The International Cessna 170 Association

Recently when the fuselage is pushed or rocked sided ways from just forward of horizontal stab., with the tail wheel
centered, the stresses cause a snapping sound from inside the tail cone assembly. My IA and I have checked everything
we can see, including crawling inside to rear bulkhead station 205.812 and can see nothing move when the noise occurs.
Also looked with a probe in every opening available. If we can not determine what the cause is our next step will have
to be removal of the vert fin, rudder, and horizontal stab. , which are firmly attached. Anyone have any ideas?

My first thought would be to put your hand on the interface of the tailwheel spring assembly to the tailwheel bracket while you have someone move the aircraft in the manner you describe. There is probably some movement there that is making the noise. Hope that helps.

Theres an old automotive trick that might work in at least narrowing down the location----using a short piece of garden hose (Water removed) , put one end up to your "Good" ear if you have one and with the other end search for the noise. You should be able to narrow the area down.

I concur with N3092A. The noise is probably being generated by the tail spring and or tail wheel. I would lift the tail cone up and place a support under the tail wheel bracket just forward of the rudder. I would then go to the elevator tips and gently rock then to produce the fuselage twisting or flexing than might be going on when you rock the side of the fuselage. But this time the spring and wheel with not have any pressure on it. This will either eliminate the tail spring bracket, spring and wheel from consideration it the noise persists or pin point it to just those parts.

I also concur with Minton, a garden hose or any other convenient tube can make an excellent stethoscope and narrow down the point of a noise.

BTW have you simply checked the tightness of the Scott 3200 to the tail spring?

Dave, maybe one of these would help. I would loan you mine but you are all of Texas and several tiny states away.

http://www.harborfreight.com/automotive ... 66550.html

Dave, Harbor Freight also has an inexpensive stethoscope if you don't happen to have one. I have one & if you don't get your culprit located in the next day or two let me know and I'll fly up there and bring mine.

John, that video inspection camera is something I missed at HF. Is the probe small enough to fit through our spark plug holes so we could use it as a poor man's borescope? How good is the picture resolution? I might have to acquire one of these if it fits.

170C wrote:Dave, Harbor Freight also has an inexpensive stethoscope if you don't happen to have one. I have one & if you don't get your culprit located in the next day or two let me know and I'll fly up there and bring mine.

John, that video inspection camera is something I missed at HF. Is the probe small enough to fit through our spark plug holes so we could use it as a poor man's borescope? How good is the picture resolution? I might have to acquire one of these if it fits.

Frank,
The probe does fit through a spark plug hole and the resolution is good. When you go to Harbor Freight you have to ask as they keep these guys under lock and key.

Thanks for the imput. Regretably I don't have an oppurtunity to quickly check further. We are leaving for a week in Ohio
tomorrow. Had looked forward to flying the plane. Changed oil, filter, and decided to have my IA take a look. Oh well!!
Bruce, everything you can lay your hands on or see is tight. My IA did use some type of video probe, pencil size end and
flex shaft with an approx 21/2 inch screen. Nothing. I will say it takes a strong push to cause the snap. More than I can
imagine occurring in flight or any of my landings. Ha Ha! When I return will follow up on these suggestions. Sure hate
to think of taking it all apart.

The pawl-spring and pawl in the tailwheel assy may break/fracture and will cause such a shap when the tailwheel assy reaches the internal locking position.

Another common noise-source is rudder cable slap when the rudder moves in response to the tailwheel movement.

Dave, does the movement-required to produce the "snap" cause the unlocking of the tailwheel? (This would strongly point to the tailwheel assy itself.)

When you raise the tailcone and rest it on a pillow-on-a-box ( a-la Bruce's suggestion) ... try moving sideways the tailwheel it'self into a deflected postion to see if the snap is reproduced.

I agree with all above, but can add another idea. A skin "canning" can make a popping or snapping noise, so look at the skins on the upper and lower sides of the stabs, and at the tail cone skins in the areas where the tail spring support stringers extend forward into the tail section, about where tail pull handles would be installed. Do you have tail pull handles? If so, and they were installed to "tight" (to far aft, to low, or clocked wrong), they could pre-load the skin

Mine does this as well. I have the old style smaller bent tailwheel mount (I need to upgrade). I always assumed it was either a crack under the tailwheel mount at a rivet hole or a loose rivet and the skin is sliding on the rivet. Both situations are not so good. I always do a through preflight of the area, and will evetuall replace the tailwheel bracket. I am sure I will find the culprit once I drill off the bracket.