Using a hangar winch with a DA40

Any DA40 related topics

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Lance Murray
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Re: Using a hangar winch with a DA40

Post by Lance Murray »

Forgive me for being blunt but winching the airplane in by pulling on the tail is a really bad idea. You have no idea of what stresses you are putting on the airframe. Operate the aircraft in the manor it is designed. You are taking chances with the lives of everyone that sits in the airplane from now and into the future. Not only are you risking yourself, friends and family you are risking the lives of future owners and occupants that will have no idea of what stresses you may have put on the airframe.
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Steve
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Re: Using a hangar winch with a DA40

Post by Steve »

Lance, don't you think that's a bit histrionic? Winching the airplane slowly on the ground is not going to subject the airframe to anywhere near flight loads. None of the future owners or occupants of your airplane will have any idea of what you subjected the airframe to in the air either. Ever exceed Vno and get some unanticipated turbulence? I sure have.

I'm not advocating doing crazy, stupid stuff with the airplane, just using common sense. If you are concerned about loads on the tail fin when winching by it, calculating them is doable (even for folks like me who are 4+ decades distant from my E Mech and physics courses). Having said that, I use a PowerTow on my airplane, because I have a 44 foot wide hangar opening. If it were tighter, I would likely have constructed some kind of winch along the lines of others on this thread. Their likelihood of damaging the airplane is probably much higher from a wingtip strike trying to back it in using a towbar arrangement than pulling on the tail...

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cptndavid
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Re: Using a hangar winch with a DA40

Post by cptndavid »

If one were to use a tie down for your airplane (as I do) I am reasonably sure your airplane is subjected to greater wind forces than pulling the tail or the mains with a small winch.
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Re: Using a hangar winch with a DA40

Post by Rich »

Consider also the stress you occasionally put on the tail tie down when the plane is put on jacks, necessitating installation of a tail-stand. A different kind of streets, of course, but considerable.
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Steve
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Re: Using a hangar winch with a DA40

Post by Steve »

Rich wrote: Tue Dec 03, 2019 4:28 pm Consider also the stress you occasionally put on the tail tie down when the plane is put on jacks, necessitating installation of a tail-stand. A different kind of stress, of course, but considerable.
Considering the lever arms involved, you would have at least 300 pounds of vertical force on the tail skid when you pull the engine (below):
IMG_3040.jpg
Different vector than the tow cable situation, but as Rich states, considerable...
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Re: Using a hangar winch with a DA40

Post by Sandy »

Has anyone considered connecting a winch to either the wing tie downs (similar to the OP connecting it to the gear legs) or to the nose gear (which is intended to be an attachment point for pushing/pulling the plane using the tow bar) or to some combination of wing tie downs, nose gear, main gear legs, and/or tail tie down? If the nose gear tow bar fittings are used, you would still be able to lean on the fuselage to lift the nose gear off the ground to steer it into the hangar.

While I understand that the tail skid is attached to the fuselage using six bolts, those bolts are only subjected to a direct downward shear force if the tail tie down is directly below the skid. If a tail tie down is behind the plane, as they virtually always are, the bolts are subjected to some degree of shear force. Does anyone know what the maximum "safe" shear force is, as I really don't think it could be any greater than the force exerted by the winch rolling the plane along a flat hangar surface, particularly when the plane, when tied down outside, is also subjected to additional wind forces.

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Steve
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Re: Using a hangar winch with a DA40

Post by Steve »

For the M6 SS bolts used to secure the lower fin, the tensile strength is 8040 Newtons (1800 pounds). It is likely that the composite of the lower fin would fail well below that value.

For shear, an M6 bolt will have a shear strength of approximately 600 MPa, with a yield at approximately 75% of that value. Shear would be approximately 12000 Newtons, or 2700 pounds. Again, the composite would fail below this value.

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Re: Using a hangar winch with a DA40

Post by MarkA »

For some additional context... the carabiner we use to connect the winch cable to the landing gear harness is rated at 110 pounds. I didn't measure it but my guess is it takes less than 1/2 of that to pull the plane into the hanger.
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Re: Using a hangar winch with a DA40

Post by Rick »

Before I bought my winch many years ago, I was also worried about forces on the tail skid, so I ran a test. There is an old thread on this very topic, see this post from back in 2016.
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Re: Using a hangar winch with a DA40

Post by Colin »

I miss Greg Wroclawski, but it's nice to have some engineers here still.
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