Flight test: de Havilland Fox Moth
- Credit: NA
Once a commercial workhorse, the DH83 may look like a ‘fat Tiger Moth’ but the many differences include brakes, more speed, folding wings and a passenger cabin
Everyone likes the Tiger Moth. There are still any number plying their trade around the world, taking brave souls aloft in warm jackets and Biggles hats for the ten shilling tour?albeit inflation has somewhat caught up. These intrepid aviators are reliving the exploits of their ancestors, or simply ticking the ‘open cockpit biplane’ box on their bucket list.
Some pilots seek out a Tiger having been told “if you can fly a Tiger you can fly anything”. Whilst perhaps not strictly true, it is a blooming good trainer for tailwheel (or -skid) conversion and will certainly give a modern pilot’s feet a good work out, and improve overall coordination and judgement.
Having mastered the Tiger, our tyro pilot starts to feel like a real aviator?and I don’t disagree. However, and I’ll say it quietly as it’s bordering on heresy, a Tiger is not actually that agreeable a machine to fly! Yes, it’s epic as a trainer, historically significant, and holds a soft spot in many hearts.
Even after it’s mastered it still provides buckets of challenge, offering satisfaction in flying and pride in ownership. Nevertheless, it is still a bit of a draughty relic with poor handling?even the most ardent Tiger proponent will admit to that, although it may take a few beers! Personally I find vintage machines one of the most enjoyable facets of aviation, but the Tiger isn’t the best of the bunch handling-wise.
So what about the Fox Moth? Isn’t it just a fat Tiger, I used to ask myself? But I certainly wasn’t going to say no when the opportunity to fly one arose. Absolutely not! In fact, I was honoured, nay chuffed, to be deemed capable of looking after such an historic machine, one of only three or four flyable worldwide back then, although today there are about eight and more in the pipeline.
A few years ago I flew a big figure of eight around New Zealand’s North and South Islands in an Auster, accompanied by a few other mostly DH machines. One of these was a Fox Moth, and it was in company with the Fox that I flew down the west coast of South Island.
This is wild rugged country, truly overwhelming in its magnitude, and really remote ? roads didn’t properly get there until the ’60s. It also has some totally crazy weather ? it’s capable of going through all the four seasons in a couple of hours. The Fox Moth was pivotal in opening this area up and, along with the twin-engine de Havilland Dragon, provided a lifeline for those tough enough to try and scrape a living on this barren coast.
We picked our weather carefully but, pottering along in the Auster, my respect for the guys who operated a scheduled service (as well as cas-evac) soared. Alone in the Fox Moth’s open cockpit, no assistance for navigation or anything else, battling the winds and fog, following the shoreline between isolated and distant landing grounds, few places to land and no radio to summon help if it went wrong ? not that there was anyone there to help! No wonder the Fox Moth and the hardy souls that flew them earned respect: they certainly have mine.
As a happy coincidence, the Fox Moth was also one of the first aircraft to provide these guys with a sensible profit; with four squeezed in the cabin, the passenger miles per gallon made economic sense for the first time. Indeed, it was along this coast and other hostile parts of New Zealand that the machine featured here spent its entire commercial life.
Sold directly to NZ by the Hatfield de Havilland factory in 1934 as ZK-ADH, this Fox was the ‘speed model’ with a canopy and fairing along the turtledeck. Speed doesn’t help with landing in fog though, and ’ADH was written off in 1936 trying to do just that.
I don’t know the exact circumstances but suspect it was almost inevitable operating in the NZ wilderness. A new fuselage was ordered from Hatfield to assist with repairs, but with the Fox Moth by then out of production the new fuselage was built specifically by the apprentices in the DH Technical School.
This fuselage carried a new construction number resulting in a new registration: ZK-AGM. As ’AGM it resumed operations from Hokitika on the west coast of South Island in 1938, continuing in commercial service up until 1963, when it was wrecked in another accident near Lake Wanaka in the middle of South Island.
After a long period of storage, current owner Bruce Broady acquired the wreck. A New Zealander, Bruce was then flying for a UK airline so brought the remains to the UK for restoration by the Newbury Aeroplane Company, who did an extraordinary job: Bruce has won most major concours events and trophies. I came in at the end of the restoration.
Having flown Newbury’s earlier Fox restoration and being unable to say no (even to Tigers), I was enlisted to do the initial post-restoration test flying.
