Sonnufa....


Got a offer of help with the welding and in my excitement I failed to check the tail post. It's bent so now I have to cut off the brace we welded last night.

DRLpatrol wrote:

Kevin wrote:...... I made my gear legs 3" taller as my ski's I have for my ship have some really low pedestal's, that is my only design change and I ran that by Mr Barrows before I did it......

Kevin, Do you hang out at bearhawkforums.com much. I would like to hear more about the extended gear. Did you make it with heavier wall tubing or just longer? Are the legs 3" longer or does the plane actually sit 3" higher? I am just getting started on a Patrol and would like it to sit a little higher, I'm 6'5" so a little higher would make it easier to get in. And look cool.

Doug

I don't think the airplane sits more than an inch and a half taller due to the trigonometry of the gear being slightly wider. I used the .the spec'd out .065 for the gear legs. I have 8.50's mounted and may try some of those new smoothies that Desser has available but doubt ABW's are in my future. I would stick with stock length if you are planning ABW's, also if you plan on big rubber remember the gear leg trailing edge fairing needs to clear your tires. Johnson Creek is probably as back country as I will get. As to the B hawk forum I'm more of a lurker than anything. I've built several rag and tube airplanes and have my own way of getting tasks accomplished so don't post opinions much as I don't want to debate anybody on building techniques. Sorry for piggy backing your thread Whee. I will abstain from that from here on. Look forward to seeing your progress.

Kevin wrote:Sorry for piggy backing your thread Whee. I will abstain from that from here on. Look forward to seeing your progress.

No worries. Be sure to speak up if you see something and have a thought.

I might not say much Whee, but I am reading all your post on the Bearhawk. Keep us posted.

Cheers...Rob

Looks like a helluva cool project Jon...in the f.w.i.w. dept. i know the best welder in this town if u need it...way reasonable and a pro for sure...and i think he is only working parttime right now...just an idea...he would dig ur project for sure...just an idea if u want a little help...he doesnt need the $, but he is very good at that craft....JO

Kevin wrote:

DRLpatrol wrote:

Kevin wrote:...... I made my gear legs 3" taller as my ski's I have for my ship have some really low pedestal's, that is my only design change and I ran that by Mr Barrows before I did it......

Kevin, Do you hang out at bearhawkforums.com much. I would like to hear more about the extended gear. Did you make it with heavier wall tubing or just longer? Are the legs 3" longer or does the plane actually sit 3" higher? I am just getting started on a Patrol and would like it to sit a little higher, I'm 6'5" so a little higher would make it easier to get in. And look cool.

Doug

I don't think the airplane sits more than an inch and a half taller due to the trigonometry of the gear being slightly wider. I used the .the spec'd out .065 for the gear legs. I have 8.50's mounted and may try some of those new smoothies that Desser has available but doubt ABW's are in my future. I would stick with stock length if you are planning ABW's, also if you plan on big rubber remember the gear leg trailing edge fairing needs to clear your tires. Johnson Creek is probably as back country as I will get. As to the B hawk forum I'm more of a lurker than anything. I've built several rag and tube airplanes and have my own way of getting tasks accomplished so don't post opinions much as I don't want to debate anybody on building techniques. Sorry for piggy backing your thread Whee. I will abstain from that from here on. Look forward to seeing your progress.

Kevin,
Thanks for the info. I have also been looking at those Desser smoothies. As far off as I am they may have the bigger ones out by the time I am ready. I could not afford or really need the real ABW's.
As far as being a lurker I am not much for debating either but do like to pick up new ideas from people.

Zzz, I agree with the big tires being better but if I only go to 8.50's I would like longer legs too.

Sorry Whee, Back to your regularly scheduled broadcast.
Doug

whee wrote:Sonnufa....

Man... that sucks!

Last night I cut off the brace so I could straiten the tail post. I carefully trimmed it off and was ready to straiten things out so I had my wife come hold the fuselage from moving while I carefully pulled on the post. The post was bent at the top longeron; it was pushed forward 3/4" at the upper rudder hinge location which is ~24" up from the longeron. It wasn't going to take much to get it straight so I pulled very carefully. This is where my metallurgical lesson comes in. This fuselage had been TIG welded with no stress relieving done and according to everyone I spoke with, no problem.

