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n85ae
Joined: 14 Mar 2007 Posts: 403
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Posted: Fri Jan 09, 2009 2:36 pm Post subject: Re: Trailering a Kitfox |
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All of which, in addition to the obvious are darned good reason to
not tow with the wings spread.
I was only talking about the comment about the Skystar trailer towing
G-Meter readings. Engineering calculations are boring, by the way, that
sounds too much like my job.
Realistically, the average bumpy landing is more harmfull to your plane
than towing. Not to mention landing and taxiing in a bumpy field. My
honest opinion is that the most likely damage you'll sustain from towing,
is if the wings get banging around. I have taxied mine across bumpy
grassy fields, and those worry me a lot more. if you are on main roads
you'll likely not have any sort of bumpy enough ride to damage your plane on a trailer. UNLESS it is loose, or the wings aren't supported
or somebody runs into you. Or it gets hit by a rock.
Half the toys I've had I've towed, from dirt bikes, to cars, and planes,
boats and my camper, and the only damage has been from stuff getting hit by road debris.
I worried a lot about the effects of towing mine, until I actually did it.
The experience of hauling it behind my truck, changed everything I
really worry about. I only worry about two things now - Some jerk hitting
it, or my tiedowns coming loose.
Jeff
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msm_9949(at)yahoo.com Guest
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Posted: Fri Jan 09, 2009 2:48 pm Post subject: Trailering a Kitfox |
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Man, and I thought we lawyers liked to argue! I had no idea engineers were so much like lawyers . . . but with math!! How's this:
Lots of trailering = 1 reportedly damaged airplane. Can we move on now?
Marco Menezes N99KX
Model 2 582-90 C-Box 3:1 w/clutch
do not archive
--- On Fri, 1/9/09, Bob Brennan <matronics(at)bob.brennan.name> wrote:
[quote]From: Bob Brennan <matronics(at)bob.brennan.name>
Subject: RE: Re: Trailering a Kitfox
To: kitfox-list(at)matronics.com
Date: Friday, January 9, 2009, 3:52 PM
[quote]--> Kitfox-List message posted by: "Bob Brennan" <matronics(at)bob.brennan.name> The Kitfox airframe, which is fabric covered metal tube, does not have a posted MTBF that I know of, probably because the airframe is designed not to flex under load. Sorry, I should have been more clear in stating that aircraft whose frames are made of metal (rather than "metal airframes" have an MTBF of parts according to the stress they are subjected to. To be even more clear - I meant airframes of almost all airline aircraft and most standard type GA aircraft such as Piper and Cessna, which rely on stressed metal monocoque skins to form the "airframe". And all such MTBF numbers are based on the metal flexing under "momentary spikes", not constant loads. My reply is to this subject: "This is completely flawed, because these momentary spikes mean nothing." And this although I think "Rexinator" already replied better than me: "They completely lacked the engineering brainpower to realize that load is related to force over time." The 3 wing attach points on the Kitfox seem to be designed well for the published maximum plus and minus loads in flight, but the designers seem to have failed to design for the stresses of the unsupported wings in the trailering position, or failed to publish limits or recommendations on how to rig the wings for trailering. I'd be happy to be proved wrong on that last point and get some real numbers, but in the meantime it seems it is left to us to hash it out here and hopefully provide some rigging recommendations that work. I know I personally have learned a lot from these discussions, but don't want to discuss "hogwash" really. I'll leave that to farmers. Bob Brennan - N717GB ELSA Repairman, inspection rated 1991 UK Model 2 ELSA Kitfox Rotax 582 with 3 blade prop Wrightsville Pa --
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matronics(at)bob.brennan. Guest
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n85ae
Joined: 14 Mar 2007 Posts: 403
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Posted: Fri Jan 09, 2009 2:52 pm Post subject: Re: Trailering a Kitfox |
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Quote: | I don't have a trailer so for me this is all really theoritical, but Denney
built trailers that towed tail first with the tailwheel elevated, Skystar
did the same. |
A good reason for this is axle location and tongue weight, when you
design a trailer, you need to locate the axle, and this affects the tongue
weight. To keep the tongue weight reasonable you end up with the
axle location of the trailer pretty close to the planes cg. Considering
you need to be able to turn as well when towing you pretty much end
up sketching and calculating to the point where you have a backwards
towing rig. Which is exactly what I did. Somewhere I have an excel
spreadsheet with all the calculations I did for the trailer in the
previous picture.
