Update – MAC Mamba

Chief Aerodynamicist on the Mamba project is Paul Hughes, an engineer with over twenty years design experience. Mr Hughes explains how the development of the Mamba has progressed.

When Jess Smith (MAC Managing Director) originally conceived Mamba, it was to have been an ultralight, but it soon became clear to us that if the plane was to have any substantial market, we would need to have it meet the US FAR23 standard, which meant a fully certified craft.

“This decision meant that we would design it to meet the Australian ANO 101. 22, which has very similar requirements. “In fact this change really only required one substantial redesign. that of the empennage. ” While the basic parameters of the aeroplane were set, much of the detailed proving work was carried out using computer simulations. Using British ESDU (Engineering Science Data Unit) Sheets as the basic input and combining these with data from items such as the NACA wing section performance data, Paul wrote a series of original computer programmes which can run on a standard personal computer.

“These programmes were written to predict the aerodynamic characteristics of the aeroplane. We didn’t have access to a wind tunnel but, with the speed and power of modern personal computers, we were able to assess how the aeroplane would perform. “In fact I have separate programmes covering stability general performance, propeller performance, engine cooling and takeoff performance. ” All this work was done before the prototype was completed and provided valuable input to final specifications. The flying programme commenced in January (see test pilot Vic Walton’s flying impressions), although the prototype has only flown a few hours as yet. Nevertheless, there have been sufficient tests already to provide confirmation of much of the computer data.

“For example the aircraft’s trim point was exactly as calculated. Another example is the rate of climb. The computer simulation predicted an initial climb of 800fpm and the aeroplane made 780 on the first attempt.

“Of course, with a completely new aircraft, there will be some elements that you need to evaluate based on the actual feel and the amount of control input. A good example of this is the tailplane setting. We were concerned about the amount of control column input to unstick the aeroplane at takeoff. As part of the development, we constructed the tailplane so that its angle of attack could be quickly modified.

“In the event, we were able to make a small change within a few minutes, the Mamba was able to take to the air again and the test pilot pronounced the changes completely satisfactory, all within half an hour.

“Another area that needed the assessment of a test pilot was the balance of forces on the control column. Many pilots may know that because human arms exert more force in some directions than others there is an ideal balance of forces on the controls in the ration 1:2:4 for ailerons, elevators and rudders respectively.

“In our case, because of the forward-hinged design of the ailerons on the Mamba, we expected that a little ‘servo’ effect would be required. For this reason we had designed some small balance tabs, which reduce the load on the control column, but we wanted to try the plane without them first. This is because they add drag, which of course, reduces performance. ” In the event, the balance tabs have proved to be necessary and the team are making final adjustments to this system. Apart from ensuring that the balance of forces is satisfactory, the team also want to ensure that the aircraft is responsive to fly and not sluggish in any control input.

The early flight tests of Mamba have generally shown the plane to be an outstanding performer. One reason for this is the quite narrow section wing profile which has been chosen. In fact its lift characteristics are so satisfactory that Paul Hughes says they will be able to shorten the wing span in the next aircraft, which will further reduce drag and increase performance. The shorter wing will also mean a reduced bending moment, which will give it a better fatigue life.

Another feature of the current prototype is the underwing tanks. These were chosen because of the narrow wing section and concern about structures required to accommodate fuel in- side the wing. In the event, the project engineer, Merv Reed has found a way to put the tanks inside the wing without the compensating structures being too heavy. The change will provide another reduction in drag and is expected to further aid performance.

The only difficulty encountered so far has been a slight instability in the yaw mode. Paul Hughes attributed this to the narrow tapering at the back of the cockpit and has already designed changes to overcome it.

Other minor modifications to be made, cover items such as the engine cowl (to provide for improved cooling and a different exhaust system) and some minor changes to the cockpit size, for better pilot accommodation.

All in all, the general results of early testing have been extremely successful, with the craft showing very good climb, cruise and handling characteristics.

