Spring loaded locking pin

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Will Aldridge

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I'm starting this new thread because I feel we've hijacked this thread enough.

I have modified Danas tailwheel design shown in the above linked thread to accommodate a larger tailwheel and a locking mechanism that will release the tailwheel to swivel freely when the stick is full aft. I'm looking for a 1/4" spring loaded locking pin. Searches through ACS, Home depot, Amazon, and a Google search didn't yield any results that I find promising. Anybody have any suggestions?
 

BJC

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..... a locking mechanism that will release the tailwheel to swivel freely when the stick is full aft. .... Anybody have any suggestions?
Suggestion: Change the action to release the lock on forward stick rather than aft stick.


BJC
 

bmcj

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Suggestion: Change the action to release the lock on forward stick rather than aft stick.


BJC
YES! Depending on how well or poorly behaved the plane is on the ground, you might not want to have the tail wheel unlock on you just as you touch down with full aft stick.
 

Dana

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I have modified Danas tailwheel design shown in the above linked thread to accommodate a larger tailwheel and a locking mechanism that will release the tailwheel to swivel freely when the stick is full aft. I'm looking for a 1/4" spring loaded locking pin. Searches through ACS, Home depot, Amazon, and a Google search didn't yield any results that I find promising. Anybody have any suggestions?
A "spring plunger" is what you're looking for. For example, see here. As others have said, releasing on forward stock, not back, is what you want. I didn't find it necessary, the springs I used were light enough that the wheel would swivel 90° with a touch of brake, and to move the plane backwards, the tail was so light that it wasn't an issue.

Dana
 

Toobuilder

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Concerning the fore or aft stick unlock, I agree that aft to unlock is a bad idea. I'd also suggest that fwd stick to unlock is also a bad idea. Though its typical practice, the airplanes that it is employed upon are big, heavy things that are not going to go on their nose with a gust of wind. Ive been through this thought process when I did the locking unit on my Rocket, and the thought of landing in high winds and trying to do a 180 with a lot of power AND needing down elevator is a sure fire recipe for a prop strike/nose over.

I'd suggest a discrete locking lever.
 

Will Aldridge

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Glad to be getting this info before I go any further. If memory serves the P-51 had a locking tailwheel released by full back stick. In addition to that I had heard that the WAR Corsair should only ever be landed on the mains and i was going to make that my practice with this aircraft.
 

Toobuilder

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You might want to take a "wait and see" approach to things like landing technique. Your airplane might just as easily be a benign pussycat as a tiger by the tail. Fly it and see what it likes. Truth be told, the Rocket and its RV cousins are pretty indifferent to landing style. Due to a less than positive locking pin spring, most of my landings have been with essentially a free castoring tailwheel. Its only a problem when taxing with a crosswind. Your little bird might have the same behavior.
 

Will Aldridge

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This is all highlighting my lack of experience in taildraggers. I have all of 13 hrs which culminated with me dumping a legend cub on its nose on my first solo no less. That was 3 or 4 years ago. Really need to get back in the saddle.

If I do go with a discreet locking handle for the tailwheel I'm thinking a cam locking spring plunger with a Bowden cable to actuate it would work pretty good, if I can find a small enough one. So far the smallest pin size I've found is 5/8".
 

Dana

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The McMaster-Carr ones I linked to go down to 5/32" diameter with a 1/4-20 threaded body, which is probably too small. McMaster's are probably made by Vlier or Reid Tool.

-Dana
 

Will Aldridge

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The McMaster-Carr ones I linked to go down to 5/32" diameter with a 1/4-20 threaded body, which is probably too small. McMaster's are probably made by Vlier or Reid Tool.

-Dana
https://www.google.com/search?q=cam+locking+spring+plunger&client=ms-android-verizon&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjt75GKgPvTAhWGjlQKHaJLCogQ_AUICigC&biw=360&bih=560#imgrc=49YDQ0TvzidrXM: is what I'm thinking of. I didn't see anything like that on the McMaster carr page. If I missed it please point it out.

