The Aircraft

Mudry Cap 232

The CAP-2x family was designed specifically for competition aerobatics. The CAP 23x series was developed from the CAP 21 single seater by strengthening the airframe to cope with a 300 hp 6-cylinder Lycoming AEIO-540 engine instead of the 200 hp 4-cylinder Lycoming AEIO-360. In 1990 the CAP 231 was born. It had a wooden wing and was stressed to +10/-10 G. It was an immediate success because of its impressive power to weight ratio giving it a climb rate of more than 3000ft/min and because of its precise controllability. It had large ailerons which covered ¾ of the trailing edge of the wing. However the roll rate was a little disappointing at 270 degrees/sec. This was mainly due to the flexing of the wooden spar allowing the whole wing to twist with full aileron deflection.

In 1994 the CAP 231ex was built using a carbon fibre wing purchased from the German Extra factory. This stiffer wing increased the roll rate to an astounding 420 degrees/sec. After building just 7 of these, Avions Mudry developed their own carbon fibre wing spar and in 1995 the CAP 232 was born!

The new CAP 232 wing offered several advantages. The carbon fibre spar is lighter and still offered a +10/-10G limit. The 232 was about 30kg lighter and this weight savings in the wing meant that the roll inertia was much less. Therefore it was easier to start and stop rolls which is so important in modern competition sequences which involve endless segments of 2, 4 and 8 point hesitation rolls. In vertical up and down lines, getting the rolls done quickly is a must before the limits of the airspeed indicator signal that you’re out of time!

Another major additional benefit was the addition of wing tanks. The original CAP 231 only had a 67 litre capacity. Not very useful for transiting to competitions. The new CAP 232 wing added 2 x 57 litre tanks making it an impressive cross country performer. Typically at 2000 ft and 55% power…… (2000rpm / 23.5 inches manifold and 45 litres/ hr) one would see 150 kts cruise for 3 hours with reserve. It is possible to cruise 20kts to 25 kts faster but the fuel flows make your eyes water! At max power the fuel burn is almost 95 litres per hour!

Alternatively if you can get up high, it is possible to plan for 8000ft and 45% power (2000rpm 18.5 inches manifold and 38 litres/ hr) and cover more than 600nm.

But the CAP wasn’t made for cruising! It was designed for jaw dropping aerobatic performance. The majority of flights are just 30 minutes duration. But you can do a lot in 30 minutes. Very little time is needed to climb. So let’s start by having a look at the front.

G-IIAI has an MT 4 bladed variable pitch / constant speed propeller to convert the 304hp into thrust. From a VNE dive and 7.5 G pull, the aircraft will zoom climb 2300ft in 15 seconds before gravity wins out.

From a maximum straight and level speed of 184 kts, a 2000ft vertical climb is possible. To perform an upward half loop, a minimum entry speed of only 95kts is necessary and still one can gain 600 feet. These numbers mean that a pilot is spoilt for energy management. You can waste a lot of energy in a sequence with lots of high drag yawing, gyroscopic tumbling and flat spinning and yet still be able to manage height well. The CAP makes it easy!

The big 4 bladed MT propeller spinning at up to 2700 RPM is a powerful gyroscope and one of the laws of physics is that if you tip a gyroscope, it will process, The large rudder and elevator can create sudden rapid yawing and pitching movements. Tipping the propeller disc so dramatically, will unveil the often misunderstood gyroscopic forces necessary to make modern aerobatic aircraft tumble in seemingly unnatural and impossible looking ways. Simply said….. push the stick forward and the nose yaws left / Pull and yaw right. A boot full of left rudder and the nose pitches up / Right rudder and expect a pitch down. When flying at more than 100 knots, the longitudinal and directional stability of the aircraft will largely mask and overpower the gyroscopic forces of the propeller. But at lower speeds, a pilot can exploit these forces and supplement them with control inputs that result in a new
dimension of flight!

G-IIAI Symmetrical Wing
The symmetrical wing and the aileron spades. When the airflow strikes the spade surface it helps to deflect the ailerons making the control pressures very light.

