Most of us use .25 & .28 Magnum engines and use a 9x5 prop. What size props do most of yall use for your .25 size combat planes? I have been looking for a prop to get some more speed, any suggestions?


FUZZ

Try the APC 9x6. Tuned exhaust is worth a look too.

Most RCCA open B events I've been to, everyone is using MAS 9x4, with or without tuned mufflers.

If I'm using piped Norvels, I go with a Master Airscrew 9 x4. An APC 8x5 screams big time, but I usually need more than a 6 oz tank for a 5 minute round.

Without pipes, I like APC 8x5's on Norvels.

OS FX 25's seem to like Master Airscrew 9x4's, even unpiped they scream and hold speed.

APC's are probably better props, but I break them too often in the air and like the durability of Master Airscrew. I hate not finishing a round because I hit someone with my prop, and break it.

I went out and did a lil combat with a few other local guys. One had an ASP .25 and the other has an MVVS .26 with a tuned pipe and I had a magnum .25. The MVVS was incrediably fast. The MVVS has to be one of the fastest combat engines that I have seen.


FUZZ

My Mag .25's with mousse can seem to like the APC 9x4 best, though it will bleed some speed in turns this way.

The Mag .28 is a much more powerful engine than the Mag .25, and it likes the MAS 9x4. I also run the KY mousse can on them.

Generally, APC props are more efficient, but load the engine more than the same size MAS. I think I read somewhere that the MAS props are actually pitched differently, so that a 9x4 MAS is roughly the same load on the engine as an APC 9x3. If I had a 9x3 APC, I'd try it to see what happens. But I don't, so I stick with the MAS 9x4 on most of my combat planes.

The lower pitch results in higher RPM, which actually makes the plane fly faster than with a higher pitched prop, and the 9x4 won't bleed speed in turns like the other props, and in combat turns are where it's at. Straight line speed isn't very important anyway.

Is there a website that will have instruction on how to make a muffler out of a mouse can? Do you have a pic of it? And appx how many more rpm do you think it makes with it over the standard muffler?

Thanks,
FUZZ

Fuzz,
Take a look at these threads:
http://www.rccombat.com/forum/topic....=Modifications

http://www.rccombat.com/forum/topic....=Modifications

http://www.rccombat.com/forum/topic....=Modifications

HTH,
D

I've seen 1200 to 1800 rpm improvements, depending on engine and prop. Well worth the effort or money, buy a Jett tuned muffler or Nelsen Ultrathrust if you've got more money then time or engineering skills.

Fuzz:

Most of the guys I fly combat with use MA 9X4. Also for the mouse can muffler, take a look at Tattoo's design at www.spadtothebone.com. This type works great for Irvine and Norvel and does not require a Mac's header.

Good luck!

Flying Z hobbies has the mouse can ready to use for 8$. The also sell the headers you will need.

Flying Z Hobbies makes a complete mousse can and sells it with the Mac's headers for $28. The cans alone are $8. They add 2,000 rpms to Norvel .25BB engines.

Address for Flying Z is www.flyingzhobbies.com

Good luck.

Do they have the mouse can tuned pipe and header to fit a Magnum .25 & .28?


Thanks,
FUZZ

I use the KY Mousse cans from Flying Z hobbies. They aren't very expensive, even counting the $20 for the mac's header. I get over 2,000 on my Mag .28, they tac over 18k on the ground with the MAS 9x4. And that's with no modifications to the engine besides the can.

Get the "OS" header pipe. The Mag bolt holes are very close to the OS .25FX, but not quite. I then take a drill and ream out the holes on the crankcase just a hair. We are talking a small enough reaming that you can't tell if it's been done to the engine or not until you install the pipe. It just takes a moment.

I went to the SPAD website and followed their directions on the mousse can muffler and it was actually alot easier to build than I had imagined. I am now ready to test it out on my new modified Gremlin.


FUZZ

I went to the SPAD website and built a muffler exactly as they specified and I saw very little if no improvement to my Magnum .28. I am using a MA 9x4 prop? Any suggestions? I am running Omega 15% fuel and am only turning around 15,000rpm and just a couple of hundred rpm more with teh mousse can.


Thanks,
FUZZ

Is your engine broken in? I saw a pretty good increase with my Norvel.

The engine is new but I had already ran appx 3 tanks of fuel through it before adding the mouse can, I really expected something more than what I got. Im just unsure of what the exact problem is.


FUZZ

I don't know what you are doing, but my Mag .28XL with KY mousse can is turning over 18k with the MAS 9x4 on 15% Omega fuel. (I was tached at 18,400 at one contest, but I don't normally use a tach, mine is broken).

You should turn over 15k with just the stock muffler, never mind the can. I'd say the engine isn't broken in yet, or you're having some kind of fuel or carb problem. Or your tach isn't working right. It's possible that the can is causing too much back pressure. How does it tach with the stock muffler? Also, in theory, you want the inner pipe to be "tunned" to specific length and distance from the back wall of the can. With the KY cans, I can sometimes increase RPM by moving the can in and out on the silicon coupler, though I usually don't bother.

Well,....... I went out and flew some combat this weekend and my new modified Gremlin flew great and I still managed to keep the weight down to 2lbs 14oz. I put the mousse can muffler on my Magnum .25 and I did see a noticeable performance increase. I think that the problem with the .28 magnum is that its just not broke in yet.


FUZZ

Fuzz

I remember helping a guy a couple of years ago that was testing a Norvel (bearing not the bushed). He had a 9x4 with a mouse can. I don't remember what he was taching, but after shaving the sharp edges off the prop and replacing a plastic spinner with a spinner nut, he picked up 800 or 900 rpm. I had forgotten about this, but I have tried to use spinners on combat planes instead of nuts and have picked up considerable rpm after changing. I don't know how shaving the prop (usually done so we don't cut fingers when hand starting) can account for better rpm but it sure did in this case. Obviously we want our props balanced and I know plastic spinners, especially if they are oversized can be out of round/balance.

Greg

You're saying that a spinner had a lower rpm than a prop nut? That doesn't make sense to me, except maybe as a vibration thing, though I certainly don't know enough to be sure about that. My guess would have been that a spinner would have higher RPM than a prop nut, as the spinner covers the hub of the prop and smooths out the airflow in that area. But I am totally guessing about that. Hmm, now that I think about it, maybe it's a rotational inertia issue? A spinner has more mass farther from the center of rotation than a prop nut? I'm still guessing though.

One thing I do know from first hand experience is that a spinner can give you a higher level airspeed compared to a prop nut, depending on the airframe and the size of the spinner. But I had never heard of an RPM difference between the two.

Shaving off the mold flashing on the prop makes perfect sense to me, though I had never thought about it before. I assume the airflow over the blades is smoother, creating less turbulance, and therefore less drag on the prop blade, which results in higher RPM. I do shave my MAS props to keep from getting cut and to reduce damage to anything I might hit, but I never considered it a performance thing. Interesting.