A much faster Kitfox?

[DesertFox4]

Paul, a couple of the items on your Kitfox speed mods. wish list have been done.

The strut to wing attach points for instance. Murle Williams had them on his Model 5 years ago. I have had a set of the same plastic fairings sitting in my hangar since before I first flew my Model 4 back in 2003. I just never painted them and installed them. They do look nice though.

Also the landing gear (Grove) have been faired into the fuselage on a couple Arizona Kitfoxs going back to Murle Williams 1997 model 5 Grand Champion. Phil Laker I think did that mod to his Vixen also.

All those mods should be effective for increasing speed. We just don't know exactly how effective. It would add build time to the aircraft but for some that isn't a concern. Weight has to be factored in also but most of the mods you mentioned can be, and some have been done, with careful attention to minimizing weight gain.

It is always nice to pick up a few mph to your cruise speed and or reduce your power setting and leave more fuel in your tanks for the same cruise speeds.

[av8rps]

Yes, I remember Murle doing some of those mods. And I can't say I know this factually, but I've always heard that not only were Murle's Kitfoxes beautiful, but they were also light weight, and fast. So when I was thinking about what I initially wrote, I was thinking alot about what Murle has done over the years.

However, using the wing strut fairings he made as an example, while lightweight and very simple, I believe they could be made much more effective if we just studied some older airplanes.

My mentor at EAA's Oshkosh Seaplane Base is Bill Brennand, who I've come to know very well now for over a decade. Bill not only founded that Seaplane Base, but also was a world class winning air racer, and Steve Wittmans right hand guy (Bill and Steve's original air racer "Buster" hangs in the Smithsonian today). So he knows a thing or two about making an airplane go fast. One day with my Kitfox in front of us, I asked Bill about a bunch of my ideas about how to make a Kitfox fly faster.

In Bill's normal fashion, he was quiet for a long time, and then responded by saying "Just look at what we did back then to our racers. We didn't always have the option for more power, so we typically used small engines with low drag airframes. So if you look at what guys like Wittman did, you'll find all your answers." Then he went on to say he was surprised that as popular as the Kitfox was that anyone hasn't already done that. He laughed a bit while half joking "If Wittman would've owned one, it would've probably been 40 or 50 miles an hour faster with the same engine".

So I've been studying all that ever since he told me all that. And I've concluded that while any fairing is probably better than no fairing, the superior fairing ideas are likely to surprise people with their amazing results. But again, there is no one magic bullet for speed. It is a combination of effective airframe cleanups as well as lightening techniques. Heck, just look at what wing strut fairings do for our faster models (10-12 mph is pretty common).

On an entertaining note about Bill, one day he told me to look at one of his old air race photos that was taken right after a race he'd won. Prior to the race Wittman had decided that to save weight they were going to make the side glass out of aluminum rather than a heavier transluscent material. Bill admitted he could see almost nothing to his side, describing it like a race horse with blinders on. But ultimately, he won the race . He said the only time that caused him real concern about not having side visibility was when he was in that little 15 ft winged racer during the qualifying laps and the prop disintegrated in flight, forcing him to land between a bunch of automobiles and people in a busy parking lot . He said it was uneventful, and they still qualified for the race the same day, and won. Wittman of course proved his point that every clean up one can do, and every ounce of weight savings, can be the difference between winning and losing.

But Bill chuckled with his final statement, shrugging his shoulders and saying "But he didn't have to fly the airplane... I did".

Based on all the things Bill has taught me over the years, I feel like I still have a lot I need to know

Paul, a couple of the items on your Kitfox speed mods. wish list have been done.

The strut to wing attach points for instance. Murle Williams had them on his Model 5 years ago. I have had a set of the same plastic fairings sitting in my hangar since before I first flew my Model 4 back in 2003. I just never painted them and installed them. They do look nice though.

Also the landing gear (Grove) have been faired into the fuselage on a couple Arizona Kitfoxs going back to Murle Williams 1997 model 5 Grand Champion. Phil Laker I think did that mod to his Vixen also.

All those mods should be effective for increasing speed. We just don't know exactly how effective. It would add build time to the aircraft but for some that isn't a concern. Weight has to be factored in also but most of the mods you mentioned can be, and some have been done, with careful attention to minimizing weight gain.

It is always nice to pick up a few mph to your cruise speed and or reduce your power setting and leave more fuel in your tanks for the same cruise speeds.

