Kitfox SS-7 build ?

[herman pahls]

I have been flying my Model 2 Kitfox for 18 years.
My model 2 has turned into a very capable but slow cruise and high fuel burn backcountry airplane with 29" bushwheels and a few other mods.
I base off a 650 foot one way grass strip and my hanger requires folding the wings which only takes 2-3 minutes since the flaperon push rods do not need to be disconnected.
I have been looking for several years (and so have many others) for a Model 4 powered by a 912S.
I assume that since the Model 4 is ~100-150 pounds lighter than a Model 5-7 with the same wing and 912S, it is very desirable with the short field crowd.

What I want is the short field performance of a Just Highlander and the cruise speed of the SS-7.

So I have several questions regarding the SS-7 which will help me decide regarding the SS-7

1. How long does it take to fold the wings solo on the SS-7 by the time you disconnect the pushrods and support the flaperons so that they do not get damaged in the folding process?

2. How do you manipulate and support the flaperons after disconnecting the pushrods?
Can it be done properly solo?

3. How light would it be possible to build a 912S powered SS-7 with

a. no upholstery other than the seat cover?
b. no adjustable rudder pedals?
c. minimal flight and engine monitoring instruments?
d. no co-pilot brakes?
e. no lights?
f. no transponder or radio?

I was told that weight could be saved by eliminating the SS-7 trim system and go with an elevator trim tab.

Also weight could be saved by not air foiling the tail feathers.

According to the Grove gear website the SS-7 gear leg weighs 35 pounds which I assume does not include the axles.
I appreciate the simplicity and less drag of the Grove gear but it is heavy in comparison to Cub style gear like John Roberts builds for the Rans S-7 which is a very capable backcountry airplane.
Also I feel the Grove gear is not tall enough to get the angle of attach that I desire even with 29" Airstreaks.


I realize it does not make sense to save a few pounds if you ruin the flight characteristics of the plane.
Also, omitting many features will make re sale more difficult.

I will appreciate comments from this forum regarding my intended use for the SS-7.
Thanks
Herman

[tommg13780]

I can help with one item on your list. When changing the gear on my model 2 from bungee to Grove I did a bathroom scale differential weight on the components and measured 19# more to convert to the grove.

[Esser]

If you want performance I would highly recommend air foiling the tail feathers. This will add a lbs tops and make your plane much for enjoyable to fly i would think.

I also this it is doing to be hard to eliminate the electric trim to save weight. If you took out the elevator trim servo, you would still have to put something in it's place to attach the elevator too as the trim servo is the elevators mounting point. By the time you modified the airframe to attach the elevator direct and then modified the elevator to have trim tabs(Which if you look at the Series 5 are quite large) I dont think you would save any weight at all. Even if you removed quite a bit of weight back there, you might have to add it right back on for C of G reasons.

I think if you really wanted to save weight you could go could fabric cover the turtle deck and remove the lexan. I personally would not want to do this but you could save a few pounds there. You could make the seat pan out of carbon fibre which I bet would save 5 lbs. (Make sure you put a kevlar lay up in there so that if you were ever in an accident you you dont get CF splinters through your body). You could replace the cowl, boot cowl, floor boards, centre consol, and panel with carbon fibre which would save a lot of weight in your plane and wallet. I would also recommend the cub style gear but you will lose a couple MPH on your cruise if you do that. I don't know your build but I think the easiest and cheapest way to shave weight off a plane is to shave weight off the pilot.

To sum up your one question, Phil Laker built a Kitfox SS7 under 700 lbs. I think he clipped the wings but he also had a nose gear which you could save some weight on.

[neville]

I transport my SS7 (912iS) to the airport nearby on a trailer. I have the
factory transport kit. Takes about 1/2 hr to remove transport braces, unfold wings, attach flaperon horns, install turtledeck, and fuel plane.
Takes some longer to load back on trailer as I usually have excess fuel
which I drain to both tanks below 1/8th. I drain from a gascolator drain.
.

[t j]

1. How long does it take to fold the wings solo on the SS-7 by the time you disconnect the pushrods and support the flaperons so that they do not get damaged in the folding process?

Don't know if the 7 has any more monkey motion involved than a 4 but it takes about 5 minutes to fold the wings on my 4. The disconnect on the flaperons is a safety pin and a a wing bolt. I put a padded seat cushion on each side of the tail to keep the flaperons off the vertical tail. Be sure to push the control rod on the wing being folded down first or the flaperon will hit it. You just hold the flaperon level with one hand until it clears the flaperon horn bearing area then tilt the trailing edge up as you swing the wing the rest of the way back.

