David Hipperson describes his 54" span plan build model - 27/1/11
For all that its gangling, angular appearance made the Fieseler Fi156 one of the most ungainly aircraft of the Second World War, the Storch - or Stork - was also one the most capable machines of its type. Whether working as an ambulance, artillery spotter or courier, the Fi156’s remarkable short take-off and landing (STOL) characteristics made it the perfect utility vehicle in support of troops - on both sides of the conflict! Virtually every captured example was pressed into service by the Allies; even Monty acquired one, which Churchill borrowed when he wanted to review the progress of the D-Day landings.
Conceived by Fieseler’s chief designer, Reinhold Mewes, and first flown in 1936, the Storch answered the German Air Ministry’s demand for a STOL aircraft in unequivocal style: given a light headwind, the Fi156’s slow-flying wing allowed the machine to take-off in a little over 60 yards, and land in just over 30! Powered by a 240hp air-cooled Argus As 10C, and using wholly conventional steel tubing and fabric fuselage construction, the Fieseler achieved this gravity-defying act with its remarkable wooden wing, which featured fixed slats running the full length of its 46’ span, and Fowler-type flaps that increased the wing’s area by 18%.
Though credited as the last aircraft to be shot down over W.W.II’s western front (downed by pistol fire from a Piper Cub, no less!), the Storch actually had a busy post-war career, being produced as MS500 by the French manufacturer Morane-Saulnier, and as the K-65 Cap by the Czech company Mraz.
My version of the Storch belongs in the ‘cartoon scale’ section of our hobby - easy to build and fly, but with enough of the original’s look about its lines to be instantly recognisable.
Construction, in fact, could hardly be any easier: the fuselage has been slimmed down to a balsa box with the minimum of fiddly bits; the wing has been stripped of its ailerons, slats and flaps; the tail surfaces are flat sheet; and the undercarriage reduced to absolute basics. The result, however, is a model that has all the storkiness of the full-size aeroplane that inspired it, yet is light enough to fly on any decent 400-size motor (given the right cells and prop’), and which provides heaps of fun using a simple three-channel radio set-up to control elevators, rudder and throttle. It’s so docile, in fact, that it would even make a great trainer.
If I may offer you one small piece of advice before you get started, though, it would be to choose your wood carefully: use light, springy balsa and avoid both the soft white pithy stuff or the rock-hard stock that’s to be found at either end of the quality range.
Using the two triangles on the plan as guides, cut the two fuselage sides from 1/8” sheet. The curve on the bottom edge isn’t super-critical, so just get as close as you can; the rest is just a series of straight lines, so you can make quick work of it with a scalpel and long steel rule. Next, cut out all the liteply components, including the piece for the fuselage floor, which needs to be marked with a centreline, plus the stations for the formers and undercarriage. While you’re at it, you may as well use a 1mm drill and make the holes through which the undercarriage will be stitched into place; it’s easier to do it now rather than when the fuselage is built up.
Having glued the formers to the fuselage floor, taking care to check that they’re square and vertical, you can attach the sides. Start by gluing the front in place then, once set, work down the fuselage until you can eventually pull the sides together at the tail. Spending a little time and care in getting the fuselage box true will pay dividends later in terms of flight characteristics.
You can now fit the servo mounting plate or bearers, and either line-up the pushrods or install the ny-rods. Whichever type of actuator you decide to use, however, remember that the control surface loads on this model are minimal, so choose rods that are as light as possible - otherwise you’ll only be adding excess weight aft of the centre of gravity.
The cowl cheeks and upper section of the nose are made either from planking or 1/32” sheeting laid over a shaped plug of soft balsa or blue foam, which should be hollowed-out for lightness. I also made the nose itself from balsa, using a small rotary sander to remove the excess wood inside the block, and to form the cooling and prop’ shaft holes.
THE FLYING GREENHOUSE
With all its glazed facets, the Storch’s cabin looks as though it should be very fiddly to make. In practice, though, it’s actually quite easy: the basic framing is fashioned from 1mm-wide strips of 3mm balsa glued to the fuselage sides, with 1.5mm sheeting laid over the top. If you cut the pieces of sheeting a fraction oversize and them trim them in situ, you’ll find that it doesn’t take long to make a neat and tidy job of things. Just don’t get carried away and forget to fit the 1mm plywood tabs to which the upper end of the main undercarriage struts will be attached; you need to glue these to former B before fitting the windscreen.
The upper and lower surfaces of the rear fuselage are now sheeted with 1/16” balsa, and - if you’re keen to recreate a little of the original’s tubing-and-fabric character - you can also add the stringers. These don’t impart any strength, so if the spirit doesn’t move you, don’t worry!
