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View Full Version : Not OT, any airplane mechanics here, Evan?



Michael Az
09-08-2005, 10:11 PM
One of my customers that reburbish's airplanes came today to pick up a part and said there was something else he needs made. Balancing knives for alerions. He said whenever they paint a plane they have to be rebalanced and he isn't at all happy with the setup he threw together. He explained the base needs to be heavy and I have some steel that measures 2" X 4" X 16" and he thought that with a steel plate on the bottom should be close for the base. So I am trying to think how the knife should be made. I would think it should have a means to level it each time it is used, bubble level inserted in the tool? Anybody familiar with what I'm talking about? Any pictures out there? Thanks
Michael

agrip
09-09-2005, 12:10 AM
Michael
The reason for a mass balance of an aileron is to put the cg of the aileron close to the hinge center line.
Because if'n it aint, the doubled momentum of the translating mass and the rotating mass can get a flutter situation going.

Can't do much about the rotating, but the translating you sure can.

Because accurate hinge center location is kinda important, dont use knife edges in the hole, put a appropriate fitting pin in there and balance off the pin.

There is/ am/ are/ various ways to balance off the pin.
A couple of small, closely spaced, and clean free rolling, ball bearings set so the pin is trapped in the notch between the bearings works quite well, and rolls, well, like it is on ball bearings.

As a practical matter, the aileron balance does not have to be knife edge perfect, as the old analytical balances were.

Every day dirt, bird doo, and hangar rash are clear examples of why balance is an ever changing thing.

In the esoteric dept.
Finding the middle of the hole with the knife edge (BOTH side to side and up and down isn't exactly easy since there isn't anything there unless an adapter is in, and with all of that just use the appropriate pin.

Some pins are .070" dia anyway and about the only practical way of rigging those is with the an aligned and mating other half of the hinge.

Hope this helps.
Ag

Evan
09-09-2005, 12:14 AM
If it's a certified aircraft you don't have a lot of choice. The counterbalance will have to be made to manufacturer spec and material and then passed off by an AME. If it's an experimental you can pretty well make whatever works best.

I can't tell you more than that because there are as many different syles and types as there are aircraft types. Some are internal to the wing and some are external below the aileron extending forward of the hinge point. Some ailerons are counterbalanced by virtue of where the hinge point is relative to a weighted tube in the aileron.

winchman
09-09-2005, 03:25 AM
IIRC, the aircraft service manual describes the procedure for balancing the aileron after painting or repair.

I remember doing it once when I was helping out in the maintenence shop. I don't recall what plane it was or exactly how we did it, but I remember that it involved some calculations because the procedure didn't use the hinge line as the balance point.

Roger

Michael Az
09-09-2005, 11:15 AM
Thanks fellows for the advise.
agrip, the customer drew me a little sketch while explaining what he needed and he showed the pin installed in the alerion and I assume there will always be a pin and that is why I was thinking a knife edge on the pin. The bearings sound interesting and I will ask him about going that route.
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Evan
If it's a certified aircraft you don't have a lot of choice. The counterbalance will have to be made to manufacturer spec and material and then passed off by an AME. If it's an experimental you can pretty well make whatever works best.
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I would imagine these are all certified Evan. I don't know much about the aircraft buisness but he is currently using something he cobbled together and didn't mention anything about being certified so I am in the dark there. This is wild and wolly Az and maybe he is like a neighbor I have that has a helicopter and flys it without a license!
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Roger
I remember doing it once when I was helping out in the maintenence shop. I don't recall what plane it was or exactly how we did it, but I remember that it involved some calculations because the procedure didn't use the hinge line as the balance point.
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Hopefully he has all that info. My main concern is to make him a good tool that will work.
Thanks again
Michael

Evan
09-09-2005, 12:59 PM
If you are being asked to make a part for a certified aircraft without normal inspection and certification of the part then forget it, even if the certification has already been violated by the owner. Especially a part for the flight controls. Walk away. Modifying a type certified aircraft without approval makes you liable. All modifications must have a STC (supplemental type certificate) from the FAA.

