The plan build article by Brian Cooper - 9/8/10
Ever since the first R/C Dart flew indoors at Olympia in 1995 / 96, there has been considerable interest in it wherever and whenever it goes out to play. Having witnessed the performance of my young lad’s rubber powered BMFA Dart, and being highly impressed, I decided to scale up the design. In fact, it was not just his that caught my eye; it seemed as though (no matter how ham-fisted the builder) they ALL flew well - much to the delight of numerous children.
As a tribute to these little rubber powered models, my first R/C Dart was finished in the same colour scheme as its little brothers, then fitted with three-function radio and a tiny 1/2 cc PAW diesel engine. Even with this miserable amount of power, the performance was noteworthy, and the handling gorgeous. It was highly manoeuvrable, yet solidly stable.
Soon, we got around to wondering what the R/C Dart might be like with more than double the original power. Enter the ‘jet’ age... well, an MP Jet actually. A 1cc high performance diesel engine, with fairly good throttle response, and enough power to go vertical. Experiments were undertaken which involved altering the sizes and positions of various wing / tail / radio components, with a view to improving the already good flight characteristics; two subsequent versions became major milestones. The Mk. 4, which we thought could not get any better, was one - and this, The Mk. 9, which has done the ‘impossible’ and taken everything one step further.
So, what’s new? Well, for a start, the Mk. 9 was developed to fly outside. It’s all very well designing a model for indoors, but let’s face it, more people prefer the field. Whilst it will never be happy in some of the rougher weather this country of ours can produce, the Dart can handle gentle breezes without too much of a struggle. Extra power and a slightly higher wing loading allow this, without compromising the superb turning circle, or the cute and cheeky handling for that matter!
Now sporting an O.S. 10 up front, this is a well balanced model, with enough power to put a smile on your face. However, if you want more, a .15 will make it a very serious Dart, that will probably out-climb an average .46 powered sports model.
So, there you go folks. Sadly though there’s a down-side which might come as a shock to some of you... If you want one of these, you’re going to have make it yourself. In other words, it is not an ARTF model. Oh gosh, fetch the smelling salts...
UP TO THE OCHE...
The fuselage is made from 1/4” sheet balsa. Cut out holes for the servos, and slots for the engine bearers; insert 1/4” ply for the bearers and servo mounts, then cover the left-hand side with a 1/64 ply doubler. Before gluing on the right-hand side doubler, cut out your servo holes. Also, put 1/64 ply doublers at the tail end, as shown on the plan. Don’t forget to glue on some triangular strip at the rear to increase the tail’s gluing area - you can do this with the wing too, if you wish.
Next, we need to make a fuel tank bay and a receiver bay, plus two covers: one on the right-hand side, another for the servos (to help keep any goo off them). All mounting holes for the engine and servos are best sorted before the wing is glued on, as are the ‘pin hooks’, used to anchor rubber bands which secure the fuel tank. Now it just needs a coat of fuel-proofer, and some drying time - so let’s get on with the rest of it.
Wings, tail, fin, rudder and elevators are all made from 3/16” medium grade balsa. The tail ‘feathers’ are simply built over the plan, though you should not glue in your control horns yet. They go in AFTER everything is built, covered, glued in place, and you have made up the control pushrods. In other words, LAST!
Begin by constructing two ‘A’ frames. These are joined to the centre sheet by four pieces of 1/64” ply, which act as very efficient dihedral braces. Joining the wings is probably the most fiddly part of this whole project. Arrange things so that you get 51/2” under each wing tip, and glue in the lower braces with cyano. It’s best to cut all the braces oversize and trim them when the glue has set. With the top braces glued on, your wing will be surprisingly strong, and ready for sanding smooth prior to covering. Regarding the latter, use Solarfilm or similar - but don’t reach for the heat gun yet. If you do, the wing will bow in the middle, and you’ll have difficulty gluing it to your fuselage. So, do it the other way round, i.e. fix wing to fuselage, and then shrink the film gently, until those wrinkles just about disappear. Be careful not to overdo it.
Once your tail parts have been covered and hinged, glue them on, and progress to the radio gear installation. To simplify this, the Rx was secured on spongy Velcro. Don’t worry about the servos being exposed because, using an O.S. 10 with its standard silencer, most of the exhaust goo ends up under the tail. Control runs are made from 20 gauge piano wire, supported at regular intervals by bits of snake inner, whilst horns are cut from 1/16” ply, and secured via thin cyano as and when each servo and control surface is centred. Easy.
Our Mk. 9 uses a 250 mAh NiMH battery, which is positioned to achieve the correct C of G. (If you plan to use a .15 engine, it might be best to push the servos back a little). Using this, we’ve managed to obtain over one and a half hours of flying time on a single charge - and it was still not flat! However, if you plan to use your Dart a lot, a spare battery or fast charger might be prudent.
There is no undercarriage to worry about, so your model should now be raring to go. Charge her up, stick in some fuel, and go fly!
IT’S A BULLSEYE!
Controls on the Dart are highly effective, and it can roll very quickly on full rudder deflection. If you’ve exponential available on your tranny, then I’d recommend using it on both elevators and rudder - especially the rudder - to help tame the model’s responses to your stick inputs.
We have minus 20% on our elevator, and minus 30% on the rudder. The stall is virtually non-existent; get her nose high, and she’ll simply sink, very gently - no violent wing dropping here.
If unfamiliar with responsive controls, you may want to reduce the throws a bit. This is where rate switches come in handy, of course.
GOOD GAME, GOOD GAME!
Tie on a crepe paper streamer, and see if you can cut it yourself by chasing your own tail. A 4ft. turning circle can be achieved with very little practice. Or, try hovering the Dart at the end of your tranny aerial, almost in a prop hang. This thing is so stable that it will just sit there in a gentle breeze. If that doesn’t take your fancy, make it dance by gently applying a little rudder one way then the other.
You could put out some balloons on the patch and try to pop them, using the prop. No? Well, how about just going for height before enjoying the long glide back down.
A lot of fun can be had with this simple little model. It’s quick to build, cheap to build, and cheap to run. What’s more, it can be flown all afternoon on a humble pint of fuel!
Try handing the tranny round at your patch, then stand back and watch - believe me, it won’t be long before even the hot shot pilots are giggling. Get your clubmates interested and you’ll soon find the patch innundated with these little aircraft buzzing around the sky.
Name: Super Dart Mk. 9
Aircraft type: Unorthodox funster
Designed by: Brian Cooper
Wing area: 650 sq. in.
Wing loading: 3.5 oz / sq. ft.
All-up weight: 1 lb.
Engine: .10 cu. in.
Fuel tank: 2 oz.
Propeller: 7 x 6”
Rec’d no. of channels: 3
Control functions: Throttle, elevator, rudder
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