Gross weight increase Kitfox IV 1050-1200


24 posts in this topic

Posted

Does anyone have the instruction and pictures (both rod through carry through tube and strap between strut attach points) of the Kitfox modification from 1050-1200 for float operation?
The reason for asking is that I intend to operate the plane on floats and would like to make it as rigid as possible, not to exceed the gross weight limit.

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Posted

I’m wondering the same. Or if anyone has any problems being over gross in there kitfox 4 with 912 1050lbs.

i have ordered a new set of struts and I was going to do all the modifications.

it kinda sucks because I think a lot of people fly over gross but won’t talk about it

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Posted (edited)

I don't have the instructions but the good news is that yes alot of over gross flying has inevitably happened in Kitfoxes and I believe they still claim zero in flight structural failures with all the kits they have sold (as told to me by John McBean at OSH 2017)

Edited by Yamma-Fox

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Posted (edited)

Pic of float brace here: LINK

Pic of fuselage lower 'tube-within-a-tube' cross brace below.

image.jpeg

Edited by dholly
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Posted

If it was a licensed aircraft, whatever the gross weight listed at the time of the AW inspection is what it is. I don't believe that can be changed legally without FAA approval. And good luck with getting their approval.

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Posted

Different with experimental from certified, although probably you mean an aircraft with a valid AW cert.  You do have to go back into phase 1 however for an increase in gross weight.  JImChuk

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Posted

Can you show me where the gross weight is listed on the AW for a EAB or where it is required to be listed anywhere?  If you built your kit, your are the manufacture and can assign it what ever you choose.  Not that it is prudent to do so, however, unless something has changed I nthe last 6 mo or so, there is NO SUCH THING as a "gross weight" for EAB.

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Posted

Its not listed on the AW cert, operating limitations, or on the tail placard, maybe on some placards, but it is in the paperwork that was originally filed with the FAA when it was first issued the AW cert. Its also on the weight and balance sheet that is carried in the aircraft or should be.  And it does require FAA's blessing. One can't just say "now the gross weight is xxxx " and go about their merry way. And we are talking about experimentals and not certified aircraft.  And yes one can assign whatever gross weight they choose but they have to do it when the AW cert is applied for. And some inspectors will want to see factory approval if it is a manufactured kit and not plans built, not all but some will. There is a paperwork trail to change the gross weight after it is a legal aircraft. And has nothing to do with the safety factor which could be involved.  FSDO's are beginning to tighten up on paperwork snaffles. I am done!

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Posted

Its not listed on the AW cert, operating limitations, or on the tail placard, maybe on some placards, but it is in the paperwork that was originally filed with the FAA when it was first issued the AW cert. Its also on the weight and balance sheet that is carried in the aircraft or should be.  And it does require FAA's blessing. One can't just say "now the gross weight is xxxx " and go about their merry way. And we are talking about experimentals and not certified aircraft.  And yes one can assign whatever gross weight they choose but they have to do it when the AW cert is applied for. And some inspectors will want to see factory approval if it is a manufactured kit and not plans built, not all but some will. There is a paperwork trail to change the gross weight after it is a legal aircraft. And has nothing to do with the safety factor which could be involved.  FSDO's are beginning to tighten up on paperwork snaffles. I am done!

The reason I ask is because I have the CD from the FAA on my plane and there is nothing in my paperwork that indicates a GW.  The original build logs and any phase I paperwork were lost in a house fire years ago.  So, if there is nothing on file with the FAA and no records exist of any recorded gross weight other than what I choose to put on the WB sheet, what legally sets the so called "gross weight" on an EAB?

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Posted (edited)

The reason I ask is because I have the CD from the FAA on my plane and there is nothing in my paperwork that indicates a GW.  The original build logs and any phase I paperwork were lost in a house fire years ago.  So, if there is nothing on file with the FAA and no records exist of any recorded gross weight other than what I choose to put on the WB sheet, what legally sets the so called "gross weight" on an EAB?

 

You could put it in Phase one, load it up to what ever gross weight you want for your maximum gross weight, test fly it at that weight, make an entry in the aircraft log book similar to the paragraph that is in most if not all experimental operating limitations that says everything is good to go at that weight with the V speeds and CG location you flew it at.  There you have it... A legally set maximum gross weight on your EAB.:)

Edited by tcj
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Posted

Leni, the FSDO office that originally issued the operation limitations and SPECIAL airworthiness certificate should maintain a file, on your particular aircraft, in the actual FSDO office... NOt all the documents are required to be sent to OKC however I used to send in as much as I could because that stuff has a habit of getting lost. FAA Order 8900.10 FAA Inspectors handbook will have a section on certification of amatuer built aircraft... .. SO if you can determine which office originally certified your aircraft as EAB,(look at your Pink Airworthiness Certificate and  you might be able to contact them and ask for copies of whatever records they have in their office file.... I always thought it was a poor way to maintain records for EAB because often the aircraft moves from one region to another sometimes several thousand miles away during its lifetime. The FAA in DC wants the Government ASIs out of the business of certificating EAB aircraft for lots of reason so they push it off on DARs, however dont think there are too many in AK.