The Lycoming is an AEIO designation and that stands for “aerobatic /engine/ fuel injected / horizontally opposed”. It has some additional features that help it to survive the abuse of aerobatics. The crankshaft is solid, because gyroscopics create a lot of torsional forces internally. There is a Christian inverted oil system so that lubrication continues regardless of the attitude. There is a flop tube in the aerobatic fuel tank to scavenge fuel regardless of the attitude. And there is an extra oil cooler because of all of the high power low speed exposure.

Aircraft design involves a series of compromises. The Cap wing has no dihedral, no angle of incidence, no wing wash out and it uses a symmetrical airfoil cross section which is all great for aerobatics but is costly in terms of cruise efficiency. The CAP wing has the same curvature on the top and the bottom surfaces. So how does it fly you might ask. Did we not learn in aerodynamics 101 that lift is created by the greater curvature on the top of a wing? Well the lift formula also says that angle of attack is a major part of the game and this CAP symmetrical wing works equally well whether the angle of attack is positive or negative (ie upright or inverted) and the stall speed is the same both ways. This makes axial rolling look more precise and the pushing performance is equal to the pulling! Modern unlimited competition sequences are drawn with a lot of red ink which means pushing is something you just have to get used to.

G-IIAI Cockpit
The sequence card holder takes up the most space on the panel. Black lines denote positive angles of attack and Red ink denotes negative angles of attack. Triangles signify that one or both wings are in stalled flight (i.e. flicks or spins)

Attached to the wingtips are the sighting devices. These large triangles are simply there to help the pilot more precisely move the horizon to a particular vertical or 45 degree angle to satisfy those picky judges. Simply drawing lines on the canopy would serve the same purpose and would be cause much less aerodynamic drag but as the pilot’s head position is constantly being forced in different directions, referencing a sight picture that is just inches form your face is never going to be as accurate as something out on the wing tip. And being precise is what Aresti competition is all about. Additionally, there is a piece of string attached to the trailing edge of the sighting device and its sole purpose is to indicate when you’re going backwards. One might think that this moment is easy to detect but that is not the case and as flying controls will work in reverse when the airflow is coming from behind such as during tail slides…….this is the hi-tech indicator for the pilot to know when to reverse the controls.

G-IIAI Sight Gauge
G-IIAI Sight Gauge

The cockpit seating has been designed so that the feet are at the same height as your hips. This increases G tolerance. The rudder pedals have cycling clips so that the pilot’s feet do not come off of the rudder pedals during –ve G. The 7 strap hooker seat belts harness employs heavy duty ratchets to pin the pilot into the seat during negative G pushes. I often get bruises on my hips because I need to ratchet myself in so tightly.

Handling is as good as it gets. The Ailerons, Elevator and Rudder are perfectly balanced, are all large and very effective.

The ailerons can be deflected fully up to 178kts to generate a roll rate of 420 degrees per second. The control forces remain light because of the 4 aerodynamic spades to assist the pilot. The aileron set up can be varied to some extent to suit a pilot’s preference. The spades can be of a variable size for greater or lesser assistance. Too much spade assistance loses aileron feel and makes over controlling the stops on point rolls a common problem. Adding aileron hinge gap seals can improve the roll rate particularly at high angles of attack but this also can reduce the centering feel. Some pilots will add p-strip or triangular wedges of varying length ahead of the ailerons to produce an aerodynamic null zone and thus recreate this centering feel. This can prevent the bobbled stops on hesitation rolls.

The elevator and tail plane have been positioned in a more forward position than is typically seen on light aircraft. This is to ensure that the rudder is not blanked during spin recoveries and allows for very predictable and instantaneous recoveries form spins and tumbles. The elevator has large aerodynamic horns and it is also servo assisted to keep the control forces light when at high speed. This is to reduce fatigue and make precise inputs more achievable. However above Va 178kts, it is possible to exceed
the maximum G limits with a little too much adrenaline when diving into the box to start a high speed first figure. The G meter therefore has a memory which cannot be reset or erased by the pilot if an over-stress occurs.

