Intermediate aerobatic trainer with classic lines
Words: Nick Bloom; Photos: Keith Wilson
A high-wing aeroplane performing aerobatics looks somehow inappropriate. However, there’s no reason why an aerobatic machine shouldn’t have a high wing, particularly if it has a transparent roof in the cabin. Personally I rather like to sit under the wing – it gives you an uninterrupted view downwards when not flying aeros. A high-winger with tandem seating (exit the side-by-side Cessna Aerobat) short wingspan, 210hp and a CS prop is even better. Enter the Xtreme Decathlon.
A flying club thinking of acquiring a 200hp Extra or a used Slingsby T67, or a pilot thinking of taking up aerobatics, might want to consider one of these high-wing aeroplanes.
For a short spell in 1960s America, the Citabria (‘Airbatic’ backwards) was the only affordable aircraft certified for aerobatics. A specially-strengthened variant on the Cub-like Aeronca Champion, the Citabria implanted itself into the American psyche just as the Piper Cub did for primary training and low-and-slow, affordable flying. Over the decades, a steadily ageing group of pilots harked back to their youth when they wanted something in which to fly the occasional loop and roll. “I want one of them Citabrias,” they said. Only what they actually wanted was a Citabria that was brought up to date with a modern engine, more horsepower and more performance.
The Decathlon was the result ? effectively a souped-up Citabria with a semi-symmetrical wing section. As the trend to ever-better performance continued, the Super Decathlon followed and now we have the Xtreme Decathlon.
I’m not normally a fan of taking a good formula and adding power, because with power comes weight. A heavier engine is thirstier, so bigger fuel tanks are needed, and then you need to beef up the airframe to cope. In aerobatics, light airframes make for smaller, tighter loops. So my key questions for the Xtreme Decathlon are: will it make a good display aircraft? Will all that weight and power have made it unpleasant to fly? And will it manage a vertical roll?
The Xtreme Decathlon on test belongs to ex-Aerostars pilot and airline owner Gene Willson and his 24-year-old son Patrick, who works at Stansted as an aircraft engineer. It’s based at Audley End and has an N-registration. Flying alongside us will be eighty-something ex-airline pilot Digby with cameraman Keith Wilson in a Cessna 172 from Anglian Flight Centre.
Patrick will be taking the rear seat and I will be in the designated solo pilot position. He tells me he has more or less learned to fly on the Xtreme, meanwhile mastering tailwheel flying. Now, with 115 hours power, plus a few on gliders, he is learning to fly aerobatics in it. The Xtreme has enabled him to do all this with a single aeroplane. Plus it has the potential for him to fly airshows in a two-ship, father-and-son formation act with the XtremeAir XA42. Both aircraft are in the colours of Titan Airways, Gene’s charter airline.
PPL training in the Xtreme makes sense, because despite the clipped wings (31ft as against the Champ’s 35ft), powerful controls and bigger engine (210hp as against 65), it is still at heart a Champion, which was designed to be a basic trainer. And the Decathlon has long been the club aerobatic trainer of choice in America. I was told a few years ago by occasional Pilot contributor Don Peterson that in his home state of Texas (where the airfields are hot ’n’ high) they occasionally run Sportsman aerobatics contests with a single Decathlon. Contestants take it in turn to fly the sequence two-up, with the instructor in the back seat. That places a lot of demands on the aeroplane (not to mention on the instructor), and says a lot about its inherent strength.
I begin with a quick walk around the aircraft. It’s 1940s technology ? welded steel tube fuselage and tail surfaces, the wings with aluminium spars, internal bracing wires and ribs cut and bent from sheet aluminium, and aluminium sheet over the wing leading edges. It’s all covered in dacron fabric, stitched-on, heat-shrunk, taped and covered in a paint that (today’s technology) fills the weave and ends up looking like plastic film. The wing spars are secured to the top of the cabin by a single bolt each side ? effectively a hinge ? and braced by two lift struts, stiffened by jury struts mid-span.
Wittman spring legs carry the mainwheels, fitted with toe-operated hydraulic disc brakes, and the steerable leaf-sprung tailwheel is linked to the rudder with coil springs. There are handles at the back of the fuselage for lifting the tail. I try and can’t quite lift it. Americans seemingly are obsessed with protecting the propellers of their tailwheel aircraft and set the main wheels further forward than in most European designs, and the Xtreme is no exception. There is a penalty to having the main wheels further away from the centre of gravity ? it takes longer to lift the tail at takeoff (so you start blind), there’s a greater propensity to groundloop, and it makes it harder to land tail-high.
