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FireFly Landing Gear Leg Strength Improvement
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jbhart(at)onlyinternet.ne
Guest

Posted: Sat Oct 06, 2007 6:54 pm Post subject: FireFly Landing Gear Leg Strength Improvement

FireFlyer's



After lightly plopping my FireFly and being surprised as to how easy it was 

to bend the legs, I started thinking about how to support the existing legs. 

 I took some measurements, made some assumptions, and ran some numbers.  I 

found that at gross weight the gear legs can support a 1.8G to 3.4G landing. 

 Where the 1.8G represents landing on a very slick surface, and the 3.4G 

represents landing on dry pavement.  The FireFly landing gear is very tire 

to surface friction dependent in that there is nothing but the legs to keep 

the wheels from spreading.



I looked at attaching a 1/8 inch diameter cable to the axle to leg 

attachment bolt and running it to either the leg attachment bolt in the cage 

or to the opposite leg just below the socket.  By doing this, the 1.8G 

improved to 3.9G for the leg attachment bolt, and to 5.2G when connecting to 

the top of the opposite leg just below the socket.



This may be a good low cost and light weight improvement.  More about how 

these numbers were calculated can be seen at:



http://www.thirdshift.com/jack/firefly/firefly134.html



When, I get the parts fabricated and installed, I will put up another page. 



Jack B. Hart FF004

Winchester, IN

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Oct 06, 2007 7:38 pm Post subject: FireFly Landing Gear Leg Strength Improvement

> This may be a good low cost and light weight improvement.



  > Jack B. Hart FF004



Jack H:



I have a few hours flying the FF, so I consider myself a Fireflyer also.



We horse around with the airplanes at the factory and Sun and Fun, and 

Oshkosh.  In other words, they get flown hard and to extreme most of the 

time.  Knock on wood, I have not stalled one in and bent a leg or two. 

That's the only way they bend, unless you run over an obstacle or through a 

deep rut or in a hole.  Next time you see Dick Rayhill flying the FSII at 

OSH or S&F, the gear legs will be bent and sagging.  Reason, he approaches 

and lands the FS right on the edge of the stall.  Sometimes he screws up and 

stalls prematurely.  If ya drop it in, the gear legs will bend.



Seems to me putting a cable brace on your gear leg will take most of the 

flex out of it, then load up a point where stress is concentrated and fail 

again.



Cables hanging down there also invite noseovers if you should land in the 

beans, high grass, weeds, or brush.  For sure cotton and corn.  They'll put 

you on your nose with or without gear leg cable bracing.



As long as i have been flying Kolbs, I still bend gear legs.  Not because 

they are poorly designed.  They were never designed to be stalled and 

dropped in a couple feet or more above the ground.  I screwed up and bent a 

gear leg this summer because I stalled the mkIII too high with a wing low. 

That will get them quicker than stalling and falling in a wings level 

attitude where both gear legs are sharing the load.  Looks like you dropped 

yours in on one leg too.



Let us know how your experiment turns out.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

1planeguy(at)kilocharlie.
Guest

Posted: Mon Oct 08, 2007 6:25 am Post subject: FireFly Landing Gear Leg Strength Improvement

As long as i have been flying Kolbs, I still bend gear legs.  Not because   

they are poorly designed.  They were never designed to be stalled and   

dropped in a couple feet or more above the ground.  I screwed up and bent a   

gear leg this summer because I stalled the mkIII too high with a wing low.   

That will get them quicker than stalling and falling in a wings level   

attitude where both gear legs are sharing the load.  Looks like you dropped   

yours in on one leg too.  

   

Let us know how your experiment turns out.  

   

john h  

mkIII  

   

<snip>  

   

With much fear of the poke the angered dog with the stick one more time syndrome setting in...  

   

Could I take this opportunity to point out that those VG things soften the stall a good bit and greatly lessen the chances of bending gear legs??!!??!!  

   

If you work'em hard enough they also slice and dice and can make Julian fries   

   

Jeremy "I'm so ashamed" Casey  

   

P.S.  I only sent this message to try to secure the VG thread as the all-time winner of longest thread and most non-“controversial” debate ever…  

   

P.S.S. Pennzoil sucks!!!  (Will that get a good 2-stroke oil fight going?)  

