About ten years ago I designed a 25" span biplane that flew on a 1.5cc diesel engine. This model, which performed nicely but was definitely not for those of a nervous disposition, was published in Radio Modeller as a free plan called Yuppy Love.
Yuppy Love was a very simple cabin biplane. With ailerons on all four wings. It was a quirky looking design, and rather appealing in its own way. Shortly after publication, one enthusiastic reader sent in a photo of his twice-size version; his reason for it was that he liked biplanes but not the usual cabane struttery. Apparently, he wanted a nice, slow flying model. Well, with the vast wing area of a 50" span version, he got what he wanted.
Some time later, while looking in a DIY store, I spotted a box containing a plastic decorators table. To show how versatile the table was, some box art depicted a model aircraft - that's a neat little biplane I thought.
Then the realisation began to dawn that the design shown looked rather familiar... it was Yuppy Love down to the last detail, including the plan. Nobody ever asked if they could copy my photo or plan! Lets just say that had they asked in the first place, it would have been a lot cheaper.
Anyway, a little while ago, searching for inspiration, I decided to go down the road of making something for an O.S. 40 Surpass, that would be not too hard to build, rather different, and fun. I decided on a one-and-a-half times Yuppy Love with improvements. And so Toot Sweet was born. It came out at just 36" span, but with 657 square inches of area, which is over four and half square feet - combine that with a weight of 66oz., and you get a wing loading of 14.5 ounces per square foot. This is getting down towards fun-fly figures, and yet we're talking about a model that will fit into a normal car fully assembled!
Toot Sweet is very simple to build; in fact, it's as easy as a monoplane, and even simpler than some because you don't even have a dihedral wing to join.
Now you know the history, but before deciding to build Toot Sweet, consider how it flies. Take-offs are a dream, she will ROG in a few feet from concrete, and quite rough surfaces present no problems. If your flying field really is poor, Toot Sweet can be hand-launched quite safely.
She's very responsive, rolls are fast, and flick rolls even faster - do two, and you have to wait for your eyeballs to stop rotating in sympathy with the model. Loops and bunts are smooth and easy; make the loops too tight, and she will try to screw out of them, but that's normal. Inverted flight is easily achieved, with hardly any down trim needed. A gentle squeeze on the stick does the trick, because any more will have her climbing.
There is one aerobatic manoeuvre in which Toot Sweet surpasses everything that I have ever flown. In knife-edge the model will follow the horizon with hardly any top rudder at all! Apply a touch too much top and she tries to do a knife-edge loop. Use a bigger engine, say a 48 Surpass or even a .52 FS, and she would almost certainly perform a knife-edge loop.
With the wing section employed, and all that area, Toot Sweet can be flown very slowly. In a breeze she'll land like a helicopter - just be ready for one of those sudden lulls as the wind drops to nothing. Having the ability to fly slowly certainly doesn't mean she's slow; pile on the coals, and Toot Sweet really nips around the sky. The lack of drag-producing struts makes her very fast for a biplane.
This model is agile and responsive, but doesn't want to bite... its just pure fun.
Building Toot Sweet is very easy, though having said that I will just run through the various stages as there are one or two areas which, though simple, are a little different from run-of-the-mill practice. Start off with four pieces of 3/32 sheet, 4" wide. You could use 6 x 3 wide if you wanted to.
Join them edge to edge, to form two very wide sheets. Mark and cut out two fuselage sides, plus the 1/32 ply doublers, then glue the latter into position (I find that Thixofix is the best contact adhesive for this job). Add the 1/4 x 1/8 longerons.
Using some scrap trailing edge to form a tail post, join your two sides at the rear with F4. Do this over the plan. When dry, add F5, F6 and F7. Still working over your plan, pull the front end together and join with F3, F2 and F1 in that order. After making sure the model is straight, fit some wing seat treblers.
At the tail end, add 1/4 x 1/8 strips under the tailplane platform and then add the platform itself, followed by the 1/8 ply tail skid and strut mount. Locate and feed your snake outer runs, and then cover the rear of the fuselage with 1/16 sheet, making sure the grain runs from side-to-side. At this stage, its a good idea to fit the wings, along with their relevant 1/4 ply plates for the blind nuts. This allows you to drill through F2 for the front wing dowels.