The ailerons have a neat pushrod inboard to the upper surface, and bulge noticeably outside the section of the wing, presumably for increased power and perhaps to counter adverse yaw. They are not differential, going down by the same deflection as up.
This being essentially a no-frills aeroplane, there are no flaps and only one set of instruments ? the rear seat occupant has to peer over the shoulders of the person in front (not that there aren’t frills, notably the wheel spats). There is space for 100lb of luggage behind the rear seat.
The ‘built to a cost’ theme is perhaps most noticeable in the flat section of the vertical tail surfaces and their external wire bracing; few manufacturers build tails like that these days. Forty gallons (US) of fuel is placarded, and it’s held in two twenty-gallon wing tanks. There are cold and hot air vents on the fuselage walls under the instrument panel and a parking brake. Fuel and oil systems allow inverted flight.
As opposed to the Cub, the Champ and its descendants have a high-sided cabin and a relatively short rear fuselage, giving the Xtreme a slightly dumpy look. The door on the right-hand-side swings forward and locks and you climb in via a step below the lower longeron, with plenty of struts in the fuselage available as handholds.
The seats are bolted-to-the floor and of the ‘throne’ kind (upright with single, aerobatic-style five-point harnesses for each occupant). Elevator trim is manual, on the left wall, the throttle lever is above and, between the two, there’s an alternate air lever. The control sticks have two curves built into them ? very graceful.
I hoist myself up and try the seat, which seems to be adequately high and close to the rudder pedals. I have short legs and someone with longer ones would just have their knees a bit higher. (The front seat is adjustable.) The cockpit is enormous and has lots of clear Perspex and room. Patrick sits behind me and I close the door, which has two extra safety catches as well as the handle. And there’s an emergency door release, a fire extinguisher and other ‘Fed’ safety requirements mandated in US certification. There’s a window on the left side, opposite the door, which you can open in flight up to 130mph.
Time to go, so I run through the start-up procedure, directed by Patrick. This involves twisting around to operate switches on the left wing root and eventually pushing the starter button on the instrument panel. The engine is warm from taxying to the pumps and starts on the third try in lean. I push the plunger to rich and it settles down. We don our noise-suppressing headsets ? a must in this noisy boom-box with 210hp up ahead ? and I do my best to get to grips with the glass panel technology in front of me.
This comprises an EDM-930 for the engine, a GTN 650 Garmin GPS navcomm unit and an Evolution 1000 EFIS, but there are analogue flight instruments for a dinosaur like me. Patrick tells me that he finds it easier to work from the Evolution 1000.
Taxying is dead easy with the steerable tailwheel and toe brakes, although this variant on the Decathlon had perforce to be fitted with longer legs to maintain prop clearance. So even from the front seat I have to taxi in a series of S-turns, as I can’t see over the nose.
We run through our preflight checks, which for us are cycling the prop, ‘full and free controls’, mag checks and slow running. The C172 lumbers down the runway. I wait until its wheels are just clear of the grass then open the throttle smoothly all the way forwards, applying rudder to counter spiral airflow from the prop ? at this point the rudder is light.
The acceleration is impressive, but with stick fully forwards it still takes three seconds before the tail lifts and I can see over the nose. The main legs (aluminium) have a fair bit of springiness, and give and flex rather more than is comfortable over Audley End’s somewhat undulating runway. It’s a bouncy ride. I sense there’s a rather high wing loading and although we gather speed quickly, we’re half way down the runway before I feel confident about lifting off.
We are now catching up the 172, so I throttle back and raise the nose to keep a safe distance. This can feel awkward in some aircraft ? we are only 100ft above the trees ? but the Xtreme seems happy enough and soon I am able to add power. Patrick asks me to back off the propeller rpm, so I pull the blue plunger out a fraction.
First impressions are that this is a good formation aircraft with lots of control authority, easy to position and with few blind spots. The ailerons are light and sensitive, the elevator less so, and the rudder a trifle heavy, so control harmony is traditional, although perhaps not ideal for aerobatics.
The final photoshoot manoeuvre calls for me to take the lead so I can roll inverted for a photo of the aircraft upside-down. I open the throttle (too much as it turns out) for some compensating power. A touch of right rudder at knife edge keeps the nose up, and then, forewarned by Patrick, I give a lot of forward stick and get the nose higher than one would expect. Under the negative G, my baseball hat and headset levitate off my head and ascend to the roof, leaving me with no means of communication and no ear defence. It’s pretty noisy.