Well...
IMG_1295 by whee8e, on Flickr

IMG_1298 by whee8e, on Flickr

IMG_1296 by whee8e, on Flickr

It broke like a dry stick. This is completely my fault, I knew I needed to stress relieve it but I believed the people I had asked and I even read the study that was done that is used to say you don't have to stress relieve thin wall 4130. Under normal use not stress relieving is probably fine but as I have shown it does make the material more brittle than gas welding does. My concern now is given the amount that the fuselage flexes under load I'm concerned about cracks forming around the welds. I'm not excited about stress relieving all the clusters because I don't have a jig for the fuselage and it could twist from all the heat. Not sure what I'm going to do about stress relieving.

I've talked to Bob about how to fix it and he suggests I splice in a new piece rather than replace the whole thing. Replacing the whole post leaves more room from things to move; the risk is greater than the reward.

If it were me, I would realy inspect all welds. Being an engineer, do you have contacts of any certified welding inspectors? Your tailpost may have already had a crack??? Cold cracking, tungsten inclusions, and hydrogen cracking are all common in tig welding. If youre concerned about other welds, dye penetrant inspection is quick cheap and easy.

whee wrote:Last night I cut off the brace so I could straiten the tail post. I carefully trimmed it off and was ready to straiten things out so I had my wife come hold the fuselage from moving while I carefully pulled on the post. The post was bent at the top longeron; it was pushed forward 3/4" at the upper rudder hinge location which is ~24" up from the longeron. It wasn't going to take much to get it straight so I pulled very carefully. This is where my metallurgical lesson comes in. This fuselage had been TIG welded with no stress relieving done and according to everyone I spoke with, no problem.

Well...
IMG_1295 by whee8e, on Flickr

IMG_1298 by whee8e, on Flickr

IMG_1296 by whee8e, on Flickr

<snip> I don't have a jig for the fuselage and it could twist from all the heat. Not sure what I'm going to do about stress relieving.
ds. I'm not excited about stress relieving all the clusters because I don't have a jig for the fuselage and it could twist from all the heat. Not sure what I'm going t
I've talked to Bob about how to fix it and he suggests I splice in a new piece rather than replace the whole thing. Replacing the whole post leaves more room from things to move; the risk is greater than the reward.

Whee, how in the world will you ever know if you don't stress relieve? Somewhere in the back pages of my mind I recall a procedure calling for clockwise or anti-clockwise heating from cluster to cluster beginning at the firewall and moving aft. Apparently this minimizes the distortion. I dunno, more research is needed. Call an EAA tech counselor. The other option is to assemble and cut some surplus steel to the dimensions needed for a frame of some sort. Make the connections to the fuselage with short pieces of lumber or plywood and the steel frame from channel bolted to the floor. With new steel you'll need several hundred dollars but with surplus it would be about half that. Still several hundred. Ha! Anyway, the suggestion to hire the local professional sounds good to me, even if only to get a plan in place. BE SURE!

On the tail post it looks like the heat affected zone is close to the joint. The particular joint could have been subjected to a rapid cooling. I would splice in a new one and move on. The sky isn't falling, you can stress relieve around your fuselage without turning it into a twisted mess by careful use of your torch. You may not need to but now you are concerned and I can understand why. There are so many opinions on stress relieving or not and I won't enter into that debate. I personally don't stress relieve fuselages but I always do engine mounts. Do a lot of research when reading internet opinions, including mine.

Another vote for sleeve splice. It'll be plenty strong, no one will ever be able to see it, and you should be able to get some pretty low profile welds that won't show through the fabric.

Don't be afraid to enlist some pros, or at least more experienced guys. You'll get a good final result, and learn something from them regardless that you can use the next time something similar occurs.

How many people have seen steel fuselages crack that were attributable to weldment stress? I'm honestly curious.

Kevin wrote:There are so many opinions on stress relieving or not and I won't enter into that debate.

Thanks, I don't really want to get into that debate either.

I don't know anyone that is a certified weld inspector. I was getting certified when I left my previous job but that was 4 years ago and never finished. The A&P that looked at the welds was of the same opinion as me; some of them aren't pretty but they are airworthy. We are still deciding what to do about stress relieving . For the post we are just going to splice in a new section. I'll have my friend that helped me the other night, who is a professional welder, TIG it then I'll stress relieve it. He is good and I doubt it will even be noticeable once covered in fabric.

