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weird prop question

Old 03-05-2008, 12:24 PM
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Default weird prop question

hey guys i have kind of a weird question for you, i have a hobbico plane that uses a 46 size engine and i used a 10X7 prop on it. the engine is screwed up and and i'm kinda experimenting with the plane now i'm i'm trying to mount a 25 os engine in it. i know its wayys to small but i wanna try anyways. i just wanna know what size prop i should try. i really don't totally understand how the size thing works and how to decide what size to use when, so if you could explain that it would be great......thanx guys.
Old 03-05-2008, 12:29 PM
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Default RE: weird prop question

http://www.uoguelph.ca/~antoon/hobby/props.htm

Try this link and see if it help.
Old 03-05-2008, 12:33 PM
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Default RE: weird prop question

You want to try to pull around a 40 size plane with a 25 engine? Ok.. let us know how that works out.. and if it even gets off the ground.

You will need something with enough pull to get airspeed up, and enough power to hold it there. You may get the thing up, but I imagine that you will be at full throttle no matter what prop you select. So, select something with a good diameter and a good pitch.. perhals 9-6 may work? Then again, the engine may not get enough RPM up to place it in the power band.

CGr.
Old 03-05-2008, 12:36 PM
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Default RE: weird prop question

Hey welcome back to the real world CGR
Old 03-05-2008, 12:50 PM
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Default RE: weird prop question

I'd try a 9-6 like CGR suggests. It really depends on which OS 25 engine you have, and what kind of plane you are trying to fly. If you have a .25LA and are trying to fly a sport plane, it may not get off the ground. A .25FX on a .40 size trainer might fly, but you will really have to fly it, it won't have power to spare.

If you have a .25FX, you could probably go to a 10-4 prop.

Good luck.
Old 03-05-2008, 12:51 PM
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Default RE: weird prop question

I believe I fly a 9x6 prop on my OS 25 FX. If it's an OS 25 LA, you may want to drop down to a 9x5. As CGr said, a 25 FX might have half a chance at getting a .40 size plane in the air, but I'd bet the 25 LA would not.

EDIT - I guess Mclina beat me to it!
Old 03-05-2008, 12:51 PM
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Default RE: weird prop question

Of course, you will have to rebalance the plane to account for all of the weight loss in front.
Old 03-05-2008, 12:55 PM
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Default RE: weird prop question

Yeah..yeah.. yeah... We got to Tampa at 1:00 for a 3 PM flight. The security line was fairly long, but, I must admit, pretty quick. Once through, we ate lunch and went to the gate. "It's gonna be late", the gate guy told me, "because it hasn't left Philadelphia yet".

Next thing, it comes in about 10 minutes early... but left a half hour late. Go figure.

Then, half way home, the pilot slows down and tells us that we are in an ATC hold for a traffic backup and are going to be delayed on landing for about 30 minutes.

Then we land at Philadelphia, taxi over near the gates, and the announcement from the pilot is that we are going to have to wait to go to the gate because of the conjestion on the ground. So we wait.

Then, we're off the plane, have carry on baggage so off to the car we go. By now, it's about 7:15 PM. We head over to the Walt Whitman Bridge into NJ... traffic is backed up starting on the Pennsylvania side of the bridge.. took us over a half hour to go 2 miles. Jeech.. genious's in the NJ DOT decide to close four lanes of a 6 lane highway, then work in the gutter lane on the right side with all four closed lanes not in use. Jeech.. Brilliant. We finally got home at about 8:45 PM.

Welcome back, ya say?

What did H.G. Wells say? "All things considered, I'd rather be in Philadelphia." Nah.. I wanna go back to Florida!!!

How's it going, Irish?

Dick.
Old 03-05-2008, 12:56 PM
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Default RE: weird prop question


ORIGINAL: CGRetired

You want to try to pull around a 40 size plane with a 25 engine? Ok.. let us know how that works out.. and if it even gets off the ground.

You will need something with enough pull to get airspeed up, and enough power to hold it there. You may get the thing up, but I imagine that you will be at full throttle no matter what prop you select. So, select something with a good diameter and a good pitch.. perhals 9-6 may work? Then again, the engine may not get enough RPM up to place it in the power band.

