Continental 65 HP or more, Ok on Model 4 ????

[szicree]

Final note: With my counter weight design, the amount of weight is adjustable.

I think the point of the post about moment of inertia was that the aircraft might find its way into a a spin and be unable to recover. I suspect an aero engineer could tell you roughly what the impact of the extra pounds in the tail would be without having to try it out first. Any such folks on this forum?

[MotReklaw]

Question.

What engine was the models 5-7 designed for?

Thanks,

[rogerh12]

Oh gosh, maybe I should have mentioned something important.

My Kitfox-4 does not have a tail wheel or the speed tail kit. That's right, I have converted it to a noise wheel plane using the factory noise gear kit and yes, I know this does not make it a REAL kitfox to some, but it sure looks sweet !!!!

The point being, my tail is light. Maybe, I don't know 5-10-15 lbs? So really, I guess I have room to add weight to the tail. Plus, the main wheels get moved back with the tri-gear, and I am going to a spring gear and WT600 wheels which weight more than stock. How all of this will affect the CG, I am not sure. Also, the Kitfox VW engine mount is supposed to place the engine in the right location, but the weight of VW engines varies, as does the disbursement of the weight (I.E. do I have magnetos at the back of the engine, or a distributer and secondary ignition at the front of the engine.)

Having the option to easily add weight to the tail adds peace of mind to me, but in the end, my tail, even with extra weight added, still might be lighter than a fellow with a honking aftermarket tail spring, tail wheel and speed tail kit installed.

Or not.

Roger

[HighWing]

John,
I think you got this spot on. I have a model IV and a Series V in my hangar and the V, as I understand it, was designed exactly as you suggest as a possible platform for the O-235. The fix is relatively simple going from heavy engine to light by simply changing the location of the engine. My hangar examples - the IV with 912 with the engine four inches forward of the firewall measured from the right air filter flange and the V with the engine (912S) 13.5” forward of the firewall. Actually, my IV has the engine 6.5 inches forward for similar reasons that you suggest. I installed full gap seal cuffs on both horizontal and vertical tail surfaces and even though I vacuum bagged everything for weight considerations, I still calculate that with trim servo motors for both elevator and rudder – elevator with trim tab and rudder by warping the two bottom ribs, I added about six pounds at about a 14 ft. arm which suggested moving the engine about 2.5 inches forward. That helped accommodate a better located oil tank as Model IV pilots will understand. I did the empennage thing on my first Model IV and had to placard the baggage sack at 25 lbs. rather than the 40 lbs. in the design because of my new tail weight.
There was a recent thread on extending the length of the airframe. That would help with a heavy engine as it would fit into the same thinking as extending the length of the engine mount.
With your SS and the Corvair,there is probably not nearly the issue, as you have room to reposition your engine aft. With the Model IV, unfortunately there is no room for a more rearward positioning of the engine - ballast is the only option, and this is the issue at hand.
As another aside, I made some U shaped pieces of 1/8” rod, threaded on each end and glued into the channel on the forward side of the door post. These were to secure a thin piece of aluminum to cover the wires that run from the panel to the bottom of the door then aft. I showed them to a friend (Model I and three Model IVs and a Rans S-7) and asked his thoughts. His response was, “heavy”. It seems we all have a mission in mind for our projects.
Lowell

[jtpitkin06]

Question.

What engine was the models 5-7 designed for?

Thanks,

From the Kitfox LLC site under History

"In 1994, SkyStar aircraft was faced with an increasing demand to produce a significantly larger version of the Kitfox that would be able to utilize contemporary certified engines (Continental and Lycoming) in addition to the Rotax 912 engines. The answerer to this demand was the entirely new Kitfox Series 5. While appearing very similar to the Kitfox Classic 4, it is, in fact, a completely new design."

[jtpitkin06]

Lowell,

I'm working on the engine mounting and cowling for my Corvair at this time. It's a matter of all the components coming together. Windshield, glareshield, cowling and engine. I made a wood mockup of the engine and prop hub. It helps determine the placement of the other items and getting the cowling right. The mockup is a lot easier to wrestle on and off several times than the engine.

The engine is mounted just 4 inches from the firewall. I can't go further aft due to the foot wells that protrude into the engine compartment interfering with the intake manifold. I see on the Rotec radial Kitfox they left off the foot wells.

The Corvair engine is just 26 inches long. The prop spinner backing plate is 30 inches from the firewall. That is aft of where the Continental prop hub is located so i have to cut 4 inches out of the Continental cowling to match the Corvair spinner.

I'm putting in some extra effort to get a straight horizontal cut line on the cowl to match the fuselage side stringers. That will eliminate the bent fuselage look.

It's all part of the fun.
John

[desertfox1]

Um.. no John, the Kitfox Radial has foot wells. When Prokes
and I did the molds for the cowlings they sent down a stock
Rotax firewall and the new engine mount. You may have seen
a picture of a builders plane before John did the factory
firewall forward.

By the way, are you using a boot cowl? I have found it quite
helpful when adapting cowls to the Kitfox. I'm very interested
in your build, spent some time with William at Osh.

Phil, DesertFox1

[jtpitkin06]

Hmmm... must have been another Radial.


Yes, I'm doing a boot cowl. I'm slicing the Continental cowling in parts. The upper half gets split at the firewall to make a bonnet and the lower half get sliced at the side panels. The side panels will be glassed to the bonnet. Then the forward sections get shortened to match the spinner flange to the engine.

This should make it easy to pop the forward cowling off while keeping the cockpit sealed.

JP

[rogerh12]

Ok, I just checked with an Aerospace engineer on the question about effects of increasing the rotation inertial on the Kitfox-4 by adding weight. I even showed him my plane with the weight bolted in to the tail, as I have been fitting them to the bare fuse in my garage. Bet you didn’t know Aerospace engineers make house calls !

Actually, he stopped over to pick up a rental application on my duplex (where I live next door), and happened to mention he just got a job at the University as an Aerospace engineer. What Luck !
As it turn out, part of my rental application includes the need for tenants to mow the lawn and to analyze my Kitfox design modifications (it’s in the fine print).

Ok, so in short, this is what he said. Though until he does a calculative analyses on it, he can’t be sure, but basically the mode of flight where someone could get into trouble by having increased the rotational inertia of the plane (by adding weight to the tail) is very much aerobatic. And the main issue would be controlling an established rotation in the pitch access, at reducing airspeeds, such as when someone does a sudden pitch up maneuver (such as the Lomcovák). Obviously, this is a mode of flight that the Sunday kitfox flyer is not even going to approach, thus it should not be a concern with the kitfox.

He did however point out one thing I had not thought about, because my Kitfox would be switching from a geared down rotax engine to a high rev’ing direct drive VW engine, the prop blast velocity will be higher on the tail and thus likely providing greater pitch control at slower speeds, if full throttle is applies.

I hope he does move in, I have more questions for him already !
(oh ya, maybe you guys could slip in a few too !)

[kitfoxnick]

Pardon me if this sounds stupid, but doesn't the gearing down of a rotax make the prop rpm close to that of a direct drive. What rpm range does a vw direct drive run at?