George E.

My Feedback: (16)

OS .46FX (baffle removed) running 10% fuel and a 12.25x3.75 prop on a 5.0 lb Morris Knife. Unlimited vertical but barely. Engine running at 11.5k.

Realizing I need to get into the thirteens to start making real power I switched to a Tower muffler. No change in rpm.

Switching to 11.5x4 prop with Tower Muffler 13.6k

The plane now rockets vertically out of sight in about 15 seconds

Out of curiosity I put the OS muffler back on with the 11.5x4 prop. Lost 1000 rpm


Bottom line. If you need some more power out of your OS .46 FX or TT .46 put on a Tower muffler AND switch to a prop that will get your engine running at 13.5k or more.


One drawback of the Tower muffler is the reduced muffler pressure. If I try to hover the Knife with the Tower muffler the engine sags due to lack of fuel. The tank is in the wing and has to travel about 5 inches vertically when in a hover to get to the engine. I now have to mount the tank externally to get it closer to the engine but the power is incredible.

Kevins_RC

My Feedback: (1)

Instead of using the Tower Hobbies muffler, replace it with a mac Header and long tuned pipe. I have found that the long tuned pipe will give you more RPM as opposed to a mini-tuned pipe. Also, instead of locating the pressure fitting in the tuned pipe to pressurize the fuel tank, locate the pressure fitting in the header (i.e. Morris headers). You'll get more pressure to the tank and you will not have to move it out of the wing unless you really want to.
Hope that this helps you out!

George E.

My Feedback: (16)

Kevin4hsrcm

If I get the mac header what tuned pipe do I use? You said "the long tuned pipe". How long?

To move the fitting did you just drill and tap a hole in the header? Is the pressure greater there? The exhaust velocity is greater so the pressure is lower (Bernoulli effect)? Right?

I don't want to move the tank closer to the engine.

Thanks for the tips. I will try them.

Billy Hell

My Feedback: (2)

Hey Geo
Go here. Maybe it will help.
http://macspro.brinkster.net/tuning.asp

George E.

My Feedback: (16)

Thanks Billy

I think I am just going to mount the tank on the side of the fuse closer to the engine; that will be the easiest and cheapest solution.

The Macs products look interesting but I really like the Tower Muffler. I only spent $13 for the muffler and $3 for the new prop and my calculated horsepower went from 0.92 up to 1.30. Not bad for only 16 bucks!!

Billy, you will really like your Knife if spins, elevators and hovering are what you are after.

Let us know how you like it.

Kevins_RC

My Feedback: (1)

The Tower muffler is a cheaper route, though the Mac Header and Long tuned pipe has serveral advantages:
1. More HP - even over what you are using,
2. Ability to custom tune the header. I run mine about 1/4-1/2" longer than what is recommended. The extra length induces extra back pressure, whicgh moves the power band closer to the mid range RPMs, where you want it for a Fun-Fly.
3. Makes cleaning the aircraft allot easier, because the exhaust outlet is further back on the aircraft (I'm lazy ).

As you probably saw on Mac's website, they only offer the mini tuned pipe (which is not as good as what you are using now), and the long pipe. The 40 - 50 size motors require a 6.5 mm tuned pipe - for future reference. Once you try this set-up, you'll never want to go back.

rightflyer

I am not sure moving your tank will help. I had the same problem with a SE and the tank is near the firewall.

elvis-RCU

hey man try a smith power pipe works great on a os 46 15000or better on a 11x4 prop . engine has good transition and VERY reliable . it's a bolt on item pre tuned and ready to go for $45.00 contact wilson's rc hobbies www.wilsons*********.com you cam email them threw there sight
BREAK A PROP!!
ELVIS

George E.

My Feedback: (16)

I left the original tank in the wing and mounted a small tank to the fuse using eye bolts and rubber bands. This Saturday I'll see if moving the tank closer to the engine eliminates the engine sagging.

If that doesn't work, my only fall back is to squirt some Armorall into the gas and see it the problem was fuel foaming.

My feeling is the problem is a lack of fuel pressure since the engine works fine with the original OS muffler, but it could be some weird resonance due to the tower muffler.

CONTENDER

Hey Geo,
One of the cheapest speed secrets out there is just picking up the Macs muffler for the engine you are using. They are light, one piece, and usually cheaper than the stock muffler.
I have used them on on both the Max 49fx, and 32sx, with great results.
Have fun,
CONTENDER

George E.

