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I started this thread off of some discussion in this other one about some control stick drawing issues: http://bearhawkforums.com/forum/bear...rawings-issues
I figured it was better to split the discussion here.
We (my father and I) are building Bearhawk LSA 041. For reference, we are at the point on the fuselage where we need to work on the boot cowl and other aluminum stuff. The tail has been rigged and there isn't much welding left. The fuselage is being plans built because there was no kit available when we started it, at the very end of 2013. However, the wings were purchased from Mark a few months later as they became available.
There aren't a lot of specific LSA resources available yet, that we've found. We are grateful of the many resources provided by builders of other models of the Bearhawk. So here are some thoughts and notes about our fuselage. Please forgive me if some of this is already well-known with other Bearhawk models. If you can identify a common issue with other models, please speak up! It has been very helpful cross-referencing what others did on other models.
There is a lot of stuff I am no doubt forgetting, but here goes:
I mentioned in another thread somewhere here that the plans don't give the drawings for the horizontal stabilizer streamlined tube endings. We worked out our own solution.
We were not sure if there were one or two trim tabs. We made two.
This probably won't make sense, but I'll mention it anyway in case someone might benefit: We were confused about vertical alignment of the stations in relation to the top and bottom fuselage frames and how that would be affected after bending. But we built both the top and bottom frames to the dimensions in the plans, then jigged them up and bent them at the specified joints and filled in the vertical tubes and everything seems to make sense that way. The plans took it into account. It seems obvious now that we did it, but it was not mentioned in the manual so we had to spend some time thinking about it.
I seem to recall the top tube of station C-S (in the upper right of drawing 16) was not quite the right dimension, like maybe an inch short or something (don't quote me), so watch out for that.
For us, the landing gear hinges were hard to keep aligned with the 1/4" all-thread technique mentioned in the manual. We ultimately failed to keep them aligned coaxially as we anticipated. In the end, after we built the landing gear to fit, the misalignment turned out NOT to be a problem and the gear pivot just fine. Whew!
Because of the experience with the gear hinge alignment, we used 1/2" conduit with some nuts welded on the ends, with bolts and spacers screwed into those ends, for aligning the wing mounts, in place of the all-thread in between the mounts. That worked great. I will try it for the gear hinges next time, if I do another build.
We bought the shock struts from Mark because we felt they would be a PITA to do ourselves. They are great quality overall, and happened to fit our landing gear layout perfectly, but one of the piston rods was a hair too large so we had to carefully file and polish it to fit, on the lathe. Prolly coulda sent it back to Mark but we were too impatient since we were working on the gear when we discovered the issue... I still think they are worth it, and I would certainly buy the shock struts again if I do another build.
Aligning the front seat and rails was hard to get right. I suspect we were just dumb about it, but it's worth mentioning that it can be a fight if you don't pay particular attention.
Positioning the aileron pulley mounts has been highly frustrating (for me). We are waiting until we get the wings test-fit on the fuselage, without covering, to finish this. The dimensions in the plans do not seem to work with reality, but perhaps we are misunderstanding it.
Existing modifications that we've done, or are in-progress:
We found a picture online (Mexico factory picture?) which showed a short tube going vertically from the lower longeron up to near the rear seat, which was not on the plans (Note that it might very well have not been intended for the plans). We thought it was a good idea, so we added it. If you do that too, be sure to make it tight, or even slightly long, because shrinkage may unexpectedly suck up the longeron. Unlike every other joint on the fuselage, that one is a T joint with no other tube to resist movement from welding. We screwed that up and it was a pain to fix.
We didn't know what to do about the orientation of the rear seat mount "clips" (as we call them), as that does not appear to be specified in the plans. Ultimately we mounted them with the slots pointing upward, but we don't know if that is correct. Then we didn't like it much, so we cut the back off the seat and welded a tube across the bottom of the back and made two more clips to make it a two-piece seat sort of like the Super Cub. To us, the fussy nature of the rear seat in the plans wasn't worth the weight gain of an extra tube across the lower edge of the back seat, and the two mount points for it. Your mileage may vary.