       [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Oct 08, 2007 10:37 am Post subject: Re: FireFly Landing Gear Leg Strength Improvement

Jack,



I very much enjoyed your detailed description of calculations and intended remedy for gear leg bending. Please keep us posted on how that works out.



For what its worth, on my recent stall from a few feet into a pothole at Bob Bean's field which broke the left wheel axle fitting and resulted in me ending the landing upside down, the longer than standard 4130 tubing gear legs were not bent in the process.  This, even when the leg without the axle fitting dug into the ground as I was still moving forward at about 30 mph.



I've become a believer in heat treated 4130 tubing gear legs. I have no idea if they are heavier or lighter than the stock gear legs, which I know is always important to you for staying under 254#.

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Oct 08, 2007 11:19 am Post subject: FireFly Landing Gear Leg Strength Improvement

the longer than standard 4130 tubing gear legs were not bent in the 

process.



 	  Quote: 	
		   Thom in Buffalo


	


Hi Thom:



To what RC rating were your gear legs heat treated?



I have been using 48 RC since we started experimenting with and using 4130 

gear legs in 1988, on my FS and mkIII.



IIRC the weight of the mkIII aluminum legs were about the same or a tad more 

than the 4130 legs.



I use 1 1/8" .120" wall 4130 legs on the mkIII and also on my FS.



In addition, my tailwheel strut is .120" wall 3/4" RC 48.  I think the OD is 

3/4.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jindoguy(at)gmail.com
Guest

Posted: Mon Oct 08, 2007 1:02 pm Post subject: FireFly Landing Gear Leg Strength Improvement

Thom, Of course, the other side of this coin, as Travis reminded me, is that aluminum gear legs save cages. 

No use speculating on how your arrival would have gone if you'd have had aluminum legs, but I've done some real whack's, straightened the legs that night, and flown the next day. 



Rick



On 10/8/07, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:[quote] --> Kolb-List message posted by: "John Hauck" <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)>



  the longer than standard 4130 tubing gear legs were not bent in the

process.

 

 	  Quote: 	
		   Thom in Buffalo


	


Hi Thom:



To what RC rating were your gear legs heat treated?



I have been using 48 RC since we started experimenting with and using 4130

gear legs in 1988, on my FS and mkIII. 



IIRC the weight of the mkIII aluminum legs were about the same or a tad more

than the 4130 legs.



I use 1 1/8" .120" wall 4130 legs on the mkIII and also on my FS.



In addition, my tailwheel strut is .120" wall 3/4" RC 48.  I think the OD is 

when you live at the airport.  [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Oct 08, 2007 5:14 pm Post subject: Re: FireFly Landing Gear Leg Strength Improvement

John,



I have no idea to what RC the legs were heat treated to because it was done by someone else before I bought it. I only know that it was done or the tubes would have buckled in a heartbeat without the heat treating. They look sort of funny because even with the FS empty, they are slightly bowed and have visually obvious negative camber but no toe-in/out that I can tell. When loaded with me and fuel I'm sure it looks even stranger but they track straight and true and don't bounce much at all with imperfect touchdown. I expect that with much use on paved runways, where I'm located, the inside sides of the tires will wear first, then I'll turn them around and wear out the other side.



Great gear legs is all I can say. If my pothole landing did not result in damaged sockets it is unlikely I'll ever have that problem, without breaking a lot more too.



Almost done with the wingtip structural repair. Boom tube is next.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

ElleryWeld(at)aol.com
Guest

Posted: Mon Oct 08, 2007 5:25 pm Post subject: FireFly Landing Gear Leg Strength Improvement

Thom

 What is wrong with your Boom Tube? that you have to do a structural repair on  that sounds  scary

  

 Ellery or Curious George on this one 

  

 do not archive





  [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Oct 08, 2007 5:37 pm Post subject: FireFly Landing Gear Leg Strength Improvement

They look sort of funny because even with the FS empty, they are slightly 

bowed and have visually obvious negative camber

 	  Quote: 	
		   --------

 Thom in Buffalo


	




Thom:



The 4130 legs can be pressed straight or a little past straight to give you 

some positive camber.  Not only does it look much better, but when loaded up 

from landing forces, the positive camber will get pulled toward neutral 

camber and load everthing more evenly.