At the FAA academy the instructors would tell us if we ever had to license an amatuer built aircraft, to tell the owner/pilot to wait until we were out of sight before they flew it!! True story....

I never questioned the Gross weight but was required to see a weight and balance sheet and some kind of proof that the all up flying weight CG was within the area determined by the designer. Other wise we normally went with 10-25% MAC for CG location at the test flying weight with pilot, fuel.

 

Look at http://www.supercub.com/pdf/Forms/Certify_Homebuilt_Airplane.pdf

AC 20-27 is an advisory circular that sorta provides guidance however it is the actual FAA Order that dictates the rule.

So look at FAA Order 8130.2 as revised and it has a section on licensing Experimental amatuer built aircraft...

FAA Order 8900.10 is hard to navigate thru but it has some info on licensing amatuer built aircraft as well.

From memory, a 3 view drawing, a duplicate airworthiness certificate, a copy of the operating limitations, , application for an airworthiness certificate are some of the items requires to be recorded in OKC. They are copied onto one of 3 digantic HD in the basement of the FAA AIrcraft registry office.

Ive been away from it all for 7 yrs and my head still hurts trying to sort it all out...sorta makes me want to go slam my head in a file drawer.... God Im glad to be outta there......!!

Also worth noting, amatuer built aircraft do not have a standard airworthiness certificate. As such, when you sign the condition inspection you should state'

blah blah blah, /......and was determined to be in condition for SAFE flight". Do not use the word airworthy. IT is not built to any type design or TC.

ALso note that "special flight permits" or ferry permits have the same verbiage......"determined to be in a condition for SAFE flight"

 

I hope you are totally confused now!!!! IF so, I have done my job.. good night!

 

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Posted

these are the kinds of burning questions that come up from time to time within the FSDO offices. They are referred to the TEchnical Standards Branch (so called experts within the FAA), usually at Regional branch level,  but more often than not, they dont know either so then it goes to Aircraft Certification or maybe Legal and it takes weeks or months to get an answer....

YOu might call EAA and ask if they have a technical adviser who can connect the dots on how to determine Gross weight and how to change it after the EAB airplane is flying.. Id try that and the FAA last.....

 

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Posted

Hi all, and thanks for the answers. I think the topic sidetracked a little from my original question. I should probably have used another headline. All good information is appreciated, but I wonder if someone has some more input to the original question and the answers from dholly?

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Posted

Snowpaw,

I have done a bunch of looking for that same information and have not found it yet either. I have not given up yet though so will post it when or if I find it. 
Did you ever find anything out about it? 

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Posted

I have a Kitfox IV 1050 that the W&B says weighs 560 pounds empty. Thinking about some of my flights with my instructor I think we were probably 100 lbs over gross once or twice and the airplane performed fine. This was back in warmer weather about 85 deg F at 600 ft msl field elevation. Performance wise with the 65 hp Rotax 582, I didn see a problem. 

The manual for my airplane says it is stressed for ultimate loads of +5.7 g, -2.85 g at 1050 lbs. So if we ran this airplane at 1200 lbs without any mods it would be good for an ultimate load of 5.7*1050/1200 = 4.99 g and -2.85*1050/1200 = -2.5 g. With a 1.5 safety factor it would be good for +3.325 g, -1.66 g. A little below what the FAA considers a "normal" category airplane which is +3.8 g, -1.52 g. Another way to look at it would be to say it is still good for 3.8 g, but with a 1.3 safety factor rather than 1.5.

The other consideration is performance which could be the limiting factor on gross weight, but as I said, from my little flying of a Kitfox with just 65 hp I just can't see this as an issue, at least at lower density altitudes.

 

I too want to get amphibious floats at some point. I have read that when it was Denny Aircraft that there was a document that authorized a float equipped Kitfox IV 1050 to operate to 1200.  The mention of this document came from John McBean on a post over on the TeamKitfox forums, so I believe it is real. I have searched for this document, but have not found it anywhere. If anyone has this document I would like a copy.  Even so, I will likely at some point do some strengthening mods on the airplane.

