prop for LA .25

[DanielGelinas]

Hello All,

I've recently changed my fox .35 for an LA .25 on my super clown. I'm running a 9-4 prop. I need to fix the fox BURP issue. The plane flies great with the LA .25. Is there any advantage trying a 10-4 prop for this plane and engine. I'm flying on 60 foot lines.

I'm asking because I'm really not very good at understanding propeller dynamics.

Thanks,

-d

[Bill Little]

Try an APC 10-4.  Many of the people say that it is a good fit for the .25LA.  Then again, I have heard of several using the APC 9-4 to good effect.

A larger diameter prop can give some benefits in different parts of the pattern.

Big Bear

[wwwarbird]

 I use a black Master Airscrew 9x6 on them and spin it up, works great for me.

[Dan McEntee]

  When I first put together my Primary Force ARF, I used the LA.25 just because that's what they showed in the manual. I used an APC 10-4 on it, (a 40+ ounce model)  at around 10,000 to 10,500 RPM at take off and it had a nice run. The model was just a bit too heavy for the LA .25 even though the flight performance was OK, I decided to try an FP.25 and use the same set up on that engine today. I think which prop you use would depend on the size and weight of the airplane you have the engine in.
   Good luck with it,
   Dan McEntee

[John Eyer]

d

[john e. holliday]

I use an APC 10-4 on my Primary Force and muffler pressure on this particular LA .25.   I have a couple that don't like the muffler pressure.  Also uni-flo tanks.

[wwwarbird]

I think which prop you use would depend on the size and weight of the airplane you have the engine in.
   Dan McEntee

...that would definitely be the first consideration, but for a typical .25 size model, say in the 38" to 42" span range, the 9x6 works really well.

[Brett Buck]

I mounted an LA 25 on my 90% profile Cavalier and it took off right slowly, too slow, no line tension.. The 9 x 5 just didn't do the job, so I went to a 10 x 5 Y&O, yes an original Y&O, and what a difference it made. Tension, nice lap times and 8, countem, 8 over head eights in a row. That engine needs to be loaded, and a 10 x 4-5-6 will do it.

   That's interesting, I have found unloading all these engines works wonders. I would have started with a 9-4 APC, and launched at about 12000.  It pulls a Nobler OK, it should fly the heck out of a reduced Cavalier.

    Brett

[Dwayne]

I've never tried a small prop I used a 10X5 powerpoint on a Twister I launched at 9,600 and it worked quite well with good line tension but it did lie down a bit in outside maneuvers   I'm wondering now if a 9X4 might have been better.

[Paul Smith]

You need to get a tachometer (about $30) and do this by engine RPM.  The most important thing is getting the engine to its happy speed.  Without pulling the paperwork, 14,000 comes to mind for an LA25.

Most of this talk leans toward massive over-propping.  For an LA25, it an 8x5 or 8x6, or maybe a 9x3 or 9x4.  No more.  Nothing in the 10" size.  Increasing diameter increases load to the fourth power.  Increasing pitch is linear.   

That extra inch of diameter adds a BIG dose of disc area that's traveling farther and faster than the previous size, not to mention mass.

[Tim Wescott]

All I can say is that discussion is bringing out my rule of thumb for any engine: get a bunch of props and try them all!

[Brett Buck]

You can all say what you want, but if you witnessed the flights, as many did, you too would agree as it flew MUCH better with the 10 x 5 Y&O as opposed to the smaller prop. 

   I am not disputing your observations, of course. But there's a sort of "dead spot" in the 20 and 25FP at the revs you need for 5" of pitch.

      Brett

[Steve Helmick]

  I am not disputing your observations, of course. But there's a sort of "dead spot" in the 20 and 25FP at the revs you need for 5" of pitch.

      Brett

Yeah, but the subject is the .25LA, not the FP. They do run differently, and the .25LA will turn a bigger prop.
I've tried the 9-4 APC, 9-4 Graupner (about equal), a 9-5 APC, and a 10-4 reworked TF Power Point. All worked fairly well, but I'd like to try a 9.5 x 4.5 APC, which is a little hard to get, but would probably work very well for something like a Super Clown, Flt. Streak, or Ringmaster. I read that the Ring Brotherhood agrees on that prop as being good for the .25LA/Ringmaster combo.  Steve

[DanielGelinas]

Well thanks for the replies!
I was going to try the 10-4 today but we are getting the tail end of this hurricane here in the eastern townships, Quebec, so no flying today.
I did begin construcion on my son's akromaster thought.
The 9-4 pulls the super clown fine. It just doesn't look right to have such a small propeller on this plane...

Regards,

-Danny

[Elwyn Aud]

The APC's must be pretty tough. One of our members managed to break the cylinder off of an LA-25 without breaking the prop! Notice the scuff marks along both blades where they hit the take-off pad. Not likely to happen very often I'm sure. Perhaps there were some minute stress fractures from a similar landing a few months ago.

[john e. holliday]

Well I got a third place today in Topeka with the set up I posted.  I messed up the hour glass royally.  Not the combinations fault.  It was the pilot not flying enough.