de Havilland DHC-1 Chipmunk

Apr 13, 2010 No Comments by

 

It all Started With Bubble Gum

by Budd Davisson


It’s funny what you remember about your roots in aviation: I remember, for instance, how hard I used to search for airplane bubble gum cards. The gum was usually mouse colored and shattered on impact, but the cards were works of art guaranteed to fire a 12-year-old imagination. Even then, however, I prided myself on my good sense; I didn’t eat the gum and I lived for the day I got a deHavilland Chipmunk card.

The Chipmunk is, was, and always will be, one of aviation’s pleasures for the eye. As a teenager, I liked the way it looked. And, although I’m a hell of a long way from being a teenager, I still like its looks. The Chipmunk is ageless. I, unfortunately, am not. I am, however, one of the many thousands who agree com-pletely on the aesthetics of the Chipmunk; it is an airplane with the lines, performance and pedigree of a pure-bred. So, what’s not to like?

The Chipmunk, believe it or not, is the direct successor to the Tiger Moth as the RCAF/RAF primary trainer. After the British had squeezed all the service they possibly could out of the hopelessly dated mess of wire and fittings that was the Tiger Moth, they skipped directly to the Chipmunk, an airplane light years away from the Tiger Moth in design.

Where the Tiger Moth was possessed of every trick of the bridge-building trade circa 1925, the Chipmunk was state of the art aircraft design for its day, circa 1946. Made to perform on exactly the same engine as the Tiger Moth, the 145 hp Gypsy Major, the Chipmunk outperformed the Moth in every possible way and still managed to have the same forgiving landing characteristics. To do that, with one less wing, means the airplane has to be light . . . and it is. The wings utilize a metal torque box forward of the main spars, but the aft sections are fabric covered, as are all controls. The fuselage is covered with the lightest possible metal with what looks to be a thousand stringers running to and from inside to stiffen things up.

The aerobatic Chipmunk “Specials” such as Art Scholl’s or Bob Russell’s are obviously very beefed up versions that bear little or no resemblance structurally to an original Chipmunk. The fuselage is usually double skinned, the center section strengthened every way possible, the tail volume is increased and attach fittings beefed up. As originally designed, the ‘Munk could, and would, do excellent, graceful acrobatics, but they were of the low-G variety rather than the all out, vein-busting airshow or competition types we see today.


 As with everything British, there are dozens of variations on the Chipmunk theme. Early specifications for the airplane call for three slightly different variants of the British versions, T.10, T.20 and a civil T.21. The Canadian built ‘Munks were either DHC-1 Bs or DHC-1 C. With the exception of the two-piece, bird-cage canopy on some of the British models, they all appear identical from the outside. Structurally, however, the Canadian built aircraft are preferable because of a series of mods made late in the production program.

Although there were a total of 1400 Chipmunks produced (1200 British and 200 Canadian) and hundreds have been imported into the U.S., there are really very few of them around in original condition. Many Chipmunks have been clipped, beefed, re-engined and lightened for aerobatics, and others have been Americanized for convenience with a Lycoming or Continental replacing the cute, but aging, Gypsy Major. In fact there are so few absolutely original Chipmunks around these days that when one does make an appearance, it is an occasion worthy of a few snapshots.

Richard Bidlack of Fremont, Ohio is one of those few who has chosen to repair and maintain his Chipmunk rather than go the modification route. His airplane is so authentic that the fuselage paint is what it was sporting when it was released by an RAF Flying School. Only the wings have been refinished. The originality extends to the inside, where all is still British, as it was when loaded on the boat. The ridiculous brake system is still intact, as is the shotgun shell starter, the nautical style horizontal compass, and all the other quaint and very British accoutrements that make RAF/ RCAF aircraft what they are.

I had the opportunity to strap on Bidlack’s airplane and sample the classroom through which every British and RCAF aviator of the 1950′s went. It was also an opportunity to wonder at the incredible diffusion that must exist within the British aerospace industry. I say ”diffusion” because here is a typical early British /Canadian design, and the ‘Munk is an excellent design, but when you get right down to working with the systems, some of the excellence gets bogged in workings that vary from being ridiculously simple to Goldbergian complicated. A case in point is the Chipmunk braking system.

