8KCAB Frame mods

Big Ed

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
1,938
Location
Tampa, FL
What frame mods are recommended when restoring a 70's Decathlon?

Ones I have heard rumors of:
  • Larger gear leg openings to accommodate aluminum gear
  • Bracket for new style fuel shutoff valve
  • 2nd lug for lap belt anchors
  • Tab on spar carry thru for shoulder harness yoke
  • Baggage door (not doing that one)
  • Larger tab for mixture vernier??
What else?

Am particularly interested if they have extended the stringer braces on the belly to get some clearance between the elevator cables and the fabric.
 
Dale would be the guy to talk to about that. Ideally, you could bring the frame to ACA and let them re-jig it and do all of the updates/repairs it might need. If that's not an option, and I don't blame you if it isn't (especially with gas over $4 per gallon!), a list from Dale with parts from ACA and a good local welder will be the next best thing. There are also some frame reinforcements that you didn't list but Dale will be able to help you out.

Bart
 
I'd love to take it up there, but that is a long 2 day drive, and I doubt I could get it done on my timeline. Am hoping to have the frame ready for assembly in 30 days or so.

I have a good welder here, so I just need plans or photos. Do you have any pics of the reinforcements?

What is the best number to reach Dale at?
 
Spoke to Dale and Chad. Here is what I got from them:
  • Baggage door frame
  • Gear leg fairings
  • Fuel shutoff valve bracket
  • Mixture Vernier tab
  • 2nd seat belt lugs
  • shoulder harness center lug
NOTE: there are no structural improvements to the Decathlon fuselage such as gussets. There are some in the gear leg area for the Scout, presumably due to different mission, but they have not seen any issues with Decathlons. Good to know it is a strong structure, proven over time.

I will definitely do the gear leg fairings, Vernier tab, and 2nd seat belt lugs. All 3 are simple mods with minimal welding and add value. Parts with drawings are available from ACA. No brainers.

Leaning away from the shoulder center lug. It involves welding a truss into the roof frame so reinforce the spar carry thru. Apparently a stronger approach from an engineering perspective, but I see no immediate operational or value benefit. Either way I'm gonna have Hookers installed safely.

Also leaning away from the new style fuel shutoff bracket, mostly due to cost. If I swap the valve, then I have to swap the gascolator too, and pretty soon I have added $1K to the project. Parts are not available for the old valve, so we will inspect it closely and decide what are the odds of getting another 25 years of service out of it. I use the damn thing maybe once a year, so that's not a whole lot of cycles.

Still on the fence about the baggage door. It does not appeal to me much for bag loading, but I can definitely see the merit for ease of battery maintenance. The ACA guys are big advocates of it, and it seems to have some market value. But also adds $1K to my project price.
 
On the shoulder harness mount - one way to avoid augmenting a structural failure with force in the middle of an easily collapsible tube is to put the mount on the left side, at the cluster.

On the J3, putting the front shoulder harness in the middle of the tube separating the rear spars is a prescription for aiming the collapsing tube at somebody's head - at least if you land in a place where the wings hit trees or poles.
 
Bob Turner said:
On the shoulder harness mount - one way to avoid augmenting a structural failure with force in the middle of an easily collapsible tube is to put the mount on the left side, at the cluster.

On the J3, putting the front shoulder harness in the middle of the tube separating the rear spars is a prescription for aiming the collapsing tube at somebody's head - at least if you land in a place where the wings hit trees or poles.
Click to expand...

That is the logic that Melhalf used in redesigning the center attachment point with a truss behind the tab. I have not seen the diagram, but assume it goes to the next set of clusters back. Bart, any chance you have a photo?

I guess my question is whether the alternative of an H harness attached at 2 points shoulder-width on the carry-thru is sufficiently strong. Any Bellanca aircraft with a Hooker has been set up like that for decades.
 
I am using two separate straps in the Cubs, mounted at the cluster. Very comfortable - in the front you do not feel the offset angle. In the back you don't even see them.
I dislike the "Y" shoulder harness. I would imagine an "H" would be worse, and probably get tangled pretty good while you are trying to fasten it.
 
Big Ed said:
That is the logic that Melhalf used in redesigning the center attachment point with a truss behind the tab. I have not seen the diagram, but assume it goes to the next set of clusters back. Bart, any chance you have a photo?

I guess my question is whether the alternative of an H harness attached at 2 points shoulder-width on the carry-thru is sufficiently strong. Any Bellanca aircraft with a Hooker has been set up like that for decades.
Click to expand...

can do but won't be until tuesday. watch the headliner video maybe, it is probably visible there.
 
