BioniX and NuviX wings


What is the difference? The BioniX came first as a versatile wing for the Tanarg. Some pilots wanted more speed than the Ixess15 wing, so Aircreation came up with the Ixess13 wing. It was faster, but throughout the speed range. This solution was not ideal in a country where there are thousands of short private air strips.

Aircreation came up with the Bionix as a safe wing to cater for all needs. The BioniX has a corset in the middle which pulls on two kevlar bands along the trailing edge of the wing. Tightening this corset tightens the whole wing and changes the profile. Changing the profile does a couple of things, it reduces the amount of lift at higher speeds and reduces the amount of induced drag at the same time. The BioniX has winglets at the tips to ensure directional stability all the way up to the VNE of 185kmh (115MPH).  There are many other small details that make this wing so versatile, to see more click on the link to the Aircreation website on the right, it is in English too. The beauty of the BioniX is not in the top speed, but in the fact that it is a very slow wing to land, even at the MAUW of 472kgs.

For many machines the BioniX is perhaps too high tech and is capable of more than what can be achieved by the trike it is attached to. For this reason Aircreation came out with the NuviX wing. It has the same 15 squre meters as the BioniX, but is more suitable for trikes with lower power. It has a VNE of 165kmh (103mph) so does not need the winglets. It is also a bit lighter than the BioniX giving it a slightly lower stall speed in the slow mode. It is also about 20% cheaper than the BioniX.

The first question that people ask is why not a topless (strutted) wing. In my opinion topless is just cosmetic and despite what some manufacturers tell you about drag etc, has no real advantage. The following quote is from Aircreation – a company that has been making microlights for many years:

1. To hold up the structure under negative loads, of course. That’s not the problem, we could have done without it and maintained the strength by means of rigid wing struts or other systems. But these solutions will always be heavier and more expensive.
 
2. A proven ability to best ensure the stability of the sail in climb or descent the twisting and/or the profile reflex must imperatively be mechanically operated. To do this, we use luff lines that run from the top of the kingpost to the tip of the battens. The advantages of this system are reduced weight, efficiency that increases with speed, and freedom of movement of the sail lobes, thanks to the lateral freedom of the luffline bridle.
 
Without a kingpost floating rods are commonly used. These are secured to the leading edge with or without support from the lateral battens. The advantage is reduced drag, but efficiency tends to fall as speed rises because of twisting of the structure under increased forces. Another disadvantage is that the left and right straight rods do not depend on one another, as do the luff lines. When entering a turn, if the systems are set vertically and close to the trailing edge for maximum effect, the outside rod curbs movement of the flat part of the sail lobe and manoeuvrability is reduced, especially at low speeds.
 
No flight test can show the effectiveness of these “topless” pitch stability systems because their effect is only felt in circumstances outside of the “normal” flight envelope. Only aircraft undergoing specific tests, such as those performed by the DHV in Germany, can be tested for stability at a pitch of up to -15°. That’s exactly what we do for all of our models. The only sour note is that the maximum speed of the aircraft tops out around 120km/hour. Higher than that, this stability remains in the realm of hypothesis. Fortunately the curves obtained with luff lines at higher speeds call attention to an instance of reflex in pitch that rises with the speed. We can thus reasonably expect an improvement in the reflex couple at speeds that exceed that of the aircraft.
The pitch stability systems are designed for extreme manoeuvres, intentional or not, high turbulence, stalls in flight that can force the wing out of its flight envelope. It’s here that their relative effectiveness can make a difference. That’s why we currently prefer to use luff lines whose effectiveness rises with speed, and that don’t curb handling at low speeds.
 
3. The report of drag caused by the upper cable system in a wing like the BioniX suggests the possibility of a maximum gain of 8% in total drag at 130km/h, if the kingpost were eliminated in favour of rigid wing struts. This hypothetical gain is certainly consequential, but it’s possible to achieve similar results by reducing twisting. This is the case of the BioniX whose washout & billow can be reduced to a minimum at high speeds thanks to the “CORSET” system, without reducing manoeuvrability at low speeds, as would be the case of a standard wing.
This hypothetical gain is also counterbalanced by the 10-15% extra weight due to the wing struts and floating rods, and the additional cost, estimated at 20%.
It is still true that a topless wing offers the possibility of folding the wing on the trike and a lower height to enter certain hangars.
The first point is an advantage for the encumbering of hangars, but its practical usefulness is relative, especially in the case of a fast wing with its many battens. The system is in fact only attractive if it can be done quickly & easily, even in windy conditions, without excessive exertion nor risk of damaging the equipment. Flexwings by nature take up little space in a hangar because of the flexibility of their sails, allowing for multiple juxtapositions. For long-term outdoor parking, there are simple solutions such as disassembling the upper beam and setting the wing upon the a-frame or lying it flat on the ground, according to circumstances.
As to the reduced height in order to enter certain hangars, the advantage is incontestable, but how often is this really a problem?
To sum up, our position is simple: it is first of all in order to use a proven stability system concerning which we have no doubts, the luff lines, that we do not at the present time produce a topless wing. And this in as much as the final results (performance, weight, price, practicality) do not seem to us sufficiently in favour of the system.
We have thus chosen to explore other solutions whose benefits seem wider and which allow a complete exploitation of the speed range, the main problem of flexwings. Considerably lowering the power necessary to fly level at speeds upwards of 120km/h is a good thing. We have been able to do so while retaining a kingpost and sufficient surface to allow for short take off & landing, even at maximum load; But one must not forget in an aircraft where we still have the pleasure of flying in the open skies, the drag of the trike and the comfort of the occupants remain natural & inevitable limitations on performance at high speeds.
That’s why we believe that reducing fuel consumption drastically in daily usage is possible and more important. In order to do this, one must favour peaceful cruising with a comfortable wing at low speeds, and reserve the potential of high speed cruising for cases where speed is really necessary (travel, wind…)
That is the philosophy behind the BioniX and its “CORSET” system.
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