We are doing a skylight, so we deviated from the plans and are going for more of a Super Cub style front and rear mount. We think it's easier because there are no particularly difficult bends in the steel, except for a finger brake needed for the rear mount because of the "roof pitch" left and right from center. Hard to describe this, but if you've seen the Cub you'll know what I'm saying here. Instead of jogging or bending back, like in the plans, they're just a single bend with riveted plate-nuts, and the fabric will wrap easier on the rear, and the skylight simply screws down on top, with aluminum strips over the perimeter, similar to the Cub. The two sides are channel, again like the Cub, instead of tube as specified in the plans, although the center is square tube. We're going to try to simply tap the side channels for the skylight screws. We plan on bedding the lexan on silicone.
Hard to describe: We made the trim handle assembly out of aluminum and made two brackets to mount to instead of the one mount system in the plans. There is an aluminum plate that sits on top which the handle is mounted on and has or slots for the mouting bolts to the two steel fuselage brackets, so that the whole handle assembly can be slid forward/aft for tightening the cables, instead of expensive, heavy turnbuckles. It's light and seems like it'll work great, but it hasn't been flown yet, obviously.
Skunkworks modifications that aren't done:
We are working on doing a left door, because Dad has a seaplane rating and really likes that sort of flying. Therefore we're also designing float mounts that are inside of the fabric and can be covered when not on floats. No specific plans for the actual floats yet. We are also planning on making both doors gull wing style, and made out of aluminum, with aluminum piano hinges. It seems like we might save a bit of weight (wishful thinking, I know), considering how much steel tubing for the doors is called for in the plans. We need to get the wings on first (test fit with no covering on the fuselage) to finish the design, because we need to see where the struts are exactly. We might not be able to swing the doors, pardon the pun. Also working on a removable throttle linkage for the rear seat, because of the left door seaplane thing.
I figured it was better to split the discussion here.
We (my father and I) are building Bearhawk LSA 041. For reference, we are at the point on the fuselage where we need to work on the boot cowl and other aluminum stuff. The tail has been rigged and there isn't much welding left. The fuselage is being plans built because there was no kit available when we started it, at the very end of 2013. However, the wings were purchased from Mark a few months later as they became available.
There aren't a lot of specific LSA resources available yet, that we've found. We are grateful of the many resources provided by builders of other models of the Bearhawk. So here are some thoughts and notes about our fuselage. Please forgive me if some of this is already well-known with other Bearhawk models. If you can identify a common issue with other models, please speak up! It has been very helpful cross-referencing what others did on other models.
There is a lot of stuff I am no doubt forgetting, but here goes:
I mentioned in another thread somewhere here that the plans don't give the drawings for the horizontal stabilizer streamlined tube endings. We worked out our own solution.
We were not sure if there were one or two trim tabs. We made two.
This probably won't make sense, but I'll mention it anyway in case someone might benefit: We were confused about vertical alignment of the stations in relation to the top and bottom fuselage frames and how that would be affected after bending. But we built both the top and bottom frames to the dimensions in the plans, then jigged them up and bent them at the specified joints and filled in the vertical tubes and everything seems to make sense that way. The plans took it into account. It seems obvious now that we did it, but it was not mentioned in the manual so we had to spend some time thinking about it.
I seem to recall the top tube of station C-S (in the upper right of drawing 16) was not quite the right dimension, like maybe an inch short or something (don't quote me), so watch out for that.
For us, the landing gear hinges were hard to keep aligned with the 1/4" all-thread technique mentioned in the manual. We ultimately failed to keep them aligned coaxially as we anticipated. In the end, after we built the landing gear to fit, the misalignment turned out NOT to be a problem and the gear pivot just fine. Whew!
