Empty Weight

[Danny]

Where do you think you saved weight on the airframe?

John Pitkin
Greenville, TX

John,
I love all of the bells & whistles as much as anybody, but I purposely decided against loading down the plane with every available toy. No panel mount radio or transponder, just a handheld Icom & a portable GPS. I can go pretty much anywhere I want with those 2 items. Not as nice as a panel mount, but I will still get there.

No carpet or upholstry, just the Kitfox supplied seats. Carpet just collects dirt anyway. Had rather have nice varnished wood floorboards. Old school I guess.

No redundancy with instruments, etc. The Grand Rapids EIS has more features than I will ever use & if it stops working, I'm confident that I can manage to keep the engine running without it. If you have ever flown Champs or Cubs, you know what I mean. No need for dual electrical busses & batteries, etc. I have the basics for VFR day flight. No lights, so when the sun goes down, I will park the plane.

The items I just listed will easily add more pounds than you would think possible. Their addition can certainly add to the enjoyment of flying and at some point I will add some "extras". But for now I will be satisfied with the basics & enjoy the added bonus of a great performing aircraft.

I also followed the Poly Fiber manual closely. I used Poly Tone for the final color coat and didn't go overboard in adding extra layers of paint & sealing materials. High gloss fabric looks good, but I'm sure the end product will weigh more. And I think the Poly Tone finish looks "right" on a fabric airplane anyway.

So, no magic here in the building process. Just have to remember that there is always a tradeoff for every item you add. And I'm sure as time goes by, my airframe will pick up some weight with added toys. But I'm confident that I can add the toys that I want and still have an airframe that will come in under 800 lbs. That still leaves over 500 lbs useful load with a 1320 gross. I can live with that and be VERY happy.

Certainly not knocking the Rotax, but I think I proved that you can build a light Kitfox with a Continental 0-200 engine without trying too hard.
Danny

[jtpitkin06]

I decided to build a low and slow airplane for VFR flying.



I too, am building with a minimum panel. I have a basic “4 pack”. Airspeed, Altimeter, VSI and Turn coordinator. I added the T/C because it was a good deal at $60. It will be nice to have on those days when the horizon is a bit vague and it wasn't much of a weight issue at less than 1 pound.

I have steam gauges for engine monitoring. One lightweight com, and the omnipresent King 76A transponder. ELT is stuffed behind the cargo sack with the PC680 ships battery.

No GPS yet, but If the right deal shows up on a something-96 I might add it. I learned to fly with a clock and compass. Spent 30 years flying heavy iron with G-whiz navigation boxes. They are good for crossing oceans or the Amazon, but I’m building a Kitfox to get back to basics. Needle, ball and oil pressure is just fine for me.

I’ll be using Stewart Systems coatings and spray all the layers for a thinner coat and uniform application. I think it’s easier to control the thickness with spray than with brush or roller.

I did add some things that upped the weight, but the performance gain should make it a wash. Specifically:


Razorback – adds stability. about 12 ounces.


Bottom false ribs – help to maintain airfoil shape. added about 2 pounds


Tail speed kit – ribs to improve rudder and elevator effectiveness. About 1.5 pounds


Lift Strut fairings – increase cruise speed 10 to 14 mph. About 12 pounds.

That stuff added maybe 16 pounds but the performance increase is worth it.

On the other side of the balance scales:


Grove landing gear. I’m not building LSA so the extra weigt capacity is worth the empty weight penalty.


Cargo sack. Does anyone build a Kitfox without a cargo compartment? I think it weighs about 4 lbs.


LED lighting – Less than a pound, including the wire.


Dual brakes – no performance gain – small increase in weight. Maybe a pound or so.


No carpeting , Fabric covered seats (lighter than vinyl.)

I haven’t hung the engine, yet, so I don’t have the prelim weights. Maybe by the end of June.



JP

[kitfoxvixen9095]

I think you should recheck your weight with different scales. In my opinion, there is now way you could be that light with an O200 engine, my guess is your off by 75-100 lbs. The scary part is that your weight and balance may be off.

[Danny]

]


I thought the same thing. Double checked scales. They were calibrated & cross checked with another set of scales. Everything was checked & rechecked. Leveling the plane was rechecked. I'm confident that the weight/balance is correct.
Danny

[MotReklaw]

Well Danny, I am impressed with your numbers here and the information behind them. I'm going with a O200 too and have the lightweight starter and alternator. I think less is more when it comes to adding things to the project to 'trick it out.'

Have a xponder but plan to leave it and a few other things off to see how my first weigh in works.

Thanks for the post.

