David,

I never did this with K&B engines, but in the 1950's I did fly an ENYA 29-III shifted to reverse as you mention. It worked. The shaft port timing numbers seemed to be very similar both ways, as observed by in-flight performance. No, I didn't measure shaft timing 50+ years ago...

One problem that may have been involved, but I don't recall fussing with, was tank height effects: the NVA turns with the intake housing, right? On a profile, the NVA (and fuel jet) are about centered, vertically, with the  shaft centerline. Turn the venturii 90° and that changes... with a "vertical" (upright or inverted) engine in a built-up body, your "normal" condition is the NVA not vertically in line with the shaft centerline. Rotating the intake front end moves it to about in line...

As to which way to rotate the intake housing, it doesn't matter - the result is the same. If you rotate the housing 90° CCW seen from the front - normal prop rotation direction - you move the shaft port opening in the housing 90° "later" in a prop revolution than stock.

The housing's port opening also meets the opening edge of the shaft port 90° "later." Voila, total shift of 180°.

Now, if you rotate the housing 90° CW, you shift the housing port 90° "earlier" regarding a stock CCW revolution, and also meet the shaft port 90° "earlier" - again total shift is the same 180°.

It is conceivable that you might want the intake on the side opposite the cylinder for some reason; mount the housing rotated 180° from stock, and you're back to stock CCW timing!

ENYAs front housings are dismountable; on some K&Bs - and other engines - both front and back housings are dismountable. Any engine with the intake housing mounted with a pattern including four screws 90° apart, on the same radius circle, can be reversed by this simple method. Other numbers of bolts, or a non-90°-symmetrical arrangement will not allow it.  Some engines' intake housings have a clearance cut-away for the piston at Bottom Dead Center - for normal rotation. Rotating the housing 90° either could cause the piston to strike the housing...

Some engines, and I suspect including high-performance K&Bs, have biased intake timing to favor performance with stock rotation. Any timing advantage for stock rotation becomes a disadvantage if rotation is reversed. How serious a disadvantage depends on the degree of radical hi-RPM timing bias...

The ENYA seemed timed nearly the same either way... Factory CW shafts for Fox Stunt 35s are (were?) available, and run just about identically CW as a stock, CCW Fox Stunt.  Examples of basic, traditional bread-and-butter layouts...

A problem today is the availability of useful CW rotation tractor props. I wouldn't use an 'electric' LH prop on a thumping 1-cylinder recip internal combustion engine...

Some racers and some Carrier fliers use CW rotation, don't they? The advantage of torque reaction on the engine mounts tending to roll the model out of the circle when the model is upright? Should help a racer take off cleanly, and a Carrier model in lo-speed to roll away when the throttle is goosed...

If anybody tries rotating the front intake of an Enya or K&B, it would indeed be most interesting to find and post or publish the effects on tank height.

There have been two who experimented with raising/lowering the NV in the venturi, and both reported that no change in tank height was required for a change in spraybar location. Those experimenters were Al Rabe and Ted Fancher. Both reported on their tests while they were the Stunt Columnists for MA or AAM or whatever it was called at the time.  I take their word as fact, so it would be very interesting if the above experiment also showed no effect, which I think is at least a possibility.  Steve 

With all due respect to Ted and Al, my experience is that the uniflow outlet in the tank needs to be at, or very near, the vertical level of the hole in the spraybar.  I say very near, as all my tanks are modified by me.  Perhaps the uniflow did not end up exactly where I think it is at some time period after making the tank. 

Gents,

The voracious ether is, I hope, digesting my long reply in this thread. SH apparently doesn't have it...

Anyway, having been in the US Army for a career, rarely in places where I could enjoy CL flying, I tended to do a lot of thinking about it. When I did get opportunity to fly, I pretty much had a check list for what would or would not work...

One area was tank height.  Ted's and Al's musings were part of my thoughts. So, built a test rig to determine what "tank height" an unfamiliar engine "preferred." Too many details off among the Northern Lights, or somewhere NOT on this site...

Regrets... I've always admired Ted F for his terse, clear and efficient phrasing. (Yah ,right...)( No offence, Ted, just a tweak from another wordy birdy... )