|Articles We Have Published In The Comanche Flyer|
|In April of 1990 I published an article in the Comanche Flyer about cowl flap control cables, a topic that is largely ignored in the Piper Service Manual and before that date had not been mentioned in the ICS Tips manual. Since the time of the article I have come to learn that it is much cheaper and fairly easy to simply "sweat" the old cable out of the handle and replace it as I mentioned in the closing paragraph.|
|article continued below|
|I wrote a second article published in October, 1995 on the emergency landing gear release mechanism.|
Emergency Gear Release Arm Problems
by David R. Clark ICS #8592
Most of us have enough sense to know if our gear motor and transmission are not working smoothly or sounding right. If they aren't, we repair them immediately because we don't want to be at the mercy of the emergency gear extension mechanism even though theoretically it is designed to get the gear down, no matter what. A problem arises when our backup system doesn't work, i.e., the release arm doesn't uncouple the landing gear from the motor drive shaft.
Many of us may be vaguely aware of how this system works and a few may have even pulled the handle when the plane was up on jacks at annual inspection. Maurice Taylor encourages us to familiarize ourselves with this system while on the ground and to learn how to re-attach the extension mechanism to the gear motor so that we might eventually be able to practise lowering the gear by the emergency system while in flight (and then be able to re-attach the gear to the motor again prior to landing). Note: Piper advises us that if we utilize the emergency gear extension system while in the air the proper technique is to land the airplane and put it up on jacks and re-attach the gear motor torque tube to the landing gear drive shaft. You can judge for yourself what you are comfortable with, but not being knowledgeable about this system may unnecessarily distract you at a time when other things demand your full attention. Don't try activating the emergency system in the air for practise unless you are really adept at doing this task on the ground with the plane on jacks.
Although I realize that other things can go wrong with this mechanism, I have encountered two particular problems in my twin Comanche emergency gear release that I think ICS members should be aware of. I have found both bent links and a missing cotter key/clevis pin on the emergency release arm.
1. The next time you get in your Comanche, pull up the emergency gear extension door in the floor and look at two things: the links attached to the red emergency gear release arm and the clevis pins which hold the release arm assembly on the drive shaft.
2. Inspect the release arm assembly carefully. This assemby rides on a bushing that encircles the tubular drive shaft and is held on by means of two small clevis pins. There should be a small flat washer and a cotter key on both of the pins. If either cotter key is missing, carefully replace the washer and insert a new cotter key without pushing on the clevis. (If you push it into the tube it will cause you great inconvenience.) If the gear is operated with the cotter key missing, the clevis pin can fall into the tube and jam the landing gear in any position.
3. Next, inspect the two links attached to the red arm to see if they are parallel and straight when viewed from above. If they are bowed outward, you will need to straighten them with a large pair of pliers. The consequence of them being bowed out is that the sleeve (or release tube) cannot slide forward completely to uncouple the torque tube from the gear drive shaft. This will effectively prevent you from manually lowering the landing gear during a real emergency ( I finally got your attention).
4. But the real acid test is to put the plane on jacks (like at the next annual) and test the emergency gear release arm to see what happens. If it is difficult to disengage the torque tube and even more difficult to hook it back up, then likely a problem with bent links has occurred. It should be fairly easy to do the "acid test" and if the gear extension system is not working smoothly, now is a better time to fix it than when in the clouds.
A. The links:
The most common problem by far is the links attached to the red arm being bent. Not only can they be bowed outward but can be bent fore and aft so that the approximate 110 degree angle the arms make could be compressed to 100 degrees. If after straightening out any bowing sideways you are still are not getting a good opening below ( the sleeve is not sliding forward enough to allow access to the groove or slot in the shaft), you may need to bend or change the afore-mentioned angle to improve this access and thereby allow the drive shaft to engage and disengage easily with the mating pin on the torque tube.
B. The clevis pins:
A much more rare situation occurs if you find one of the clevis pins has lost its cotter key and the clevis has fallen back into the tube. If you have worked the gear motor, by now you have ground up the clevis in the worm drive. Don't despair. This can be fixed.
1. First of all you must remove the gear transmission and gear motor.
2. Remove the cotter key on the opposite side of the assembly and push that clevis pin back inside the tube. You can now remove the red arm/release tube assembly and the bushing it attaches to. You can see two holes approx 3/16 inch diam on the sides of the tubular drive shaft. These serve as a recess for the clevis heads to rest in, so that they don't interfere with the transmission screw inside.
3. Twist the transmission screw up to the bottom of the holes, and holding the whole apparatus motor end down, tap lightly on the side of the drive shaft tube and see if you can fish any metal debris (as well as the good clevis you just pushed in ) out from inside the tube. If you can easily screw by hand the drive shaft tube up and down the shaft, chances are you don't have any metal left inside.
4. I assume that eventually you will want to put all this back together and here's how: Get two new clevis pins and cotter keys. The clevis pins must be identical to the old ones (not just close). If you have studied the reassembly of this drive shaft/bushing/arm you realize that it looks nearly impossible to put back together the way it was. So think of it like a puzzle with a kind of trick solution.
5. Before you start make sure that there are no burrs on the clevis pin heads and that the clevis can pass easily through the holes in the bushing and the red arm assembly. Dress out the openings in all these parts with a drill bit if necessary. Take a small piece of 4# test monofilament fishing line and put it through the eye in the clevis and tie a small loop about one inch in diameter. Cut off the excess. Repeat this process with the other pin. Put both pins and their loops inside the holes in the drive shaft tube.
6. Next put the bushing over the drive shaft tube and center the holes over the openings in the tube. With a small 2 inch piece of safety wire with a tiny hook bent on the end, go inside the tube and patiently fish out the loops of fishing line through the holes (one on each side). Slide the red arm assembly over the tube and feed the fishing line loops through the holes in the phlanges from inside to outside.
7. At this point you are pulling the clevis pins through the holes in the bushing and the holes in the red arm assembly phlanges. The clevis pins are coming from the inside to the outside through the bushing and the phlange using the fishing line as your guide. You may need to make gentle alignments with an ice pick to insure the clevis pins come through easily. Pull the pins through the openings to where the eye in the clevis is showing. Engage the eye of the clevis with a dental pick or the like and twist and pull it until it is seated.
8. Put a washer over the clevis. Cut the fishing line loop and carefully insert a cotter key. The washer needs to be thick enough to insure that the clevis remains seated and doesn't work backward into the tube.
9. Now put the transmission and motor back into the plane. Hook them up and cycle the gear.
I realize the last part of this procedure sounds far fetched but it can be done and I will be glad to answer questions about the method and if you really need some help put the whole thing in a box and send it to me and I'll put it back together for you.