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15 size speed plane( my own design), & prop question

Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

15 size speed plane( my own design), & prop question

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Old 11-04-2002, 01:34 AM
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ajcoholic
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Default 15 size speed plane( my own design), & prop question

I have been flying a Sig wonder with an old but potent Rossi "record" FIRE .15 on a full pipe. I am currently designing a conventional style speed plane for the engine, and have a question:

currently run an apc 7-5 and 15% nitro, turning 19,500 rpm on the ground. I plan to make a lighter weight airframe than the wonder. I am thinking I want the engine running in the 25,000 range (they will turn up to 30,000 with a smallish prop but then breaking cranks and rods is too much of a possibility so I dont want to go that high).

I was thinking small diam/big pitch would be better than my current prop. So, I have some apc 7-7 props I was going to cut down, maybe 1/4" at a time. Is that a good start or should I stick with less pitch?

Any help appreciated if you have attempted the same thing.

Thanks,
Andrew Coholic
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Old 11-04-2002, 03:00 AM
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Default 15 size speed plane( my own design), & prop question

I seem to remember FAI control line speed models using little high pitch 6 inch diameter narrow bladed props. Perhaps try looking at that option.

Some ground tests to move up to the 20,000 rpm range would be appropriate. You could certainly start with the APC 7-7's but once you start getting them shortened down the airfoil at the tip may be too wide and thick.

When I fly free flight sometimes a couple of the FAI power guys come out to practice. These are Rossi's turning about 25000. The are using 6.5 to 7 inch diameters and the blades look to be about 5/16 to 3/8 inches wide and very, very thin carbon fiber.

This is all second hand I know but perhaps it'll help steer you in the right direction. Some web searches for these areas may turn up some more hard facts for you.
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Old 11-04-2002, 03:55 AM
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Default apc pylon props

Thanks for the info... I have friends that are into FF competative but I thought they used a lower pitch for fast starts. They only get something like 7 seconds or so running - need a good accelerating prop.

I went to APC website, they have 1/4 midget (15 size) pylon props in 6.5-5 to 6.5-6.5 sizes. I will see if Great Hobbies stocks any of these.

I think thats the way to go rather than take a "sport" prop and rework.

ANdrew
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Old 11-04-2002, 07:28 AM
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Default 15 size speed plane( my own design), & prop question

You're right about the finer pitches for FAI free flight. But it's still the blade size. And the fact that when you go up in pitch you need to go even smaller in diameter and blade width to keep the revs up. I didn't realize that APC had the 15 racing props available but the sizes don't surprise me.

And I seem to recall that APC's competition line has beefier hubs to take the high rpms and not fatigue. Nice to know when your arm is just a few inches away from a 20,000 rpm flesh ripper.....
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Old 11-04-2002, 12:04 PM
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Default Fast 15's

Hey AJC,

My current project is a 70% scale version of the Malina brother's Miss RJ FAI racer. Power is to be an Uctkam 2,5 kp with full pipe (it is a Russian copy of the Rossi Mk III) Also having trouble finding props that fit, mainly because the hubs are too thick. I have managed to rework an MA Scimitar 7x4 down to about 6.5 diameter and thin the hub enough to be able to fit the spinner on too. Initial runs are promising. BTW, I am running the MVVS 2.5 throttled carburettor instead of the open venturi. I may also need to use tank pressure, but have not yet decided to tap the pipe or crankcase.
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Old 11-04-2002, 04:41 PM
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Default 15 size speed plane( my own design), & prop question

Derfly, you may want to re-read my second paragraph above about hubs blowing up. There's a reason the hubs are so big. If the commerciall ones don't fit you may want to consider going for good quality carbon props with the smaller hubs. I really don't think modifying hubs is a good idea other than minimal reaming out for shaft fit. Your jugular may thank you for that.
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Old 11-04-2002, 05:35 PM
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Default 15 size speed plane( my own design), & prop question

Well, I ordered the APC 6.5 pylon props in 5.0, 5.5, 6.0 and 6.5 pitch to try all 4.

I also think that once you start running a small prop upwards of 22,000 to 30,000 possibly that thinning the hub is scary. Thats why even the "sport" apc props I wont modify except cut down.

The easiest/safest way to get the thicker hub on the engine is to buy or make a sleeve nut, that will fit into the hub (after you ream it out) and give enough threads to hold securely.

I will not have the props for 2 weeks or so (out of stock) but will post some RPM's when I get them.

Andrew
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Old 11-05-2002, 12:39 AM
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Default .15Size....

Andrew, in the late eighties, I built a .15size RC speed plane for our Mr. Speed competitions (still have the plane too..) The plane was powered by a Qmidget modified Cox Conquest running a tuned pipe. On 35% nitro, it turned a modified Rev-Up 7-6 or 7-6 in the 23k to 26k range.
In the end, the plane went through the traps at 157 mph.

I think I have seen the Rev-Up props on Ebay several times in these sizes.

Best of luck, and post your speed.
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Old 11-05-2002, 01:43 PM
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Default 15 size speed plane( my own design), & prop question

Matchlessaero,
Thanks for the tips - I may have a few revups in my big bag o' wood props! But I am going to try the APC pylons first, since I have them on order allready.