The handle on it looks like it could be modified to accept the end of a Bowden cable if i were to make a lever in the cockpit to lock the tailwheel as opposed to stick position.
 

Dana

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Did you want a locking one? I wouldn't think so; I think you'd want the cable to pull it, that's exactly what, say, McMaster's "pull ring" style does.

Dana
 

Will Aldridge

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Concerning the fore or aft stick unlock, I agree that aft to unlock is a bad idea. I'd also suggest that fwd stick to unlock is also a bad idea. Though its typical practice, the airplanes that it is employed upon are big, heavy things that are not going to go on their nose with a gust of wind. Ive been through this thought process when I did the locking unit on my Rocket, and the thought of landing in high winds and trying to do a 180 with a lot of power AND needing down elevator is a sure fire recipe for a prop strike/nose over.

I'd suggest a discrete locking lever.
Did you want a locking one? I wouldn't think so; I think you'd want the cable to pull it, that's exactly what, say, McMaster's "pull ring" style does.

Dana
Based on TB's post i am considering having a lever in the cockpit to lock/ unlock the tailwheel and i am trying to get the mechanism to be as low profile as possible partly for aesthetics and partly because if I come down hard on the tailwheel it will hit the underside of the fuselage which will of course be reinforced to handle such impacts but the pivoting arm I all visualizing to actuate that pull ring you are suggesting would be a little taller. This is somewhat difficult to explain because I only have internet on my phone and I can't post screen shots of my design but I modified your tailwheel design buy putting a three inch diameter disc on the top of it and drilling a hole in the outer edge of it for the locking pin which will be as far aft on the assembly as possible.
 

Toobuilder

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My tailwheel has a spring loaded pin on the front of the unit which slides aft into a hole drilled in the pivot pin to lock. A cable runs forward from this pin to a bulkhead near my left knee. The forward end of this cable is secured to the bulkhead, so that pulling the cable up or sideways from anywhere along its length will unlock the pin. Some guys will simply hook this cable on a suitable bolt head or other hook so that it remains "unlocked" for taxi/ground handling, but I wanted a more failsafe method. Instead of grabbing the cable by hand, I have a lever on my throttle quadrant which pulls the cable up via a tension spring. The lever comes up/aft and stops just over center to unlock the tailwheel. The part that I like is that with the lever "up", it blocks the throttle lever. If I forget to lock it before takeoff, the advancing throttle knocks it back into the locked position.
 

Will Aldridge

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The design I have isn't ideally suited to a horizontally mounted locking pin as you suggest but I have a way to make it work. I think I'm going to copy your throttle quadrant setup as well.
 

Toobuilder

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No I wouldnt copy the pin through the axle either... It sucks. My point was to illustrate that a small tug on the cable is all thats required to unlock. And in that case, my lever on the quadrant works great. Copy away!

Youve seen the pictures on the other threads... Or should I post it here too?
 

Will Aldridge

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20170519_210525.jpg

Here is a literal screen shot of my design (Dana's modified tailwheel). The bracket on top of the tailspring would have been the mount for the arm that the cable connected to that actuated the pin and you can see the hole in the disc that the locking pin would go into. That disc is half an inch thick, I ought to be able to mount the pin on the underside of the spring horizontally and drill a hole in the edge of the disc.

For those interested, modifications to Dana's design include using a 120mm scooter wheel (instead of the 100mm wheel) which is wider and requires the delrin block to be 1.25 inch thick, otherwise dimensions on the block are the same. The arms also had to be lengthened and the style changed to suit my aesthetic tastes and lastly the 1/4" thick 3" diameter disc added on top. Since the aluminum angle used to make the arms is also 1/4" thick I'm just going to fill the spaces around the edges of the arms underneath the disc so there is a continuous 1/2" wide surface for the horizontally mounted pin to ride on.

BTW Dana my plane will be landing at probably 60-70 kts, do you think the scooter wheel can handle that kind of speed? According to sale pages I've read I need the higher durometer rubber for higher speed applications (88 is the highest I've seen).
 
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