I sustain inverted for a slow count of twenty, take a quick, belated look at the ASI and am startled to see the airspeed has risen to 120mph. We had agreed on a formation speed of 95. We haven’t been in a dive, it’s that extra power, which has speeded us up to a rather surprising degree. Clearly this aircraft doesn’t come over all draggy when upside-down. I swing the stick left, with left rudder, and we roll upright.
Patrick has retrieved my headset and my hat, and offers to adjust my headset. “I’ve never had it come off,” he says. “Maybe it’s your hat!” It does seem more secure, adjusted and minus hat.
The first aerobatic manoeuvre I attempt is a loop. I expect the Xtreme to be one of those aircraft with a high wing loading that likes plenty of speed, so I dive to 130mph before beginning the pull-up. I haul back on the stick quite lustily but not enough, and the aeroplane makes a big loop. My pull on the recovery is short of what is evidently required, so we lose height. That elevator really is heavy at aerobatic speed.
After climbing and repositioning, I try again and make something more nearly round ? but I have another problem, which is introducing aileron during the loop. It’s partly, I can see, a result of having the wings up there, so I have less horizon to line up on once the nose starts to rise. Also, no doubt, having a heavy elevator and light ailerons makes it easy to introduce unwanted roll inputs while hauling back on the stick. My next try is better, but the combination of limited view, heavy elevator and light ailerons does make accurate looping tricky.
Next I try stall turns. I suspect this is an aircraft where I will need to make rudder adjustments (to offset spiral airflow) during the pull-up, or I’ll arrive at the vertical one wing low. So as I pull up, I turn my head to both sides alternately, trying to get the same picture on the right and the left. This head-turning, while pulling G and trying to make sure the wings are level against the horizon (which you can only do while looking forwards) is unnatural. Generally it’s only necessary when stall turning in an unfamiliar aircraft.
Despite my best efforts, we hit the vertical right wing low. At least we’ve plenty of power, hauling us vertically upwards as I apply left rudder to try and straighten up. I allow this rather uncertain and wobbly ascent to continue for maybe three seconds, then kick in full left rudder. The aeroplane pivots neatly and now we’re pointing straight down. Interesting ? it could have rolled, slid backwards or misbehaved in various ways, but it didn’t. So the Xtreme is easy to stall turn.
I work on my verticals for a while, trying to get the rudder right, but also adding first a quarter-, then a half-roll while vertical and before stall-turning. It helps a lot when I finally start really pulling on the stick to get to the vertical. I’ve been squandering energy on a huge quarter loop. However, the most that I can manage is a three-quarter roll, which is still good enough for Intermediate level competitions.
Patrick says the Xtreme performs noticeably better without a passenger. He thinks that, one-up, it will just manage a full vertical roll. This can perhaps be exited with a half-loop (a ‘humpty bump’ in aerobatic parlance) or stall turn. “But,” he suggests, “probably not a fly-off” (i.e. pitching forwards into level flight).
I then try something I suspect will be a lot easier, a four-point horizontal roll (with hesitations at each quarter). This goes well, although the rudder feels heavy in the last quarter. When I say ‘heavy’ I mean I have to push hard enough to make me fearful of getting cramp in my calf muscle.
Patrick has never experienced a rolling circle and I am curious to know if I can still fly one (it’s been a while). I try turning through ninety degrees while flying a roll, coordinating the two into one flowing manoeuvre. It’s rough but I just about manage it. This time the rudder push required is a limiting factor, the manoeuvre calls for more push and I can’t summon enough muscle-power to deliver it.
It’s not the aircraft that’s the problem, it’s me. The Xtreme is a bit of a brute. However, so was my Skybolt, decades ago, which had similarly heavy elevator and rudder, so much so that to begin with I flew competitions with both hands on the stick. I soon adapted and after a while the rudder and elevator no longer felt heavy.
Next, I try a half reverse Cuban, half-rolling on a 45-degree climbing line, then pulling through three-quarters of a downward loop to end in level flight. You can draw a long climbing line in this aircraft, since the half-roll is fast and the aeroplane will climb steeply for a long time before it runs out of energy, so this is a pleasant manoeuvre.
I say ‘the half-roll is fast’, but in fact the roll rate depends on what you’re used to. By the standards of a Pitts Special or an Extra, it would feel painfully slow. Against a Tiger Moth, lightning-fast. I would say it’s above average for an aerobatic trainer, faster than a Chipmunk, Cessna Aerobat or Stampe. Patrick says it’s 180 degrees a second. So a slow count of two for a full roll.
