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scottr
07-26-2009, 06:16 AM
I building a Kitfox V and have a couple of questions about the seat installation. In my builders manual it shows using tie-wraps to hold the seat pan in. Somewhere I thought I saw a picture using cable clamps instead, are the newer Kitfox's seats installed differently? Can anyone send pictures and info?

I also saw that some builders are installing straps to support the seat. Are these available to buy or do builders fabricate these? Are any pictures or info available?

Thanks for the help in advance!

TeamKitfox is great, it's really helpful with all sorts of information and I like the support it provides from other builders too.

Dave S
07-26-2009, 10:33 AM
Scott,

There have been a couple oop-oops in kitfoxes where seats have collapsed and the pilot's weight on top of the alieron rod under the seat has prevented movement of the alierons - an ugly situation. There is some indication that these oop-oops may have been related to some extent to the seat not being installed correctly - in any case there is no redundance with the plain seat design.

Some kitfox builders have fabricated web straps under the seats and over the tubing to act as a redundant support for the seat - pretty simple and frugal on the added weight - I am hoping my buddy from the same 'port I fly out of has some photos of his because he did just that.

John McBean has some under seat storage bays that work out pretty neat as another solution to redundant seat support. I went this route. Basically the under seat bays work out as an excellent aux storage place for tools etc - and the location helps the CG a bit to get some dense stuff like tools and spark plugs a bit more forward. In this case - a person makes a hinged door to get to them under the seat cushion. These things basically put a substantial block between the seat bottom and the bottom of the aircraft - the seat cannot come down on top of the alieron link.

I believe the newer SS models have a seat with built in storage bays that are part of the fiberglass work for the seat - these look really nice.

As far as the nylon zip ties - for me they went the way of the milspec fuel hose - to a safe repository in the basement where they can't hurt anyone.....<grin>....

An aircraft hardware supply place like Aircraft spruce has some uncushioned aluminum clamps which fit neatly around the tubing and a person can firmly screw the seat to the tubing without taking up so much space that it is hard to fit the seat over the tubing. One of my pals showed me how a person can use a little hockey-stick tape (conveniently sold in white and black version to match the most popular airframe colors of the average kitfox) A single layer of the HS tape provides adequate cushion to separate the tubing from the aluminum clamp without adding any significant thickness to interfere with fit.

Let us know what you decide - it is interesting to see what each of us does for these unique situations.

Sincerely,

Dave S
K 7 Trigear
912ULS Warp

Agfoxflyer
07-26-2009, 10:54 AM
I used four hose clamps (the screw type) for each seat pan. Also installed straps from the same type of material of seat belts, but a little thinner. Works well. Takes a few minutes to get the clamps off at annual.

scottr
07-29-2009, 07:29 PM
Hey thanks guys, this helps out a lot. I like the idea of under seat storage and using the clamps. I'll follow the placement like the manual states for the clamps and use the underseat storage.

Thanks again, I appreciate the help.

ALAN
07-30-2009, 10:23 AM
I had one of them oops it was not a good thing just after take off I had the seat pan drop down It was a bad few min B-4 I could get my fox back around and put her down I knew what the prob was as soon as it happened the zip ties had snaped and I had a 200 lb guy with me. We had to hold our body's off the seat to get her down safe. Go with good clamps no zip ties.

Alan

darinh
07-30-2009, 05:07 PM
I added straps made of webbing similar to seat belt material. I secured it with a tri-clamp. The webbing is about 1" wide and is rated at 3000 lbs. tensile strenth or something crazy like that. I'm sure there are many that will call me crazy, but I have never seen the need for the zip ties or clamps at all on the seat. Mine has a lip on both the top and the bottom that nicely wraps around the tubing and stays in place. Any situation such as turbulence or negative g's, are not an issue because the seat belts are holding me firmly in the seat and thus keeping it down. I have around 60 hours in my Kitfox and don't see the need for the ties. Makes removing and checking the fuel system much faster and easier.