As for the comments that the max gross weight is set in stone by the original builder, I don't buy it.  I won't get into it but IMO, the official aircraft file is the one in OKC, and even if a FSDO did save some paper about a homebuilt it doesn't matter. For one, even if this is the case, there is about a 0.0001% chance that the paper at the FSDO will ever see the light of day even if something happens. Second, I have all the paper submitted for the Sonerai that i built and not one piece of paper says anything about weight. There is nothing about weight in the file from OKC either.  My Sonerai was inspected by a MIDO inspector and the MIDO office he worked at closed. What do you think the chances are that they could even find any paper on my airplane if it ever existed. Bottom line, the weight is set in phase 1 testing and if you want to change the "authorized" weight it it is just a matter of re-entering phase 1 and verifying it and record it in the aircraft records. Now whether that new weight is safe or not is another question.

In my opinion, I am not concerned about performance at higher weights, and if I happen to exceed the 1050 once in a while I'm not concerned about structural strength, but if I were to operate above 1050 regularly I would do some mods including beefed up carry  through tubes, strengthened strut attach and heavier struts. None of these are particularly hard for someone with some welding experience.  

I have my fire suit on

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Posted

Somewhere in any design there is a breaking point that can be reached.  I don't plan on finding it. Excess weight is a performance killer and sometimes a pilot killer.

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Posted

Snowpaw,

I have done a bunch of looking for that same information and have not found it yet either. I have not given up yet though so will post it when or if I find it. 
Did you ever find anything out about it? 

Happy New Year!

No, I have not found out anything more.

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Posted (edited)


Well, you asked specifically about the float brace and thru tube brace. There is also some general info about changes in the KF1 thru 4-1200 in this old newsletter.

Kitfox_Pack_News_July1990.pdf

Edited by dholly
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Posted


Well, you asked specifically about the float brace and thru tube brace. There is also some general info about changes in the KF1 thru 4-1200 in this old newsletter.

Kitfox_Pack_News_July1990.pdf

I couldn’t get that link to work Doug. Maybe it is just me? 

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Posted

Unless I am missing something (other than my brain these days), I don't see anything in the article about the Kitfox IV. 

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Posted


That first picture I don't know about that one. To install that tube you would have to completely drill through the Longeron to get inside the lower spar carry through. I think the strap would be a better way to go.

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Posted

There is another article "Kitfox Arrives" in Flying magazine October 1992 that describes it more clearly.

"Denney says he tested a 1,050-pound airframe to destruction to ascertain which areas needed beefing up for a 1,200-pound limit The airframe was loaded with weight equivalent to 5. 7 Gs at 1,550 pounds, which produced some deformation in the wing attach pins. At 1,600 pounds there was a quarter-inch permanent displacement at the tips of the spars. At 1,650 pounds the fuselage tore apart at the tube that runs across its bottom and connects the two liftstrut attach brackets; thicker-wall tubing is now used here. The steel-tube lift struts of the 1,050-pound airplane also wouldn't take -2.85 Gs at 1,200 pounds, so they have been changed on the 1,200-pounder to one-inch diameter with a wall thickness of .049 inches, compared with 7 /8ths and .035. The Kitfox's directional stability has been somewhat lacking, and so the vertical surfaces of the Kitfox IV-1200 have grown in height by seven inches; the rudder chord has been extended by two inches."

For the full article you can find it here if the link works: https://books.google.com/books?id=2dy-fCMhHwYC&pg=PA84&dq=kitfox+arrives&hl=en&sa=X&ved=2ahUKEwin1tfpkIfnAhX1dc0KHdMuD3cQ6AEwAnoECAEQAg#v=onepage&q=kitfox arrives&f=false

 

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Posted

There is another article "Kitfox Arrives" in Flying magazine October 1992 that describes it more clearly.

"Denney says he tested a 1,050-pound airframe to destruction to ascertain which areas needed beefing up for a 1,200-pound limit The airframe was loaded with weight equivalent to 5. 7 Gs at 1,550 pounds, which produced some deformation in the wing attach pins. At 1,600 pounds there was a quarter-inch permanent displacement at the tips of the spars. At 1,650 pounds the fuselage tore apart at the tube that runs across its bottom and connects the two liftstrut attach brackets; thicker-wall tubing is now used here. The steel-tube lift struts of the 1,050-pound airplane also wouldn't take -2.85 Gs at 1,200 pounds, so they have been changed on the 1,200-pounder to one-inch diameter with a wall thickness of .049 inches, compared with 7 /8ths and .035. The Kitfox's directional stability has been somewhat lacking, and so the vertical surfaces of the Kitfox IV-1200 have grown in height by seven inches; the rudder chord has been extended by two inches."

For the full article you can find it here if the link works: https://books.google.com/books?id=2dy-fCMhHwYC&pg=PA84&dq=kitfox+arrives&hl=en&sa=X&ved=2ahUKEwin1tfpkIfnAhX1dc0KHdMuD3cQ6AEwAnoECAEQAg#v=onepage&q=kitfox arrives&f=false

 

Perfect that is what I was looking for and couldn’t seem to find. Thanks 

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