There are no separate brake pedals. Rather, there is a brake lever on the left side of the cockpit with a ratchet affair that allows you to set it partially on. With the lever partially pulled, you get both brakes if you have the rudder bar centered, or one brake if a rudder pedal is depressed. This sounds fine except that when taxiing, you find yourself working the brake lever with your left hand and crossing over with the right hand to use the throttle. This leaves the stick to do whatever it wants to. On rollout, to make a turn off the runway or to do any kind of quick maneuvering to clear the runway, you have to let go of the stick or the throttle and grab the brake, a decidedly unnatural thing to do.

Where the braking system is complex, a central portion of it, the rudder system, is simple in the extreme, as it is nothing more than a bar with a bolt in the middle of it. So, your feet, situated on either end of the bar, travel in a little circle when you use the rudders. The carb heat is equally simple, a cable with a latch on the end that you pull back and latch down when ready to reduce power.

Since the shotgun shells for the six-shooter style cartridge starter in the Chipmunk cost from $5-$10 each, Bidlack props his airplane to get it started. This involves priming the machine until it starts to vomit raw gas, then pulling it through a certain number of times to wet all four cylinders before throwing the mags on. Then, when mags are on, you get some hapless soul who has a great love for aviation and well developed shoulders to do your slave labor. This particular day the engine was hot and we were just about to start on the second shift of proppers before we got the boiler lit.

Taxiing the airplane was, at first anyway, a challenge to my natural instincts. Although I was strapped into the front pit, the normal solo position, and had fair visibility, I felt uncomfortable as hell trying to taxi an airplane with the stick flopping around free. The airplane didn’t seem to mind, but it was certainly starting to tweak my nerves. The rudder will almost, but not quite, steer the airplane itself (there is no tailwheel steering) so occasionally, I’d have to reach down with the left hand tug on the brake lever to tighten a turn.


When you’re taxiing something military, even something as docile and benign as a Chipmunk, a neat little quiver starts to work its way from your butt to your brain; flat black paint, placards in a language that only vaguely resembles American English, controls and knobs that are of a size and placement that say they mean business. Although it is a trainer, it’s a military trainer and that removes it a far, far reach from a C-150 or a Cherokee.

I worried mildly about getting the ‘Munk aimed more or less straight down the runway for the initial part of the takeoff roll. I had visions of a flurry of hands and feet filling the cockpit, as I would try to get some braking action, while advancing the throttle, to keep it straight until the rudder had enough air in it. However, upon poking the 145 fine English ponies in their rumps, I found that the slightest amount of prop wash was enough for that sail-sized rudder to keep things lined up.

The little 145hp Gypsy engine is identical to the original Tiger Moth engine and turns a special, twisted-metal prop that requires the mounting pads serial numbered to that exact prop and they aren’t easy to find. 

It seems deHavilland has a fetish for rudders. Everything they’ve ever designed had enough rudder area for two or three airplanes and the Chipmunk is no exception. When I picked the tail up on takeoff, I found myself having to be a little careful and use rudders sparingly because the slightest amount of rudder pedal was enough to send the nose hunting off in the daisies. It was far from being sensitive, but there is no doubt that your feet have complete control of your destiny when on the runway.

There is something very tangible about the way the Chipmunk lifts you off the runway. It isn’t a violent lurching where the engine plays as important a role as the wings and it isn’t a vague separation of pavement and rubber. There is a very real feeling that the wings have filled with buoyancy and have overcome gravity with the miracle of their airfoil shape.

Only in sailplanes have I been conscious of the feeling of flight begun, of the absolute separation of flight and lesser activities’ on the ground. In the Chipmunk, I had that feeling. It actually flew into the air. It wasn’t dragged, clawing and screaming, into an environment it would rather avoid. It eagerly lifted itself into a place where it knew it belonged. And it made me, the passenger/ pilot, feel as if I belonged as well.

The moment the Chipmunk is off the ground and doing its best to climb at 700-800 fpm, you know you have ahold of one of the finest sets of controls in the world. Everything about the stick and rudders is smooth and light. There is no friction and the forces are almost insignificant. However, to give the pilot a chance at precision control without oversensitivity, the stick ratios are fairly long; you have to move the stick a reasonable amount to effect the change you desire. It is the best of all possible combinations because the light forces and immediate response of the airplane combine with the right amount of stick movement to make it an almost unbearable joy to ask the Chipmunk to take you where you please.

