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Aerobat

by Bob Folie

Plan No.655

Aerobat

Plan Detail:
Plan No. 655
Price: AU$48.00 (3xSheets) 
plus P&H (AU$4.00 within Australia).

Order Details:
Order On-Line

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(03) 9333 5100
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PO Box 30 Tullamarine,
VIC, Australia, 3043
We now have the answer: - The "AEROBRAT", a very attractive realistic looking model, easy to construct & very easy to fly, is aerobatic and also very forgiving, so let's get started.

The best way after studying the plan thoroughly, mark out and cut all components out, I photocopy all components off the plan, place the photocopy face down on the timber and with a very hot iron, iron the back of photocopy. This process transfers the component shape onto the timber. To make the assembly of all the sections easier, place all components of the sections in plastic bags and label them accordingly.

tail feathers

I chose to build the tail feathers first. Lay the plan out on a flat building board and cover with grease proof paper or plastic film to protect the plan. I purchased clear vinyl from one of the "cheapie shops" for this purpose. Lay the components out on the plan to trial fit. I use lead sinkers to hold the components in position. When happy with the fit start gluing the components together, I use C.A. type glue for this purpose; it is very light, very strong, and very quick drying. The lead sinkers also hold everything flat till the glue dries.

Repeat the same steps for elevators, fin, and rudder. When these components are assembled, lightly sand the faces to remove any prickles or high spots. Next with slow setting C.A., glue the soft 1.5 mm balsa skins onto these completed frames. When glue has set, leading and trailing edges can now be sanded to shape. Also bevel the leading edges of rudder and elevator. The fin can now be glued into the tailplane making sure it is square and true. All the hinges can now be temporally fitted and checked for true fit and sufficient travel.

wing

Next we will start on the mainplane, once again lay the plan out on the building board and protect with greaseproof paper or plastic film.

Place the lower main spar and again hold down with pins or lead weights, also do the same with the aileron spar. Fit and glue rib W1, making sure it is angled for correct dihedral, now fit, and align and glue ribs W2 through to W13 with C.A. glue. Fit and glue the upper main spar. The cross-grained sheerwebs can now be fitted and glued between ribs across upper and lower spars.

The upper 1.5mm balsa wing sheeting can now be fitted from main spar to leading edge.

When the glue has set the wing half can be removed and the same steps taken to assemble other half of the wing. Fit the undercarriage blocks between W3 and W5 using epoxy glue on both wing halves.

The slot for the dihedral brace can now be cut into ribs W1 through to W4. The two wing halves can now be glued together with the dihedral brace DB1 using epoxy glue. Fit and glue dihedral brace DB2 and 12.5mm support blocks and scrap balsa infill on front edge. The lower front 1.5mm balsa sheeting can now be fitted from lower main spar to leading edge.

With a long piece of sandpaper glued to a flat piece of wood, carefully sand the leading edge till the sheeting is flat with the ribs. The leading edge can now be fitted and glued.

Thee aileron controls should now be fitted, I decided to fit servo's into the outer wing panels instead of using bell cranks. Either way it's up to you. I also fitted a very thin walled plastic tube through ribs to take the servo leads.

Fit balsa blocks for the hold down bolts between ribs W1 & W2. Sand the aileron spar and hold down blocks to the contour of the ribs. Now fit the 1.5mm balsa aileron capping. The remainder of the upper and lower wing sheeting can now be fitted together with rib capping.

Chamfer the aileron leading edge spar to the profile shape of the aileron, then lay the 1.5mm balsa sheeting over the protected plan. Glue on leading the edge, then ribs W5a through to W13a. Fit 3mm ply between ribs W8a & W9a for the aileron horn mounting. Sand a chamfer on the trailing edge of lower sheet to line up with upper surface of ribs, then fit upper 1.5mm balsa sheet. Repeat above steps for other aileron. I leave the drilling and fitting of the wing locating dowels until the wing is being fitted to the fuselage.

The wing tips are laminated with 12mm balsa and cut roughly to shape then glue them to wing and sand to final shape.

Fuselage

Assemble the fuselage frames F3, F6, F7, & F8 as per the plan. Lay the fuselage sides on a flat building board with the tops together. Fit and glue 6.5mm X 3mm spruce longerons, fit and glue DB1 1.5mm ply doublers, fit and glue rear fuselage doublers. Fit and glue 12.5mm balsa triangle longerons.

If you have a fuselage jig it makes the assembly a lot easier. I will describe my method using the jig.

The fuselage can be assembled in the jig and aligned without glue to check the fit of every part. When happy with the alignment and fit, CA glue can be applied to all joints. It will wick in and make a very strong joint. Epoxy was used for 12.5mm balsa triangle to former F1. The 3.5mm balsa tank floor and sides can now be glued into position. Fit the 6.5mm square stringers on upper deckings. Fit and glue fin/tailplane assembly, checking for correct alignment.

