I've never tried an exotic motor on this plane, but with it's bog standard geared Speed 400, the performance will surprise most of you. Mine has a 45 degree climbout and will loop continuously from level flight with ease. Even without a rudder, the plane will take off from the ground with ease, even soft snow.
Don't expect great speed from the plane, I designed it for close in aerobatics and good low speed handling. I fly mine from some very restricted spaces, the ability to turn on a sixpence is useful...
Roll rate is whatever you want, and with it's symmetrical wing section, inverted flight is just as good as the right way up.

Design notes and stuff...

Designed as an electric fun-fly plane, this one is is built light, and I mean *really* light! After designing 3 other Speed 400 powered planes, I've got the hang just how little wood is needed in an airframe, trust me... don't even think about beefing up this one. Just remember, you're aiming for just 18oz AUW.
The basic shape of the plane is based on one of my previous glow powered designs, although for the second one (the yellow one) I built, I changed the shape purely for cosmetic reasons.

After trying several motors, umpteen prop and gearbox combinations and running the setup through Motocalc, I came up with the following power train:

Graupner Speed 400 6v motor... other makers motors are marked differently; so no, a (for example) Multiplex 6v motor isn't the same.

3:1 gearbox... I like the ones that Irvine (UK) do, also available from Al's Hobbies. They are also marked "MAXX".

8 cell Sanyo 500AR or 600AE pack... A 7 cell pack will need a different setup, so you're on your own there! I'm shortly going to check out the new high capacity NiMH cells that are being made.

10"x4" prop... I make my own so this could be a difficult one... I've also used a 9"x6" with success. Buy a wooden prop and sand a decent airfoil shape on the blades, thinning it as you go...

Speed controller is up to you... don't suppose there's much difference between them nowadays.

Building...

If building the main wings doesn't get you swearing, you're a more patient man than me! I've used 1/32" quarter grain balsa for the ribs, if you can't get hold of any, or find they are just too fiddly, use very light 1/16" balsa instead. Spars are 1/8" square spruce or bass, just make sure it's straight. I spaced the ribs using the 1/32" vertical grain shearwebs, so don't worry too much if the rib spacing doesn't match the plan.

On my first prototype, I used Hitec HS81 servos in the centre of the wing. You could probably get away with a lighter 9 gram servo. Don't bother using anything heavier than balsa servo bearers.

The wingtips are shaped especially to be easy to cover... don't change them!

The fuselage starts life as two identical side frames built over the plan. I make a set of struts and formers all to the same width to make joining the two fuselage sides easier.

A view of the former that also serves to locate the wing.

The cut-out matches a block that's glued to the central shearweb in the wing...

The block in this case is beech, but an offcut of 1/4" square spruce would do the job.

Looking in the canopy opening. The floor that the receiver is velcro'd to is 1/16" balsa with the grain running across the fuselage. It's got enough strength this way to support the battery pack which lives under the front decking. This 1/16" balsa floor is supported on the fuselage sides by a 1/8" square length of balsa that runs from the firewall back to behind the servos.

Notice the shape of the former that supports the rear decking 'cos I can't be bothered to draw it on the plan for you!

The 9 gram servos for the rudder and elevators are fitted before covering, behind the wing seat. The servo bearers are 3/32" liteply.

Note the wing bolt plate, liteply with a 4mm threaded hole. The wing-seat is reinforced with 1/8" sq. balsa strip, which also helps hold in the wing bolt plate.


The motor is held into a rolled 1/64" ply tube with tape. The rolled tube extends back into the fuselage through a hole in the firewall and is strengthened with liteply braces. A wrap of masking tape makes the motor a good push fit into the tube.

Inside view of the balsa sheet cowl. Use the lightest balsa you can find...

The cowl fitted to the fuselage. I use a couple of bits of diamond tape to hold it in place.


The undercarriage is fitted to an liteply former at the rear and hard-points at the front. The front hard points are small lengths of 1/4" sq. spruce inside the fuselage. The clips that hold the undercarriage are made from lithoplate.

Some detail of the tail end... The tail-skid is glass fibre rod with a small plastic bead stuck on the end.

Rudder and elevator horns are brass or alum'n alloy tubes, flattened at one end. They glue into holes drilled into the control surfaces. Perfectly good enough for the expected loads they are subjected to.

Note also the piano wire joiner between the two elevator halves, and the short spruce brace across the centre of the tailplane.

A couple of places (above) where I've used tape to stop the covering from splitting when I've made a hole in it. The first pic is where the servo lead exits from the top of the wing, the second is where the wing bolt passes through the covering on the bottom of the wing.

I used tape hinges for the ailerons, although I've found that tiny hinges made from draughting film work well on these light models. Use as you would any other mylar hinge, the difference is that the draughting film is thinner.

The carved foam canopy is hollowed out to a thickness of about 1/4". 1/8" balsa braces locate it on the fuselage.



The battery pack is used to balance the plane. Use a foam spacer behind the firewall to set the position of the pack. Velcro holds the pack in place, aided by a a foam packing piece (see pic above).

Any problems? Just give me a shout...

Have fun!

You can download the plan for free, subject to the following conditions:

1. You don't publish the plan on any other website. Link to this website instead.
2. You don't sell the plan to anyone else.
3. If you give the plan to anyone else, you give them any documentation that goes with it.
4. You don't publish the plan for profit.
5. And if you possibly can, send me a picture of your finished plane.

Available format: A ready to print Adobe Acrobat (.pdf) file that'll produce tile pages that you can stick together, dxf and TurboCad.

Sp400aero.pdf

Sp400aero.dxf

Sp400aero.tcw (TurboCad)