There is no chance I would work on any aircraft that doesn't have proper certification, either approved type or experimental (homebuilt or decertified/modified aircraft). A standard type that has been modified without a STC must then be reregistered as experimental.

SJorgensen
09-09-2005, 02:42 PM
Evan,
I'm sure that you are right in general, but I'm not sure that this would also apply to making and using a fixure that is only used to facilitate the adjustment. On this I think it would all have to rely on the A&P's certification of that adjustment and that the adjustment was made according to the regulations and requirements. I am not an A&P, but I am a licensed SEL pilot since 1982. I haven't been active for a few years, but at one time I was familiar enough with the FAR's to write to the publisher of ASA's FAR/AIM to show them some errors in their manual. They thanked me, and sent me a coffee mug. Of course the A&P's work from a different book.

Evan
09-09-2005, 03:27 PM
I still wouldn't get involved if everything isn't going to be fully inspected after the work is done. There is also the question of if the tool made in this case is adequate for the job. The flight controls are obviously most critical, especially balancing them correctly. If not balanced correctly they can exhibit an alarming tendency to fall of at inopportune times. A lot of FAA regulations apply strictly to the design and maintenance of the flight controls.

Jigs and fixturing for this sort of thing must meet manufacturer specs at the least. Also, unless the person doing the balancing actually knows exactly what they are doing they may make a serious mistake. A lot of flight control surfaces are not just statically balanced, the are aerodynamically balanced as part of the overall balance.

Dick Plasencia
09-09-2005, 05:10 PM
Michael, I'm a FAA DER that's a designated engineering representative of the FAA. My advice is stay the hell away from that deal. You can do the job and you can also get away with it but.....
But should anything happen, even a flat tire there could follow a FAA check and you will have no end of trouble after that.
Even painting an airplane needs to be done by certified/licensed personnel. The Feds are pretty much a PITA in my opinion in many cases where oversight is not really required.
Making a counterbalance is an example.

Michael Az
09-09-2005, 05:24 PM
Fellows, don't misunderstand me, I'm not doing any of the work at all, just making the tool. He has been doing this with a makeshift jig and like you say, I don't want to get involved doing the work. I won't even give him a reciept except for some steel plate.
Michael

SJorgensen
09-10-2005, 12:47 AM
Don't worry Michael,

Not everyone is too pansy assed to help a flyer make a tool just to adjust an airframe. I'm also surprised that a certified FAA DER would suggest that if an airframe had a flat tire that a person who had made a tool intended and used to help adjust the balance of ailerons would be suspect or sued. I know that it has happened though. A friend of mine whose company made chillers for fishing boats made an air-conditioner for a yaught. It sank. All the companies that had anything to do with it was sued in proportion to the depth of their pockets because the cause and fault could not be fixed. I don't really know if this is true, but that is what I was told. I'm sceptical.

Still, if you want something made and can give me detailed information I would concider it. As long as it isn't a part of the aircraft and that the proper performance of the tool and the adjustment made with it can be verified before any flight.

I guess hunger overcomes deep pockets once in a while. Post some drawings.

Jim Caudill
09-10-2005, 03:29 AM
I've been an licensed A&P for over 20 years and flew as a pilot in the USAF and then corporate. What you are hearing is the result of miscommunication. Remember the line in "Cool Hand Luke"... "What we have here, is failure to communicate...".

If you built an apparatus to balance the ruddervators on a V-tail Bonanza, complete with instructions on how to use the device, then you would be sticking your neck out. If a crash then occurred and flutter was a factor, then you could kiss your *** goodbye.

On the other hand, balancing wheels, props, flight controls, etc using knife edge stands is/was relatively common and primitive. You are not making an apparatus, but essentially supplying a pair of sawhorses. The "sawhorses" can be big or little, flat or "knife-edged"; The person performing the balancing is responsible for compliance. He is the one determining the suitability for whatever hardware is used.

This ain't rocket science here, and the guy already has his knife edge. He just wants a heavier - more stable base.