jetjr Posted December 19, 2013 Posted December 19, 2013 I believe older jabirus, with shorter wing etc didnt show the problem. New long narrow wing has different struts maybe and different vibration isues I used some mylar strips on the gaps on the elevator-mainly trying to tidy things up as original fabric tape fell to bits. At high cruise speed it howled loudly and flung itself to bits, went back to outdoor tape and no problems. If i couldnt see it, it would have been concerning and caused landing.
Dafydd Llewellyn Posted December 19, 2013 Posted December 19, 2013 I believe older jabirus, with shorter wing etc didnt show the problem. New long narrow wing has different struts maybe and different vibration isuesI used some mylar strips on the gaps on the elevator-mainly trying to tidy things up as original fabric tape fell to bits. At high cruise speed it howled loudly and flung itself to bits, went back to outdoor tape and no problems. If i couldnt see it, it would have been concerning and caused landing. On the subject of gap seals, what's the objection to brush seals? Why does everybody persist with tape seals?
ianboag Posted January 19, 2014 Author Posted January 19, 2014 Replaced the aileron cables - problem is fixed - now there is no flutter/buzz/vibration. The stick feels like the aileron cables are running in glue - so cable tightness and friction are obviously significant damping factors. Pulling one of the cables was a bit hard because the hole in the wing was a tad small - it was necessary to grind down the rod end to pull the cable through. That was the old (sad) rod end which we then threw away. 1
Keenaviator Posted January 19, 2014 Posted January 19, 2014 Replaced the aileron cables - problem is fixed - now there is no flutter/buzz/vibration. The stick feels like the aileron cables are running in glue - so cable tightness and friction are obviously significant damping factors. Pulling one of the cables was a bit hard because the hole in the wing was a tad small - it was necessary to grind down the rod end to pull the cable through. That was the old (sad) rod end which we then threw away. When I installed my aileron cables I first removed the rod ends. Laurie.
ianboag Posted January 19, 2014 Author Posted January 19, 2014 When I installed my aileron cables I first removed the rod ends.Laurie. Understood. I had the drawstring tied in the rod end hole and couldn't see any other way to attach it securely. Losing the drawstring off the cable part way through the exercise would have been a real bad hair day. One of the cables went in smoothly - the other one had the nogo problem. I had difficulty extracting the old one on that side, but I figured that as I got it out eventually I would get the new one in eventually. Didn't happen until I slimmed the rod end down a bit. So I have now acquired a new skill (inserting Jab aileron cables) that I will hopefully never have to use again :-)
Keenaviator Posted January 19, 2014 Posted January 19, 2014 I had the same concern of losing the draw string on the cable but tied and taped it securely. Even more fun was getting the wiring in for wing tip lights; ended ip using yellow tongue from floor board to push a draw string it in then fishing around with lock wire to hook it then pull out the wing tip. Laurie 1
Old Koreelah Posted January 19, 2014 Posted January 19, 2014 On the subject of gap seals, what's the objection to brush seals? Why does everybody persist with tape seals? What are brush seals?
PA. Posted January 20, 2014 Posted January 20, 2014 What are brush seals? They are the ones who clean the poo off the rocks at the beach. 2
Dafydd Llewellyn Posted January 26, 2014 Posted January 26, 2014 What are brush seals? You'll find them in Bunnings, for sealing the gaps under doors etc. Normally black nylon bristle trapped in a tiny aluminiun channel, which is in turn mounted in either an extruded aluminium housing or a plastic housing. They seem to me to be very suitable for preventing (well, almost preventing) flow through control surface gaps, where the control surface has a semi-circular leading edge that is centred on the hinge line. They will not alter the control surface hinge moment, so they are not a substitute for the "under & over" fabric strip seal that is sometimes used on welded steel tube elevators & tailplanes 1
Dafydd Llewellyn Posted January 26, 2014 Posted January 26, 2014 The original stuff looks like spring steel (it's magnetic). The replacement wires we have put in for now are bronze. We had some suitably sized (fatter) bronze wire. It's not going to wear out or break in five minutes and I will be replacing the hinges anyway in the not too distant future. The original hinges are almost certainly made from MS 20257 piano hinge - probably -5 size. See http://hinges.ladeau.com/viewitems/mil-spec-hinges/ms20257 These hinges are rolled from 5052 grade aluminium alloy, and the pins are normally cad. plated piano wire (spring steel wire). The reason cad. plating is used is that it helps prevent electrolytic corrosion between the pin and the hinge, at least until the plating wears out. Replacing it with bronze wire is asking for very rapid electrolytic corrosion of the aluminium hinges, especially if you are anywhere near salt water. If your hinges have loosened, it's almost certainly because the plating has been consumed and electrolysis has started eroding the aluminium. That should be fixed by replacing the hinges before further flight, NOT by putting oversize pins in there. made of material that would convert the hinges into a battery. Potential Darwin-award stuff. 3 1
Old Koreelah Posted January 26, 2014 Posted January 26, 2014 Thanks for the info on gap seals Dafydd. Looks good, but probably not suited to my wooden contruction. I have spent a lot of time searching for mylar-type sheet suitable for my aircraft. The gap seals used by sailplanes etc is far too narrow. Mine would need to be 50mm. I have had some success with ordinary cloth tape stuck onto the "hidden" surface of the wing and control surface, but it starts to peel after a year or two.