My Feedback: (16)

Moving the tank closer to the engine solved the problem. The Tower muffler and new prop really made the engine come alive. The Knife rockets vertically and has great throttle response. I am getting another muffler for my TT .46

rchobbymaniac

These engines should well be be running over 14000 rpms! Especially the OS .46fx

gtalbot

My Feedback: (5)

Contender

The one piece Macs muffler looks simple, being one piece and all.
It's also cheaper than the tuned pipes.

What kind of performace boost does it give?
Will it help with the fuel pressure to get the fuel up to the engine in hovers?

PaulSwany

My Feedback: (45)

I've used the one piece Mac's muffler before... Marginal increase over stock.... 400 - 500 rpms.... I've had better luck with the Tower Muffler on a 46... 500 - 600 rpm increase...

CONTENDER

gtalbot,
I have only had a tac on the 46FX combo, and if you believe the reading, it was showing close to 16K with a Master Airscrew 10/6. To be honest, I have only used these for outright speed, not on hovering type models. The 32fx is on a very light , stock Diamond Dust, and there is a noticeable speed increase over the stock muffler. ( Using a 9x7 APC).
The 400 to 600 rpm range increase sounds about right. The biggest value, is the cost, and the weight!! You will have to re-balance your plane after you change from the stock muffler.
Try one , you will like it!!
CONTENDER

SWICK

My Feedback: (4)

I HAVE A KNIFE AS WELL WITH A 46FX AND HAVE HAD THE SAME PROBLEM HOVERING IT WOULD LEAN OUT WITH A MACS PIPE AND A TOWER PIPE. I HAD TO PUT THE STOCK MUFFLE BACK ON WITHOUT THE BAFFLE AND A 11.5X4 PROP WORKS GREAT BUT STILL AT TIMES IT LOOSES PRESSURE IN THE TANKS ANY OTHER RECOMENDATIONS BESIDES MOVING THE TANK CLOSER TO THE ENGINE?

WHAT ABOUT MOVING THE PRESSURE FITTING CLOSER?

George E.

My Feedback: (16)

I left the original tank in place and capped it off. Tie wrap a second 8 oz tank to the side of the fuse, works great and you can do a flyby to see if you're low on fuel

SWICK

My Feedback: (4)

I JUST MIGHT HAVE TO TRY THAT.....I DIDNT REALY WANT TO MOVE THE TANK OUTSIDE BUT I GUESS I WILL.

Texas 3D

My Feedback: (16)

I mount the tank on the outside of the fuse on all my profiles and just notch the wing a litte, so you can adjust height of center line of tank. No problems what so ever by doing that. Here is a pic of the tank on my GWB.

Hacker

i have os46fx tank in wing using mc pipe set up...never a problem in hover....nacs pipe 22$ moose can 1.98$...kinda fun to build

planecrazy101

I noticed you said you were using 10% fuel. Try some 15%.

Hacker

just came back from flying...hovered the knife out of fuel..dorked it from 2 feet....no damage....my set up is os46fx with mcp. tank in wing switched to 10% cool power to nite (usually use 15% lhs was out of15%)...had to "richen it up about 1/4 turn" i have never had a flame out or had it go lean and sag(tonight was the 1st time i ever flew it out of fuel) it ran perfect to the last drop.
when i set my engine i" peak" it then back off slightly. i have noticed that if i peak it on the ground then it will lean in the air.
hope this helps

Dogdewd

My Feedback: (6)

I have the exact same setup. Knife, 46FX, tank in wing. Tower muffler, 12 x 4 prop cut down to 11.5. Unlimited vertical at 1/2 to 5/8 throttle and have never had a problem with the engine sagging with this combo.

However, I did have a problem with the engine getting too hot when I was using a 12.25 x 3.75 APC. I wonder if the drop in RPM is due to the engine over-heating?

Hacker

Fred H,
i use the 12.25x3.75 apc...it does run hot...think i will go back to the 11.5x4...or maybe i can talk kevin in to just one little bitty
"hand made custom cut props" he makes

stomper

My Feedback: (20)

Kit built Knife at 4 pounds 9 oz. OS 46FX, Tower muffler, APC 12.25x3.75 prop, 10% fuel. This thing is a rocket! The throttle stick is rarelly near the top during flight.

Doug