RV6flyer
12-18-2020, 10:35 AM
I can not picture how the tri-clamp is used to secure the straps.

alexM
12-18-2020, 10:51 AM
Super old thread but I had never heard of a tri-clamp before. I don't see how that could be employed here either.
In regards to straps, one can't overlook how much they stretch. I had to specify some for my day job to restrain a decompression panel and had to account for the stretch, which was about 25% if I recall correctly. Let's just say it was a good thing that the person sitting in front of the panel would be pushed out of the way in the 28 milliseconds for the entire event.

Maverick
12-18-2020, 01:25 PM
I put the storage compartments under my seats but I still had an issue of the front lip of the seat pan pulling off, over, and down behind the cross member. I put blocks of wood under the seat pans but that didn't do it since when I am pushing on the brakes the pressure is going back toward my lower back instead of down thus, the blocks helped to keep the pans off of anything underneath but did nothing for the pan going backwards. I made some 1/8" thick X 1" wide hooks out of a sturdy steel. These J-hooks are attached under the seat pan. They wrap around the cross member tubing. They terminate at the vertical wall of the seat pan on the back end. There are two, one on each side, and are attached so that the bolts, with wide area washers, go through the seat pan and the flange of the storage box. I can remove the seat pan in seconds for maintenance and now the seat pan stays put.

RV6flyer
12-18-2020, 01:53 PM
Are you saying these J hooks go all the way from the front to the rear of the seat pan?

Maverick
12-18-2020, 04:45 PM
No. Maybe this will help explain what I am trying to say. I put the hooks centered off of the control stick. I re-read my previous post and now see that I was confusing. When I said the back end, I meant the back end of the J-hook. Sorry for the confusion.
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RV6flyer
12-18-2020, 05:29 PM
No. Maybe this will help explain what I am trying to say. I put the hooks centered off of the control stick. I re-read my previous post and now see that I was confusing. When I said the back end, I meant the back end of the J-hook. Sorry for the confusion.
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Thanks, I do not have the tool box. Just order them by the way.

Allan

n85ae
12-18-2020, 09:05 PM
There needs to be a forum FAQ, with links to "seat install", "fuel tank kreem", "spar sloshing", and
"uneven fuel flow from tanks".

I reinforced my seat, put a block next to the control to keep the seat off it, and use 1/2" wide zip ties

Jeff

airlina
12-20-2020, 05:49 AM
As Jeff says this has been an issue for a long time . Back in the late 90's when I was building my Series 5 , I was shocked by the fact that the Skystar manual called for zip ties to hold the seat pan in place. thought to myself ....... self this won't do , dumb idea , so I decided to upgrade the attach points to SS wormdrive hose clamps with a rubber wrap . Also added another layer of fiberglass at the attach point areas, and for triple redundancy , belt type straps under the seatpan . There were a few accidents way back when that were linked to the seat falling on the controls (one I recall was a hard landing , seatpan fell into controls ,airplane bounced , resulting in a loss of control and wrecked airplane ) The green doohicky in the photo is just a rubber cap to keep the SS clamp screw head from abrading my control stick upholstery.Bruce N199CL

desertdave
12-20-2020, 09:00 AM
The seat pan on my Model 6 was trimmed up a bit to much and on 2 occasions (200 Lbs me and a 210 Lbs buddy) the zip ties snapped on landing. Here is how I permanently fixed the situation:
1/16" aluminum flat
Hysol or epoxy
Cable clamps
Rivnuts

For the front I used a rubber mallet and matched the curve with the bullnose edge of my workbench and glues it in place. You can see a previous repair from the first time the zip ties failed and the pan developed a slight crack.
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For the top curves I used a deep socked to make this radius and again glued them in place.
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I probably didn't need to make them this long but I had the material and figured more glued surface would be stronger than less.
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Here is a demo that I made for a friend to show how the rivnut would be used. I used a step drill to slightly enlarge the clamp hole. I then slipped the clam on the airframe cross pieces and then pulled the rivnut. I also trimmed the rubber after it was in place so the seatpan fit snugly.
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Thats what the finished product looks like once installed. Much stronger than using zip ties and to pull the seat pan out it is just a matter of pulling 8 screws.
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RV6flyer
12-20-2020, 09:23 AM
Did you do this just on the back?

desertdave
12-20-2020, 09:29 AM
The first photo is the front lip reinforcement. Four anchor points on the front and four on the back.

