Can I use 9010 bungees in place of 9090

[PA1195]

Re: Can I use 9010 bungees in place of 9090

Good info...now there's a mystery to be solved.

Still -40F plus some extra below here so anything new about the Taylorcraft would be interesting. Maybe pics tomorrow of mine buried in 2' of snow and cold.

Gary

[PA1195]

Re: Can I use 9010 bungees in place of 9090

Bungee info from discussions here:

http://vb.taylorcraft.org/showthread.php?2401-Shock-Cords

http://vb.taylorcraft.org/showthread.php?1830-Pre-war-landing-gear

Sorta' answers some of the frame<>gear dimensional questions. On my '41 there's plenty of room for 9010HD-CW's, and only a hand made Volvo (or similar) car jack and part of a grooved pulley welded to a chain will lift them off the truss. Weld a pin to the bottom of the jack to fit the top holes in the truss. Weld a chain or attach a cable to the lifting arm close to where it attaches to the main jack. Weld about 1/4 of a curved grooved pulley to the other end of the chain and insert it under one bungee at the truss. Screw the jack arm up and lift the bungee off the truss arm.

Edit: The pulley mentioned is made of steel and only the curved and grooved rim portion is welded to the chain, not the pulley center. The ends of the grooved pulley are ground in a taper so as to slip between the bungee and truss mounting tab when the jack is cranked up away from the truss. Eh?

Gary

[Robert Lees]

Re: Can I use 9010 bungees in place of 9090

Slight thread drift here, for which I need you cold-weather operators and cleverer folks to edumicate me.

Does 4130N or 1025 get more brittle at -40F temperatures?


[I used to work in the warehouse industry, whereby the steel used in the construction of the fork-lift trucks for cold-stores at -40F had to be of a "special" variety (and I can't recall what) compared with warmer climes, which used regular "mild steel". Frozen thanksgiving turkeys in a Wisconsin warehouse was the project!]

Rob

[ifdale]

Re: Can I use 9010 bungees in place of 9090

Rob, was recently reading a thread re: cold wx ops and its impact on steel on the supercub forum...I'll look for it, Anyway one of the guys there might have been an engineer for caterpillar. He was referring to the equipment they run on Alaska's north slope. From what I recall he was asked if steel became more fragile at severe cold temps, his reply was something like, the cold weather really only has an impact on the running components, i.e. engine/pump systems, etc. As far as the frame and structural components, the effect as I recall was nil. Down to maybe -70f or so. Could be wrong....Isaac

[Guest]

Re: Can I use 9010 bungees in place of 9090

Slight thread drift here, for which I need you cold-weather operators and cleverer folks to edumicate me.

Does 4130N or 1025 get more brittle at -40F temperatures?


[I used to work in the warehouse industry, whereby the steel used in the construction of the fork-lift trucks for cold-stores at -40F had to be of a "special" variety (and I can't recall what) compared with warmer climes, which used regular "mild steel". Frozen thanksgiving turkeys in a Wisconsin warehouse was the project!]

Rob

I looked in MIL HDBK 5j and found general info but no metric that would differentiate 4130 and 1025. There are a bunch of alloys made specifically to deal with fracture toughness and none of them are 4130 or 1025.

I posted a few pages below and they refer to -100 as reference point.

[Dick Smith]

Re: Can I use 9010 bungees in place of 9090

On the offshore oil platforms, here in Cook Inlet, cranes are derated based on cold wx. Our temps are no where close to those they experience on the North Slope.

I plucked the following from an article regarding cold wx considerations:

ASME B30.20 Below the Hook Lifting Devices states that additional considerations need to be taken if the working temperature is outside the range of -4 degrees C to 66 degrees C. It suggests that engineers either de-rate the capacity or use steel that is better suited for low temperature service.

The Impact of Cold on Steel and other Construction Materials
These and other standards reinforce the point that “standard” lifting equipment may not be suitable for use in extreme cold. The temperature limitations set forth in these documents may vary slightly from one standard to another, but they all recognize that temperature can negatively affect the safe working capacity of lifting equipment.

Cold temperatures can adversely affect the tensile toughness of many commonly used materials. Tensile toughness is a measure of a material’s brittleness or ductility. Ductile materials can absorb a significant amount of impact energy before fracturing, resulting in deformations (bending) that can alert the operator to an overload situation before a failure occurs. Brittle materials, on the other hand, can shatter on impact. Many materials experience a shift from ductile to brittle if the temperature drops below a certain point. The temperature at which this shift occurs is commonly known as the “ductile-to-brittle-transition” temperature (DBTT). Any brittle failure will be catastrophic and the failure will not necessarily be predictable. It can occur from a random impact, dynamic loading or can propagate out of a stress riser such as a crack or nick.

[astjp2]

Re: Can I use 9010 bungees in place of 9090

My dissertation is on cold weather error management, so if someone wants some dry reading material about working in the cold, I can forward my literature review....hahaha

[swoeric]

Re: Can I use 9010 bungees in place of 9090

On my '41 there's no bottom wooden/faired/whatever you call it frame cover. The fabric covers the belly front to rear and the bungees and inner gear fittings extend below the belly a little. I bought and tried to fit the metal bumps but of course there's a gap. So we made a cold weather flexible fabric cover for wheels/skis to seal around the edge of the exposed bungee ends (to exclude exhaust), and another to completely cover the holes while on floats. Glued a rectangular piece of thin polycarbonate to the belly fabric and covered that with stits fabric. The flexible cold weather seal material then gets laminated between an aluminum external skeleton and the imbedded polycarbonate by PK screws.

