T-34 spar update

[Dave Siciliano]

Flew up to Ada, Oklahoma yesterday to visit with George Braly from Gami. Several folks on the Bonanza Net got together and chipped in to assist him in deferring some of his expenses associated with solving the T-34 spar issue. The group presented George a nice plaque and over $10,000 in donations to off-set research costs.

ITMT, George showed us where the cracks were occurring, gave an explaination of what was causing them and how they were coming on a repair. All of us own Beecraft and felt that the research would directly assist us in keeping the fleet flying!!

George showed a stress test type stand that they put an airframe in and flex it to identify where the stresses transfer. He then showed us how the stresses transfer from the wing spar to the center carry through. It was very interesting!! There are nine rivits that transfer load to the carry through from the spar and the last rivit was failing with cracks around the two closer ones. don't know if I can explain it; I was probably the only non-maintenance type fella there, but the load is transferring through to the end of the attachment point in a manner not anticipated. The potential fix is a rib attached under the bottom of the wing at the attachment point that will transfer some of the load there.

All sorts of neat test stuff in the hanger at Ada. If any of you have some extra money or think flying is expensive, wait until you see what they have spent to address these issues. There was a small piece of equipment (a little smaller thatn a lap top computer) that George said costed $24,000. It's used to detect metal fatique and cracks.

They were attaching small electric circuits at critical load points that would report the amount of stress at that point. They had half a dozen of these on each spar carry through. They'd fly a plane, or put it on the test stand and measure the stress at each measuring point. Quite impressive!! This would be a great place to meet sometime (if it could be arranged). If you really want to understand the details behind the research, it's pretty impressive.

Wish Lance could have been there to provide a more technical explaination!!

Best,

Dave

 

[gismo]

Wish Lance could have been there to provide a more technical explaination!!

I've got to get to one of their seminars soon. I really like the work they do and the way they approach a problem.

-lance

 

[Let'sgoflying!]

Good report Dave, are any pics available online somewheres?

 

[Dave Siciliano]

Geesh Dave, you think I would have taken some. We were kinna caught up in the presentation. Let me see what I can dig up.

Yes, Lance. You guys were made for each other. If you go there would you just let me come and be a fly on the wall B) . Every time I go up there, I think it'll just be for a little while and I'll be on my way: they're busy--I'm busy. Can't believe the amount of time they spend with folks showing 'em round and 'xplainin things. As they go over things, I understand everything completely. Then later, when I try to tell someone else what happened it's like I have a photographic memory--but no film!! Very frustrating!! What was the show 'bout the kid growing up in the '60s that loved the little girl nextdoor? Every time he saw here, he planned all he was going to say, but it just wouldn't come out right?

Dave

 

[Dave Siciliano]

Here's a response from George. I tried to draw something on MS Paint, and didn't get far. sorry.

David,

Good to have you, again.

I don’t have any ready pictures.

However, the devices are “strain gages”. These are thin metal foil etched matrix of wires mounted on a polyamide plastic backing. Then they are “stretched” – they change resistance.

You can bond the polyamide to a metal surface and then as you pull on the metal surface, the resistance changes in a highly linear manner with the “stretch” of the metal. Amazingly simple and it is used in one form or another in almost all transducers that measure loads or pressure.

The equipment in the background consists of a 32 channel data acquisition system which can record up to 32 strain gage signals, simultaneously, and do that about 100,000 times/second.

You can fill up a hard drive, in a hurry.

Regards, George

 

[gismo]

Yes, Lance. You guys were made for each other. If you go there would you just let me come and be a fly on the wall B).

I'll be sure to let you know when I sign up.

What was the show 'bout the kid growing up in the '60s that loved the little girl nextdoor? Every time he saw here, he planned all he was going to say, but it just wouldn't come out right?/QUOTE]

Spiderman?

 

[Richard]

Yes, Lance. You guys were made for each other. If you go there would you just let me come and be a fly on the wall B).

I'll be sure to let you know when I sign up.

What was the show 'bout the kid growing up in the '60s that loved the little girl nextdoor? Every time he saw here, he planned all he was going to say, but it just wouldn't come out right?/QUOTE]

Spiderman?

