wafer
Well-Known Member
- Joined
- May 12, 2006
- Messages
- 155
I have been reluctant to post because I believe my situation is isolated. After some discussions under the “Bent Bolts†thread recently, I reconsidered as it may help someone.
The attached subject damage was to my LTS, which uses a different method of attaching the gear to the fuselage than 1, 2, or 2L. If you have a stretch taildragger, and built to plans, you have the same set up too, as well as a 2L tri-gear, I believe. The set-up is 2 bushings per side welded to the longeron with a .063 stiffener (attached plans). Each gear hole for the four mounting bolts have an upper and lower chamfer to allow the gear to flex. A few discussions here on the forum about the design, but no failures reported.
The damage mostly consists of a crack in the longeron by each bushing. Additionally, there is a crack in the weld area between a bushing the .063 stiffener on the right forward section. Sickening is another description, as I have been in some form of shock since discovering in May.
After cutting off the damaged areas, you can see the real force the longerons were under, with a heavy pulling force from the most forward bolts.
I have over 120 hours on the airframe, with a guess of ~200 landings. All landings were on a hard surface, as tri-gear Sonerais are not to operate off sod. A few landings were “not perfectâ€, but nothing to warrant this damage. My typical gross weight is under 900 lbs. And my main wheels rotated/spun well with little drag. Brakes were not applied/locked during landings.
So what caused this damage? In the past, both Pitts (with spring gear) and Christen Eagle owners suffered similar problems when operating off rough surfaces. The fix were “radius plates,†like those offered through Grove. But talking with Grove, this situation where the gear is actually mounted to the frame with bolts through the gear, radius plates will not help.
One possible cause is the mounting bolts were too tight and did not allowing flexing in the camber area. I first discovered the situation because the bolts were actually loose in the front. I replaced the bolts (no, they were not bent, and nor this damage present), and tightened to maybe 20 ft. lbs. I am not aware of any torqueing limit, as I just made sure they were tight. About 10 hours of flight later, I noted play in the gear. I was close to annual time, so I started unbuttoning and… well…, you saw the pics.
Another possible cause is the use of round tubing. The stretch plans call out for square ¾ .035 longerons in this area. Back in 1993 when I obtained my plans and ordered my tubing, it was a common practice to substitute round tubing for the square tubing longerons due to costs. So I have round tubing at the longerons, as an exception to the plans. Otherwise, my building of this area was done per plans. The bushings would have more of an area to be welded to with a square longeron/stiffener, offering more rigidity and less flexing during loads.
It was suggested in the “Bent Bolts†thread that extending the bushings past the bottom of the longeron/stiffener could translate too much loads on the longerons. My stiffeners were rounded, but offered a flat surface for the gear to touch. The bushing were filed to be flush with the stiffeners, so I do not think this was the root cause.
One final cause could be the landing forces for a tri-gear. The gear is mounted close to the CG, under the wing. I hold off letting the nose down as long as I can after touchdown, and eventually rotate to the nose gear -- typical for tri-gear operations. But different than taildraggers, that land in an almost taxi ready configuration. The momentum of the fuselage on landing wants to get the tri-gear nose on the ground, so holding off the flare puts some additional force on the most forward bolts.
So what really caused it? Well, looking back I would have opted for square longerons as they provide more bushing rigidity. My front bolts loosened, I suspect from the tri-gear forces slowly working the elastic nuts loose. With the front bolt being loose, there was some “slapping†action upon landing that I suspect actually started some longeron and/or weld failures. After tightening, the loads got transformed to longerons even greater, and given the round tube situation it went downhill real fast after that. So, some form of everything is my guess, that started with the bolts loosening.
I have been slowly licking my wounds to fix this. Man, you forget how much assembly went on until you have to disassemble! Since I want to use the existing gear, I need to mimic the previous longerons as to locate the bushings in the same locations. Thus, I have spliced a new .035 longeron tube via rosette welding a 5/8 .049 thick tube within the longeron. A side note….I am gas welding this area and was not sure how far the heat would transfer. With the use of silicone “hot plates†and cutting away the fabric from the repair center, I have been able to keep the heat off the fabric. .
After tacking the bushings in place, I plan to use a square 4130 7/8 tube .049 thick to “cap†around the longeron, with cuts around the bushings. I will then bend the .063 stiffner per plans and weld it up. And as noted, make sure the bushings are filed flat with the stiffener, and not extend into the gear. This will get me pretty close to the plans.
