Maximum engine size

[SkyPirate]

I would think you might need to do something concerning P factor and allot of horse power,..an equalized rudder maybe

[n85ae]

That one doesn't count, that's the secret airplane ... However after that I'll
build an O-320 Fox, and sell N85AE! You got your ski's on up there Bruce?

Jeff, you better finish the one in the garage first!

[jtpitkin06]

I'm sure lot of you know that I am planning on putting a UL520i in my plane. My question is do you think that I should enlarge the rudder create a control horn at the top for it? Having never owned a Kitfox before I'm not sure if the larger rudder is needed or not.

The present size rudder on the model 7 is adequate for a more powerful engine. Probably up to 180 hp.

Look at the present rudder/vertical stab and ask if is big enough now with 100 or 115 hp on tap. The answer seems to be yes. No one claims a need for continuous full rudder on takeoff or in climb to hold things straight.

Let’s suppose you mount an engine with double the power. It doesn’t take twice the rudder deflection to maintain direction. Angular deflection of the rudder to counteract yawing from p-factor is not linear. Where it might take 5 degrees deflection for 100 hp it might take just 7 degrees with 200 hp. But that is only at the first application of power where you only have the prop blast flowing over the vertical and rudder. As soon as the airspeed picks up the flight controls become more effective.

I think the limiting issue on putting a larger, more powerful, engine on the Kitfox is propeller size. In order to absorb 150 or more hp the prop will need to be proportionately larger. Because the diameter is limited by ground clearance the prop must have a wider chord and ideally controllable pitch.

More power to you.

John

[airlina]

That one doesn't count, that's the secret airplane ... However after that I'll
build an O-320 Fox, and sell N85AE! You got your ski's on up there Bruce?

Jeff, skis are on and I have a couple of ski flights under my belt. It had been a few years since I have been on skis due to our mild winters. This winter is making it up with a vengeance as you know as well and lack of snow is not a concern. I forgot how much fun it is-like landing on a featherbed-half the time with new powder , you can't tell if you've touched down . Just remember no brakes! this is usually not a concern unless you are on ice or hard packed snow. Under normal conditions, it takes 1500 RPM to taxi so as soon as you throttle to idle, you stop. Up to 50 deg tomorrow- bummer sticky snow

[jmodguy]

okaaaaaayyyy...
I bought a KF V project recently and have been gnashing about an engine to put on this project. I have researched the various 912 options and the O-200/O-235 options and have read through numerous posts on TeamKitfox. I was seriously considering a Corvair as well. Even bought the Corvair manifesto... er manual.
I have an O-320 D1A sitting in my garage collecting dust. Guess where its going.... I will be adding taper fin cylinders, lightweight starter and a lightweight sump. That should shave about 10-12 lbs I am guesstimating. I'll be trimming weight wherever I can. I will be using a plenum from James aircraft to optimize cooling vice building baffles.
I realize this will impact the useful load. Thats fine by me. Don't care about sitting in the aircraft for a 4 hour stretch. Mans gotta pee.
The IO-240 is similar in weight and I have heard of some flying with the O-290 which is also similar in weight. I don't think the fuse needs any reinforcement or these "heavy" engines would be falling off the airframes and we would know about it.
Leaning towards a Catto prop too...

[Av8r3400]

It's not going to be the total weight that will cause you heartburn, but the location of that weight.

You are considering an engine that will go 275 pounds, at least, installed with baffling and exhaust, plus mods to the cowling to make it fit and cool.

All that weight will be at the extreme forward end of the envelope. This will require a massive amount of more dead balast weight in the tail to balance. Or a stretch modification to the tail.

There's an excel spreadsheet floating around the forum here to download which you can use to crunch some weight an balance figures.

Weather the airframe can handle that kind of torque and power is another, separate discussion.

[jmodguy]

AV8R,
I figured you would chime in!
Out of curiosity I went out to the garage and weighed the engine. It is disassembled so that made it easier!
I used a "highly accurate" wal-mart mega pound bathroom scale and came up with 254 lbs total. This number was calculated using B&C lightweight alternator and starter, ECI tapered fin cylinders, and a Superior cold air sump and allows 2 lb for an oil cooler. Also accounted 10 lbs for coil packs and wires (for EI), 6 lbs for flywheel, 4 lbs for carb. That puts the O-320 pretty darn close to an IO-240. Conti claims a dry weight of 240 lbs per their website.
Yup I'll have to add exhaust and will have to account for the Sam James plenum but I don't think those will be that much off of a Conti IO-240 setup - probably less.
I am more convinced this will work.... Thanks for making me look!

Regards
Jeff

[Esser]

This may have some useful info in it for you: http://www.teamkitfox.com/Forums/showthread.php?t=6556&

[jmodguy]

Thanks Esser. Been watching you... Your build thread that is! When it comes time dont be afraid to build your own mount. Its not that hard!
I built an engine mount for my GP-4 and saved a TON of $$$. In Canada that would be $$$$ eh?
I used the site below and it made coping the tubing ends pretty easy. I was cutting out a tube every 30 minutes. You will have to build a jig but that is also not difficult.

http://metalgeek.com/static/cope.pcgi

[jrevens]

When it's all said & done you will be carrying the weight of an extra adult passenger in the airplane all the time. A hunk of it will have to be in the tail. Not to be too much of a naysayer, but it will probably change the wonderful light feel of the airplane, and make it basically a one person machine. More power is nice, you've got the engine, and you are a true experimenter... I admire that. I've got an O-320-D2A in my Thorp, and it's a great engine.