Oz build SS7

[DesertFox4]

Nice photos Ross.
I've also found that unorganized aviation can be fun.

[rosslr]

Maybe a question for the factory but I am sure the collective experience here has come across this before.

In regard to the 4 bolts attaching the main gear to the fuselage:

1. Why does the manual say them to install them 'nut up' when convention suggests nut down?

2. I can not fund any torque value for these nuts in the manual - I imagine this would be fairly critical given the landing forces being spread at attachment points on fuselage. Perhaps this is just an omission in the manual or am I missing something?


cheers

[Dave S]

Ross,

Assuming you are talking about the Grove gear.

Regarding the "nuts up" vs "nuts down"....consider that the installation might not be quite "conventional"

Let's say you have nuts down and one or more of the nuts fall off.......what's going to happen to the gear?

Let's say you have nuts up and one or more of the nuts fall off.......what's going to happen to the gear?

I am sure there is a reason for this configuration but I could only guess at what it is.....possibly the cotter pins are less suceptible to damage or corrosion on the top?....don't know.....Does it have to do with the smooth shank of the bolt as opposed to the threaded part where it might be better to have the smooth shank on the end where the movement occurs with the rockers???? don't know. Nuts up might keep those of us who's last name ends in "....son" from scratching our knuckles up with the cotter key ends too often.

In the end, the conventional wisdom regarding nuts down to prevent the bolt from falling out should be just a theoretical but remote issue if proper torque and cotterpin installation is assured anyway (and a person keeps up on their inspections). Seems we have been flying a lot of kitfoxes with the nuts up and I don't recall anyone's gear falling off due to losing their nuts - again, which could happen anyway if the nut was on the bottom - provide all 4 fell off at the same time...rather unlikely in either case..

As far as the torque values....check the "Builder Tips" at the front of the manual page 9....sort of hidden; but, this gives min & max torque values for AN3 - AN9 steel tension bolts.

Take care...it's been fun following your progress on the list....kind brings some of us back to when we were building

Keep up the great work!

Sincerely,

Dave S
Kitfox 7 Trigear
912ULS Warp

[jiott]

FWIW, an interesting fact about bolt torque is that the clamp load (applied by torquing the nut) must ALWAYS exceed the max applied load. By doing this the bolt never sees any load cycles to cause fatigue failure. The reason for this is that the applied loads will pull on the bolt, transferring most but not all of the clamp load to applied load. The bolt itself always sees a steady load equivalent to the original clamp load with no stress cycles. This is why proper torquing is important. Over torque will fail the bolt quickly, and under torque will subject the bolt to eventual fatigue failure (of course depending upon the actual applied loads). Proper torque also slightly stretches the bolt, giving it a spring effect which also helps this process.

[rosslr]

Thanks Dave for articulating what I was ruminating on. Either way it will be an easy inspection item. And Jim, I follow your technical explanation - not being from a technical or engineering background, I appreciate it - and it gives clarity to why we need to follow the prescribed torque. So, if I look at the min and max torque values in that table Dave, it seems that it would still be critical to have a calculated (prescribed torque value) for the specific purpose within that range if we are to achieve what Jim describes. I will investigate further - even though there doesn't appear to be problems, I am just curious now why they don't prescribe a value for these when they do for most other parts in the build. I will post my findings.

cheers guys

[Dave S]

Ross,

The Kitfox builder's manual is pretty darn complete in most respects. It is rampant speculation on my part; however, my guess is that the reason the torque value is not given on the particular page the assembly is shown on may have to do with a simple unintended oversight......there is a lot of detail in the entire manual and if there wasn't an occasional miss along the way...it would be...well, you know, we are all human...even tech writers

Dave S

[rv9ralph]

This is an interesting discussion on the gear, bolt orientation and torque. I am considering converting the gear on my KFIII, so I was looking at the Grove website. They have installation instructions there with torque values. The link is: http://www.groveaircraft.com/kitfoxinstallation.html.
I'm not sure if this applies to your installation but it may help.
Ralph

[Dave S]

Ralph,

Interesting....the link to Grove is for the III & IV and shows the nuts on the bottom. I didn't see instructions for the later models on Grove's Site. Looks like the assembly is constructed differently for the rockers on the III & IV than for the 5, 6, 7 series. For some reason - there was a change...guess it depends which model a person has.

Dave S

[PapuaPilot]

I was surprised that there wasn't a torque given in the manual too. I just installed my gear leg last month. You need to find the standard torque for the bolt/nut combination; AC43.13 would be the best source.

When you torque a castle nut the goal is to get the hole to line up somewhere between the minimum and maximum torque for the hardware. After you found the correct min/max torques set the tq. wrench to the minimum value and tighten the nut to that. If it didn't line up then set the tq. wrench to the max value. Tighten the nut as much as needed to line it up to the hole, but stop if you get to the max value and it still hasn't lined up. In that case it is usually best to try another nut and repeat the same procedure.

I noticed the torque value on the Grove site for the axle nut is 60 in-lb. The problem is that the axle nut is an castle nut. You really need a min/max for that. there is only about a 5-10% chance of it lining up at 60 in-lb.

FYI when you torque an axle nut you typically do it in two steps. First you go a higher value, loosen and then the final torque. Example: the Cessna Caravan manual says to torque to 60 in-lb while turning the wheel, loosen to zero and retorque to 30-60 in-lb (while turning the wheel). Even then you won't always get the hole to line up. The reason for the higher initial torque and spinning the wheel is to seat everything and push out any extra grease.

[jiott]

Just email the McBeans; I'm sure John or Debra can get you the torque value they use at the factory.