Considering the airplane’s size (34 foot span) and weight (2100 pounds loaded), it is notable that only 145 horses can make it perform as well as it does. 700-800 feet per minute climb puts it right up with the 7KCAB Citabria and Decathlon which have more horses, and the 115-120 mph cruise is about what a Cherokee does. So it need apologize to no one for its normal performance specs.

What performance specifications don’t reflect is the explosion of emotion that comes from being able to pull up into an absolutely effortless four-point roll. In most airplanes, such a maneuver is done against the airplane’s own wishes, it fights you and you have to force it to deliver every nuance a hesitation roll holds. Not so with the Chipmunk. It is ahead of you all the way because it gives the feeling that it enjoys doing rolls and loops much more than you do. Without an inverted system it coughs and chokes from lack of nourishment when you put negative Gs on it, but otherwise, it is possessed of grace and dignity in all of its maneuvers.

The airplane’s stalls just about aren’t. As the airspeed falls under 40 knots, the stick will begin rattling and shaking and the airplane starts bucking, telling you it’s about to stall. A few knots slower and all the commotion settles down to a continuous buffet as the stick comes back against the stop
and the airplane mushes gently forward. Flaps down, the effect is the same, although a slight break can be forced by accelerating the stall in a bank.

When doing anything at reduced power settings, Bidlack cautioned that carb heat absolutely had to be employed. Apparently the Gypsy is notorious for spitting ice cubes out the tail pipe at temperatures as high as 85 degrees. Some RAF and RCAF training squadrons had the carb heat permanently in the “on” position.

Coming back into the pattern, Bidlack leaned forward over the back instrument panel and told me to carry about 65 knots on final and to wheel land it. Apparently it three-points okay but it wheel lands even easier and since I had no brakes to speak of for control, I was perfectly happy to take the easy way out.

As I turned onto a short final, it became obvious that this was probably an airplane in which a side slip was used a lot because it just doesn’t want to come down. Those same slabs of lift on each side of the fuselage that made the takeoff so enjoyable also keep the Chipmunk in the air a long time with no power. I had a healthy head wind, so a slip wasn’t necessary, but even so, I didn’t come down exactly where I wanted.

As the runway came leisurely up to meet us, I leveled off at what I hoped was several feet high and began holding it off waiting for it to decide to descent. And I waited . . . and waited. Finally, at some number that hardly shows on the airspeed indicator, it decided to come down and I gently felt for the pavement. Chunk! I kissed the runway a little harder than I hoped and got a slight hop. Bidlack shouted that the mains hadn’t even left the ground, but even so, when  things felt solid again, I pinned the airplane down with just a bit of forward stick. In that position, rolling on the mains, it felt as solid as a tri-gear bird, with visibility to match. Once again the rudder told me that it was more than capable of handling the job and reminded my feet that excessive force was going to be rewarded with excessive dancing around on the runway.

When the tail came down and I began thinking about turning off the runway, Bidlack shouted for me to just let go of the stick and do the old cross-the-cockpit hand-jive with the throttle and brake again. Very, very strange!

As I swung into a parking slot I pushed the mixture all the way forward, that’s right, forward, because it works backwards. Still the engine didn’t show any signs of strangling, so I twisted around and asked Bidlack how to shut this thing off. He described a gizmo down in front of my right knee, which looked like a giant hand grenade pin. I wrapped a finger through the ring and pulled. Instantly the engine acted as if I had a hold of its windpipe and died. I couldn’t help but smile a little at the crudeness, but efficiency of the shutdown procedures.

There are plenty of Chipmunks to be had these days, most of them being Canadian models with bubble canopies and the various modifications. Even when they first began to show up as surplus, they weren’t cheap, because everybody immediately recognized them for what they were . . . an affordable light plane with a warbird’s tendencies.

I’ve often wondered, even as a kid, why the RAF/RCAF should have picked such a trivial name as “Chipmunk” for their new airplane. I mean, a service with a history of names like Spitfire, Sea Venom or even of Tiger Moth or Fox Moth surely could have found a better name. Or so I thought. Upon flying the airplane, I now find the name fits it perfectly. It has the kind of perky personality that you’d expect of a chipmunk. It’s joyous and full of fun and generally likes to cavort and play in the sun.

So the name is as right as everything else about the Chipmunk.

–BD

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About the author

Senior Technical Editor About Me: I have a lifelong passion for all things scale, and I love to design, build and fly scale RC airplanes. With 20 plus years as part of the Air Age family of magazines, I love producing Model Airplane News and Electric Flight.
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