Spitfire Mk 24 (oz12493)
About this Plan
Spitfire Mk 24. Radio control scale model for PSS.
Quote: "Lots of Spitfire plans are on the market, so I just built this one with the idea of this being a one-shot deal, where I would have my own Spitfire, but no plan would be made. During the first flight on the slope I couldn't believe what I saw, and later on, others got the chance to fly my Spit and they all said the same thing: This is the most perfect model I have ever flown.
I knew I had to draw a plan for this model and here it is, she's my favorite model, and she arrived just at the right moment as I was retiring my 6 year old favorite, the Firefly. The Spitfire adds to the perfection of the Firefly by doing exactly the same things the Firefly does, but with just a touch more flair and ease. Besides, is there anyone out there that doesn't like the elegant lines of a Spitfire. The model is built in the proven manner of foam-veneer wing, and a lost mould fuselage, let's find out what there is to do.
Building: Cut two side view and top view fuselage templates from thin cardboard (such as cereal boxes), leaving the canopy, horizontal stabilizer and wing off, but including the engine exhaust bulges. Fix the side view templates on either side of a hardfoam block (pink, blue, yellowfoam, or whitefoam with 25 kg/m3 density), and cut with a hot wire. Remove the templates from the foam, and fix the top views on either side, and cut again. Remove the templates, and draw the outlines of the engine exhaust bulges on the sides of the foam block. Cut and sand the fuselage to shape, at first without touching the exhaust bulges. Once the rest of the fuselage is shaped, sand the latter to shape. Smooth with 600 grit, and cover the entire fuselage with brown packaging tape, heat-shrinking it with an iron at low temperature. Make sure the covering is leak proof, as any polyester resin, reaching the foam will dissolve the foam prematurely.
Apply a coat of de-moulding wax (floor-wax will also do the job), next are two layers of glass cloth 180 gm/m2 and polyester or epoxy resin, followed by a final layer of 80 gm/m2 and resin. Let the laminate sit for an hour, then cover it with a thick mixture of resin and microballoons.
After curing, cut the edges from the wing seat, horizontal stabilizer seat, and the end of the fuselage. Sand the fuselage to shape, using a 600 grit. Use the microballoon-layer for sanding, don't sand into the glass fiber too much, if there is a gap to fill, use filler, or some more microballoons.
The wing is from white 25 kg/m3 foam, and a total of 6 panels need to be prepared for cutting. The outer two panels are oversize, as they will have to allow for the elliptical shape of the wing to be sanded at a later stage. Look at the planfor the dimensions of the panels, and for the wing section templates. After cutting all the panels, glue the panels for each wing together with epoxy, lightly sand the joints, and veneer the wings with limba, obechi, balsa, or any other suitable veneer.
Glue 5 mm balsa into place for leading edges with white glue or epoxy, and use the same glue for the balsa wing tips. Sand the wings to shape, and cut the ailerons out. Sand ailerons from hard balsa.
Glue both wings together with the dihedral, shown on the plan. Glue the dowel with the ply reinforcement into place, and apply a layer of glassfiber on the wing joint. Glue the ply 2 mm reinforcement into place under the trailing edge. Cover the wings with solarfilm or oracover.
Make the aileron torque rods from 2 mm piano wire and a plastic tube for a bowden cable. Make sure the outer bend of the torgue rod will fit inside the wing, but make it as long as possible. The inboard bend will have to be about 1.5 cm long. Open the wing up and install the aileron torque rods, close the wing back up with scrap balsa, and sand smooth.
Glue the balsa/ply bulkhead into the fuselage, as well as the ply F1. Use epoxy for glueing into the fuselage, but use some sandpaper to roughen the spots where the glue will be applied. Drill the hole for the dowel, fit the wing onto the fuselage, and drill the hole for the nylon M5 bolt. The wing fairing is made from scrap balsa, and this is fairly easy if you use a little trick. Draw the outlines of the fairing onto the fuselage. Use cyano to glue 1 mm balsa strips onto thefuselage, and keep cutting it down so you can still see the outlines. Once the layer of balsa is thick enough, sand a flat surface onto the balsa. Now you can glue thicker pieces of scrap balsa onto the fairing. Fit to the shape of the wing, and sand to the correct shape.
The tail surfaces are cut and sanded from balsa, and covered with solarfilm or oracover before installing onto thefuselage.
Make a 2 mm piano wire torque rod for the elevators, and hinge them onto the tail plane. Glue the elevator onto the fuselage, cutting the solarfilm or oracover off from the spots where glue will be applied. The angle of incidence should be around 0. 5 to 1 degree but will generally be all right if you made good fuselage templates from the plan. Glue the vertical stabilizer onto the fuselage, and hinge the rudder to it.
The model will gain realism in flight if you add a pilot, so make the effort, then glue the canopy into place with epoxy.
Make the oil scoop from hard balsa, and cover it before gluing it into position. Make the oil coolers from 5 mm balsa, sand to shape and cover them before gluing into place. Make the exhaust stubs from balsa, and glue them into place.
It's easy to cover the fuselage with the same film as the wings, and it keeps the weight down since there is no need for paint or filler.
