erratic Tower 75
 

Hi guys,

I Have a tower 75 in a seagull extra. I have had nothing but problems since I maidened it. So far 4 deadsticks resulting in damage and a few others that I recovered without damage. I have a jtec pitts muffler on it. I can adjust the mixture to run a nice high speed and idle good too. I can hold the aircraft vertical for 30 plus seconds with no sagging. Then I take off and it all goes downhill. Anytime I pull positive Gs the engine sags in RPM's. Today I ran the engine up on the ground everything was good and as soon if I took off it died again. Luckily I have adopted the habit if taxing all the way back so I was able to save it before the trees this time. Also when in the air it sounds like a 4 cycle type sound anywhere in the midrange. I was thinking this was because the muffler has two outputs but I was wondering if that sound is normal. (It absolutely sings a solid 2 cycle note at WOT)

Any ideas on keeping it running would be great.

FWIW I am running 15% Omega and McCoy plug with an Idle bar.

RE: erratic Tower 75
 

G'day Mate,
First off, get rid of that plug, use an OS #8 or equivelent, richen your top end, it should gain a few revs when the nose is held up, if it is rich enough, & if the midrange is rich, you need to lean you low speed slightly & do the pinch test at idle.
I assume you know how it should perform, when doing the pinch test.

RE: erratic Tower 75
 

Pilot,


The fact that your engine sags when you pull positive G hints of a fuel tank location issue...

It might be mounted too low, relative to the engine...

The correct level is: fuel tank center-line must be level with the center of the carburettor's barrel (the fuel nozzle).
There is very little latitude for variation from this level (±3/8").

Also, the fuel tank must be isolated from any part of the fuselage, using latex foam and be as close as possible to the engine.

The J'Tec Pitts muffler provides insufficient fuel pressure as well...

RE: erratic Tower 75
 

All things I have been considering. The fuel tank is pretty much level with the barrel. I think it's within 3/8" in but I will measure it later. The fuel tank basically sits in the formers so there is no insulating foam. I will try to sand it out and put some foam in. I was also thinking about the pressure the high speed needle runs at about 2 full turns out. I was thinking about blocking one of the holes from the pitts muffler to see if that would help. Any more advice would be great.

Thanks

Pilotman520

RE: erratic Tower 75
 

This engine was the last straw for me, now I'm an OS only man myself.

RE: erratic Tower 75
 

Would it be possible to try leaving the cowl off, and using the Tower muffler? I wouldn't be surprised if all your engine problems went away by eliminating the pitts muffler. I know that 2S mufflers are ugly, but at least you could narrow down your variables this way.

RE: erratic Tower 75
 

....put the stock muffler back on and get rid of the idle-bar plug, and
the engine will run perfectly. ;)

FBD. :D

RE: erratic Tower 75
 

Did you do a break-in on this engine? How much fuel through the engine before you started flying it?

What prop are you using? What brand? What size?

What RPMs are you getting on the bench with this prop?

RE: erratic Tower 75
 

I did break in the engine about 3 yrs ago on a sig 4*60. It ran good but has always sagged when pulling up hard. Never had the dead stick problems though. I am using an APC 12x6 prop. I tached it the best I could and it was about 11800 to 12000. I think I will put the stock muffler back on and leave the cowl off and try to get it running better. Then maybe i'll put the pitts back on and try plugging a hole.

RE: erratic Tower 75
 

Pilot,


Redo the break-in on a test stand, following [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this thread[/link] closely.

Use a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJA89&P=ML#mults]TowerPower[/link] plug (instead of the idle-bar jig you now have). It is medium heat, made in Japan and less than half the OS #8's price.

Dave Gierke saw 12,150 on this prop, immediately after break-in.

You should too...

RE: erratic Tower 75
 

The Tower engine is like a Super Tigre and does not really like 15% nitro. Plug 1 outlet on muffler and their is nothing wrong with a Fox Idle bar plug , but I'm not sure about a Mc Coy Idle bar plug..........