Jeff
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matronics(at)bob.brennan. Guest
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Posted: Fri Jan 09, 2009 2:59 pm Post subject: Trailering a Kitfox |
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All good points Jeff, except for one. You *knew* I'd find at least one
didn't you?<g>
With the wings out all the forces along the wings are perpendicular to the
fuselage and concentrated on 3 connect points, which is well documented and
presumably designed for and tested to the stated maximum loads.
But it seems that with the wings folded and only supported by 2 of the
attach points, now with the force-moments *parallel* to the center line of
the fuselage - stuff can break. And worse yet it can be damaged via metal
fatigue rather than wings snapping off during transit. These are things I
try to do my best to understand, and avoid.
bob
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matronics(at)bob.brennan. Guest
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Posted: Fri Jan 09, 2009 3:02 pm Post subject: Trailering a Kitfox |
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2 reported damaged airplanes Marco, so far. 1+1=2 with math<g>
I don't want to be number 3
tedious bob
do not archive
From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Marco Menezes
Sent: 09 January 2009 5:47 pm
To: kitfox-list(at)matronics.com
Subject: RE: Re: Trailering a Kitfox
Man, and I thought we lawyers liked to argue! I had no idea engineers were so much like lawyers . . . but with math!! How's this:
Lots of trailering = 1 reportedly damaged airplane. Can we move on now?
Marco Menezes N99KX
Model 2 582-90 C-Box 3:1 w/clutch
do not archive
--- On Fri, 1/9/09, Bob Brennan <matronics(at)bob.brennan.name> wrote:
[quote]From: Bob Brennan <matronics(at)bob.brennan.name>
Subject: RE: Re: Trailering a Kitfox
To: kitfox-list(at)matronics.com
Date: Friday, January 9, 2009, 3:52 PM
[quote]--> Kitfox-List message posted by: "Bob Brennan" <matronics(at)bob.brennan.name> The Kitfox airframe, which is fabric covered metal tube, does not have a posted MTBF that I know of, probably because the airframe is designed not to flex under load. Sorry, I should have been more clear in stating that aircraft whose frames are made of metal (rather than "metal airframes" have an MTBF of parts according to the stress they are subjected to. To be even more clear - I meant airframes of almost all airline aircraft and most standard type GA aircraft such as Piper and Cessna, which rely on stressed metal monocoque skins to form the "airframe". And all such MTBF numbers are based on the metal flexing under "momentary spikes", not constant loads. My reply is to this subject: "This is completely flawed, because these momentary spikes mean nothing." And this although I think "Rexinator" already replied better than me: "They completely lacked the engineering brainpower to realize that load is related to force over time." The 3 wing attach points on the Kitfox seem to be designed well for the published maximum plus and minus loads in flight, but the designers seem to have failed to design for the stresses of the unsupported wings in the trailering position, or failed to publish limits or recommendations on how to rig the wings for trailering. I'd be happy to be proved wrong on that last point and get some real numbers, but in the meantime it seems it is left to us to hash it out here and hopefully provide some rigging recommendations that work. I know I personally have learned a lot from these discussions, but don't want to discuss "hogwash" really. I'll leave that to farmers. Bob Brennan - N717GB ELSA Repairman, inspection rated 1991 UK Model 2 ELSA Kitfox Rotax 582 with 3 blade prop Wrightsville Pa --
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n85ae
Joined: 14 Mar 2007 Posts: 403
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Posted: Fri Jan 09, 2009 3:07 pm Post subject: Re: Trailering a Kitfox |
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ok, ok, ok. I Have the solution.
A really BIG box, and styrofoam peanuts!
Those packaging engineers aren't dummies, they invented that stuff
for a good reason.
Have a nice weekend.
Regards,
Jeff
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gary-n-dorothy(at)tctwest Guest
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Posted: Fri Jan 09, 2009 4:09 pm Post subject: Trailering a Kitfox |
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So --it seems that we need a structural engineer to design a 3 rd attachment point/ brace to be used for transport , locating it to the outboard end of the wing, and attaching somewhere near the rear of the airframe, the wing forming a triangle / or a truss, better spreading the load to the airframe and eliminating the "lever action" the wing imparts to its two attach points when folded.