G-IIAI Elevator
The horizontal stabiliser and elevator are positioned forward to assist in spin recovery. The massive rudder still has light control forces.

The rudder is massive and surprisingly light considering the puny aerodynamic horn. The rudder is very effective and combining this with the fat sided fuselage allows a pilot to generate significant fuselage lift when in knife edge or sideways flight. Below 100kts, full rudder deflection can create an immediate 45 degree yaw. Combining a figure which has a side slipping finish with a following figure using opposite rudder, can allow the pilot to produce an illusion of being able to change the direction of flight by yawing a full 90 degrees instantly. This impressive sidewise lift make the CAP arguably the easiest aircraft for rolling circles.

What is best about the aircraft is how easy it is to fly. It is completely predictable and does exactly what you tell it to do. And with enthusiasm. One might expect that the powerful controls could possibly make a newbie over control but everyone who has taken the leap of courage to fly a CAP single seater for the first time when a dual check out is just not possible has come down smiling and remarked how well-mannered it is. If you can land a Cub you can land a CAP. Keeping it between the positive and negative critical angles of airflow will mean you will enjoy an easy and well-mannered machine.

That’s not to say it’s for complete novices. There are a few points to highlight. The wing air-foil has been designed so that sudden and complete airflow separation will occur easily. This makes initiation of flick rolls easy. Reattaching the airflow is equally easy.

There is no cockpit stall warner. You wouldn’t want it anyway as it would be annoyingly and constantly bleating away during every aerobatic flight. However, the natural airframe buffeting and elevator nibble is easy to detect but the pilot needs to be relaxed enough to be receptive to these signals. As I said earlier, the elevator is quite light and a ham fisted pilot could easily bring the stick back just a tad too far. As I said earlier, there is no wing wash out. So if you do stall, the whole wing will let go of the airflow and the wing drop could be rather dramatic if the ball is out of centre. The powerful rudder and elevator can fix things in an instant but it’s really necessary to get some dual in something like a 2 seat Extra or a Pitts before going solo in a CAP. On approach to land, you do have to slip in order to see because at approach speeds and without flaps, the high nose attitude will block the view of the runway.

The aircraft has had an impressive safety record for an unlimited aerobatic machine. The exception was in 2005 when a wing separated in flight causing a fatality. Investigation revealed the cause to be due to damage during ground transporting the aircraft without the correct support frame. As a consequence, all of the CAP 232s were recalled to reinforce the wing / fuselage join and the maximum G limits were reduced to +/- 9.2G. The maximum flick rolling speeds were also reduced.

So there you have it. It really is a dream machine. CAP have made an aircraft that is easy to fly and has outstanding performance. It quickly will build confidence in the pilot to allow him or her to expand the envelope. The 3 dimensional possibilities are almost endless and as such one will never completely master this aircraft. There is always something to learn. The pursuit of the Holy Grail in aerobatics is to invent a new maneuver or to at least give the illusion that the aircraft is doing something that hasn’t been seen before.

  • Length: 6.75m / 22ft
  • Wingspan: 4 m / 24 ft
  • Height: 90 m (6 ft in)
  • Wing area: 2 m2 (110 sq ft)
  • Empty weight: 615 kg
  • Max Aerobatic weight: 780 kg
  • Takeoff Weight: 820 kg (1,807 lb)
  • Luggage Capacity: 35 kg
  • Powerplant: 1 × Lycoming AEIO-540-L1 B5D air-cooled 􀃓at-six, 224 kW (304 hp)

Performance

  • Never exceed speed: 219 knots
  • Maximum level speed: 184 knots
  • Cruise speed: 172 knots (75% power)
  • Range: 653 nm
  • Fuel: total usable capacity 166.5 L / 62.5 L aerobatic tank
  • Stall speed: 59 knots
  • Glide speed: 80 kts
  • Landing Vref: 75 kts
  • Rate of climb: 3,091 ft/m
  • G-loads: +9.2 G; -9.2 G
  • Roll rate: 420 degrees/sec at 178 kts