Finally, I plan to use drilled bolts with cotter pins to mount the gear, and inspect more frequently than annually.
Maybe this is some help to you; maybe not. But thanks for listening!
The attached subject damage was to my LTS, which uses a different method of attaching the gear to the fuselage than 1, 2, or 2L. If you have a stretch taildragger, and built to plans, you have the same set up too, as well as a 2L tri-gear, I believe. The set-up is 2 bushings per side welded to the longeron with a .063 stiffener (attached plans). Each gear hole for the four mounting bolts have an upper and lower chamfer to allow the gear to flex. A few discussions here on the forum about the design, but no failures reported.
The damage mostly consists of a crack in the longeron by each bushing. Additionally, there is a crack in the weld area between a bushing the .063 stiffener on the right forward section. Sickening is another description, as I have been in some form of shock since discovering in May.
After cutting off the damaged areas, you can see the real force the longerons were under, with a heavy pulling force from the most forward bolts.
I have over 120 hours on the airframe, with a guess of ~200 landings. All landings were on a hard surface, as tri-gear Sonerais are not to operate off sod. A few landings were “not perfectâ€, but nothing to warrant this damage. My typical gross weight is under 900 lbs. And my main wheels rotated/spun well with little drag. Brakes were not applied/locked during landings.
So what caused this damage? In the past, both Pitts (with spring gear) and Christen Eagle owners suffered similar problems when operating off rough surfaces. The fix were “radius plates,†like those offered through Grove. But talking with Grove, this situation where the gear is actually mounted to the frame with bolts through the gear, radius plates will not help.
One possible cause is the mounting bolts were too tight and did not allowing flexing in the camber area. I first discovered the situation because the bolts were actually loose in the front. I replaced the bolts (no, they were not bent, and nor this damage present), and tightened to maybe 20 ft. lbs. I am not aware of any torqueing limit, as I just made sure they were tight. About 10 hours of flight later, I noted play in the gear. I was close to annual time, so I started unbuttoning and… well…, you saw the pics.
Another possible cause is the use of round tubing. The stretch plans call out for square ¾ .035 longerons in this area. Back in 1993 when I obtained my plans and ordered my tubing, it was a common practice to substitute round tubing for the square tubing longerons due to costs. So I have round tubing at the longerons, as an exception to the plans. Otherwise, my building of this area was done per plans. The bushings would have more of an area to be welded to with a square longeron/stiffener, offering more rigidity and less flexing during loads.
It was suggested in the “Bent Bolts†thread that extending the bushings past the bottom of the longeron/stiffener could translate too much loads on the longerons. My stiffeners were rounded, but offered a flat surface for the gear to touch. The bushing were filed to be flush with the stiffeners, so I do not think this was the root cause.
One final cause could be the landing forces for a tri-gear. The gear is mounted close to the CG, under the wing. I hold off letting the nose down as long as I can after touchdown, and eventually rotate to the nose gear -- typical for tri-gear operations. But different than taildraggers, that land in an almost taxi ready configuration. The momentum of the fuselage on landing wants to get the tri-gear nose on the ground, so holding off the flare puts some additional force on the most forward bolts.
So what really caused it? Well, looking back I would have opted for square longerons as they provide more bushing rigidity. My front bolts loosened, I suspect from the tri-gear forces slowly working the elastic nuts loose. With the front bolt being loose, there was some “slapping†action upon landing that I suspect actually started some longeron and/or weld failures. After tightening, the loads got transformed to longerons even greater, and given the round tube situation it went downhill real fast after that. So, some form of everything is my guess, that started with the bolts loosening.
I have been slowly licking my wounds to fix this. Man, you forget how much assembly went on until you have to disassemble! Since I want to use the existing gear, I need to mimic the previous longerons as to locate the bushings in the same locations. Thus, I have spliced a new .035 longeron tube via rosette welding a 5/8 .049 thick tube within the longeron. A side note….I am gas welding this area and was not sure how far the heat would transfer. With the use of silicone “hot plates†and cutting away the fabric from the repair center, I have been able to keep the heat off the fabric. .
After tacking the bushings in place, I plan to use a square 4130 7/8 tube .049 thick to “cap†around the longeron, with cuts around the bushings. I will then bend the .063 stiffner per plans and weld it up. And as noted, make sure the bushings are filed flat with the stiffener, and not extend into the gear. This will get me pretty close to the plans.
Finally, I plan to use drilled bolts with cotter pins to mount the gear, and inspect more frequently than annually.
Maybe this is some help to you; maybe not. But thanks for listening!