Tommy Walker in Alabama

[SaintAero]

I just finished a major mod to my KFSS by replacing the engine with a Continental O-200. Prop is a McCauley from a C150. The empty weight is 850 lbs. Empty CG is 15% MAC.
Don

[Danny]

Your install looks good. I don't see an oil cooler, are you installing one? Thought I could get by without one, but oil temps were running on the high side so I'm in the process of putting one on.

If you want to save some weight you might consider a Whirlwind prop. Really like mine. It does take a little more time to change the pitch, compared to a Sensenich, but still an easy process.

Good luck with the new engine. I think you will like it.

[HighWing]

What we can save weight wise depends on what we really want in an airplane. There was a Model IV owner in the old days that was kidded about the microwave in his. It was a joke because his Model IV weighed almost 800 lbs.

Ever since the Series V, a couple of friends and I have talked about weight saving on the larger models. One thing that consistantly comes up is the adjustable rudder pedals. My thinking is like this. In the 900 hours I put on my first Model IV, I loaned out the airplane to three different guys for check rides with instructors. That would be a lot of weight and complexity for three guys to be able to stretch their legs for an hour flight as the other 877 hours with only me at the controls and I quit growing at about age 17. Then the V I am helping with has been sitting around for a long time and the concentric tubing at the rudder pedals has stiffened up a lot and will need definite attention. What I would do is use the model IV style double torque tube pedal system. Then I would cut off all weldments for the cable runs and weld a couple of tube sections on each side of the fuselage and run some Nylaflow tubing the length of the fuselage for the rudder cables like the Lancair folks do. Theirs they bond in, but it conforms to the tadpole shape of the outer fluselage skin with zero friction. Use the adjustment links. Then the cable itself. ACS lists the 3/32" cable as withstanding a force of 920 lbs (not including safety factor). The 1/8" cable standard on Series V and up is good for 1760 lbs. Cables fail from poor swages and sharp bends causing work hardening and abrasive wear, not from the strength of Pilot Hurcules' legs. A double lead of 3/32 cable in Nylaflow fairleads would weigh a tenth what the long runs adjustable set-up weighs.

Then the lift struts. Those PVC fairings are heavy. I made up some that added 3.4 lbs each side. Weighed before and after completion. If all things come together these might become available.

Attention to reasonable detail. The guy that started the V was a tank builder - I guess. Part of the cover for the elevator fuselage cutout (about 4X4 inches overall) used eighth inch solid rivets spaced every half inch to connect the three pieces that made up the cover, with #6 mounting screws spaced every inch -and there are two such covers each side. The big cover for the large opening; it is interesting that on the V at the bottom, he used the welded tabs spaced about every six or so inches, but at the top, once again #6 screws every inch. When I mounted the video camera externally on my first airplane, I used the 3M colored vinyl tape to attach the fairings. I replaced it from time to time as I modified and serviced the system, but the tape never began to peel. His fuel pump mount consised of an 8X8 inch piece of .040 aluminum connected to the bungee bulkhead with four adel clamps with AN3 bolts, nuts and two washers, add to that the two bolts to mount the pump itself.

Panel, mentioned in another post.

Wire. Use the component manufacturer's recommendation. On the V, we used probably 150 ft. of 22 ga. wire and probably 50 ft. of 20 gauge, which brings up the LED lighting options now available.

Upholstery. No leather, velour, or other heavy fabrics - ever help carry the laundry basket down stairs to the laundry room or lift a roll-a-board to an overhead bin. Fabric is heavy. The baggage sack - the super light builders I am aware of use dacron cover fabric glued in and shrunk. It is attached to a very light floor structure.

Landing gear. Unfortunately, this is likely the heaviest single component besides the engine. Grove currently lists their Model IV gear at 23.4 lbs. I called and specifically asked for the total weight including brackets and all hardware. I was promised a call back, presuming they were going to put everything on a scale - maybe for the first time. The call back reported a total weight - gear legs, brackets, hardware - 31 lbs (the original bungee gear weighed a third that, including bungees).

Paint. Polyfiber says that if you can't see the fabric weave, you have too much paint. Show planes aren't light planes. Also, the Stewart system uses fewer base coats. One caution regarding spraying the first coat. It is very difficult to fill pinholes (saturate the weave) with a spray gun. If the first coat is not applied according to the manual, you will have, to a certain extent, a fine mesh sieve covering the airplane. The Lancair skin is heavily vacuum bagged carbon fiber. The first coat of primer is rolled on and then squeegeed into the pinholes.

This could go on and on, but in short, decide what you really want. If light is a priority, make it a priority.

Lowell