Because of the experience with the gear hinge alignment, we used 1/2" conduit with some nuts welded on the ends, with bolts and spacers screwed into those ends, for aligning the wing mounts, in place of the all-thread in between the mounts. That worked great. I will try it for the gear hinges next time, if I do another build.
We bought the shock struts from Mark because we felt they would be a PITA to do ourselves. They are great quality overall, and happened to fit our landing gear layout perfectly, but one of the piston rods was a hair too large so we had to carefully file and polish it to fit, on the lathe. Prolly coulda sent it back to Mark but we were too impatient since we were working on the gear when we discovered the issue... I still think they are worth it, and I would certainly buy the shock struts again if I do another build.
Aligning the front seat and rails was hard to get right. I suspect we were just dumb about it, but it's worth mentioning that it can be a fight if you don't pay particular attention.
Positioning the aileron pulley mounts has been highly frustrating (for me). We are waiting until we get the wings test-fit on the fuselage, without covering, to finish this. The dimensions in the plans do not seem to work with reality, but perhaps we are misunderstanding it.
Existing modifications that we've done, or are in-progress:
We found a picture online (Mexico factory picture?) which showed a short tube going vertically from the lower longeron up to near the rear seat, which was not on the plans (Note that it might very well have not been intended for the plans). We thought it was a good idea, so we added it. If you do that too, be sure to make it tight, or even slightly long, because shrinkage may unexpectedly suck up the longeron. Unlike every other joint on the fuselage, that one is a T joint with no other tube to resist movement from welding. We screwed that up and it was a pain to fix.
We didn't know what to do about the orientation of the rear seat mount "clips" (as we call them), as that does not appear to be specified in the plans. Ultimately we mounted them with the slots pointing upward, but we don't know if that is correct. Then we didn't like it much, so we cut the back off the seat and welded a tube across the bottom of the back and made two more clips to make it a two-piece seat sort of like the Super Cub. To us, the fussy nature of the rear seat in the plans wasn't worth the weight gain of an extra tube across the lower edge of the back seat, and the two mount points for it. Your mileage may vary.
We are doing a skylight, so we deviated from the plans and are going for more of a Super Cub style front and rear mount. We think it's easier because there are no particularly difficult bends in the steel, except for a finger brake needed for the rear mount because of the "roof pitch" left and right from center. Hard to describe this, but if you've seen the Cub you'll know what I'm saying here. Instead of jogging or bending back, like in the plans, they're just a single bend with riveted plate-nuts, and the fabric will wrap easier on the rear, and the skylight simply screws down on top, with aluminum strips over the perimeter, similar to the Cub. The two sides are channel, again like the Cub, instead of tube as specified in the plans, although the center is square tube. We're going to try to simply tap the side channels for the skylight screws. We plan on bedding the lexan on silicone.
Hard to describe: We made the trim handle assembly out of aluminum and made two brackets to mount to instead of the one mount system in the plans. There is an aluminum plate that sits on top which the handle is mounted on and has or slots for the mouting bolts to the two steel fuselage brackets, so that the whole handle assembly can be slid forward/aft for tightening the cables, instead of expensive, heavy turnbuckles. It's light and seems like it'll work great, but it hasn't been flown yet, obviously.
Skunkworks modifications that aren't done:
We are working on doing a left door, because Dad has a seaplane rating and really likes that sort of flying. Therefore we're also designing float mounts that are inside of the fabric and can be covered when not on floats. No specific plans for the actual floats yet. We are also planning on making both doors gull wing style, and made out of aluminum, with aluminum piano hinges. It seems like we might save a bit of weight (wishful thinking, I know), considering how much steel tubing for the doors is called for in the plans. We need to get the wings on first (test fit with no covering on the fuselage) to finish the design, because we need to see where the struts are exactly. We might not be able to swing the doors, pardon the pun. Also working on a removable throttle linkage for the rear seat, because of the left door seaplane thing.