Position the engine mounts and a tapered block to give correct side & down thrust with the centre of the propeller on the centre line of the fuselage. Mark and drill holes through former F1. Now fit and glue blind nuts on the inside of the firewall. The upper 3mm balsa sheeting can now be fitted and sanded. Remove the fuselage from the jig and fit bottom 6.5mm square balsa stringers and lower rear fuselage 3mm balsa sheeting.

Fit the wing to the fuselage leaving 0.4mm gap between the front of the wing & former F3, also the top of wing to fuselage. I used scrap pieces of 0.4mm ply for this purpose. I use rubber bands to hold the wing in position. Check the incidence of the main wing to centre line & also the tailplane incidence. Adjust the wing seat till the correct incidence and alignment is attained.

Drill a 6.5mm holes through former F3 into the leading edge of the wing & insert wing dowels but don't glue them at this stage. Now drill 6.5mm holes through the rear wing mounting plate [W M]. Fit and glue softwood tapered packing blocks and blind nuts. The cockpit floor can now be fitted & glued into place. Remove the wing from the fuselage & permanently glue wing retaining dowels into the front of the wing.

Cover top centre section of wing with gladwrap or wax paper & refit wing, sandwiching .4mm ply fillet between bottom. Apply CA glue along the joint between wing fillet and fuselage. Glue in contoured gussets between the base and fuselage sides. Fit and glue trailing edge fillet.

Remove wing from fuselage, and then lightly sand the upper edge of the fillet to contour the curve. Fit and glue soft 1.5mm balsa sheet on fillet from F4 back. I used super light balsa filler to build up the front part of the fillet to match the rear section. Refit the wing then fit and glue the front bottom of fuselage. Fit scrap balsa infils on bottom of wing to match bottom of fuselage.

The cowl is built up from 12.5mm soft balsa sheet, carved & sanded to shape. Completely sand complete model prior to covering. I chose to dope & tissue the fuselage, tailplane; fin, rudder & elevator then painted with pressure pack enamel. The wings were covered in solarfilm.

Fit out the cockpit as desired, a nice instrument panel here adds to the overall appearance. Now fit canopy.

Motor

The motor chosen for the prototype is an ASP61 2 stroke with a Pitts type muffler. Install motor, fuel tank, radio gear, push rods & horns, undercarriage, & tail-wheel at this stage.

Controls were set with the following throws. Elevator 12mm up & down, rudder set at 40mm left & 40mm right. Ailerons were set at 15mm up &15mm down. Travel was measured at fuselage end of control surfaces.

Lets Fly

The "AEROBRAT" should be now ready to eat up some sky, so off to the local field to test this bird.

All systems were double checked, the model fuelled up and the engine started. A range check with engine running, all systems rechecked then the model was taxied up and down the strip to check ground handling, so far so good. Now to test the handling in the air.

With the AEROBRAT lined up on the runway the throttle was slowly opened the speed increased, Travelling straight down the strip with no control input at about 3/4 throttle it rose from terra firma slowly climbing out, wings perfectly level, course straight, I stood there amazed watching the AEROBRAT flying by itself, completely hands off. Back to reality I'd better turn this bird around before it gets out of sight. Response to control is very smooth but positive. After a few circuits for the camera and to get the feel of it a few aerobatics were tried, no problems, this bird flies on rails & just keeps going where you point it. Now for some height to check the stall characteristics. With the throttle closed as the speed drops off up elevator is slowly applied the tail drops slightly, at the point of stall, the nose drops but the wings remain level and very predictable.

After about 1/2 hour in the air & other pilots checking it out, I lined up for a landing, low power the angle of decent was excellent with good control. The mains touched down followed shortly by the tailwheel.

A stunning performance I have never had a model fly off the drawing board without trim adjustments before, I always imagined other pilots were telling a fisherman's story, but it does happen.

SUMMARY

This "AEROBRAT" is a pussycat with bite, a good looker, and it looks like a real aircraft. It would make a very good second or third model for new or experienced fliers.

A very rewarding model.

Parts cut out
Kit of Parts. Generous use of plywood makes the Aerobrat very solid

 

 

Tail and Fin Frame Construction
Tail Surfaces are flat, simple to build over the plan.

 

 

 

 

 

Wing section showing undercarriage block epoxied into ply wing ribs.
Wing section showing undercarriage block epoxied into ply wing ribs.

D-box sheeting along wing stiffens the structure remarkably
D-box sheeting along wing stiffens the structure remarkably

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

My fuselage was built using a jig for true alignment. All parts were assembled the cyno drops to hold in all joints.
My fuselage was built using a jig for true alignment. All parts were assembled the cyno drops to hold in all joints.

Engine cowl was shaped from balsa blocks. I made a fibreglass cowl from these.
Engine cowl was shaped from balsa blocks. I made a fibreglass cowl from these.

Complete model ready for covering. Clean straight forward lines with beefy control surfaces
Complete model ready for covering. Clean straight forward lines with beefy control surfaces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bob the builder proudly holds up his model, very pleased with it's flying performance
Bob the builder proudly holds up his model, very pleased with it's flying performance

 

 

Aerobat in flight

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