Negative camber makes the airplane look like it just finished making a hard 

landing.



One can also persuade the axles to bend the wheels back to positive camber 

by blocking up the gear leg/axle socket, pulling off the wheel, slipping a 

piece of water pipe over the axle snugly, and stepping on the pipe.  That is 

how I kept my FS axles happy.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Oct 08, 2007 5:52 pm Post subject: FireFly Landing Gear Leg Strength Improvement

> The 4130 legs can be pressed straight or a little past straight to give 

you

 	  Quote: 	
		   some positive camber.


	




Gang:



Forgot to add something to the last.



Not a good idea to try flying with 4130 gear legs that have not been heat 

treated.  Prior to heat treating they will be extremely stiff, and bend 

permanently if stressed to much.



After heat treating the legs become very springy, because they are springs. 

At 48 RC they make a good spring, but when pushed over the limit, they will 

bend before they break.  I do not know where that RC number is that will 

make them brittle.  I have had great luck with 48 RC.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Tue Oct 09, 2007 3:30 am Post subject: Re: FireFly Landing Gear Leg Strength Improvement

Ellery (aka Curious George),



Along with the relatively minor wing tip damage, the nose cone was destroyed and the front of the cage was bent as was the left upper longeron, one wing strut bowed, the sacrifical PowerFin prop was destroyed (blades only) and the boom tube broke just aft of the H-truss. Bob Bean repaired the cage before I removed the remains from his place where the incident occurred. The engine is fine and the empenage was untouched. 

John,



Thanks for the pointers about pre-stressing the 4130 tubes to remove the static negative camber. Once I get the FS flying again next spring, I'll see about fixing that. It DOES look strange.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Oct 09, 2007 5:49 am Post subject: FireFly Landing Gear Leg Strength Improvement

> Along with the relatively minor wing tip damage,  

 	  Quote: 	
		   --------

 Thom in Buffalo

 
	




Thom:



Sounds, to me, like a major accident.



Your FS1 a 5 rib wing?



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

ElleryWeld(at)aol.com
Guest

Posted: Tue Oct 09, 2007 6:18 am Post subject: FireFly Landing Gear Leg Strength Improvement

Now Im wondering if there wer any survivors sounds like a Total wreck 

  

 Ellery

  

 do not archive





  [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Tue Oct 09, 2007 6:23 am Post subject: Re: FireFly Landing Gear Leg Strength Improvement

John,



Yes it is a FS1 w/ 5 rib wing. 



When you start listing the damage it sounds worse than it was. One wing received no damage at all nor did the tail. Yes it is a good bit of work to fix but nothing like building from scratch. The only bodily damage to me was very bloody shins from the instrument panel trying to occupy the space reserved for my legs. All healed now.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Oct 09, 2007 7:06 am Post subject: FireFly Landing Gear Leg Strength Improvement

 	  Quote: 	
		   When you start listing the damage it sounds worse than it was.

 --------

 Thom in Buffalo


	


Thom:



I have to disagree with you.



The damage you describe indicates the FS took some tremendous hits.  The 

tailboom does not snap unless there was another action that caused it.  Did 

the tailboom fail laterally or vertically?



If it failed laterally toward the tip of the wing that took the hit, I have 

no idea how much stress was placed on the wing prior to the tailboom 

failing.



The ribs of the FS were constructed of .028" wall 5/16" 6061.  Five of the 

little rib noses carry the flight loads.  If they decide to come out of 

column, the leading edge will possibly fail up and rearward to the main 

spar.



The reason I am concerned is because this is what happened to my own FS in 

flight.



On two occassions, that I can remember, I got the right wing tip.  Was able 

to repair it both times without removing all the fabric.  To have more than 

perceived damage in the wing never concerned me until after I survived a 

failure of both wing leading edges.  The right wing failed (which had been 

previously damaged and repaired), followed almost simultaneously by the left 

wing.



