FEJ Hawk stab repair.
08-04-2014, 05:25 PM
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FEJ Hawk stab repair.
I recently acquired an FEJ Hawk that belonged to a friend who passed away before he was able to finish it. I'm honored to be able to finish what he started but obviously saddened that he never got to see it fly. I'm well aware of the troubles with FEJ so I ask we keep this clean as I'm only trying to share what I've done to fix it. First picture shows structure after I cut the skin carefully as I re used it.
08-05-2014, 08:46 AM
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It clearly has done the job and it is a well thought out and very neatly executed repair.
However had it been me I would have extended the piece at the back further out. In fact as far as I could get it, chamfering the ply down to half thickness. The flight loads on the stab get transferred to that ply box you have created and I would be concerned about the stress concentration in the wing skin at the end of the box.
Now while I just built my jets to the plans I do have some experience in designing building something similar as I was involved in the early days of F2D combat design where we wanted the lightest possible model that would cope with the airborne loads. Some folded in the air so I made them just a little stronger. 40 in span 6 oz bare weight plus engine and bladder weight was the goal. .
My gut says you may have a stress concentration, I would be interested in what others think
After all there are quite a few of these style of stabs around that need strengthening. .
However had it been me I would have extended the piece at the back further out. In fact as far as I could get it, chamfering the ply down to half thickness. The flight loads on the stab get transferred to that ply box you have created and I would be concerned about the stress concentration in the wing skin at the end of the box.
Now while I just built my jets to the plans I do have some experience in designing building something similar as I was involved in the early days of F2D combat design where we wanted the lightest possible model that would cope with the airborne loads. Some folded in the air so I made them just a little stronger. 40 in span 6 oz bare weight plus engine and bladder weight was the goal. .
My gut says you may have a stress concentration, I would be interested in what others think
After all there are quite a few of these style of stabs around that need strengthening. .
Last edited by j.duncker; 08-05-2014 at 09:00 AM.
08-05-2014, 11:20 AM
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Agree with j.duncker and Sluggo. The box you made is nice, but you can see they used honeycomb for spar material which is improper application of the material and guaranteed to fail. I am afraid your wings are likely made the same way. You need to do a full overhaul like I saw being done on the A-7 thread if you want to get many flights...
08-05-2014, 03:50 PM
#13
Same here. Nice repair job too.
A chain is only as strong as its weakest link. While the box and reinforcing you did appears to be strong, the material FEJ used is still the problem. While your repair is solid, the problem is still with the improper application of the honeycomb structure. It's too brittle to withstand flight loads unless properly supported. I fear the flexing and structural failure will be to the parts you could not get to. Like Dunker suggested, I would have extended the lenghts of the plywood you added as far out to the ends of the stab as possible.
All in all, you will more than likely get a lot more flights out of the jet than the typical FEJ construction allows for.
Best of luck!
A chain is only as strong as its weakest link. While the box and reinforcing you did appears to be strong, the material FEJ used is still the problem. While your repair is solid, the problem is still with the improper application of the honeycomb structure. It's too brittle to withstand flight loads unless properly supported. I fear the flexing and structural failure will be to the parts you could not get to. Like Dunker suggested, I would have extended the lenghts of the plywood you added as far out to the ends of the stab as possible.
All in all, you will more than likely get a lot more flights out of the jet than the typical FEJ construction allows for.
Best of luck!
Last edited by Airplanes400; 08-05-2014 at 04:02 PM.
08-05-2014, 08:12 PM
#15
Scott, The aileron servo arm came off...Plane is fine.
Lewis
Lewis
08-06-2014, 07:16 AM
#16
"Quote" I saw a big FEJ Hawk have wing flutter and it was passed off as aileron flutter and a broken linkage. What I saw was a wing fluttering and didn't look like a aileron flapping in the wind. "Quote"
I have video of the FEJ Hawk and it was clearly Aileron Flutter and not wing flutter, I have watched it several times.
P. Richards aka SwatTeam
I have video of the FEJ Hawk and it was clearly Aileron Flutter and not wing flutter, I have watched it several times.
P. Richards aka SwatTeam
Last edited by P. Richards; 08-06-2014 at 07:21 AM.
08-06-2014, 10:47 AM
#17
Exactly! The servo arm came off. The aircraft is fine.
I have video of the FEJ Hawk and it was clearly Aileron Flutter and not wing flutter, I have watched it several times.
P. Richards aka SwatTeam
Last edited by P. Richards; Today at 11:21 AM.
I have video of the FEJ Hawk and it was clearly Aileron Flutter and not wing flutter, I have watched it several times.
P. Richards aka SwatTeam
Last edited by P. Richards; Today at 11:21 AM.
Last edited by jeteye; 08-06-2014 at 02:58 PM.