I can understand the concerns brought up here. But believe that Sky star designed an airplane ---not a trailer, and I do believe that the loads imparted to the airframe over a period of time will damage the basic airframe attach points. Chuck holes, speed bumps, gravel roads and freeways, trailer spring rates, all will bring different levels of abuse, So I guess each of us in our own way will have to solve their transport problem.
Personally, I tow on a trailer , tail propped up, wings close to level with the aircraft facing forward, and the wing butts covered with a wind chock, removing it when unfolding the wings.
The box full of Styrofoam peanuts sounds fun !!! you may need a lot of help tho, cleaning runways when unpacking. :~}
have a good weekend
GG
N4276M
[quote] ---
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Fox5flyer Guest
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Posted: Fri Jan 09, 2009 4:50 pm Post subject: Trailering a Kitfox |
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Nice trailer, Jeff. Very nice. Ever thought about making plans for it?
Deke Morisse
Mikado Michigan
S5/Subaru/CAP 402+ TT
"The aim of an argument or discussion should not be victory, but progress."
- Joseph Joubert
do not archive
---
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dwight purdy
Joined: 10 Feb 2006 Posts: 85
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Posted: Sat Jan 10, 2009 5:42 am Post subject: Trailering a Kitfox |
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I have never commented on this subject and am also tired of deleting them.
That being said I must comment on this idea of fastening down tight. Who
ever built my trailer made the tongue carry through too weak and it flexes a
bunch. If you tie it down tight your plane becomes an integral part of the
trailer. You do not want your longerons doing that! I need to beef up my
trailer.
Dwight Purdy
Model II
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_________________ dwight
model II |
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pwmac(at)sisna.com Guest
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Posted: Sat Jan 10, 2009 6:55 am Post subject: Trailering a Kitfox |
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Replacement of the spar steel doubler would be one option. Pretty low
tech and it puts the plane back to what it was when built.
Examine the front/rear braces for any tell tale issues that would
give a hint of plane attachment issues?
Verify the fuge lower structure is still straight as designed.
Consider some kind of ndt for the tail spring?
Paul
==========
At 05:30 AM 1/10/2009, Dick Maddux wrote:
Quote: | I know we have beat this subject to death but I really would like to
solicit an opinion on the best way to check the rear spar pivot
point for damage. Unfortunately I had to trailer my Kitfox from just
south of Boston to Pensacola ,Fl due to the lousy weather enroute
when I bought it. It was towed on a tandem wheel trailer and it was
a rough ride on the interstate due to the light weight of the
Kitfox. The tanks were empty and the front brace bar was installed.
I examined the rear spar pivot point visually upon arrival as I
thought this might be a possible weak point. It appeared to be ok
but now with all this discussion I think I will reexamine it. Any
good ideas on how to check it other than visual (i.e.: dye
penetrant,etc) Any other areas to check?
Thanks
Dick Maddux
Fox 4-1200
Pensacola Fl
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shinco(at)bright.net Guest
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Posted: Sat Jan 10, 2009 8:35 am Post subject: Trailering a Kitfox |
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n85ae wrote:
Quote: |
ok, ok, ok. I Have the solution.
A really BIG box, and styrofoam peanuts!
Those packaging engineers aren't dummies, they invented that stuff
for a good reason.
Have a nice weekend.
Regards,
Jeff
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 23774#223774
------------------------------------------------------------------------
Checked by AVG - http://www.avg.com
NOW That is a good idea.....may be all so we could have UPS ship it for
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us.from home to airport..that way you all so would not need a tow truck
to pull it..Steve Shinabery N554KF KF2 St.Marys Ohio
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shinco(at)bright.net Guest
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Posted: Sat Jan 10, 2009 8:44 am Post subject: Trailering a Kitfox |
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Dwight Purdy wrote:
[quote]
I have never commented on this subject and am also tired of deleting
them. That being said I must comment on this idea of fastening down
tight. Who ever built my trailer made the tongue carry through too
weak and it flexes a bunch. If you tie it down tight your plane
becomes an integral part of the trailer. You do not want your
longerons doing that! I need to beef up my trailer.
Dwight Purdy
Model II
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