I need better top end

[Aaron1100us]

edge 540T 5.5lbs 55 inch wingspan, Saito .91 spinning a 15X6 APC. at 9,000rpm. Top speed is only 50 mph or so. I'd like 75-100+mph.

[Vic3D]

You are overpropped, first of all. Biggest prop I would use on that engine is a 15-4. If you want more speed try a 13-8 APC.

[Aaron1100us]

According to the Saito website, the .91 it says Prop Range:12x8 - 15x6. Will a 13x8 still give enough pulling power for hovering and unlimited vertical? You'd think a .91 would be able to pull a 6.5lb plane along at a pretty good pace. I'm just saying that because I've got a trainer plane that weighs about the same with a little OS .46AX 2 stroke and a 11X8 prop. The OS site says the .46AX is rated for an 11X8. That .91 Saito has tons more power than the .46.

There is a guy at the field that has some type of WWII airplane thats probably a .90 size or just a bit bigger that has been clocked at 110mph. I might have to see what he is using for an engine and prop. I'd love to hit those kinds of speeds but still have enough thrust for hovering.

[exeter_acres]

do you want to hover or go fast?

[Aaron1100us]

I originally wanted to be able to hover too but this plane doesn't like to go slow, the controls get mushy. I think its more designed for aerobatics. It flies better at full throttle. But full throttle is only around 50mph. That really isn't that fast. So I want top end but I still want to be able to pull up and have good vertical climbout.

I'm using 30% heli fuel, velocity stack on the carb and a performance specialties muffler.

[crazyjoe]

Is that plane designed for that speed.

[heligrom]

First off, you don't want to go TOO fast because you will overspeed the airframe and cause flutter. Secondly, I've flown this airframe and although it doesn't like to go slow, it ain't wanting to go too fast either. 50 MPH should be plenty to do anything you want.

[exeter_acres]

I'd try Vic3d's suggestion....

a 15x6 is a bit big for that motor....

[Aaron1100us]

According to the Saito site. the .91 is rated up to a 15X6. That engine has tons of power compared to my .46AX which can swing a 12X6. I did find a site that said the Saito .91 can swing a 14X8 if running high nitro content. I'm running 30% nitro so that should be fine. But that still only puts me at 68mph. Guess I'll have to live with that. I just find it odd that a .90 or 1.20 size WWII type plane can go 110mph and this .50 size plane with a .91 can't.

[Aaron1100us]

According to the Saito site. the .91 is rated up to a 15X6. That engine has tons of power compared to my .46AX which can swing a 12X6. I did find a site that said the Saito .91 can swing a 14X8 if running high nitro content. I'm running 30% nitro so that should be fine. But that still only puts me at 68mph. Guess I'll have to live with that. I just find it odd that a .90 or 1.20 size WWII type plane can go 110mph and this .50 size plane with a .91 can't.

Just read on another forum. Forgot about wing loading and wing design. My wing is thick and the one on that other plane is thin.

So whats the fastest this plane can go that wouldn't be too fast for this airframe? I know 50mph is enough but would would only 68mph be too fast? I can live with 50mph if I have to, just seems kinda slow. My 40 size trainer plane with a 11X8 goes faster.

[cjcyclesrc]

	Quote: Originally Posted by Aaron1100us
	According to the Saito site. the .91 is rated up to a 15X6. That engine has tons of power compared to my .46AX which can swing a 12X6. I did find a site that said the Saito .91 can swing a 14X8 if running high nitro content. I'm running 30% nitro so that should be fine. But that still only puts me at 68mph. Guess I'll have to live with that. I just find it odd that a .90 or 1.20 size WWII type plane can go 110mph and this .50 size plane with a .91 can't. Just read on another forum. Forgot about wing loading and wing design. My wing is thick and the one on that other plane is thin. So whats the fastest this plane can go that wouldn't be too fast for this airframe? I know 50mph is enough but would would only 68mph be too fast? I can live with 50mph if I have to, just seems kinda slow. My 40 size trainer plane with a 11X8 goes faster.

Just because the manual says the motor is rated for the max prop size doesn't mean that is the best prop for it.

Vic3d gave you some good advice. One thing you will learn is that paper calculations and real world are two different things.

[Aaron1100us]

Ok, thanks. I wonder why they would state that if its not really true? I'll try a smaller prop with more pitch and see. If I don't like it, I might go to a 15X4 or 5 instead of the 15X6.

[cjcyclesrc]

	Quote: Originally Posted by Aaron1100us
	Ok, thanks. I wonder why they would state that if its not really true? I'll try a smaller prop with more pitch and see. If I don't like it, I might go to a 15X4 or 5 instead of the 15X6.

It turned the prop and flew your plane so it is true that it will run with a 15x6. They give an rpm range as a guideline for you to prop the plane so it runs in that range. You shouldn't expect to get the max rpm out of a max size prop. Everything is a trade off. If you get more speed you will loose pull and if you get more pull you will loose speed.

[TazmanianDevil]

20% nitro.
14-8 prop.

[wylieruneyjr]

I think you should prop the engine to turn less than 9000RPM. Somewhere around 7500 RPM I believe would be plenty. Want to go fast try a 12x12 I,m running a 13x13 on a FA125, getting close to 100mph, un confirmed with a Cosmic Wind Minnow. Four strokes can go fast. You need a good dependable LOW idle with large pitch props, to be able to land. Hover is out but speed is in. Want to hover need a 4 pitch WIDE blade , no speed but pull-out of hover good 14x4w. I suggest you go to 15% nitro and save so money. I would use 30% if I was in some type of competion only. 13x6 might be a good compromise between fast and hover. Props are cheap, experiment with some. BIG TIP: Lower elevator throwws on large pitch props to prevent snaps and high speed stalls. High pitch = > 8 pitch <RUTNBUC>