Sonic Boom plans are available from: Airborne Plans Service for AU$44.00 plus P&H2 (AU$3.00 within
Is it a jet? Is it a flying wing? Is it the US Navy's latest secret weapon? What is this dashingly different model that's emerged out of Airborne's design department?
It's SONIC BOOM and it's sure to create a "BIG BANG" at the model flying field. Don't be fooled by its complex looks. Sonic Boom is simple to build, can be powered by any .40 -.60 engine, requires 4 channel radio and is very easy to fly ... ... Sounds like the basic requirements for a sports trainer. There's nothing to fear.
In the air Sonic Boom is nimble, aerobatic and has a very wide speed range. Depending on throttle setting it can be slowed to a crawl or go like a rocket. A .60 motor will give it unlimited vertical climbs but a good .46 would be almost as good.
It won't take long to convince any sport flyer that n Sonic Boom would do them good, let's take a closer look at how the model comes together.
BUILDING THE MODEL
The model is built as a single unit with nothing detachable other than hatch panels for access to fuel tank and radio gear.
The centre wing section is parallel with addition of leading edge cuffs and of course the outer wing panels.
The fuselage and tail surfaces are built up over the wing to become one integral unit. Although it may look like a flying wing the Sonic Boom does in fact have 3axis control with ailerons, elevator and rudder even though the moments are relatively short. Control surfaces are large and with twin rudders this model is designed to respond well at any speed.
The wing is built upside down over the plan as the line over the top spar is straight. The minimal dihedral is created by tapering of the underside surface of the outer wing panels.
Cut out all ribs complete with tabs as shown on the plan. These tabs are used to maintain wing symmetry during construction and are removed when the underside surface is ready to be skinned.
Protect the plan with grease proof paper before assembling wing.
Pin down the top spar after splice joining between W2 and W3 to allow for sweep back. Glue the ribs onto the spar then add the bottom spar which will now be on top. (This is more confusing than inverted flying!) Add the leading edge, aileron spar, tail spars and trailing edge.
Add the sheer webbing between the main spars.
Cut to size and epoxy the hardwood undercarriage mounting blocks into the wing ribs,
After pre-joining the 1.5mm balsa sheets the underside wing surface can be skinned, I chose to fully sheet the wing as the weight increase to having it an open structure with cap strips would be negligible. Also it looks better to have it fully skinned.
After this the whole structure was separated from the plan using a steel ruler underneath to lever the pins out.
Then the servo tray for aileron and rudder was fitted into the servo bay which is accessible from underneath through a hatch. Bellcranks and control rods for ailerons and rudders were then installed.
Set these up carefully because when the top surface is sheeted there will no longer be any access to the bellcranks.
Build up the ailerons with the triangular ribs and balsa sheet. Trial fit with hinges and test fit aileron rod connections before fully sheeting wing.
I left the final bit of wing sheeting and set up of bellcranks until after the fuselage was built.
Build up the wing tips from balsa and glue onto wing.
Cut out the fuselage sides and doublers. Glue them together for a left and right side. Add the 1ongerons.
Cut out the firewall and formers, then glue them onto the fuselage sides. Draw the ends together and check for true alignment.
Build up the entire top and bottom between F1 and F2 with balsa blocks and sheet, sand the edges round to shape. Cut away the rear hatch between F4 and F5 and tank hatch between F1 and F2.
Fit the engine mount onto firewall, then with engine mounted trial fit tank, fuel lines and throttle cable. Build up the nose cone from balsa blocks and triangle with nose ring and spinner in place. Carve and sand the nose cone to shape.
Trim and fit the moulded plastic canopy, blend into rear block.
TWIN BOOMS and FINS
Cut out the boom sides from balsa sheet.
Build up the fin framework over the plan, remember to build 2 fins. Then glue the fin frames in between the boom sides. Sheet the fins both sides, and also sheet the top and bottom of the booms.
The rudders are cut from solid balsa sheet and hinged onto the fins.
Trial fit the booms onto the wing. Finalise installation of any control rods and linkages and complete and sheeting of the wing.
Glue the twin booms onto the wing and tail area.
Glue the fuselage onto the wing and fill area behind tank hatch with balsa blocks sanded to shape.
Bend the main undercarriage wire to shape, hold on with straps onto wing.
Fit the nosewheel strut up front. For steering I used a separated servo connected with a Y-lead to rudder function.
The nosewheel steering servo was fitted onto the inside face of the tank hatch but could be installed anywhere in the wing or fuselage.
The model is now complete, ready for covering.
COVERING and FINISHING
I used white and Navy blue Profilm to cover my Sonic Boom. It irons on like a treat and is my favourite covering.
The bold US Navy insignia and lettering was computer cut vinyl. The number 654 refers to the Airborne Plan number which belongs to Sonic Boom. To contrast the underside I used orange with black bat motif. The underside outline remained white.
Although it is a sport model the finish of the model can be made to look quite "scale like" with a bit of thought and careful application of films or paint. The extra effort will be well worth while.
Install the engine, fuel tank and radio gear. Connect all control linkages etc.
Fit the wheels onto the undercarriage legs. Balance the model to C.G. marked on plan. The battery was placed rear of the top hatch and the receiver under the elevator and throttle servos.
I used an OS .61 motor so a smaller engine being lighter may require repositioning of battery to balance the model properly. Also check for lateral balance.
FLYING THE MODEL
As I don't fly and my son was too nervous for test flying we asked local bloke and well known flyer, Les Davis to take her up. So on a breezy Sunday, Les took her down the runway full throttle about 100ft, then up elevator and she bolted skyward at about 60 degrees. After a mixture of loops, snap rolls, inverted, knife edge and stall turns, my song Greg, took over and was in love with it - doing slow fly bys with only 3 clicks of throttle and gliding in at idle.
Controlling the model is smooth and easy. Having a short tail moment the Sonic Boom is really manoeuvrable but not to the point of being radical. Slowed down the model is stable and won't drop a wing. Flat out it's a real rocket that will roar up to the clouds vertically!
The plan recommends a .40 - .46 2 stroke engine but as we had a 61 OS spare, in it went, hence the climbing ability. I feel that a .46 would have no trouble giving a surprising performance.
Transport was on my mind as it is one piece and I thought of carrying it on my Commodore roof rack but found it fits in the rear of the wagon alright with the tail over the rear seat.
In summary the Sonic Boom is an impressive looking aircraft on the ground and in the air which raised plenty of eyes. It's something out of the ordinary and is a delight to fly. Ask my son!
SPECIFICATIONS Sonic Boom
Type: R/C Sports Model
Sonic Boom plans are available from:
Plan No. 654
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).
This page was last modified on the 21-May-02