I might add, I never had a 5" tailboom fail on me, but I did snap a 6" 

tailboom when I crashed on the tip of the left wing, which took all the 

initial impact.  It failed left and toward the left wing tip.



Might be a good idea to consider some suggestions I made recently to insure 

there is more than adquate lateral bracing of the leading edges of both 

wings.



I never considered a wing failure on my FS until it was too late.  The 

thought of flying the way I did, back then, on those little wings, still 

scares me.  It has been more than 17 years ago.



Give me a call and we can discuss this in more detail if you wish.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

rrhoyt_list(at)msn.com
Guest

Posted: Tue Oct 09, 2007 7:32 am Post subject: FireFly Landing Gear Leg Strength Improvement

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Jack

  

 One of the energy absorption features of the spreading struts is the  scrubbing of the tires on the ground for spring strut planes like the Cesnas.  This is the principal dampening mechanism for the bouncing of the plane  down the runway during landing.

  

 If you are seriously looking at the design of wheel struts, take a look at  "Landing Gear Design For Light Aircraft" Vol I by Ladislao Pazmany, ISBN  0-9616777-0-8. Chapter 9 will walk you through the FAA  FAR23  requirements.  While you don’t need to meet these requirements you should  understand their implications.

 [quote]   ---

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Tue Oct 09, 2007 9:35 am Post subject: Re: FireFly Landing Gear Leg Strength Improvement

John H,



I truly appreciate your comments. I know you are looking out for me and sharing your experience graciously. Thanks. Attached are the photos of the damaged areas, including the right wing tip, the nose, and the boom tube.



Bob Bean witnessed the arrival so he may be in a position to add to this conversation. I understand why the boom broke the way it did but could not communicate it effectively to Bob Bean even when he saw the whole thing so I'm not sure I can communicate it to you and the rest of the group.



Picture this, if you can:

You have a long stick with heavy weights on each end (boom tube with empenage on one end and cage etc. on other end). Somewhere sort of near the middle of the stick you have two smaller sticks(gear legs) attached to it that extend downwards as the stick is falling (more or less horizontally). Remember I stalled 2-3 feet above the ground. The two sticks attached to the big stick hits the ground first and the momentum of the heavy weights on each end want to keep going when the short sticks stop dropping downward. The result is a tremendous bending moment in the middle of the big stick. One of the photos shows where the big stick gave up the effort to resist the bending moment.... at the aft end of the H-truss.



The wing tip damage was confined to the outer most full rib, the stabilizing tubes going from the end of the main spar and the wing tip bow, the two most outbard false ribs, the wing tip bow and about two feet of the leading edge tube. All of the full ribs have the aluminum angle braces at the upper and lower camber going from the main spar to the leading edge tube. The new full rib I bought from Travis did not come with the angles but I'm adding them to the replaced full rib. I thought they would have come with the rib but they did not.



I've already done prop flange run-out check and closely examined the gearbox for cracks and it is clean. No damage to the engine nor the tail nor the left wing except for a slight bow in the left wing strut, which will be replaced.

Any more thoughts on this you might have will be welcome.

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

APilot(at)webtv.net
Guest

Posted: Tue Oct 09, 2007 12:25 pm Post subject: FireFly Landing Gear Leg Strength Improvement

I have tried the cables between the wheel axles on a Mark III Classic.

They work great.  I am sure that some cruising speed is lost.  I intend

to put a fairing over them.  I now use one 7/64" and two 1/16" cables so

that they will break at different times when overstressed.  On one

landing recently, I did not account for the wind gradient cause by a 25

mph headwind and dropped it in hard.  Both 7/64" tension wires ripped,

but the gear leg did not bend.  That proved a point to me.  Most agree

that wheel landings are the way to go.  I definitely agree.  These hard

landings are probably having a negative effect on the boom tube.  I was

wondering how to inspect it. Vic in Sacramento

capedavis(at)yahoo.com
Guest

Posted: Tue Oct 09, 2007 12:37 pm Post subject: FireFly Landing Gear Leg Strength Improvement

