External loads

Discussion on keeping your aircraft airworthy and legal and/or any technical topics.


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Dkuber
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External loads

Post by Dkuber »

I am curious what the wing struts are capable of holding (items strapped to them). Mine do not have the “no step” label like the Cubs do. Is there a weight limit on the wing struts? Is placing your foot while fueling considered ok or just bad form? Paint is not shiny or a concern for me, this is a “pickup truck” not a “show car”.
I have seen many a moose rack on planes, I know a buddies cub has an extra set of support brackets for his camera. His struts are much less robust appearing though. Thoughts & comments would be appreciated.

M4-220c
Girdwood, AK

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Mog
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Re: External loads

Post by Mog »

I have no real meaningful input except I am confident my struts would not appreciate me standing on them to fuel. They just aren’t that thick of steel and will bend if loaded wrong. I suspect 20-30lb loads would be fine if strapped properly. But I have zero experience doing that and do not know the rules as they apply to certified aircraft. I know Alaskans get away with a lot more than we do down here.

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Andy Young
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Re: External loads

Post by Andy Young »

I’ve been tempted to carry skis on my lift struts, but have not done so. My hesitation is mainly due to the fact that the Maule strut, while more robust than the Supercub strut, does not have jury struts to reinforce and stiffen it at mid span, as the Supercub does. I am concerned that this long, unsupported span would be vulnerable to developing a vibration or wave, as the skis catch the wind.

Also, just FYI, in case you’re not aware: while external loads are allowed in Alaska (unlike the lower 48, where they definitely are not) they do require a permit from the FSDO. Lots of people (maybe most) do it without bothering to get the permit, but that does expose one to a violation if an FAA inspector wants to get picky. They’re generally not hard to get.

As far as placing a foot on the strut while fueling, I do it regularly, though just for balance, and I am careful to put very, very little weight on it while doing this.

Dkuber
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Re: External loads

Post by Dkuber »

I am aware of the required external load permit. Thanks for the heads up.

After the extended gear I have found it much easier as you said to stabilize off the strut while fueling. I haven’t been putting much weight on it, just balancing. Good to know I am not the only one. I didn’t even think about it until my cub buddy asked.

Mounting back country skis are what got me first thinking about external loads. Then when I moved my kids first moose rack (a few years old and dried but still heavy) I thought about antlers on struts. All the pics I find are Cubs. Even with the doors seems like fitting moose antlers inside might not happen.
I did reach out to Airframes Alaska and inquire about their sealed struts and any “external load capability” they said they are not tested for nor do they have any sort of external weight loading info.

I also asked a mechanic buddy that has had a Maule. He responded with “People have attached items to struts. I avoid that because it can create a lot of drag on the plane but mostly due to that drag it induces a lot of sheer force on the attachment forks. The strut forks are not designed for much sheer load. That load increases rapidly as speed increases. “

Seems like it might just be smarter to avoid such adventures. Kinda like the struts where they are at.
Thanks for the replies.

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Andy Young
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Re: External loads

Post by Andy Young »

I hadn’t even thought about the shear load. Now that you’ve brought it up, that does seem concerning. Seems like it would impart a bending moment to the threaded portion of the fork. More of an issue on a Maule vs. a Cub, due to the significant speed delta.

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