Dafydd Llewellyn Posted January 26, 2014 Posted January 26, 2014 Thanks for the info on gap seals Dafydd. Looks good, but probably not suited to my wooden contruction. I have spent a lot of time searching for mylar-type sheet suitable for my aircraft. The gap seals used by sailplanes etc is far too narrow. Mine would need to be 50mm. I have had some success with ordinary cloth tape stuck onto the "hidden" surface of the wing and control surface, but it starts to peel after a year or two. No, it's a case of horses for courses; but where brush seals can be used, you don't need to disassemble them to remove & refit the control surface - and I've not yet seen a cloth tape seal that doesn't start to peel after a year or two.
ianboag Posted January 29, 2014 Author Posted January 29, 2014 The original hinges are almost certainly made from MS 20257 piano hinge - probably -5 size. See http://hinges.ladeau.com/viewitems/mil-spec-hinges/ms20257These hinges are rolled from 5052 grade aluminium alloy, and the pins are normally cad. plated piano wire (spring steel wire). The reason cad. plating is used is that it helps prevent electrolytic corrosion between the pin and the hinge, at least until the plating wears out. Replacing it with bronze wire is asking for very rapid electrolytic corrosion of the aluminium hinges, especially if you are anywhere near salt water. If your hinges have loosened, it's almost certainly because the plating has been consumed and electrolysis has started eroding the aluminium. That should be fixed by replacing the hinges before further flight, NOT by putting oversize pins in there. made of material that would convert the hinges into a battery. Potential Darwin-award stuff. Dafydd. As always, a sensible comment. I respect your views. I know about electrolysis. However ..... This was done as a short term fix for about 6 weeks so we could get on with test flying. The relevant authorities are aware of it and of what/when happens next. The rudder hinges were replaced with new factory ones when I bought the plane a few years back. I now have some new hinges (aileron and elevator) from Jab that I bought at the same time as the new aileron cables. I'm sick of being an amateur mechanic, so they will be fitted by a LAME in about 4 weeks when I am over visiting family on your side of the pond. The original pins were indeed cadmium plated spring steel. The new pins look more like stainless (?) - they certainly aren't yellow. Factory parts and all that so one has to assume it's the right stuff ....
Dafydd Llewellyn Posted January 29, 2014 Posted January 29, 2014 Dafydd. As always, a sensible comment. I respect your views. I know about electrolysis. However .....This was done as a short term fix for about 6 weeks so we could get on with test flying. The relevant authorities are aware of it and of what/when happens next. The rudder hinges were replaced with new factory ones when I bought the plane a few years back. I now have some new hinges (aileron and elevator) from Jab that I bought at the same time as the new aileron cables. I'm sick of being an amateur mechanic, so they will be fitted by a LAME in about 4 weeks when I am over visiting family on your side of the pond. The original pins were indeed cadmium plated spring steel. The new pins look more like stainless (?) - they certainly aren't yellow. Factory parts and all that so one has to assume it's the right stuff .... Good to know you have it in hand. BTW, the Piper PA 28-140 I once owned had piano hinge - but whilst they looked like the MS20257 variety, they appeared to have some sort of plastic -nylon? - bush between the aluminium and the steel pin. I've never been able to find them as a standard part; I guess they may be something Piper had made. Unbushed piano hinges that are exposed to slipstream buffet - e.g. the outboard elevator tab hinges - always generate black streaks due to the fretting between the aluminium and the steel. Back then, Lanotec hadn't been invented; if I had an aircraft with that sort of hinge on it, I'd be inclined to try some. 1
ianboag Posted January 30, 2014 Author Posted January 30, 2014 Good to know you have it in hand. BTW, the Piper PA 28-140 I once owned had piano hinge - but whilst they looked like the MS20257 variety, they appeared to have some sort of plastic -nylon? - bush between the aluminium and the steel pin. I've never been able to find them as a standard part; I guess they may be something Piper had made. Unbushed piano hinges that are exposed to slipstream buffet - e.g. the outboard elevator tab hinges - always generate black streaks due to the fretting between the aluminium and the steel. Back then, Lanotec hadn't been invented; if I had an aircraft with that sort of hinge on it, I'd be inclined to try some. The other advantage of using Jab ones is that (hopefully) the holes are in the same place as the existing hinges, so the flock bed they sit on will be the right size and in the right place .... it all gets quite a bit harder if this is not the case :-(
Dafydd Llewellyn Posted January 30, 2014 Posted January 30, 2014 The other advantage of using Jab ones is that (hopefully) the holes are in the same place as the existing hinges, so the flock bed they sit on will be the right size and in the right place .... it all gets quite a bit harder if this is not the case :-( Well, you'd have to get an airworthiness approval to use anything other than the factory-supplied ones, so yes. I don't know whether they come pre-drilled or not; MS 20257 hinge is not pre-drilled. 1
ianboag Posted February 17, 2014 Author Posted February 17, 2014 The other advantage of using Jab ones is that (hopefully) the holes are in the same place as the existing hinges, so the flock bed they sit on will be the right size and in the right place .... it all gets quite a bit harder if this is not the case :-( They weren't ... :-(
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