Airborne Magazine

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Ultimate Bi Plane

by Dr John Erbrederis


Since the introduction of the Ultimate Biplane to the modellers, there have been rumours that the full size Ultimate is an enlarged version of the miniature aircraft design. In fact, the true story has quite an unusual twist.


Gordon Price is the designer of the Ultimate Bipe which has been through three successive model changes - the first being the 10-100. This model was considerably shorter and squatter than the Ultimate we are all familiar with. The 10-100 was followed by the 200 and finally the 300h.p. version, the 10-300 - the high performance and aerobatic bipe prototype that was named Blue Hawk.

In an unusual twist, the now famous Blue Hawk is owned by noted aerobatic pilot Joan Osterud of California. She is currently reworking the 10-300 to improve the trim and has contacted model producers for advice on minor improvements.

There is a unique co-operation here between amateur modellers and builders of the full size bipe.


In the 1970 International Tournament of Champions for R.C. aerobatics in Las Vegas, the Ultimate biplane almost cleared the board of honours being placed 1st, 3rd, 4th and 5th in the top five.

First place was achieved by a then 18 year old Chip Hyde and 3rd place went to well known champion, Wolfgang Matt.


I decided to cut out all formers, ribs, fuselage sides etc. and reduce a pile of balsa, spruce and ply to kit form. I just feels nice during construction to go to the box of formed components and just build away to your heats content.


Plane pic

Glue the doubler to the fuselage sides and follow by adding the spruce longerons to the top of these sides and below the stabiliser position to act as a reinforcement. Now add the 6.5mm balsa triangle longerons to the lower edge.

Epoxy former 1 into position followed by formers F2 to F6 - use either steam or Windex to assist tapering the fuselage from F4 to F6. Glue the 6.5mm square balsa spines to the turtle deck and nose deck followed by the 6.5mm spruce nose deck spines that will support the aluminium top wing cabane struts.

Stand back and have a look, the Ultimate Biplane is starting to take shape.

Add former C2 and the cockpit floor.

At this stage fit the engine mount to F1, glue the tank floor into position and trial fit the fuel tank, engine and throttle push rods.


Build up the fin/rudder and stabiliser/elevator structures directly over the plan form 6.5mm balsa. The plans are straight forward here and you should find no problems - construction is easy and rapid. Pin the tail feathers into place on the fuselage and install servos and push rods at this early stage - it's much easier now than doing it later when the fuselage has been sheeted.


Plane Pic

The cabane structure is easily built up from 10 x 2mm aluminium strip that is both cheap and freely available at most large hardware stores. This structure is externally mounted to the nose deck for easy assembly and maintenance should it be bent on a ground loop! Fit the cabane struts to the spruce or bass longerons with 4/40 bolts and captive nuts.

It is critical for good flight performance to ensure the top wing has a 0° angle of attack - I suggest you glue a temporary template above F2 and F3 to ensure equal distance to the front and rear of the cabane support.

Glue the underside nose plate (3mm ply) and ply (or hardwood) undercarriage support structure into place - fit the dural undercarriage into place and tap the 2 x 1/4" threads to bolt this to the fuselage. Add formers F1B and F2B for the air cooling duct. Sheet the top and bottom nose decks with 3mm balsa which is also used for the turtle deck. I use Windex to assist contouring - instant cyano loves Windex and will bond Windex soaked balsa immediately and forever!


Cut out the cowl backing plate from ply or 3mm custom wood - in fact, I used customwood for nearly all the usual ply applications - it is easier to cut, doesn't feather on the edges like ply, easy to shape and just loves the cyano adhesive. Glue the 9.5mm balsa top and sides between the backing plate and the nose block, wait until hollowing out the nose block, fitting the cowl to the fuselage and installing an exhaust system before using 3mm balsa sheet to contour the bottom of the cowl. Use the three 1mm piano wire pins fixed to F1 to locate the backing plate and now fix the cowl to the fuselage with two bolts from the cowl nose ring (counter sunk) and locating into the front of the engine mount arms - phew!


Construction here is straight forward - there is no dihedral and the top and bottom wings are exactly the same. No washout is used.

Follow the usual technique of pinning down the lower spruce spar directly over the plans covered in Glad Wrap over the building board. For this I use a common, hollow ply domestic internal door - these are inexpensive, flat and present no problems to using pins.