On first sight, not only is the finish impressive but it really does look rather like a fattened Tiger Moth. A little bigger perhaps in overall dimensions, but the passenger cabin is the only obvious aspect that is different. The concept makes sense: motor out in front, pilot way back to balance that, and the fuselage widened such that cabin and fuel tank are on the C of G.
Consequently, the variable load doesn’t upset the whole contraption’s equilibrium. A closer inspection, however, reveals other differences. The Tiger’s wooden interplane struts are replaced with metal items and, perversely, the whole fuselage is wooden, as opposed to the metal frame of the Tiger.
Unlike the Tiger’s, the undercarriage is braced from behind and?wonder of wonders?has brakes. The steerable skid of the Tiger is replaced by a freely castoring wheel and the fuel tank is larger as the centre section is wider to accommodate the fatter fuselage.
Oddly, perhaps the most fundamental difference is the one most frequently overlooked: the wings are no longer staggered nor swept like the Tiger’s. Instead they are arranged without either?just like the earlier DH60, the original Moth and, like the DH60, those of the Fox can be folded.
A huge bonus for those operating commercially, as you need less space for storage, and if caught in the open a folded Moth is much less prone to damage by gusty winds than a fixed wing biplane.
Folding is a simple single-handed affair. First a jury strut is lowered from the upper wing and telescoped to extend between the leading edges at the root of the wings. This retains the rigged position as the two locking pins are pulled out of the front spars, allowing the whole contrivance to pivot aft about the hinged rear spars and lock in place along the fuselage.
All very easy, and with no aileron cables nor pitot tubes to undo, as everything remains connected. The downside of folding is that weight on the tailwheel is now significant, and without a tailwheel trolley the whole thing is very awkward to move. Nevertheless an enhancing feature compared to the Tiger.
The other missed aspect is that, due to the lack of sweep on the wings, the ribs are now parallel to the airflow again as per the original DH60, and consequently the airflow does not have to flow across the ridges caused as the fabric tightens over the ribs.
Otherwise though, on walking around the machine, there is nothing that will surprise anyone with some knowledge of the de Havilland breed. A little more room under the cowl for the Gipsy Major, but otherwise a standard Tiger Moth installation, and the spinner is higher than other types, but no, nothing unusual.
Just small oddities like the enlarged oil tank and fuel gauge on the underside of the tank as opposed to the top.
To start the motor, it’s standard Gipsy. As the fuel flows under gravity from the tank, no fuel pumps are fitted. So with the brakes on, mags off, and fuel on (a simple pull/push knob above the panel), the starboard cowl can be lifted to depress the float on the carb. It’s while doing this that you see quite how high the motor is; I can usually look down on the carb, but not in the Fox.
This results in the usual Gipsy gurgle, and a few seconds later fuel dribbles from the inlet drain. Once this has stopped the cowl is re-secured, and the prop can be pulled through to prime, but the average chap cannot reach the prop. Instead I have to push the second blade up until I can reach the blade to be swung.
Pushing with my left hand means I can only get hold of the other blade with my right hand too near the root, so I then ‘walk’ both hands along the prop until the right hand is far enough out along the blade to swing. At this point it becomes normal and, after a few pulls to prime, switches on and throttle set, off it goes.
Some people fear that the steep angle of the fuselage on the ground puts the lower prop blade arc close to the swinger’s knees, and advocate starting it from behind, but as the prop is so high the tip is well above knee height and I’m quite happy starting from in front.
I have seen Canadian-built Foxes with a set of switches and a throttle protruding from the port cowl to facilitate this behind-the-prop technique, albeit this was really for operation on floats where the prop isn’t so high, and standing in front is not an option!
Other flight tests:
After starting comes the second challenge: getting in the bloomin’ thing! The cockpit is so far aft of the wing that the standard biplane technique of stepping on the rear of the walkway and swinging a leg into the cockpit whilst hanging onto a strut won’t work. It’s also far too high, the cockpit rim almost at head height, and there’s no fold-down door like most aircraft of that era.
Instead there is a small foothold at the bottom of the port fuselage. Placing the left foot in this and jumping up for the cabane strut (which is really too far forward) allows you to swing your right leg over the fuselage and into the cockpit, a bit like a drunken hurdler.
