose job was the elevons are made from the same ultra light balsa as the wing and they are too limp. Should have made them out of medium. To compensate I cranked up the throws.

The first flight had a pretty hairy launch with a roll to the right and a dip. It pulled out and flew fine after the first critical 2 seconds after release.
This sucker is LOUD! There is an echo coming off the plane, probably from the prop passing so close to the vertical fin. It might be a signal that there should be more clearance? Anyway, the other thing you notice is that the plane rides the pylon type turns with the nose slightly up, which I'll take over a plane that drops the nose in the turns.
The dead stick glide in is very good, the first landing was a little fast, so I removed some lead for the 2nd flight.
Each and every flight after the first had a "hairy" launch with a roll to the right. I think a better prop will get the plane to pull better from the get go.
For a pusher, it flies OK. With no prop blast over the elevons you've got to remember that Golden Rule about maintaining airspeed. I'd say that this plane has satisfied my urge to build something weird, time to go back to planes with the engine up front.
I don't think I would ever subject the Cyclon to pusher duty, it's too hot back there and that engine is so heavy you'd have to build a .15 sized contraption for it to push around.