Even load testing, such as sandbagging the whole craft, have shown very good rigidity. This is reflected in good handling but will also mean that the structures should show very satisfactory fatigue life, a maintenance boon to the private owner.

Paul Hughes says the next round of tests will entail spin testing and that the final certification should be achieved in the second half of this year. The design and construction of the next prototype has already commenced and MAC expects to be in full

production of the two seater late this year or early next. The four seater will follow about twelve months later.

The Test Pilot’s View

Vic Walton is undoubtedly one of Australia’s most experienced test pilots, with over 20,000 flying hours to his credit. His work on new aircraft dates back to the Victa Airtourer, although these days he divides his time between running his Sydney based commuter airline Aquatic Airways and test flying. He offers some thoughts about the initial flights of the Mamba and how it stacks up as a new aeroplane: “The Mamba is a pretty original sort of concept. When you first look at the plane, you’ll see a cockpit layout that’s very good. In this prototype you might say it’s a little over engineered if anything, in the sense that it has so much instrumentation. Of course you normally want as much as you can get, but there’s such an array in there . . . “Entry and exit from the cockpit in the prototype is not all that easy, particularly when you’re wearing a parachute. With that on your back and my particular size and shape, it takes about four pushing and five pulling! “But once you’re in, you immediately feel at home, everything’s within easy reach. The control column is floor mounted, so it’s between your knees. And even for those who haven’t used one before, it’s surprising how fast people do adjust to it. ” (Vic commented on the fact that even with the unusual centre mounted control column on the Victa Airtourer, pilots and instructors soon got very familiar with it. )

“At the moment the rear seat is occupied by a very large ballistic parachute (a rocket powered ‘chute which will bring the whole device safely to earth in case of a catastrophic failure). I have to say I felt it was surplus to the whole programme, but then I’m just the driver.

“Of course my feelings could be influenced somewhat by the great feeling of solidity in the aeroplane. It’s built like a brick . . . er, tank! I think the structures engineer (Merv Reed) had a lot to do with that. He’s ex-TSR 2 and Concorde and you get the impression when you get into the aeroplane that that’s the sort of engineering philosophy that’s gone into it. “For myself, I’d have been just as happy with an anti-spin chute, though that’s being fitted now, for the next phase of the programme.

“Once we got the testing started, initially we didn’t have enough elevator, which we found in high speed taxi trials and test hops. But the designers, bless ’em, due to their intelligence, put an adjustable tail assembly on it, so it was just a matter of undoing some bolts and reassessing it. And now we have delightful elevator control. The modification was done in about 15 minutes, we were back in the air and it was quite satisfactory.

“The first flight of the aeroplane was very exciting. I was very much impressed with the performance. It flew well, in fact one of the better flights that I’ve experienced in a prototype. “Climb was phenomenal, from my point of view. For 115hp the aeroplane seems to have great performance. “Once we’re truly airborne, you can assess the controls and responsiveness of the aeroplane. “At the moment there are still some items we’re considering. The rudder’s quite good, although in flight we have a slight yaw problem.

In dead calm the nose yaws backwards and forwards a little. Now we’re in the process of tuft testing (small tufts of wool attached to the surface to study airflow) to see what’s causing it. . . “Also, at the moment, the ailerons are too heavy, so that balance is not there yet and the balance tabs haven’t completely fixed it “Of course both of these things could be related and when we fix one it could go a long way to fixing the other. And I should stress that they’re really very minor problems, that we’ll develop out of the aeroplane “A lot of people make an assessment first off, without realising what is required in the development of an aeroplane . . . it’s very unlikely that a new design will come off the drawing board perfect and that’s why a test programme is required. “Overall, you can really appreciate the design and construction when flying. It feels good and solid for a little aeroplane. It’s got a real, professional, heavy aeroplane feel about it, which belies the size of it. “There are still some other matters we’re looking at, such as approach speed, but the main impression I would want to give is that it’s an exciting aeroplane. I’ve really enjoyed it so far and I’m looking forward to getting back into it. ”