I understand I need to pick a prop, then turn the pipe to it correct? Also, I run only 15% fuel and will be a bit down on speed than you but should be plenty fast for me!

Winter is here, 5 inches of snow yesterday... But, If possible I want to try to get it in the air within the next few weeks. Just to try it. Am working on the airframe and will try and post some data later on...

Andrew
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Old 11-15-2002, 03:28 AM
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Default plane finished..

Well, I finished my new 15 racer tonight. Ready to test fly this weekend if the snow stops! It weighs in at 2 1/4 pounds excactly. Quite light. The wingspan is 36", faom/fibreglass with carbon reinforcement.

The full tuned pipe is inside the fuse. I have a bit of worry about proper cooling, but I ran a tank (5 minutes) through it indoors and it seemed to be OK, I have a scoop in the front and exhaust area under the rear where the pipe exhausts.

Still waiting for my pylon props but I will try it on an APC 7-5 which is what I ran in my WOnder.

Wish me luck...

Andrew
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Old 11-15-2002, 03:29 AM
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Default 15 size speed plane( my own design), & prop question

I wonder how fast it will go? Its got allmost a 2:1 power/weight ratio...

Andrew
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Old 11-17-2002, 01:28 AM
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Default It flies!

OK, the temperature was well under freezing, but the sun was out and no wind. Took the 4WD down to the field and test flew the little 15 racer today. (Man, anyone that flies in the winter knows how cold it is hanging onto a plane with bare hands...)

Anyhow, I just grabbed the fuse, throttled up and it took off right out of my hand! After trimming out, I ran the tank dry doing pass after pass at mid to full throttle. Wow, it really moves out! Has to be doing at least 100 to 120 mph, compared to some other airplanes I have that have beed radar'd. I cant wait to get the pylon props to try them. I was running a 7-5 APC and I know with the 6.5-5, 6.5-5.5 or 6.5-6 it is going to go faster still.

Just glad it flew well, tracks like a pattern plane but man can you take the corners quick!

Here are some shots...

Andrew
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Old 11-17-2002, 01:29 AM
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Default 15 size speed plane( my own design), & prop question

another..
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Old 11-17-2002, 01:29 AM
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Default 15 size speed plane( my own design), & prop question

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Old 11-17-2002, 01:31 AM
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Default 15 size speed plane( my own design), & prop question

last one! I cant believe how much fun you can have for about 6 hours of time, and maybe $30 in materials...

Speed on the cheap indeed! Just better have good eyes... These small planes get away from you REAL quick!

Andrew
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Old 11-17-2002, 05:02 AM
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Default Great!!!

Thats great man!!!!!!

I really like your plane. Glad to hear that you enclosed the pipe. So many people just want more HP and more RPMS with more pitch, it is nice to see that people do believe aerodynamics are important.

Put up some more detailed pics.
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Old 11-17-2002, 05:27 AM
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Default 15 size speed plane( my own design), & prop question

Matchless,
What do you want to see? The interior? Post #10 shows the plane pretty well (me holding it) but I can take some of whatever you ask for.

I didnt fair the engine in, may try that in the spring. Its getting too cold to fly comfortably and soon it will be too much snow to get down to the field where I fly without walking in. Winter! Arghhhh!

I thought it would be cool to enclose the pipe, and even though the engine isnt faired in, its a pretty small front profile. Behind the firewall, there is just enough room for the tank, battery pack (250mah) and on top of the tank the header pipe.

Its my first attempt at making a plane for "speed" flying, all my other planes were either fun fly or aerobatic type. I like it! Definitely going to try some more. Going fast is fun!

AJC

PS. I only have a video camera to take shots, so they are not super as you can see. still have to break down and buy a digital camera!
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Old 11-17-2002, 01:55 PM
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Default Speed plane

Andrew,

Cool plane. Thin wing, skinny fuse, I really think that's the ticket. That's why pylon racer aren't deltas.
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Old 11-17-2002, 03:43 PM
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Default Cool Plane Dude!

AJ,

That's an innovative design with the pipe inside the fuse. Great to be able to try your own idea's to see how they work and how fast they will go.

On your props, and diameter vs. pitch issues, I'd take the prop that you are using now and try reducing the diameter in 1/8" increments. You'll be suprized how quickly the RPM's will increase for a small decrese in diameter. When you make a prop shorter, thin the thickness so it's roughly the same as it was on the standard length prop at the tip. On the APC line, make sure the flashing line on the leading edge is sanded off and as smooth as you can get it. If you look carefully at the trailing edge, you'll see a hump. Get a fine three sided file and remove the hump blending the TE into a very sharp edge. These are small mods that can pay big dividends in performance. It is important to run the engine in the rpm range it's timed for and it sounds to me like you could use some more rpm's. Visit MotoCalc to get good data on pitch speeds. You'll be able to determine your speed pretty close by computing pitch and rpm combinations. Having lived in Alaska for along time, I appreciate your wintertime flying challenges. Best of luck to you..... Jeff.....
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