Glue the ribs, aileron spar and leading edge into place. Join the wing panels, add ply wing joiners WJ and ply mounting brackets B1 and B2. Add the 1.5 balsa webbing and complete the D section by sheeting between the leading edge and the spruce spars.

The centre section trailing edges and ailerons are shaped from 12.5mm balsa. Cut out the centre section trailing edge from one piece for strength as a wing joiner. Fit aileron torsion rods to lower wing only.


The Ultimate was covered in Profilm , two rolls of red, one roll of blue and one roll of silver.


  • Spend time setting up the top and bottom wing incidences to 0°.
  • Accurately balance the Ultimate as per the C of G on the plan. plus side to side balance.
  • Wheels Spats - I purchased mail order ABS Supersportster 40 wheel spats - a number of local companies supply similar fibreglass spats, any of which would be suitable.
  • Note canopy and fibreglass wheel spats for the Ultimate biplane are now available from Airborne.


Plane Pic

The Ultimate Biplane plans suggest a .46 size 2 stroke engine. The model will fly very well with this engine. With a .60 size, the performance will be exhilarating.

I chose an ASP .75 which is really over the top.

The exhaust muffler was custom made by fellow club member, David Strutt - it is a Pitts style, totally enclosed by the cowl and enhances the overall appearance of the model with twin pipes poking out below the cowl.


The Ultimate Biplane is a highly aerobatic model but totally predictable - it flies on rails! The following are suggested initial settings.


Ailerons 5mm up and down Rudder 30° each way Elevator 15° each way


Ailerons -20° exponential Rudders -40° exponential

this softens any inadvertent rudder input during elevator control Elevator -10° exponential


Plane Pic

Well, I don't know what you people are like, but I usually pick a quiet time to test fly a new model - a day when it is most likely there will be few if any other members present - you see, I get nervous with a crowd of onlookers! I chose a fine, clear, windless Saturday morning but on arriving at our flying field, I couldn't believe the number of car in the car park.

I had forgotten that this particular day was a major working bee for our club (Greensborough Model Aeroplane Club) to improve the site drainage - there were trenching machines, tip trucks, piles of crushed rock and upwards of forty members present!

In this situation, you leave the model in the car boot and pretend you knew all about the working bee. You pick up a shovel and spend the next few hours moving crushed rock. I went home at the end of the working bee and returned two hours later expecting to find the flying field deserted and ready for the Ultimate's maiden flight.

By this time the crowd had grown and there was something of a party atmosphere! When the Ultimate Biplane was unloaded the members gathered around - this plane sure does grab attention.

Poor John, anxious enough to test fly a new plane, but to have to do it in front of the whole GMAC committee, top gun model pilots etc!! Well, what do you do in this situation? Amongst the crowd, I saw a friend and expert grade pilot - Russell. You guessed it, I asked him to do the honours.

At 3/4 throttle the Ultimate Biplane rocketed along the strip, tracking true and responsive to rudder input. A touch of up control at 20 metres and the plane is into a straight, gentle climb and looking great.

At about 30 metres, Russell did a short crosswind leg and then into the downwind leg of level flight. No trim adjustments were required - hand off flying within 15 seconds of take off.

Russell was obviously enjoying flying the Ultimate Biplane. Within two minutes he was putting it through the full range of aerobatic manoeuvres from standard loops and rolls to sustained knife edge flight.

Snap rolls could only be described as eye popping with onlookers wondering whether the aeroplane would hold together. It did!

Vertical performance with a .75 ASP was staggering. At this stage the transmitter was handed to me. I found the Ultimate Biplane to be sensitive to all control input but accurately responsive - it really feels like it is flying on rails: Rolls to the right, to the left are good clean axial rolls.

This model is overpowered with the ASP .75 and flew quite quickly at half throttle. With slow speed flying the response was still clean and crisp with a gentle and predictable stall. Performance through the whole speed range is excellent.

On landing I was surprised at how quickly this bipe washed off speed making landing just that bit easier.

Ultimate Biplane plans are available from:
Airborne Plans Service
AU$30.80 plus AU$2.00 P&H1
Moulded canopy available AU$27.00 plus AU$6.00 P&H
Fibreglass Cowl: AU$30.00 plus AU$6.00 P&H

Plan No. 623

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