John , Just a question after reading the distuction of those "tiny wings" on your firestar, I take it I don't remember but you had a5 rib Firestar didn't you ?how do the wings on a Firefly compare to a 5 rib fire star ? I know they are a lot longer but being so what do you think ? Just asking before I order , Your friend , Chris 



 ---

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Oct 09, 2007 12:41 pm Post subject: FireFly Landing Gear Leg Strength Improvement

> Picture this, if you can:

 	  Quote: 	
		   You have a long stick with heavy weights on each end (boom tube with 

 empenage on one end and cage etc. on other end). Somewhere sort of near 

 the middle of the stick you have two smaller sticks(gear legs) attached to 

 it that extend downwards as the stick is falling (more or less 

 horizontally). Remember I stalled 2-3 feet above the ground. The two 

 sticks attached to the big stick hits the ground first and the momentum of 

 the heavy weights on each end want to keep going when the short sticks 

 stop dropping downward. The result is a tremendous bending moment in the 

 middle of the big stick. One of the photos shows where the big stick gave 

 up the effort to resist the bending moment.... at the aft end of the 

 H-truss.



 The wing tip damage was confined to the outer most full rib, the 

 stabilizing tubes going from the end of the main spar and the wing tip 

 bow, the two most outbard false ribs, the wing tip bow and about two feet 

 of the leading edge tube. All of the full ribs have the aluminum angle 

 braces at the upper and lower camber going from the main spar to the 

 leading edge tube. The new full rib I bought from Travis did not come with 

 the angles but I'm adding them to the replaced full rib. I thought they 

 would have come with the rib but they did not.



 > --------
	


 	  Quote: 	
		   Thom in Buffalo


	




Thom:



Looks like you have it all figured out.



Let me be blunt, if I may.



Based on what little experience I have crashing Kolbs, your crash rates 

right up there with a hard, very serious crash.  You are lucky you walked 

away with only bruised shins.



Your idea of how the airplane is set up is somewhat askew from mine.  The 

tailboom butts up against the gear leg sockets into a steel ring that is 

welded to them.  The legs are inside these sockets.  They are at the forward 

end, not in the middle.  The center of the H brace is about (WAG) 1/4 to 1/3 

of the boom from the forward end.



The tailsection is not that heavy, acts to dampen some of the inertia during 

a crash as it moves through the air laterally.



 	  Quote: 	
		  From the looks of the right wing tip, that is what stopped the forward 

motion, in conjunction with the nose of the fuselage.  This is based on 
	


damage I see in your photos.  If the gear legs and/or their sockets did not 

fail rearward in the crash, it was because the airplane was on its nose and 

right wing tip.  The gear legs probably did not dig in.  When the legs made 

contact with the ground, the tail came up and the nose and right wing tip 

contacted and stuck in the ground.  I am familiar with the terrain at Bob's 

airstrip.  I think the soil and sod would be perfect to stop a good crash. 

  That wing tip is 12+ feet from the fuselage, a very long lever.  The 

photo indicates the nose and the wing tip stopped suddenly.  Even though you 

were only a couple feet in the air, as you say, I think you had already 

stalled the aircraft higher and did not realize it.  This is a very common 

experience for Kolb pilots, even though they may be very experienced 

aviators.  The other major component was your forward speed, coupled with 

your vertical speed, resulting in a very hard crash.



My thoughts and experience only, for what it is worth.



Personally, I would not fly this airplane until I had pulled the fabric and 

gone through both wings, not only to insure integrity of standard 

components, but to also beef up lateral bracing of the leading edge.  Those 

rib bays are very big.  At the center of the rib bay the leading edge is 

drilled top and bottom for a false rib that adds no significant strength to 

the wing.  If anything, it tends to set up this point for failure.  The 

drilled leading edge is also .028", which is weakened by the drilling.  The 

center of the rib bay between the 2d and 3d rib from the outboard end is the 

weakest point of the wing.  That is exactly where the failure of both my 

right and left wing was initiated.



I won't try to tell you what to do, but wanted to share my experience and 

thoughts with you.  I have personally experienced the demise of all three of 

my airplanes, more than once, while sitting in the pilot's seat.  Not 

bragging.  Trying to prevent someone else from duplicating my mistakes.



Take care,



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

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