There is ample room in the fuselage for the radio gear, but try to keep it as far ahead as you can to reduce the amount of lead you'll have to add to get the center of gravity right. The CG position on the plan is the ideal spot, making the model perform quite well in weak winds, but preventing her from doing accelerated stalls. The aileron servo is in the center of the wing, and the torque rod system works well.
Flying: As mentioned in the beginning of the article, the Spitfire was simply delightful to fly right from the start. I did play with CG positions and control deflections, but quickly came back to the values shown on the plan. The Spitfire flies at a very realistic speed, and is nicely stable. She'll respond to any control input immediately and honestly. Stalls are only possible by pulling the nose up into a climb, and quickly bleeding the speed off. Upon reaching the stall the model will drop the nose, and pick up speed. Pulling a hard, steep turn will usually not get the model into an accelerated stall, when you do get one, the Spitfire will wallow without anything nasty happening.
Spins are possible, they are steep and easy to recover. The model will pick up a flatter attitude, and will turn quicker during inverted spins, recovery is easy. Flat spins are not possible.
Roll-rate is a good 160 degrees/sec, and beginners may want to reduce the aileron-deflections by 1/3. There is no adverse yaw, and there is no problem doing 5 or more consecutive rolls along the slope. You have to push the stick forward quite a lot to maintain inverted flight, otherwise there is no problem to keep on flying like this. Strangely, the model doesn't seem to like to be flown on elevator and rudder only, but it was not designed to do so. You will be able to get it to turn, using rudder only, but there will be a lot of slipping involved, keep the bank reduced to a minimum because the model will not recover from steep turns by rudder only.
Anyhow, this is just fooling around, aerobatics are a true delight, as the model responds very honestly and quickly. The Spitfire performs well in weak winds, and it's such fun trimming the model to do it's own passes along the slope edge, giving you the chance to enjoy it's clean lines.
So there you have it, another Spitfire plan, but this one is well worth building. Give it a shot, I know you'll fall in love. "
Spitfire 24, Quiet Flight International, August/September 2000.
Direct submission to Outerzone.
Supplementary file notes
Article pages, thanks to RFJ.
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User commentsCan we some how end this practice of so-called experts tell neophites to sand styrofoam with 600 grit sand paper when the styro foam has a sanded finish of about 60 grit which cannot be sanded any smoother.
james R. Olson - 26/09/2020
Actually styrofoam can be sanded very smooth. It won't be glass smooth and will need filling/covering for a good surface finish but it can be sanded smooth, certainly smoother than 60 grit paper.
There are plenty of examples of styrofoam models being sanded to shape and covered in tissue, brown paper, film/tex etc. That would not be possible if it could not be sanded smooth.
Noted designer/builder Chris Golds has often used sanded styrofoam on his model, finished with a coat of pva and then film.
Also Paul Jansen has designed and built many models using this technique, very succesfully, so I presume he knows what works for him and is passing that knowledge on.
Martin Hodgson - 27/09/2020
The fuselage is supposed to be a lost foam glassfiber construction. The article does not mention how to lose the foam. Perhaps that was taken for granted, among potential builders.
perttime - 27/09/2020
600 grit? I have sanded common white styrofoam up to 1200 grit myself. All it takes is careful progressive application of finer and finer grit, wet-and-dry applied wet. With the initial coarser grades take care not to drag individual foam spheres out or you run the risk of scoring your surface. Each extra hour worth of care will save you two extra hours of filling and re-levelling.
The 'secret' is patience, light touch, several different sanding blocks each attuned to the type of contour you're tackling, and frequent cleaning of the abrasive surface.
A well smoothed foam surface is a pretty sight in itself, a pity it has to be covered as Martin describes.
Miguel - 27/09/2020
Hi Perttime, perhaps you won't like this but in less enlighted times the lost foam method consisted of after the GF was fully set a good amount of a strong styrofoam solvent like acetone was poured inside and stirred, and the resulting goop was poured away and disposed off. Absolutely not to be done at home, and test it on a spare cured GF patch first just in case it eats that up too!
I suppose using an electric cutter for foam core wing spar troughs would be more civilised.
Miguel - 27/09/2020
A some what safer alternative solvent for expanded polystyrene foam is petroleum naphtha. Lower volatility and much higher flash point than acetone.
Jan Novick - 28/09/2020
If I recall, from an article Paul Janssens wrote for QFI magazine, after curing he dug out as much as he could via the canopy and wing cutouts. That would get the majority out. He then poured some (I think) cellulose thinners in to melt the remnants. He then peeled out the brown parcel tape, along with the gooey mess, to leave a clean fibreglass fuselage.
Martin Hodgson - 28/09/2020
I hope you people "love the smell of napalm in the morning" because I'm seeing something close to one of the formulations of exactly that! I advise very soft landings on models made using this "styro + petroleum distillates" method.
Miguel - 28/09/2020
I always find it useful to know what grit folk use, I often start there but it depends a lot on the particular material and paper.
Mike Chantler - 29/09/2020
That's correct, Mark, of course that 1200 grit is far too much for most modelling purposes, you'll need much less than that for say a brown paper covered surface. An engine cowling for a smaller scale model would require finer treatment.
Miguel - 01/10/2020
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