The kit aviation boys do this all the time. Bet ya there’s something here that would work:
My knowledge here is extremely limited, but eons ago I did own several pairs of Hexcel skis. These skis were extremely light and featured an aluminum honeycomb core. They also flexed easily and freely. In other words, the honeycomb did not stiffen the skis. It merely served as a spacer between the top and bottom plates which were then wrapped in fiberglass to create a torsion box that was laterally, but not longitudinally stiff. I would be very reticent to bond a honeycomb panel to your beautifully prepared door without a knowledgeable structural engineer telling you it will perform as you intend. If you had to remove it, it could make a mess of your fine work.
Specificity in epoxies I like. I used an aluminum based epoxy as filler in the doors, bootlid and bonnet. It’s specifically formulated to bond to aluminum. We used it in industry to repair aluminum pump casings. Tough stuff, though if you sand it within a couple of days not bad to work. Feathers well.
Sounds like sage advice.
Interestingly, Hexcel skis stopped manufacture after a few years mainly because they could not solve the vibration damping issue. At speed, skis will tend to get quite lively as they are basically a spring. Over the years, various devices have been used to dampen skis with varying success. Hexcel found it needed to add weights to the tip and tail to control the harmonics, but this turned their light weight ski into something heavier like every other ski on the market.
It could be a spring that returns to its at-rest condition might be an approach. I can imagine a problem if a honeycomb structure should permanently warp and take the flatness of the skin with it.
On the other hand I might be contemplating a solution in search of a problem.
Kraft board is quite a good and lightweight stiffener (used bonded bits of it in various race car panels) but again, it needs to kept dry and the bonding has to be perfect.
Race car bodies don’t take as long to fix, and have a fairly short half-life.
That’s never happened here JL before - perhaps we need to create a badge?
Have you done the math yet, and figured out just how much growth that skin will see on a 40 Deg. C day? The door inner restraining it is going to grow as well.
You could bond some Peltier elements to the inner surface.
3 Likes
The coefficient of thermal expansion of aluminum is .000023 m/degree C. To do an accurate calculation you would need to know the exact size of the doors at the factory as well as the temp of the metal when they were stamped. Someone better at math than me will need to do the calculation. It works the other way as well. How much shrinkage will there be on a bitterly cold day?
…hooked to a Web-linked software package, downloadable to your smart device, programmed to apply just the exact voltage, based on the ambient temperature, such that the panel is cooled–or heated–to the exactly correct temperature, to perfectly balance the attendant expansion/ contraction.
With the option of a multi-colored LED indication panel on the dashboard, from blue to red, indicating the applied voltage, as you drive.
Do I quality for a Jag-Lovers Overthink(c) badge?
The chosen color of the paint effects surface temps, for sure BRG will get a lot hotter than white.
BTW, better check how much room you have to stick something on the inside surface of the doors, those pocket inserts get real close to the skins on the 120. That was the case with mine, had something like 1/4" to 3/8" to work with fitting an original insert. I put up a photo a while ago showing reinforcements I installed for body finishing. Truth be told I don’t see how gluing something to the inside of the door is going to prevent metal expansion from the heat of the sun.
The fact this car will be BRG is what triggered the original question. I had my E-type - also BRG - parked outside in the driveway in the sun while working on the 120 and after a few hours you could fry an egg on the bonnet.
I expect when a tight, almost flat door skin heats up and expands it will introduce oil canning into the panel. I’m thinking Lovell’s observation might be pertinent, that is the original 1/8" thick tar paper glued to the inside may have had a greater function than just sound insulation. While I was thinking it would be a good time to laminate in a stiff material when I take the doors off to shoot the inner surfaces I’m thinking now that I should see what the extent of the problem is first, before applying a solution (I’ll take that badge now, Andrew). Maybe start off with a similar material to what was there originally.
1 Like
Because it’s not going to.
oh my word Nick, that is a wonderful job. if i lived two lifetimes i could not get anywhere near that skill level.
Damned near drove me to drink to see it in person!
…why??
Because whenever I try to fix a small dent, the car ends up looking like it’s been in a rollover.
Reminds me of a song from my early youth (1955): "Son, you’re gonna drive me to drinkin’ if you don’t stop driving that hot rod Lincoln (Jag content: it was a 12 cylinder).
1 Like
Having done this sort of calculation innumerable times during my engineering career, I think I can say with some confidence that the doors on these cars are not going to get hot enough to make thermal expansion an issue. Also, the coefficient of thermal expansion is not a constant, it varies with temperature, so things shrink less in extreme cold than they grow in heat. If you are using some sort of non-metal reinforcement, plastics generally have much higher expansion coefficients than metals.
1 Like
Thank you, Phil. But it’s been half a lifetime I’ve been dragging this project across the country so the projects:lifetime ratio is not impressive.
Actually, you were drinking at the time, Andrew. You were holding a glass of good cab, looked at me and said without the slightest hint of humour, “You’re insane.”
I was hoping an engineer would offer a perspective, Mike. Having to learn to weld and shrink aluminum for this resto I was amazed at how well it conducts heat and how much it moves when heated up v steel. Where the door skins are most rigid, like at the tight 90 degree radius bend at the bottom and the larger crown up top, and where it’s braced as open box sections on either end, it takes more heat to get the metal to move. But if the entire aluminum structure heats up evenly at the same time maybe no movement at all.
Where’s that Overthinking™ badge, Andrew?
1 Like
…well, yeah.
You own not one, but TWO Jags.
1 Like