I think the actual additionl time to fold is just the time it takes to pull a safety pin and spin the wing bolt out of the flaperon control. About 15 seconds on each side.

I like my kitfox bare bones and if I built a 7 it would be like you are thinking. light as possible. My opinion is the faired tail is mostly cosmetic. Wing strut fairing will be worth more than the weight penalty though.

[HighWing]

Herman,
My buddy and I have had this conversation many times. It would be a dream of ours to see it done to have all the answers.

I added rudder trim and elevator trim on my IV using electric servos with gap seals and ribs made of very light weight glass and foam and it added about 6 lbs to the tail. Doing without would save that with likely lower cruise, but cruise doesn't seem to be your goal. My basic reason was for clean - fuel economy.

From a selfish perspective I wish you were a neighbor so I could help.

[herman pahls]

I appreciate this forums responses on my potential light weight SS-7 build including one post that questioned the pilots weight as a factor.
The mention that Phil Laker built a sub 700# SS-7 with clipped wings is encouraging.
I would want the full length wings for the best short field performance and tail wheel should be less weight than a nose wheel.
The Just Highlander would most likely meet my short field needs the best.
My wish is that the faster cruising Kitfox SS-7 if built light will give me similar short field performance as the Highlander.
The Highlander has an undercambered wing like my Model 2 which is not known for fast cruise speeds at the same fuel burn.
I would not consider carbon fiber due to added cost and complexity to the build unless these parts are readily available.

So here are a few more questions that your responses generated.
1. Are carbon fiber smooth cowls and seat pans readily available or custom made?
2. How much does the SS-7 Plexiglas turtle deck weigh?
Maybe some weight could be saved by using a sheet metal turtle deck like
my model 2 has.
3. How empty do the wing tanks need to be before folding the wings on a SS-7 in the tail dragger configuration so fuel does not flow out the filler caps? Since my hanger requires the wings will be folded every time I fly, draining fuel would be a major deterrent.
4. Is there weight to be saved by not having a center console since I will not have adjustable rudder pedals for weight savings?
Or is the center console needed for the flap detents and the fuel selector or anything else?
5. Since the SS-7 is set up for Grove gear, does the fuselage have float attach points like the Model 4 has?

I realize that most of these questions could be answered if I had a SS-7 near to look at.
I live on the southern Oregon coast.
Are there any flying or nearly completed SS-7's in Oregon that the owner would show me?
Thanks again
Herman

[Esser]

Hi Herman,

Yes it has float attach points. You need your centre console for your flaps, fuel shut off, parking brakes, and to run your fuel lines through.

John Mcbean said they were working on carbon fibre everything. If you search this forum you can find it. I know that Paul Lederbrants new SLSA has a carbon fibre cowl. I haven't seen them in their catalogue yet

I'm not sure the exact weight of the turtle deck but it is probably around 5-7 lbs if i had to guess.

Here is the link for the thread for Phil's lightweight Kitfox http://www.teamkitfox.com/Forums/sho...ghlight=presti

I believe the wings have to be abotu 1/4 empty. An easy fix for this is to make a dolly you can lift your tail onto so your wings are level when you fold them.

[HighWing]

I suspect many of the ideas you will get regarding your questions will be opinions. Again referring to discussions with my buddy, we both agree (our opinion) we would never have a center console. The most frequent reasons in our discussions has to do with the foot comfort space at the rudder pedals and unnecessary weight. Since none of the early models had a console, there is no doubt in my mind that things could be worked out by routing things elsewhere as was done before.

I helped finish a Series 5 with console and it was a tough part of the finish fitting everything that passed through it through the seat front bulkhead. Lots of moving things there that need separation from fuel line and wiring. And then once installed, completely out of sight with the exception of a couple of inspection holes. All that could easily be routed down the two sides at significant weight savings. Example: the Lancair I helped with had Nylaflow tubing glassed to the inner sides of the tadpole shaped fuselage for the rudder cables. That could easily be done near the floor under where the console is placed - eliminating virtually all hardware. The detents for the flaps could be modified or redesigned to work without the outer console skin. And the fuel line and wiring could be routed like it is on earlier models.

[Dave F]

Well Weight is your emeny and if you limit the weight then you will gain the STOL ops.......... and still cruise 110 to 120 mph