The 9010HD-CW's are commonly used by many up here and work as expected with no adverse consequences that I'm aware of.

Gary

could i get a pic of this cover

[PA1195]

Re: Can I use 9010 bungees in place of 9090

could i get a pic of this cover

I will take one and post. Raining today but will see what I can provide.

It's as described. I suspect sometime in the last 76 years since new the underbelly's wood frame dissolved and the rebuilders decided to just cover the metal tubing and leave the gear exposed. It's a common mod here and mine isn't the only example. Might cost some speed but have no way of knowing. Now sealed I get no indication on my CO detector of that gas in the cockpit.

Gary

[PA1195]

Re: Can I use 9010 bungees in place of 9090

Ta Da!

The hole in front of the gear in pic #3 is for my water rudder retract fixture that's removed when not on floats. It's sealed from above.

The black material that's the seal is split on each side to fit over the bungees. It's cold weather flexible fabric used for on-ground fuel tank leak sump liners. The mechanic glued a polycarbonate support ring to the belly fabric with Stewart's, taped over it, and covered with Stewart's silver. The metal overlay is screwed to the poly plastic with PK screws. A full fabric cover replaces the one with holes when on floats.

Edit: We also considered adding partial covers over the exposed bungees. Something like a U-shaped piece of that tough vinyl material over each cluster and then extended up into the fuselage and fastened to the bungees. But tech met time and this is as far as we got.

Gary

[Robert Lees]

Re: Can I use 9010 bungees in place of 9090

Why not use proper bungee covers? That's what those three little screw attachment tabs are for.

[PA1195]

Re: Can I use 9010 bungees in place of 9090

Why not use proper bungee covers? That's what those three little screw attachment tabs are for.

Because my aircraft belly is different than standard. If the rotten wooden underlayment is removed and the fabric attached to the tubing (see Pic #3) those covers (I bought a set from David Wenglarz) don't close up against the offset created by that wood framing. There's a gap the thickness of the woodys between the metal covers and the belly fabric that would allow in exhaust gas and whatever.

This configuration is not uncommon in Alaska. The addition of seals is something not every owner has done. Some just let it all hang out.

Edit: That part of the airframe restoration was done by a former FAA PMI. If it was good enough for him it's good enough for us.

Gary

[swoeric]

Re: Can I use 9010 bungees in place of 9090

I like those seals they look good. i was getting some co in the cabin as my wife would get a headache but i never felt a thing.. I like how clean that is. My lower legs are left bare and with boshwheels never noticed if the legs made a difference or not

[Mark Bowden]

Re: Can I use 9010 bungees in place of 9090

Hi Gary,

I would urge you to please get some external covers on right away to save you some money and headaches.

Exposure to elements is not a good thing for the shock cord rubber or the cotton braid and its glazing.

The braided cotton cover, is to help keep abrasives out of the rubber strands and provide some UV protection and a small bit of chemical protection. It however, also determines and sets overall performance of the finished cord, the rubber strands and braid work together.

Without covers you don’t just have abrasive dirt/sand/runway exposure, there is also water from the runway with its associated chemical contaminants from other aircraft. Obviously you have breather oil blow by but it also has combustion by products; in addition the engine exhaust is full of acid gases along with lots of water, soot and carbon.

Oil, and water makes abrasive dirt stick to the cord add ozone attack and not a good recipe for service life.

AC 43.13 doesn’t specify a time in service. It does require shock cords be clean and free of petroleum products and show no damage. AC’s aren’t regs but the FAA expects them to be followed, I wouldn’t want you to have a potential ramp, next annual inspection or early failure issue.

Maybe just use the old covers with a bit of foam to make up the gap from the earlier recover, but don’t ever fasten anything to the bungee itself.

Hope it helps.

[PA1195]

Re: Can I use 9010 bungees in place of 9090

Thanks Mark for noting the concerns and helpful advice. They've been like that since about 2010 and I only replaced the original cords because I wanted to test cold weather spec bungees. The original non-CW cords look new and weren't frayed or visibly deteriorated. But yes a better external covering would be good. I may wrap the exposed cords with similar black vinyl seal material. The cords are removed and reinstalled annually due to change to floats and back. Gives us a chance to inspect.

We considered sealing the original covers with foam weatherstrip spacing to cover the gap. That would reduce the UV and some contaminants but in reality the metal factory covers are somewhat open around the adjacent gear tubing and can allow ingress of dirt, oil , and water. Without a low point drain hole there's no way for that to escape. Plus any exhaust fumes is free to reach the cords and rise into the cockpit. It's more limited when the gear retracts into the original wood framing of course.

Now one thing that does happen to both factory and uncovered bungees here is cold weather. In the deep cold (down to -50F locally) shock cords relax and stretch especially when on skis. The skis are flat and unlike tires create their own fixed landing gear angle when on the ground. Tires will allow some camber and let the bungees initially retract. But as soon as the plane is moved in the cold or the soft Airstreak tire sidewalls flex the gear spreads and the cords are exposed by the standing weight of the aircraft. When it warms back up the rubber will try to pull the gear in but that can only happen if the tires are moved, never on skis.

One last obs. Cold weather shock cord isn't worth the additional expense over normal. These planes are so light that the 9010's rarely flex under normal loads even in summer. I can lift the opposite tire off the ground by pulling down on the other wing. The bungees never give and the tires do 90% of the shock absorption. Makes for a rough ride on skis especially on new unworked cord material.

We'll keep an eye on them at each annual.

Gary