Heard rumors of additional tabs on side for windscreen attachment. Anyone know of this?
 
Picture of new windscreen tabs. Looks like those conflict with the existing brackets. Will ask the factory tomorrow how viable that is as a retrofit.

Have to make final decisions tomorrow on A) whether to consider hauling the frame to the factory, and B) which options to go with, so I can order the parts from Chad. I want to get the frame blasted and powdercoated during June, which means I need to get the welding done in the next 2 weeks.

Right now am leaning YES on the baggage door and shoulder harness attach point, and NO on the new fuel valve.

tabs.webp
 
Stuck in analysis paralysis. Have decided YES on baggage door, NO on fuel shutoff valve.

Still stuck on the shoulder harness attach point.

Pros:
  • Stronger
  • Neater installation of headliner
  • Able to say frame brought up to 2022 specs
Cons:
  • Heavier
  • Cost for parts and labor to weld
  • Must replace my H harness with Y harness in custom colors

Thoughts? Final decision must be made tomorrow morning.
 
What's the list so far of welding work that you're definitely doing? If you're already doing a pretty good amount then just do all of the things you want to do and stop thinking about it. If the list has been whittled down to just a few things then forget the stuff you can't decide on and get going.

The days are quickly going to turn into weeks and then months so you have to get stuff done and forget about it being perfect. Unless you want perfect but then you can't worry about the time it's going to take.
 
Might be too late to avoid a major fuselage overhaul - if so, do everything that will make you happy.

But if you are still at the stage where a little sandpaper, epoxy paint, new wood, and new fabric will do, you can be flying when that engine pops out of overhaul. If you work diligently.

Then, buy a dirtbag Decathlon, take it apart, and indulge yourself in as much perfection as makes you happy. Remember, a year on the ground is a significant percentage of your remaining lifetime.
 
Bob Turner said:
Might be too late to avoid a major fuselage overhaul - if so, do everything that will make you happy.

But if you are still at the stage where a little sandpaper, epoxy paint, new wood, and new fabric will do, you can be flying when that engine pops out of overhaul. If you work diligently.

Then, buy a dirtbag Decathlon, take it apart, and indulge yourself in as much perfection as makes you happy. Remember, a year on the ground is a significant percentage of your remaining lifetime.
Click to expand...

Shooting for a middle course between those two approaches.

I am getting an overhaul to new limits from a reputable shop, and those are not cheap. I really did not feel good about hanging a $30K engine and $10K worth of new or overhauled accessories and components on a 44 year old airframe. Florida is extremely hot and humid and corrosion is a constant challenge. That frame really needs to get stripped bare and properly finished if it is going to survive this climate.

But I also don't want to overspend or get into a multi-year project. So anything that can be done with the engine and cover on gets deferred unless it really makes sense to do it now.

So, my plan is to strip the frame, do selected welding upgrades, and have it powder coated. Then install new wood, control cables, and fabric. I will reuse the old glass, interior, and floorboards, since those can be replaced at any time. Will do the electrical update service letter, but all other fuel and electrical components are "on condition". No changes to instruments or avionics; I have my panel exactly like I want it already. I MIGHT build a new harness and convert the fuse panel to breakers IF I have time.

If everything does really well, I might be ready to receive and hang the engine in 4 months, by the end of September. Worst case, I will take several weeks off for Christmas and try to finish by the New Year.

Once I get it flying, I can backtrack and do the interior and other cosmetic stuff whenever it suits me. Can also get metal wings when the time is right.
 
Bartman said:
What's the list so far of welding work that you're definitely doing? If you're already doing a pretty good amount then just do all of the things you want to do and stop thinking about it. If the list has been whittled down to just a few things then forget the stuff you can't decide on and get going.

The days are quickly going to turn into weeks and then months so you have to get stuff done and forget about it being perfect. Unless you want perfect but then you can't worry about the time it's going to take.
Click to expand...

YES:
Baggage door
Gear leg loops
Lap belt 2nd tabs
Vernier tab
Windscreen side brackets
Gusset at panel cluster (if factory confirms legit)

NO:
Shoulder harness tab
Fuel selector valve bracket
 
Just pulled the trigger on all parts. I went ahead and ordered the shoulder harness truss and fuel selector bracket. My welder can take a look at them and we can decide on the spot what to do. Price was not prohibitive on either.

Also going to get powdercoat specs and frame prep instructions from Chad.
 
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