Combat Fora .36

NICE ! Ken , It looks mean with that flying saucer looking head!! Serious looking socket head screws, Is there a reason that seems all that i have seen strong engines have square carb. / intake ? Is that an air trapper / catcher ? ERic

getback wrote:NICE ! Ken , It looks mean with that flying saucer looking head!! Serious looking socket head screws, Is there a reason that seems all that i have seen strong engines have square carb. / intake ? Is that an air trapper / catcher ? ERic

I have an Enya .35 with an externally square venturi.

All the Fox .40 stunts I have also sport the square venturi. I think the cases were based off the .36 MK combat engines though.

Ron

Designers might have been experimenting with drawing in a more laminar charge of air past the spraybar. Hoping maybe they could get a more dense(or uniform) F/A charge into the crankcase.
This is just me dreaming up wild possibilities for something that may only have been a cheaper method of molding.

This is a large intake. Obviously in mm but it measures approx 7/16" x 1/2". No spraybar though the choke area. This engine will not run on suction. When I set this engine up prior to running, I point the intake towards the ground and open the needle. Most engines I look for a drip pattern which has the fuel droplets spaced about 3/4" apart. This engine has the fuel pouring out. I've run this on 40% nitro. The whole experience is amazing. The noise, smoke, speed is totally cool. Your pitman and or starter have to know the sequence of what to do and how to do it especially if something goes wrong. This engine is generating a lot of horsepower and it's one not to be taken for granite. You don't stand in front of it especially if you have a lean needle setting and the engine starts surging. Economy is out the window with this as 4 oz's of fuel lasts less than 3 minutes .

This engine and the Nelson will do 120 mph all day long. The Fox Mk engines are interesting engines equally. The problem is that sometimes they shed parts. The MK 3 for example had a serious flaw in the crankshaft where the threaded portion was turned down . Very little to no radius was provided in this intersection resulting in a stress riser that enabled the shaft to break right where it exited the case. I had one do this while running and the engine goes into a grueling shaft run.

Wow

Here's another fire breathing monster produced by the famous Willy Wiley. Willy worked with Duke Fox and essentially designed the last two MK series engines which were the ABC MK VI and the MK VII which had a AAC piston liner assembly. This particular engine I show is a ABC .36. This engine is a bit on the heavy side but it's built like a battleship. My pinky can fit down the venturi. I never seen a engine with as large of a venturi as this. The crankshaft is massive. I like all the head bolts as well. This is a rare piece of history here. Ken

That's a beauty, it says muscle all over. 8 head bolts. I like the way it's squared off around the exhaust port. Not much for cooling fins, but I guess that because it's ABC.

Rusty, Ian raised this question in regards to the speed plane we flew last week. I meant to respond to that. A speed plane has a aluminum pan either half or full entirely on the bottom of the fuse. This acts like a giant heat sink. One thing to keep in mind is how little heat these engines do generate. Were running these engine on bladder and the fuel is pouring into the engine at a ferocious rate. The case itself is always filled with fuel. The more fuel, the more cooling. In fact I hardly ever break an engine in on a test stand using a hard tank anymore. I run them on bladder. The runs are easier controlled in terms of temps and needling. A major benefit is the engine goes rich instead of lean towards the end of the run. Tanks have the fuel foaming due to vibration and bladder puts a end to all of that. Many of the .36's use a 8" prop. This has the engine turning up with little to no load. The Fox's like a little load so I use a 6.5 -7 pitch prop on those. I use a 7.5 x 6 on the Fora and also this particular engine. This alone keeps things cool and the higher nitro keeps the engine cooler. Ken

I missed this topic but I do like the Fora engines. they are expensive little beasts - I only have the Fora Jr diesel - but I have handled quite a few.

I have not seen the Willy Wiley before but the venturi interests me. The NVA seems to be set back quite a way.

It is set back on the Fora but still in sight.

Does it form an annular ring? Or is it a slot feed?

There are many theories on NVA arrangements, particularly for screamers. I can't quite make out the feed on the Wiley but am very interested. It is obviously successful.

Ian these engines HOSE the fuel in. The fuel is pouring into this engine. Other engines I set up a drip with the bladder, this one you set a steady stream of about 3/8" wide. Get it into the air as fast as possible. Last year I ran this on 40% and I just couldn't believe the speed. The smoke, the noise It's awesome. Yesterday I had some Fox Combat Specials out on some fast planes. They were certainly doing a nice job themselves in the cold winter air. Ken

Just looking at these muscle engines paired with Ken's enthusiastic descriptions gets my heart beating faster.

The only exposure I've had is when David Smith asked me and Wayne to pit for him one recent Saturday at a Huntersville meeting. Wayne held and I cranked. It was a Rossi of some sort. I didn't think to wear my ear protection, and when it lit off I could not unhook the battery and move fast enough. It was a deafening roar and I got my ass down the hill in the pits before I turned around to see his plane in the air and David leaning back on his heels holding on with both arms. I'd like to do it again now that I know what to expect. I love dangerous loud power and smoke. But I'll wear the head gear next time. I'm certainly not prepared to fly one of them, but I'll help and watch.
Rusty

RknRusty wrote:

getback wrote:NICE ! Ken , It looks mean with that flying saucer looking head!! Serious looking socket head screws, Is there a reason that seems all that i have seen strong engines have square carb. / intake ? Is that an air trapper / catcher ? ERic

I have an Enya .35 with an externally square venturi.

I would think that the square venturi, coupled with a square gas passage in the crank, would be for precise timing as the edges run parallel. Either open or closed. No slowly fading like a round valve.
Rod.

Oldenginerod wrote:
I would think that the square venturi, coupled with a square gas passage in the crank, would be for precise timing as the edges run parallel.  Either open or closed. No slowly fading like a round valve.
Rod.

That backs up my laminar air flow suggestion in an earlier post. I didn't take it as far as more seamless flow through the the rectangular gas passage. And then wouldn't the transfer channel through the shaft need a larger interior cross section than the gas passage like an expansion chamber? I'm way guessing now. How to stuff a crankcase 101
Rusty