I am amazed that cracked with just your body weight... What did Bob have to say about that?
If it was GMAW then I would not be so surprised, but GTAW is supposed to be as good as O/A in terms of heat soaking the area, according to most.

You might like to consider re-heating the bottom cluster to a nice cherry red, just because tail wheel area will take a pounding over the years? Very easy & safe job seeing as you have the gear, and provided you take your time.
I am guessing you asked Bob about stress relieving too? I know he doesn't bother with it because he uses O/A welding.

Sorry to see that's happened Jon, I know exactly how you feel. It's not nice, it raises lots of niggley little questions in the back of your head.

Battson wrote:I am amazed that cracked with just your body weight... What did Bob have to say about that?

It wasn't even my body weight. I was sitting on a shop stool pulling with both arms; I could have broken it with just one arm and I'm not even that tough. When I called Bob I said, "I broke off the tail post at the upper longeron" and he responded, "Wow, you must have dropped something heavy on it." When I told him it was TIG welded and that I was just straightening the post the little bit he was not surprised. I can't quote what he said but it was basically: yeah, you have to be careful with TIG and you really need to stress relieve it.

I'm still thinking about what to do about stress relieving; I'm slowing things down and more completely thinking things out to prevent further issues. The tail section and the area around the cargo door will get stress relieved because they flex the most, I'm not sure about the rest of the fuselage yet. I'm going to call Bob again and pick his brain some more.

There are lots of thoughts running through my head but we're moving forward and will work through the issues as they come.

Yep, that's the way to do it alright.
I tried not to think about future problems or the schedule until the problem on hand was dealt with, otherwise it becomes too stressful at times like this. Big expensive thing that the fuselage is.
We ended up having problems which aren't dissimilar, my fault, and I had to bring in the professionals for advice and support. Now it's all done, I am glad I did. In the end, you always get through the problems, it's just a damned hassle at the time!!

It's good that you're going through a process to decide what to do.

Off the top of my head, I would be making a few small test pieces with GTAW joints, stress relieving some in the same way you would the fuselage, then bending them all to reassure yourself of what needs to be done. The findings will guide your thinking.

If it were me, and assuming you can stress relieve a cluster at a time without the rest of the structure moving, I'd target the highest stress points. You might choose to do more. The wing spar fittings, wing strut fittings, gear & gear strut fittings, engine mount fittings, clusters around the cargo door, important clusters in the belly, and cluster at the tailwheel. If that takes you 30 minutes per cluster, you're talking a weekend's work at most. Small price to pay for peace of mind. Bob can advise as to which other welds might be highly stressed. Advice from me is worth what you've paid!

But you may find some test pieces set your mind at rest. You had massive leverage on that weld that broke, the completed fuselage will have no situations like that.

Battson wrote:You had massive leverage on that weld that broke, the completed fuselage will have no situations like that.

+1. Few other joints would ever be subjected to that kind of strain.

That must have been pretty upsetting so early in the project, but sooner or later you would have had some kind of issue. I think the thing to remember is that building anything is really a series of small steps, and the trick is to keep moving forward. You seem to be on the right track to fixing this, and thinking about what it means to the whole structure.

When I was rebuilding and old wooden boat a crusty old guy told me that I should never leave a piece of wood on the boat that I was not happy with, as it would haunt me forever. Good advice. Take your time, do it right, and you will end up with an amazing aeroplane.

If those were TIG welded the guy sucks. I had the same thing happen on my plane years ago when we first welded the tail cluster up using tig.. but it cracked out 3 days later with no stress on it. Since then, I tig the welds, then heat with a torch to 800+ and wrap with kaowool and let them cool slowly. No further issues since I started doing that. I am a CWI and I flip out over most of the welds I see on aircraft. No way would they pass any code known to man, yet they have been flying for 60+ years.

I say sleeve that joint as well and keep moving forwards, but while I was welding it up, I would heat that cluster up with a torch and wrap it in insulation just for grins. Otherwise, your going to be looking over your shoulder and sucking the seat up your butt every time your TW hits a bump.

Zzz wrote:

Battson wrote:You had massive leverage on that weld that broke, the completed fuselage will have no situations like that.

+1. Few other joints would ever be subjected to that kind of strain.

I do recognize this fact but in my opinion it should not have failed, especially in that manner. I really wasn't pulling on it that hard because I knew the kind of stresses it was being subjected too.

One step at a time hopefully doing it right the first time.