I was looking at a vacuum formed kit of a plane I can’t find in a regular form. I’m considering buying it and scratch building portions of it. But does anyone have experience with these kits?
Which plane, model & scale?
I say that because some-one will know IF your chosen subject has ever been done in plastic or resin, or if there is a conversion available.
They can be satisfying, producing something few others will have even attempted, & it can get addictive.
If not, then yes it can be done, treat it as a semi-scratch build, accept that details will be soft or missing, & you may use up a few kits sourcing props, wheels, engines, seats, etc…
Once you free the parts from the backing sheet, it’s no more difficult than a major conversion, but they aren’t a shake-&-bake either, I’d suggest you get a $5.00 kit from the sales bin to practice on, & have fun!
It will take far longer than you think, & as soon as you finish it, someone will release it in plastic!
I have built a few. They turned out okay. I make some modifications. I make a “keel” of plywood to stiffen the fuselage half bond. I trace the fuselage onto a piece of plywood, typically 3/32, cutting out the cockpit area. I then glue the halves to this keel. I also leave a slot for a wing spar. The wing spar, which I also cut from plywood, strengthens the wing to fuselage joint and sets and holds the correct dihedral. Unlike the distant path, there is so much aftermarket stuff that can be used to replace the parts that do not mold well in vacuformed styrene (wheels, LG, etc.) that the results can be very nice.
I have built one… a 1/72 Archer models KC-135, many many many years ago. It was challenging yet fun. Not overly difficult to build. It just takes patience and a bit if finesse in your cutting and sanding. In a ways, it is far more satisfying of a build because the finished results are far more dependent upon your efforts and not the kit parts.
Yes and all the comments above are very good. The addition of an internal structure is critical.
I try to buy a plastic kit that’s as near a miss as possible. For instance for my Blackburn Iris I bought a Matchbox Stranraer for the props, guns, cockpit glazing and a whole bunch of strut.
The plane I want to build is available in resin but the price tag is a bit steep and I’ve built resin many times but only with ships. Its mainly an unwillingness to spend a lot of money on the subject. and I am up for a challenging build right now. I have plenty of spare parts from botched builds in the past and a ton of styrene, bass wood, and brass rods.
Making a successful vacuum formed model is usually considerably easier than building a model from scratch. However, that being said, I have seen in my life a slow but steady decline in the number of modelers doing scratch models. That is a shame.
I started in the days before plastic. The non-flying static scale models, the predecessors of today’s plastic scale models, were made of balsa, basswood, or pine. The wings were cut to planform only- you had to carve in the airfoil (cross-section). Cheaper kits had the fuselage sawn out to profile view. You had to saw it to planform and then carve the cross-section. So, in effect, the kits were not that far removed from a scratch build. You had to do a lot of carving.
As a result, folks who began modeling were much more likely to do a scratch project when they wanted to model a subject with no kit available, or only kits at horrendous prices.
There are still a few wood kits around, some created by folks who create modern kit replicas. Doing one of those old kits is a good way to get into scratch building.
Thanks everyone. How well does the testors solvent glue work? Or should I use super-glue or epoxy?
I have a large sheet brass that is thin easy to cut. I’m planning to use a piece of it to reenforce the wings. The plane I’m wanting to build is the Soviet Yak-28P “Firebar”. Its an ugly and odd looking aircraft and thats why I want one. 
I would recommend plywood for all reinforcements. You need some gluing area, especially on the fuselage, but even a wing spar needs a good area to bond styrene to brass. For the fuselage you need something at least an eighth inch thick- thicker would be better. Only half that thickness is used to bond each side. 1/8 is okay for the spar. Since the spar would be vertical it is the eighth inch thickness that bonds to top and bottom surfaces of wing.
definitely a ‘foogly’ bird. [:P] what’s not to like?
1/48th blog here, for info & 1/72nd here for more info
Boy Phil was a good modeler. Sorry to say he passed away last year.
And yes, thats one funky looking aircraft. So maybe a basket case Forger could supply armaments cockpit etc.
Thanks for the link for the Amodel Yak28P.