[HighWing]

I find this thread very interesting. Paul's thoughts seem to pretty much parallel mine since the beginning. My current Model IV has the 912UL just like my first one. I put a lot of fairings on that one and the biggest thing I noticed was the fuel burn when on our occasional flights of six to eight. We always flew as a group so the cleaner airplanes would fly at lower engine speeds resulting in some interesting observations at fueling times. Once on a three hour flight on our way to Idaho the range at Winnemucca for fuel in our flight of six was a tad over 7 gallons to a tad over 12 gallons. I have put the same fairings on the new one largely because I like the simplicity of the UL and hoped to keep up with the ULS guys.

I would also agree that climb at clean is better than climb at dirty.

In the other thread about 7SS's empty weights I couldn't keep from thinking about what we like on our airplanes. Mine is heavier than a typical IV, but I tried to make the added weight a functional addition rather than just a look good addition, though I think they look good.

I have done several of the mods Paul suggests.. I added a little over six pounds to the empennage with full airfoiled horizontal and vertical surfaces with gap seals and the strut fairings. Also the over the horizontal fuselage gap closure. I am embarrassed to say, however, that I haven't done enough flying to really report on the benefits.

Just today, I was looking at the 21" tires and thinking what I would need to mount the aft wheel fairings like those used on the Ercoupe. I've thought about that one for years

Helping my buddy on his Lancair IV taught me some interesting tricks working with fiberglass. Most of these fairing mods can be done over a finished airplane. More on the tricks later. A couple of pictures for now.

[kitfox5v]

Lowell,
You need to add this to your list of toys on HW LLC. I would like to put those on my 4. I've got the ones kitfox sells but the longer teardrop will create less drag.
How did you make the seals for the farings? What are they made of? Thanks
Hope you had a great birthday. Eddie

[av8rps]

Lowell,

That is exactly what I was talking about! I had no idea anyone was doing it to the extent you are. I also think your results from trips with similar aircraft, faired and unfaired, with varying fuel burns proves this is worth doing to our airplanes.

Paul

[HighWing]

Eddie,
I've thought about kitting the parts, but most have to be custom fit. Example - the ribs I used in the horizontal tail are patterned somewhat after the ribs in the speedster tail, but not exactly. The fairings on the struts fit the profile of my horizontal stabilizer and won't fit anyone elses

Below are some photos of the Horizontal stabilizer strut and jury strut fairing tools and procedures.

1 The fairing tooling and a couple of glass fairing pieces. The tool was made by gluing a couple of pieces of balsa of the appropriate width to a strip of thin aluminum. It is then sanded to shape and covered with a single layer of light weight glass - see below for the method. It is then sanded and primed and sanded smooth. One of the fairing pieces is glued at the trailing edge and one is still open. The airfoiled foam piece for fitting to the tubing can simply be press cut using the end of the fairing piece. The fairing section on the right is 20-1/2" long and weighs 1.005 oz.
Fairing Form.jpg


2. One of the Lancair techniques. A single layer of glass cloth is laid down on a piece of vinyl sheeting and the resin is added to the cloth. After it is saturated a sheet of thin Polyfiber or other Dacron covering fabric is laid on top of the glass.
Fairing Pour.jpg



3. another sheet of vinyl is placed on the top of the glass strip and excess resin is squeegeed out.
Fairing Squeegee.jpg


4. The bottom layer of vinyl is removed and the glass is laid out on the form - previously treated with a mold release - and all air bubbles are removed by finger pressure. The top layer of vinyl is then removed and it is rechecked for bubbles.
Fairing Bubbles.jpg


5. The clamp - couldn't find it for a separate photo - is placed to hold the glass - Dacron sandwich so it wont lift up at what will be the trailing edge and secured with a couple of spring clamps. The clamp is made from a length of piano hinge with aluminum angles riveted to the free edges forming a sort of a long clamshell clamp.
Fairing Clamped.jpg

6. The finished fairing is trimmed slowly with a table saw
Fairing trim.jpg

[SWeidemann]

Kitfox Folks,

My Vixen may be one of those Arizona airplanes you are referring to. It has a built up bunch of wood framework & stringers starting just aft the firewall, running to a channel for flush mounting the spring gear, and continuing aft & tapering back into the bottom longerons a ways back. The smooth fabric on the bottom I am certain adds some speed. I get about 120 mph with a 912 ULS. I've also got my mind on some streamlined horiz strut fairings, wing strut/ fuselage fairings & wing strut-to-wing fairings. I already have a set of gas cap fairings to install.

"Also the landing gear (Grove) have been faired into the fuselage on a couple Arizona Kitfoxs going back to Murle Williams 1997 model 5 Grand Champion. Phil Laker I think did that mod to his Vixen also."

Skot