The half Cuban I fly next (half-roll on the downward line) isn’t quite so pleasant, because you really do need to pull firmly at the end of a dive and I’m still not acclimatised to that. From an entry speed of 130mph I try a half loop, half roll ‘Immelman’ which earns a “Nice” from long-suffering Patrick in the back. Some aircraft run out of puff and sink at the top, but not this one.
Time to sample the spin behaviour. The aerobatic competition spin, which Patrick hasn’t experienced, requires a stalled entry from level flight, so I set up straight-and-level, then slowly close the throttle, progressively raising the nose so that we neither climb nor descend, being careful to keep the slip ball centred. The stall warning howling in our ears is a distraction (but the Feds will have insisted that the aircraft has one). The elevator, so heavy at aerobatic speeds, becomes progressively lighter, so concentration is required. Whether it’s that, the fuel in the wing tanks being out of balance or the spiral airflow from that big, heavy, windmilling CS prop, when the aeroplane stalls it also drops its right wing.
It’s a left-turn spin I have in mind, so I push in full left rudder (light at this speed) and pull the stick all the way back. The aeroplane hesitates, and when it does drop its nose and begin rotation, it’s untidy. For a moment it feels properly stalled and then the wings grip the air and we’re in a spiral dive. I try that stall entry a few more times and don’t succeed in getting a proper competition spin. I think I know why: the C of G is too far forwards.
That is a common problem with aerobatic trainers ? the Feds (EASA and the CAA are the same), and sometimes also the aircraft designers, are so concerned with students inadvertently getting into unintended spins that they play it safe and then ‘add a bit more for luck’. It’s probably the same thinking that’s behind the rather heavy (at higher speeds) elevator and rudder.
Having said that, I am sure that with practice and perhaps a bit of ‘cheating’, the Xtreme could be made to produce a high-scoring competition spin. The aeroplane has powerful controls, and that can offset other factors.
In a turning stall, unsurprisingly, the Xtreme goes for the safe option, rolling level. I try loitering turns at half power and low speed and the only hazard is an insidious loss of height. This doesn’t strike me as the kind of aeroplane that will suddenly flick into a rapid spin following low-and-slow abuse. If it does have a built-in risk factor, it’s entering a loop or barrel roll a little too near the ground, because it has a moderately high wing-loading and, although the power is there to get you out of trouble, you have to see trouble coming and get the nose up and the power on in time.
The wing loading of the Xtreme is 11.9lb/sq ft. For a Stampe it’s 8.9. On the other hand, for a Chipmunk it’s higher (12.8) and for a really high performance machine, like an Extra 330L, 15.2. So the Xtreme’s wing loading isn’t by any means excessive.
Given that we are near the weight limit for flick rolling, I try a low-strain variant of the manoeuvre, climbing at low power at 35 degrees nose-up, until the speed falls to 65mph, then applying full left rudder and back stick. The aircraft stalls and lazily rotates, dropping its nose.
The rotation is average ? neither fast nor slow ? but it takes quite a hefty push on right rudder to stop it. You end up in a slow-speed dive. Patrick’s not tried this (sometimes called a ‘Pussy Flick’, because it’s gentle on the airframe) and has a go. Two tries and he’s got it. Next I try an Avalanche (flick roll at the top of a loop, which is also low-strain) and it’s tricky. Probably because the rudder is heavy and I don’t push it firmly and quickly enough, the aircraft barely stalls. It begins to autorotate and then that forward C of G makes itself felt and the rotation degenerates into a spiral dive. Messy.
I try a level stall, holding the stick all the way back instead of recovering. This produces a dramatic height loss in a completely controllable mush downwards. We alternate between swooping upwards and diving. Astonishingly, the ailerons continue to work normally whenever a wing drops, even in this configuration. Very forgiving.
It’s perhaps a bit rash to draw conclusions on such a brief acquaintance, but I would think that the Xtreme is potentially capable of all the manoeuvres in the Intermediate competition syllabus. It’s probably a rather better trainer than the Extra at Standard and Intermediate level. Its lack of aerodynamic sophistication means, for instance, that although the roll rate is rapid enough to get away with just shoving the stick over to get a good score, you will have to coordinate rudder and elevator properly throughout the roll ? and that’s a good lesson.
