Better Pilot: Tactile Inspection

stick & rudder better pilot. Tactile Inspection. Don't just look at it, feel it. CLARE PATTERSON, EAA 738844. Ilike to do what I call a tactile inspection on airplanes.
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stick & rudder

better pilot Tactile Inspection Don’t just look at it, feel it

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like to do what I call a tactile inspection on airplanes I have never flown before or those I’m doing a prebuy inspection on. It’s a good way to get to know the aircraft on a personal level, and it can be surprising what you might find. It is important to note, however, that you shouldn’t do this to a stranger’s airplane without permission, and you shouldn’t do it every day to your own airplane. What follows are a few key areas to check on select types of aircraft. An experienced airframe and powerplant mechanic with an inspection authorization should be able to counsel you on what to look for with your specific type of aircraft. If you’re dealing with homebuilt models it would be a good idea to seek out someone who has experience with your specific aircraft type. You can contact EAA Aviation Services at [email protected] or 8882361025 for help locating a technical counselor.

Vertical Fin The vertical fin on a typical aluminum aircraft is held to the fuselage by as few as four bolts. The bolts hold the fin to the fuselage by clamping pressure. If the fin moves far enough for the bolts to be loaded in shear, the aluminum will be damaged; the holes will elongate, perhaps to the point of requiring replacement of the parts. To check for a failure in the clamping pressure place your open hand at least halfway up the rear spar of the vertical fin. Press sideways while smoothly increasing pressure to 10 or 12 pounds, then briskly add another 10 pounds and release. Repeat from the opposite side of the 100

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fin. Don’t confuse normal “oil-canning” for motion at the attach point. I found a loose fin on my own Cessna 188 using this method. The symptom was a popping noise from the attach area. The fairings were removed, and confirmation of motion was by the finger-across-the-parts method (place a finger between the parts that might be moving and press the fin). In the case of my 188, the torque putty was still on the nuts, but the bolts were shouldered out. We removed the fin and found considerable fretting powder

If you’re dealing with homebuilt models it would be a good idea to seek out someone who has experience with your specific aircraft type. on each surface that should have been pinched securely. We cleaned, primed, and reassembled with shorter bolts. All was well for a decade or so, until the fin was found loose again. The same techniques were used to discover and fix this condition the second time. I eventually wore out five engines on that one airframe. Not bad.

Horizontal Stabilizer This next technique applies to the bolted rigid type of horizontal stabilizers only. Place your hands under the stabilizer, near one tip. Lift upward 5 to 10 pounds checking for motion as on the fin. One time, I found a horizontal stabilizer on a Cessna 150 that just flopped without even a pre-load. The seller’s agent had just flown it to me for a pre-buy inspection.

Yikes. I offered the pilot a car, but he flew it back to the seller. Double yikes! Most trim tabs do flutter. They flutter as far as allowed by the wear in the jackscrew, rod bearings, and the hinge, but less is better. I have seen damage to elevators and rudders that I blamed on loose elevator trim tabs. This damage was located where the reciprocating loads go “around the corner” beyond the end hinge. Some homebuilts (Coot for one) and a few factory-builts (Maule for example) have an arm sticking forward with the weight on the end to balance the tab and prevent flutter from ever beginning. This counterweighted tab can be driven by cables or even a single cable with a spring on the opposite side instead of

Photos by Kelly Nelson

Check the nose strut by placing your foot on top of the nose tire and rolling the top of the tire aft a few inches, listening and observing hydraulic fluid dampening.

on a rigid rod and jackscrew, so it is a design decision. But, if the tab you are inspecting is designed like most of them, there is no counterweight for the tab itself, and the total slop in the system is the amount it will flutter.

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better pilot Elevator If your elevators are the bolted together type, it is important to check one against the other to see if there is any motion in that system. There should be none. Grasp each elevator near the inboard trailing edge. Raise them off the down-stop. Pull one upward and press the other downward, perhaps 2 or 3 pounds. Slight bending of the skin is fine, but no motion is allowed at the rivets or bolts. These problems are rare, but I have found each of these conditions. Because there is some risk of damage, use only reasonable force. If the parts are confirmed to be tight, I don’t recheck them often. It is advisable to recheck after snow-loads, jet blast, storms, hangar rash, maintenance, or time. Beech Baron and Bonanza elevators often do move one-quarter inch or more at the trailing edges, one up and one down. This is okay as long as the motion is normal wear in the bearing and pushrods of the control system. There should be no motion where the skins meet the first casting.

rity at every preflight. Some models have a nylon support, which needs to be pressed firmly against the inside of the cone, without any fasteners. A light, open-hand tap sideways on the tip of the cone can be very revealing. Creaking or popping noises might be cracking in the back plate. A heavier clunk may indicate lack of shims under the support inside. I have personally watched two spinners depart while in flight. This is rather discomforting. One spinner appeared to grow for a few seconds, then it was gone. It never hit the airplane, and there was no report of damage on the ground, but the cylinder head temperature rose. If the support had been tight, this wouldn’t have happened.

Flaps With a tactile inspection I found a torn rear spar simply by applying moderate pressure on the extended left flap, pushing in the same direction as the wind would push. The rear spar was failed. The owner thought he should still rent it out, as long as nobody used the flaps! We fixed the problem with a kit from the manufacturer.

Rudder The rudder should be checked on everyone’s preflight regularly, paying special attention to hinges and stops. It is okay to try to move the rudder up and down, but don’t damage the fabric or metal by pinching. The hinges should keep the rudder from touching the vertical fin. Don’t fly an airplane if the rudder is dragging on the vertical fin. Confirm the rudder travel stops are secure and unjumpable. During preflight, try to move the rudder beyond the stops. I saw one case where the rudder could hit the elevator! Good grief. Another good thing to do is confirm the upper counterweight is securely attached to the main rudder area. It is reasonable to pinch the trailing edge gently and shake it rapidly 1 inch left and right to see and hear any flexing between the counterweight and the main surface. Look for smoking rivets or actual change of shape of the structure.

Stabilators A similar technique can be used for aircraft with stabilators. Gently grasp the stabilator tip and apply pressure up and down, then forward and aft. Do this to both tips. There should be no clunking at the main bearings. In one case, a creaking noise led me to find that although the bearing was fine, the attachment block was loose on the inside of the fuselage. The rivets were partially failed and allowed motion of the bearing block in relation to the fuselage side skin.

Spinners The spinner and back plate should be checked for secu102

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Oleo Struts If the aircraft is not equipped with a nose-wheel pant, there is an opportunity to functionally check the nose strut. Place your foot on top of nose tire, roll the top of the tire aft a few inches, and listen and observe hydraulic fluid damping. It is common to find struts with insufficient oil in them. The strut may be the correct length, but this only means the gas pressure is correct. The sound and action of the strut are good indicators of proper shock absorption. If you hear lots of bubbles squeezing through the orifice, or if the motion suddenly becomes easy nearing full extension of the strut, oil is needed soon.

Main Gear For the flat spring-type of main gear legs, without wheelpants, place the bottom of your foot on the top of the main tire. Rock the tire one-half inch forward and back. There should be no motion between the fuselage skin and the gear leg. If there is motion, investigate. It may be a broken u-bolt; I’ve seen this at least twice.

Be Thorough These are just a few of the areas you should thoroughly inspect for signs of impending failure. A short video demonstrating some of the techniques described here is available at www.EAA.org/SportAviation. It recommended that you seek the advice of someone who is familiar with your specific aircraft type to ensure that you know the appropriate techniques and limitations for your aircraft. Clare Patterson is a professional pilot and active flight instructor.