The left leg can then be lifted over the sill. That’s the theory anyway and fine on an open cockpit version, but ’AGM, being the speed version, has a canopy and fairing that even the most athletic couldn’t swing a leg over. Instead you have to hold the strut and lean back until you almost lose your footing, prior to lifting your right leg in. Once standing on the seat you can wiggle down through the smallish opening onto the seat.
The cockpit is huge, opening up to the full size of the fuselage but entirely isolated from the cabin, with a wall in front of your knees and a false floor below the control box. It’s reassuringly familiar, bar the paucity of instruments. Throttle quadrant, brake lever and trimmer are all lifted from other DH designs and located on the left cockpit wall.
The right side just has a map pocket and the compass. The panel contains the usual stuff, and in this example a rather marvellous air log, which is plumbed into the pitot system and somehow measures the distance travelled relative to the air through which you move.
I don’t fully understand it, and those who do are probably no longer with us but it’s very interesting to see it tick around in flight. The only other oddity is a small window into the cabin that allows you to see the scalps of those sat in the forward-facing seats.
This opens, allowing small items or written instructions to be passed through. Some Foxes had a Gosport Tube-type set-up with a handset like an old telephone for communication, but I’ve only seen this once.
The worst aspect is the view ahead: sat on the ground there isn’t any. It’s a bit like being sat on a camel but behind the hump. As the fuselage widens ahead of the cockpit, and the spinner sits several feet above your eyeline the whole area ahead is obscured.
It was perhaps OK when airfields were big grass circles but it’s really awkward with all the signs, cones and other unnecessary ‘stuff’ that seem to festoon airfields nowadays. You can see a little by looking through the window in the panel and then out of the cabin side windows, but you can’t really see far enough forward for this to be of any great use. Equally the aperture of the cockpit doesn’t allow much lateral movement of the head.
So, once the engine is warm, you release the brakes and taxi very carefully. The brakes are a useful assistance, although not to be relied on, and the wider track wheels seem to make things more controllable. True, it can be a bit of a handful as the wind picks up, but you’ll still be in total control while Tiger Moths turn the long way round due to weather-cocking or wait for a ground handler.
I’ve never had to resort to getting out and lifting the tail around; despite its poor forward visibility on the ground the Fox is light years ahead of the Tiger.
With the wizardry of brakes, the power checks can be completed at the threshold, as opposed to on the chocks prior to taxying. It’s a standard Gipsy installation so no carb heat to worry about (it always runs in warm air, only automatically going to cold when full throttle is applied), simply checking mags, oil pressure and engine idle.
Then, pre-takeoff, confirm that the fuel is on, altimeter zeroed, set the trim, and a full and free check. A final shout through the panel window to ensure the passengers are secure and have their doors closed, and we’re ready.
Once lined up, you do need to take note of the wind. If there’s anything more than a couple of knots of crosswind, displace the stick toward it. The runway ahead is invisible and you rely on peripheral vision for the initial part of the takeoff roll.
Once power is applied the tail can be brought up reasonably quickly?the correct attitude to accelerate can be selected by putting the roof of the cabin just below the horizon?at which point the view becomes excellent. Now that high cockpit position gives an almost panoramic view of the airfield, and although the centreline is still invisible, enough of the runway ahead can be seen to make keeping straight a doddle.
After only a few seconds holding this attitude the Fox just levitates into the air maintaining the same attitude, and accelerating strongly.
In reality the takeoff is very similar to any other Moth’s, but with the good view once the tail is up, and the security of brakes if you run out of rudder (which will only happen if you raise the tail too early in a healthy crosswind), the takeoff phase seems easier.
A cabin full of people does mean that the tail takes much longer to rise, so the takeoff roll is a little longer, and the additional weight really shows in the rate of climb. Nevertheless I challenge you to name anything else that can legally carry five twelve-stone people and about ten gallons of fuel (just over an hour and a half endurance) out of a 350m grass strip and still top 700ft a minute on a cold day.
In this respect the Fox is truly remarkable, and it’s easy to see how it worked commercially: 800lb is an awful lot of high revenue salmon!
Initial impressions of the controls are very similar to the Tiger Moth; responsive and only just stable in pitch, and cumbersome in roll. But once you have mastered the balance, roll reversals from thirty degrees one way to the other do show a slight improvement in both rate and feel to the Tiger.