Was Spiderman even around then?

 

[Dave Siciliano]

Think it was called the Wonder Years. Kevin lived next door to Windy. He had some very elaborate thoughts 'bout how to share his feelings for her (that you got to hear watching the show), but when he tried to tell her, things didn't come out right!! (Kinna like I felt at that age when girls were so much more communicative and guys had vocabularies limited to short words and grunts!!)

Back to the spar issue.
Here's a pic of the center carry through. On the bottom left and right side, notice at total on nine rivets where the wing bolt backs up to (almost in a line). This center piece transfers the stress from the wing spar through to the center section (some folk call it the forward spar carry through). Rivet nine, closest to the middle is completely failing. Rivet seven and eight are developing cracks around them. George is developing a manner in which some of that load will be transferred to the outside of the fuselage, just under where the wing comes in.

Best,

Dave

 

[Let'sgoflying!]

Is anyone able to draw labels onto the diagram to show me the failing rivets/the 9 rivets, the wing attach bolts?
Thanks - old eyes or sumthin.

 

[gismo]

Is anyone able to draw labels onto the diagram to show me the failing rivets/the 9 rivets, the wing attach bolts?
Thanks - old eyes or sumthin.

I "penciled in a line around the "rivets" (they are actually Huck-bolts). The wing bolts are not shown, but they go through the fittings (endwise between the front and rear web) in the bottom and top of the carry through structure shown in Dave's picture. The fastener's aren't failing, the problem is cracks appearing in the web surface.

 

[Let'sgoflying!]

Thanks Lance, I can't see the cracks but can see the part well enough.
If I understand... for clarification....in non-engineer's terms....

This is the forward spar carry through. The spar bolts to a fitting. (I think I am looking at a fitting - or is it a doubler that is riveted in there? I am reminded of the aluminum blocks that cessna spars attach to carry-throughs with.)
Anyway, this fitting is riveted on the inside of the carry through. The + Gs of aerobatic flight are forcing the wing up against a fuselage that want to go down. This is putting a load on the wing bolt, then to the fitting, then to the rivets that attach the fitting to the carry-through. Because of age (and corrosion in this pic?) and perhaps loads in excess of design, the carry through is cracking around these 9 rivets.

 

[Dave Siciliano]

Actually Lance, George said the number nine bolt is being plasticized. What ever the heck that means. I just no it ain't good!! Seven and eight are the ones developing cracks around the bolt.

Think about when this was designed guys: Late 1940s. These guys sure did a great job with a drafting board and slide rule.


Dave

 

[gismo]

Actually Lance, George said the number nine bolt is being plasticized. What ever the heck that means. I just no it ain't good!! Seven and eight are the ones developing cracks around the bolt.

Think about when this was designed guys: Late 1940s. These guys sure did a great job with a drafting board and slide rule.

Interesting. Several years ago my mechanic detected some looseness in one or two of the Huck bolts in the lower port side. We used the crack repair procedure sans doubler to replace the loose one(s). My mechanic said he's seen them loosen on a couple other airframes, but according to Beech, mine was the only one repaired this way. We had been assuming that the original fasteners were improperly installed. Strangely the small crack I have is on the other side where the bolts are tight.

 

[Dave Siciliano]

Interesting. Several years ago my mechanic detected some looseness in one or two of the Huck bolts in the lower port side. We used the crack repair procedure sans doubler to replace the loose one(s). My mechanic said he's seen them loosen on a couple other airframes, but according to Beech, mine was the only one repaired this way. We had been assuming that the original fasteners were improperly installed. Strangely the small crack I have is on the other side where the bolts are tight.

Well, we didn't get into details, but George does believe all this research will eventually filter down to the Barons and Bonanzas, not to even mention the aircraft of other manufacturers. The Beechcraft, of course, have very similiar structural arrangements; so, the same fix as for the T-34 may have application.

BTW, you don't have to attend the Advanced Pilot's Seminar to stop in at GAMI and ask some questions. They have guests quite frequently. If you're coming this was sometime, we can just meet up there, or, I do have a little used guest room you can check out.

Best,

Dave