RV6flyer
12-20-2020, 10:08 AM
The first photo is the front lip reinforcement. Four anchor points on the front and four on the back.


Thanks for this. I just cut the slots for hose clamps but I sure like your method better. I have a riv-nut set but I think they are aluminum. Have to see if I can use steel ones with my squeezer.

Allan

Eric Page
12-20-2020, 10:22 AM
Very nice solution, Dave. My seat pan was... I'll be charitable and say, "mishandled"... by the first builder, so it's in need of fiberglass repairs already. Your method of securing it looks like a good way to go once that's done.

rv9ralph
12-20-2020, 02:04 PM
There may be another option, possibly easier.

Use the aluminum straps to make a loop, like an adel clamp, around the bottom truss bar, in 4 locations like on the current SS7. Close the tab with the rivets holding a nut plate to the tab.

Same on the top bar in 2 locations as is used on the current SS7.

One problem with the long tab is that the bonding agent may let loose due to flexing of the seat pan.

I would use screws through the seat pan with the largest pan head available, possible with a fender type washer.

Ralph
just my $.02

desertdave
12-20-2020, 04:22 PM
One problem with the long tab is that the bonding agent may let loose due to flexing of the seat pan.

That is why I bent the long straps to conform to the curve on the top and bottom of the seat pan. Structurally they don't even need to be bonded to anything. Physics/engineering wise they just act as backing plates for the screws. Bonding them is just a bonus and it eases the install.

Maverick
12-20-2020, 07:01 PM
Obviously there are several possible solutions to this problem, a serious design/manufacturer flaw that Skystar ignored but that Murle Williams did something about; something that John and Debra have addressed in the later models, thank goodness. I am of the KISS method but, what ever solution you land on and you're building a 5, do something about the problem before you head for the wild blue yonder.

In 2003 Murle Williams convinced me to put in the underseat compartments he designed. On my first cross country trip, near Gallop New Mexico I got into turbulence. When I landed in St.John's for fuel was when I first noticed the front lip of the seat pan was behind and below the cross member. The zip ties were useless. Had I not had the compartments I would likely be a statistic in FAA hall of fame of the not so fortunate. Thanks Murle, again.

And whatever solution you come up with for the front lip problem, seriously consider the blocks of wood beneath the compartments. I used 2x2 pieces with notches cut where the tubing is and held in place beneath the compartments by zips. Safety straps are too prone to stretching. If you have the compartments, you could get by with straps but, I like keeping it simple. As Desertfox4 would say to me when we were building our first Kitfoxes, find the most likely failure point and attack it with your ingenuity. No one wants to read about you in a NTSB report.
Blue skies and calm winds,
Fred

jiott
12-20-2020, 08:15 PM
I have the Model 7SS with built-in under-seat boxes, but just to make sure I also installed, with Hysol, the blocks Maverick was talking about; very easy thing to do.
By the way, that plastic header tank is long gone, replaced with aluminum.
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RV6flyer
12-20-2020, 10:15 PM
I have the Model 7SS with built-in under-seat boxes, but just to make sure I also installed, with Hysol, the blocks Maverick was talking about; very easy thing to do.
By the way, that plastic header tank is long gone, replaced with aluminum.
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Did you have problems with the plastic tank? I saw that some people had leaking issues with the weld job on the aluminum tank.

jrevens
12-20-2020, 11:33 PM
When I got my kit Kitfox was still using the zip ties and there were no tabs welded to the structure to secure the seat. Just like others, I wasn't really impressed with that system. I made brackets also, out of stainless steel, SS pop rivets and steel 10-32 "Tric-Nuts". I bonded these to the tube structure and created a secure clamping action with 2 rivets each, followed by installing the Tric-Nuts. I also bonded AN960 washers to the fiberglass at the 8 mounting locations. It wasn't too long after that when Kitfox started welding on tabs.