This is the easiest job of the whole build although, because the surfaces are quite large for a model of this size, you should take care to use the lightest 3/16” balsa that you can find to avoid any unfortunate C of G consequences. If you like, you can pare away some of the redundant wood by drilling holes in the surfaces - just make sure that you leave some meat around the mounting points and hinges! The tail struts, on the other hand, aren’t load-bearing, so can be cut from a piece of scrap 0.8mm or 1mm ply.
If you want to take the pursuit of lightness to extremes, you could make the control horns from printed circuit board, but proprietary fittings will be fine, especially if you use those designed for light models.
BUILDING THE WING
The first task is to make yourself a ply or alloy rib template and cut out all the ribs from 3/32” balsa (or, if you can find it, thinner 2mm stock). The ribs are all basically the same, the variations being where they’re trimmed in different ways for sheeting or to fit around dihedral braces. These braces are made from 1/8” birch ply, though they could be built-up from laminations of thinner stock, providing that you use epoxy to glue them together.
The trailing edge is ordinary proprietary stock, as light and straight as you can find, while the spars are made from hard 1/4 x 1/8” balsa. Being of the belt-and-braces persuasion, I also webbed the spars using 1/16” sheet, fitted between the ribs with the grain running vertically.
When it comes to actually assembling the wing, the flat lower section means that you can work directly over the plan, which further simplifies what is an already straight-forward job. Start with the centre-section, noting that the depth of the ribs needs to be reduced to accommodate the sheeting that’ll be added later. Follow the centre-section with the wing panels but don’t, at this stage, fit the inner ribs 1 and 2, or sheet the upper leading edges.
Once the centre-section and panels have set, they can be joined by weighing-down the centre-section on a flat surface, and then trimming the length of the spars in each panel until each one fits accurately into place with a dihedral that gives about 2.5” (65mm) underneath each tip rib. A size block or cardboard template will help with this job.
When you’re happy with the fit of the wings, glue the spars to the ply dihedral brace; slow-setting glue is best here, as it allows time for last-minute adjustments. When all this has been done, you can fit the two inner ribs and stiffening triangles, then add the upper leading edge sheeting, which you can shape using a razor plane and sanding block. You also need to notch the trailing edge to let in the dummy aileron extension, and make the wing tips from balsa or blue foam.
The strut fittings, meanwhile, are fashioned from tinplate and can either be glued into a slit in the end of the 1/4” square mount, or screwed into place (if you do use screws, harden the screw holes with a drop of thin cyano’ to give the threads better purchase). Made from 1.5mm aluminium welding rod and 1.5mm balsa, the struts themselves just clip to these mounts, and have no structural role. Welding rod is an ideal material as it’s light and malleable, and can be shaped to form bends of about 2mm radius, with judicious use of round-nose pliers. The wire’s then attached to the balsa with a few drops of cyano’ plus cotton binding top and bottom, prior to being covered.
Finally, give the whole wing a light sanding preparatory to covering.
THE GANGLY BITS
Making a sprung undercarriage at this scale didn’t seem a very practical proposition, so my design is for fixed gear. To give the model the right appearance, however, I’ve built it in the extended airborne state, as that’s how it’ll mostly be seen.
Now, I know that I’m not alone in finding undercarriages a bit of a chore, and I’m also aware that good quality music wire isn’t cheap. So, to avoid yourself ending up knee-deep in expensive rejects, you might find it helpful to make a mock-up of the undercarriage using the soft iron wire from a coat hanger: it’s cheap and easy to handle, so you can work out all the lengths and angles before you get into wire-bending proper.
When shaping the gear, you need to be aware that the rear (main) legs and their axles don’t lie in the same plane; if left flat, the legs would give the wheels too much toe-in (that’s to say, they’d be pigeon-toed). To avoid this, you need to twist the axles rearwards slightly, so that the wheels run parallel or nearly so; a little toe-in is permissible, toe-out is not. Once you’ve cracked the geometry using piano wire, you’re ready to start bending music wire (The shock-absorbing compression strut, by the way, can be modelled using bits of ny-rod, or the plastic handles from cheap paintbrushes).
The undercarriage is fitted by first sewing it to the base of the fuselage with strong thread, then drawing the legs together and binding / soldering them. For binding, I use fuse wire, but a few strands of thin copper from old speaker cable will be fine. Incidentally, make sure that everything is clean and bright before soldering, and don’t forget to make the lower strut eye, which can be bent-up from any soft, solderable wire.
When it comes to the wheels, lightness is again the key. Happily manufacturers seem to have got the message in this respect, and those dreadful heavy wheels of yore are now being replaced with lightweight wheels in a good choice of sizes.