Have got those vital holes drilled correctly, you can fit the 1/4 ply undercarriage mounting pieces, together with the related 1/4 balsa gusset and triangular stock, the latter being added on corners of the former / fuselage side joints. The undercarriage itself is made from two pieces of 8 swg wire, following the conventional torque rod idea, i.e. legs held to the bottom of the fuselage via double nylon saddle clamps.
Add the engine mount, and then the motor itself. Spot-glue the nose ring to your spinner using 1/16 scrap sheet spacers placed between spinner and nose ring to achieve suitable clearance. With the prop, spinner and nose ring bolted to the engine, build the cowling with four pieces of 1/2 sheet, filling in the corners with scrap. Shape it to blend into the nose-ring and your fuselage is complete.
Both sets are identical, except that an opening for the servo bay has been added on the upper surface of the lower wing, and to the underside of the upper wing. Note that the servo connection must be at the top on both - a bit fiddly in the case of the upper panel, but it can be done using a clevis.
The spar is webbed on both sides to form a box spar, which is very strong and resists warping. However, its not warp proof, so take care to keep the wing straight. If you do get a warp, it can be removed with the aid of a heat gun.
Cut all the webs to length first. Pin down your bottom spar, glue on the tip ribs, then position all the other ribs. Fit the top spar next, taking care that you only glue it to the tip ribs. Now, working from the tip, glue on your webs, slide the next rib up to them and glue; move on to the next pair of webs and repeat this process, until all are glued in place. When this assembly is dry, fit the leading edge and trailing edge spar. Add all corner gussets, hinge reinforcement blocks, and the bell-crank mounts. Install the bell-cranks, with their relevant push-rods.
Add sheet to the wing, noting that it fits between the spars. Cut away an area for each servo bay, then add a 1/8 liteply floor (actually, being upside-down, its a roof for the top wing!) to each cavity. As for servo mounting, I like to put mine on Radio Active brackets (Cat. No CA 190).
You'll have to shape the ailerons from 3/8 sheet, because there's no stock trailing edge material of the correct size available. Use part of this for the t.e. centre portion too, gluing it in place. Add ply plates, which spread the wing bolt loads; next, glue on the liteply tip ribs. Skin the bottom surfaces of your bell-crank bays with 1/64 ply - personally, I've found that this is the neatest and easiest way to provide slots for the aileron push-rods, and you might too.
Okay! The wings are now ready to be fitted to your fuselage, so you can drill holes through F2 for the dowels, once again making sure everything lines up perfectly.
The back end is built up as shown on your plan. You can use quite a hard wood for these parts but make the elevators out of medium soft sheet. Don't forget those hardwood strut mounts - the tailplane mount is quite narrow, and they'll prevent it from being knocked loose in a less-than-perfect arrival.
You can use K&S streamlined brass tube for the struts, or just flatten the ends of ordinary round tube.
COVERING AND RADIO
Solarfilm Supershrink Polyester was used to cover my model as it shrinks really well and doesn't bubble in the sun. In addition, it's excellent for compound curves, although you won't find many on this model. Solartrim rounds off the scheme.
Radio installation is simple. The servos are mounted low down, just in front of F2; above them is a shelf of 1/8 balsa on which the receiver is fixed via some Velcro. Meanwhile, the battery sits under a Sullivan 4oz. slant front tank.
Control throws are: ailerons 3/8 each way on high rates, 1/4 each way on low rate; elevator 5/8 each way on high, 1/2 each way on low; rudder 2 each way on high, 11/2 each way on low.
Check that the C of G is exactly where shown on the plan - this is a nice, safe starting location from where you can experiment later. Hope you enjoy Toot Sweet.
Name: Toot Sweet
Model type: Sports aerobatic biplane
Wing area: 657 sq. in.
All-up weight: 66oz.
Wing loading: 14.5 oz. / sq. ft.
Rec'd engine range: 35 - .40 two-stroke, .40 - .48 four-stroke
Rec'd no. of channels: Four - ailerons, elevator, rudder, throttle