Leaf spring p/n

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8258
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Leaf spring p/n

Post by 8258 »

Hello folks,

feeling prudent, and planning a visit to Aircraft Spruce next week, I plan purchasing a new (spare) tailwheel leaf-spring.

I have the Lang tailwheel (very similar to Scott 2000 with hard tyre) and need the leaf spring that has the profile of the side view of my existing tailwheel.

I am in the USA at present, so unable to inspect my aircraft, but believe it is the same '2 bend' set as in the other illustration.

Can anyone confirm the spring type needed for my aircraft (as seen in the aircraft tail side view) and is it the same '2 bend' as the illustration of the leaf set shown and, if so, what is the correct p/n !

hope this all makes sense

thanks
Graham
Attachments
side view of set - is this same as I have on plane at present ?
side view of set - is this same as I have on plane at present ?
Capture tailwheel 2.JPG (35.89 KiB) Viewed 4831 times
side view of existing tailwheel - are there bends at position #1 and #2 ?
side view of existing tailwheel - are there bends at position #1 and #2 ?
Capture tailwheel 1.JPG (77.79 KiB) Viewed 4831 times
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6597
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Re: Leaf spring p/n

Post by 6597 »

Graham,

The 'single bend' and 'double bend' options are based on serial numbers. See attached. A little hard to tell which you have on your bird.

I had a 'double bend' spring set on my early serial# bird and the back end was way too high.

With that said, the Aircraft Spruce catalog is very vague on which springs they have as far as Cessna parts numbers are concerned.
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6597
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Re: Leaf spring p/n

Post by 6597 »

My 'double bend' spring set on my early serial# bird...
17.125TAILCONE.JPG
17.125TAILCONE.JPG (110.86 KiB) Viewed 4825 times
My correct 'single bend' spring set on my early serial# bird....
IMG_1477.JPG
IMG_1477.JPG (150.43 KiB) Viewed 4825 times
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Re: Leaf spring p/n

Post by 5115 »

I ordered 05-07055 for my 1946 sn:9168 and it is the good match for the Scott 3200. As per 6597 second picture we can see that Scott table is parallel to ground, which is the best setup.
Martin Tanguay
Intl Cessna 120-140 Association - Canadian rep
C140, C-FJAR, 1946, sn:9168, O-200, ragwings
8258
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Re: Leaf spring p/n

Post by 8258 »

thank you Martin,

your confirmation of p/n to # of bends is helpful, as the Spruce list is very vague.

appreciate the replies - apologies for the double posting of the question.

thanks
Graham
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Re: Leaf spring p/n

Post by 6643 »

Aircraft Spruce resells Univair springs. I believe the Univair part numbers mirror the Cessna numbers, with a "U" in front.
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Re: Leaf spring p/n

Post by atypicalguy »

This discussion is great, but I still do not understand whether the angle of the leaf spring mount in the fuselage is different between early and late serial numbers, leading to the different leaf spring shapes, or whether Cessna kept the mount/attachment point angle the same at the fuselage, and just changed the leaf spring shape to change the fuselage height and the tailwheel table angle for the later serial number planes.

I have a 1946 plane with early s/n. It had the flat spring removed and replaced with the double bend spring. The table is angled upward toward the front of the plane. When I asked the previous owner why this was done, he said the steering was improved with the new spring, because he did not have to use brakes to initiate turns after he switched to the new spring. He also liked that the new spring lifted the tail higher, providing better forward visibility over the cowl.

What I find with the current (new spring) setup is that once the wheel turns, it does not want to return to center, and in fact will not do so without the plane being in motion and using the brakes, or making a very large rudder movement to pull hard on the coil spring to get it back to midline. So if it gets off center, it wants to stay off center because the tail moves down as it travels off center, and therefore the weight of the plane is pushing it away from center. I would think the same would be true when landing after bringing the stick back - what you want is a wheel that stays mostly straight, instead of wanting to fall off to either side on the rollout.

So what is the reality here? Did the mount angle and therefore the table angle change on the later planes, thereby changing the steering geometry intentionally to a better table angle than the earlier planes, or was there a different mount angle in the later fuselage, requiring the bent leaf to keep the same table geometry as the earlier planes?

I just do not understand what drove the change in leaf shape.

Thanks.
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Re: Leaf spring p/n

Post by 6643 »

Seems nobody knows for sure. Installing the double bend spring increases the castor angle. Oddly, this should cause the wheel to tend to center and be hard to steer off center, not the other way around.
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Re: Leaf spring p/n

Post by atypicalguy »

Yes it may increase the castor, but that ignores the change in the plane of rotation of the tailwheel. When that plane is tilted relative to the ground plane, a vertical component is introduced to the rotation of the wheel. When the wheel has to lift the whole tail of the plane in order to center, that tends to require more force.

I am surprised people with each version have not compared notes. I imagine many people have flown both types of tailwheels also. Perhaps the differences are simply not large enough to matter practically.

Karl
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Re: Leaf spring p/n

Post by 6643 »

atypicalguy wrote: Fri Jul 02, 2021 7:02 pm Yes it may increase the castor, but that ignores the change in the plane of rotation of the tailwheel. When that plane is tilted relative to the ground plane, a vertical component is introduced to the rotation of the wheel. When the wheel has to lift the whole tail of the plane in order to center, that tends to require more force.
You are absolutely correct. I got it wrong. It's not castor, it's king pin angle, and increasing the kingpin angle does have exactly the effect you stated.
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