Small as it is, this is an assembly unto itself. Cut the ply plate and drill it for the wire, then form the main leg - leaving off the bottom bend for the moment - and pass it through the main hole. You can sew the leg into place if you like, but a smear of five-minute epoxy will do the job. The gaiter’s made from a bit of shaped balsa with a hole through the middle. The completed plate and leg are then glued to the rear fuselage.
The finishing touch prior to covering is to glue the 1/8” keel along the centreline of the fuselage underside, and add the two pieces of 1/16” sheet around the undercarriage legs. Again, these parts have no structural value, but they do help to support the covering.
You can use almost any film or textile covering for this model as you don’t need it to strengthen the airframe, though the lighter the material the better. Before covering, I prepared the foam wing tips, the cabin, the ply fuselage base and the fuselage edges by giving them a coat of Balsaloc heat-shrink film adhesive. In the cabin area, I was quite careful to apply Balsaloc only to those areas that represented glazing or framing rather than the fuselage proper.
When you’re ready, begin with the underside. Cut an oversize piece of material and iron the centre of it along the keel, drawing it down to the lower fuselage corners, and ironing it onto the prepared surfaces; covering the forward end of the keel calls for some careful pulling and shrinking, so take your time.
The film for the fuselage sides should also be cut to a generous size, then ironed onto the stringers before moving to the cabin and fuselage edges. All this is easier to do than describe, but aim for a finish that’s as wrinkle-free as possible to really make the most of the aeroplane’s contours. Once you’ve done the fuselage, the wings and tail surfaces are a cinch! By the way, something I tried on one of my earlier versions and which you might like to experiment with, is representing the glazing with either silver or chrome film.
MOTORS & PROPS
My first Storch came out at 28oz, and flew perfectly with a Jamara HS480 Pro motor driving a Graupner 8 x 4” Slim prop’ through a 3:1-ratio Hi-mark gearbox (or Irvine, as I believe they’re branded in the UK). With a pack of 10 Sanyo 600AE cells, the performance of this set-up was excellent. My second Storch was fitted with an Aeronaut 6V motor / gearbox with a 2.07:1 ratio, powered by eight 1100HE NiMH cells and driving an APC 9 x 6” electric prop’. Despite weighing in at 30oz (due in part, I suspect, to my using Polytex to cover it), the model coped quite well on the reduced power. Even so, I decided to upgrade the motor with another HS480, using the same cells but changing the gearing to a 2.5:1 ratio. This resulted in a marked increase in power, and a corresponding drop in flight duration, which fell from 10 minutes to around seven or eight. Despite this latitude afforded by the airframe, you shouldn’t be careless about the model’s weight, and if you can build down to the 24oz mark, so much the better.
FLYING THE STORCH
Before committing yourself to the air, check that the model balances slightly nose down when supported under the wing spar. When it comes to setting the control throws, aim to have about 11/2” deflection each way on the rudder, and about 1/2” on the elevators. Once set up, all you need is a calm day for what should be the easiest part of all - flying the Storch.
I’ve found that the undercarriage’s combination of small wheels and lack of springing can make rolling take-offs a little tricky on a rough strip, so the alternative is to hand-launch the model; it’s small enough to be easily handled, and light enough to survive the odd mis-launch without damage. With range checks completed, then, and the throttle wide open, a gentle toss directly into wind is all it should take to get the model climbing away quite strongly. Once into the circuit, you should find it possible to cruise on about two-thirds throttle. Her aerobatic capability is fairly limited: the odd loop is manageable, but hardly in the spirit of the Storch. Low, slow passes are more the order of the day with this model. You don’t have to limit the model to flying only on calm days, though: she’ll handle relatively stiff breezes, but don’t forget that protracted use of full throttle will reduce flying times. Have fun and enjoy!
If you’d like to give your model more than a passing resemblance to a Storch, you may find it helpful to spend a little time looking at drawings and photos of the original Fi156. They’ll help you to get a feel for the shapes that give the full-size aeroplane its character. The sources that I used in building my prototypes include:
Hitler’s Luftwaffe by Tony Wood & Bill Gunston (Salamander Books)
Concise Guide to Axis Aircraft of World War II by David Monday (Temple Books)
Military Aircraft Markings and Profiles by Barry C Wheeler (Golden Press Pty Ltd.)
Fieseler Fi156 by Heinz Nowarra
Fieseler Fi156 Storch drawings No. 2865 (RCM&E magazine plans service)
Fieseler Fi156 Storch drawings by Warpaint (Aviation News)
Name: Fieseler Storch
Model type: Semi-scale wartime reconnaissance
Designer: David Hipperson
Wing area: 2.5 sq. ft.
All-up weight: 301⁄4oz
Wing loading: 12oz / sq. ft.
Rec’d motor: Jamara HS480 Pro
Control functions: Rudder, elevator, throttle
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