On the debit side, for Standard level aerobatics, the spin might be tricky to master. It’s a high-scoring manoeuvre at Standard, and important. On the credit side, the aeroplane is quite large and easy to judge and has plenty of performance, so maintaining height shouldn’t be a problem, both in contests and in displays. The trick will be to keep the speed up, same as with a Pitts.
Is it pleasant to fly? Not especially but then the aeroplane I fly aerobatics in every week is a low-power, light, single-seat biplane with low control forces. Were I to fly the Xtreme a few more times, I’d find it just as pleasant as my Currie Super Wot. There is (apart from the passenger seat) one huge advantage over the Wot. In cruise, the poor old Wot can only manage 85mph and has a cramped cockpit. The space I’m sitting in is much bigger.
On the journey back to Audley End, I start off at 120mph, which feels comfortable, then throttle back to 110 after discovering from Patrick that that’s what he and his dad normally cruise at. The ‘book’ figure is much higher: 149mph.
This aircraft gives a smooth ride. You can make turns on stick alone, although some rudder is required for steeper turns. The aeroplane is reasonably stable and will fly hands-off for a while before one wing lazily descends. The elevator trim is a little on the sensitive side but works fine. I try steering with rudder and it doesn’t really work ? the aircraft banks eventually and starts to turn, but by then the nose has dropped and the speed is rising.
Patrick directs me back to Audley End, but the airfield seems to be invisible and it’s only when he takes control and lines me up with the runway that I finally see it. He suggests an approach of 80mph today, “as it’s windy. You can approach at seventy for a shorter landing”. Audley End House is in the way and there are strict instructions not to overfly it. I take the difficult route, a close-in right base, and the strong crosswind and turbulence resulting from sun and scattered cloud, tall trees and a hilly approach do make it rather challenging.
It doesn’t help that I’m coming in fairly low. I’d have done better to come in high over the obstacles and sideslip once we’re over the airfield boundary. As it is, the aeroplane is bucketed about like a dinghy in a rough sea until we’re over the threshold. Once I am able to close the throttle and the ground levels out, our passage becomes less bumpy.
Elevator is definitely sensitive and we waft up and down as the aircraft begins to slow. Just when I think it’s going to drop on, it floats upwards. Thinking, surely we must be close to the stall by now, I open the throttle a tad to cushion the landing. The Xtreme drops on and that springy undercarriage makes itself felt, but the aeroplane has little energy and with some firm braking, it soon slows. One advantage of that forward-set undercarriage: you can brake firmly without fear of damaging the prop.
We’ve landed in about a third of the runway. My second takeoff is like the first ? rather prolonged, but perfectly okay. With practice I could probably leave the ground safely in a still wind in 250 metres. Initial climb rate is a healthy 1,500fpm (and you don’t need a lot of rudder during the climb). However, this isn’t quite a STOL machine.
My second landing is off a higher approach, using sideslip and coming in with Audley End House on the easy side ? my right. The view on final was manageable without sideslip in my last approach but, as you would expect, vastly better with the nose canted off to one side. The Xtreme lands a little more smoothly but it does that last minute waft upwards again.
So I hand over to Patrick to fly a circuit. I’m watching his landing and I’m pretty sure it wafts upwards for him too. My penultimate landing is an attempt to wheel on, rather than three-point, but I touch down a little too fast and the sensitive elevator and springy undercarriage defeat me. The aeroplane bounces a few times and obviously isn’t going to settle down, so I open the throttle, lift off and land on three points further into the runway.
By now I feel that I’m getting the measure of the aeroplane, so I make one last, tight circuit and finally achieve a smooth landing. This time I’m ready for the last moment ‘waft’ and cushion it with just the right amount of throttle. As we taxi in, Patrick says he spent a day at another airfield trying to wheel on the Xtreme, eventually managing to do it, “but it wasn’t easy and I probably won’t wheel it on again”.
So, to answer the three questions. Yes, it has the performance and roll rate to make a good display aircraft. Second, added weight and power have not had too much adverse effect on flying qualities and obviously have done a lot to minimise height loss during aerobatics and expand the aerobatic envelope. And, yes it should manage a vertical roll and be competitive at Intermediate level contest aerobatics.
One last thing a club or private owner will want to consider is the price, which is $275,000, (aboyt £207,000). This compares well with the Extra 200, which is listed at $370,000. I wouldn’t like to instruct tailwheel in the Extra, though, and you could in the Xtreme. Like Patrick, you could even have your primary PPL training in one, though a Cessna 152 would be easier.
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