CGr.
Probably 95 per cent of the planes you see at a typical RC field are overpowered or way overpowered. It would be refreshing to see a plane flown on the wing with adequate power for good flight. The OP didnt say what plane he has, but most 40s would fly with a 25.
Old 03-05-2008, 01:01 PM
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Default RE: weird prop question

Yeah, but not everybody flys with the throttle fire-walled (wide open throttle). It's nice to have that little extra power just in case... like coming in for a landing and need to go around on short notice.. someone walks on the field for instance.. smack the throttle to full and pull on the elevator and up ya go. Do that with under power and, well, best of luck with that.

CGr.
Old 03-05-2008, 06:13 PM
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Default RE: weird prop question

You can pull a .40 trainer with a .25 . I fly my .40 trainer at less than 1/2 throttle
it just depends what model.
Look at the .25 kadet, its about the same size as a .40 trainer.
Look at the senior kadet, that thing is huge for a .40.

9x6 or 10x5
Old 03-05-2008, 08:11 PM
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Default RE: weird prop question

(Just a joke.)
Are you also going to use micro servos and a park flyer receiver?

Ok real this time. What made you decide to use a 25 and not a 40 size motor? Is it price? The OS 46 AX is only $110 and they have a lot of deals that can cut the price.
Old 03-05-2008, 08:33 PM
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Default RE: weird prop question

springhillflyer - Which plane are you trying this with? If you are trying this with a NextStar, your have a plane that weighs 6-1/2 - 7 lbs (My Alpha 60 with Evolution .61 weights 7-1/2 - 8 lbs for comparison). It may have a more streamed lined fuselage and a lot of wing, but that is still a lot of weight for a .25 to pull. Now if it was a 5 - 5-1/2 lb trainer like the Avistar or SuperStar 40 that would be a different story. I used to fly a Balsa USA Swizzle Stick (older version of the current Stick Trainer 40) on a K&B 3.5cc (.21) and that was a 4-1/2 lb plane and 3-channels. The K&B 3.5cc is as powerful as the OS .25 FX but I found in almost every case I had to hand launch it when flying off turf.

Are you planning flying this off a hard surface runway or turf? If turf I really question if there is enough power in a .25 to get a NextStar off the ground let alone safely fly it, but the others should work. You'll just have to remember it will fly the way the old planes used to - on the wing. It'll feel sluggish and not want to climb very well, but you'll get some good experience from it.

Hogflyer
Old 03-06-2008, 11:55 AM
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Default RE: weird prop question

actually the reason is not about that price its basically for ****s and giggles. just wanna experiment. the plane is a trainer with a 58" wingspan. i'm not sure of its make.
Old 03-06-2008, 12:34 PM
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Default RE: weird prop question

pics? maybe some of us can help identify it
Old 03-06-2008, 12:56 PM
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Default RE: weird prop question

I'm thinking that if it's a Hobbico Superstar, it may work. He would need a paved runway, and it would fly a lot like a Cub. Definitely on the wing. He may have to fly scale, and avoid stunts. My Superstar flew with authority, using the 40 LA it came with. It would take off at less than 1/2 throttle, no problem. Use a 9 X 6 prop for the .25. I currently have the 40 LA mounted on a Slow Poke Sport, and I did that intentionally to make the plane more challenging. I don't expect any problems with it.

NorfolkSouthern
Old 03-06-2008, 03:51 PM
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Default RE: weird prop question

[img][/img] thats the pic of the plane if that will help you.....the one onthe right side, with the tiny engine already mounted
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Old 03-06-2008, 05:25 PM
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Default RE: weird prop question

Hi springhillflyer
On a good day you probably will be able to take off. A good day includes cold weather, about 15MPH head wind, and short grass. I had a pusher puller with two .28 Magnum engines turnig 9x6 APC props. On a "good" day I could take off with either single engine. Usually I would wait till it appeared it would go no faster, then I would "jack" it up with the elevator to get it to run a little higher in the grass. Sometimes quick jerks of the elevator worked; sometimes not. I a perfect day it could break ground with just some up elevator. Once it would break ground I would be satified with 6 inches of elevation. I would build up speed for a while and then try for one foot, etc. Choose a field and direction that will allow you to crash safely. I had a ball with mine. When it was up over 90 degrees Farenheite I could not jack it out of the grass. Once in the air it could be handle fairly well, but you do have to look ahead much further. Turning into a high wind can cause you a lot of altitude or a quick landing.You should do OK. I always had the drag of a stopped prop and the weight of a dead engine. Use a smaller fuel tank or fill it only 50% if you have to. Let me know how you do.
Old 03-06-2008, 10:47 PM
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Default RE: weird prop question

thanx alot for your advice there Villa......i will try that and let you know

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