Not to be confused with the T-6 Harvard, the curiously nicknamed BT-13 ‘Vibrator’, the definitive US Basic Trainer of WWII, was built in huge numbers, but few examples survive today
By John Kempton
Is that a Harvard?” they ask. “No sir,” you reply, “this is a Vultee Valiant?a World War Two trainer like the Harvard, but a different aeroplane.” Silence usually follows, while memory banks are searched.
The BT-13 Valiant is often assumed to be a Harvard, rather than mistaken for one. Although it shares dimensions to within inches of the North American T-6 family ? and has the same general layout, once you have seen both you will never mistake one for the other. The majority of US Army Air Force and Navy pilots in WWII, whether they flew fighters, bombers or anything else, had a solid block of Vultee BT time in their log books (see ‘Starting with the Basics’, p.31). However, opportunities to see a BT are rare today: of some 11,500 built, only about fifty are still flying compared with about 500 Harvards, so the recognition problem is understandable.
Like the USAAF and USN cadets of the early 1940s, any pilot coming to a BT cockpit today already knows how to fly, but is about to learn about flying heavier and more powerful aeroplanes; it is very different from a Cessna. The flying qualities built into the BT for its wartime role remain, and it will teach you to be a wiser and better pilot, if you let it.
It’s a big aeroplane, weighing two tons, so manoeuvring in and out of the hangar is done using a tow motor attached to the tail wheel, which makes it an easy single person job. It’s also a simple aeroplane, with most systems being mechanical and the only hydraulics being the brakes, so flight preparation is simple.
In the cockpit, check that mags are off, that the low fuel pressure light comes on when the battery master is switched on, and that it goes out when pressure is raised using the auxiliary pump handle. Check the fuel gauges down in the belly: the float gauges under-read by about ten gallons in the ground attitude, and we treat this indication as available flight fuel (the manual is unhelpful on the subject of useable fuel).
Left and right tanks in the centre section hold sixty US gallons each, and for a local flight of about 45 minutes you need twenty-plus gallons in one side to burn, and another ten in the other as a reserve. Cycle the fuel selector and leave it on either left main or right reserve, depending on which tank has more in it. (The ‘main’ standpipe in the right tank is taller, and its selection is avoided to preclude running out of gas while there is still fuel on board!)
While you are up there, check the oil tank, which is forward on the upper left fuselage: it can be filled to ten gallons, but eight is normal.
SMART CLOTHES BEST LEFT IN THE WARDROBE
It’s a good idea to wear your old clothes when you go BT flying, as you need to do a bit of crawling around beneath the aeroplane. Duck under the cowling and disconnect the hose from the quick drain fitted to the bottom of the crankcase sump, to which oil inside the engine drains. Radials leak oil, and it is better to direct it into a sealed container for reuse than to lose it onto a drip tray. The added benefits are reduced risk of a hydraulic lock and less oil thrown over the airframe on start-up. Pour the gallon or so of oil back into the tank, then crawl under the centre section and do a fuel drain from each side. Wipe hands on trousers, and proceed with a standard walk-around, starting from the left wing root.
There are a few items of note. Each aileron has a tab that works as both a servo and a ground-adjustable trim. This particular aeroplane’s wingtips are actually from a B model, with nav lights on the ends rather than above and below a few inches inboard, as an A model should have ? perhaps a convenient fix after the WWII accident that damaged the starboard outer wing.
Each gear leg bears a large brass data plate from the manufacturer, which suggests pride in workmanship and looks good, polished up. Pull the prop through nine blades as you pass the nose, to check each cylinder for potential hydraulic lock, and on the rear port side check the luggage door: the BT can take 75lb of gear ? plenty for two people. Check and tidy the rear cockpit, and you are ready to go.
The seat adjusts up and down via a lever on the right-hand side, and a foot operated toggle on each pedal adjusts the rudders. The control lock, a yoke mounted forward of the stick, must be firmly secured in its floor brackets to avoid fouling controls in flight. Standard checks around the cockpit are made from left to right: flap is selected by a crank handle which delivers two degrees per turn to a total of sixty, and elevator and rudder trims operate via two adjacent vertical wheels. Throttle cracked, mixture forward to rich, prop rearward in coarse pitch for the start. Carb heat lever cycled and left on cold, likewise the oil cooler shutter lever below. Switches for lights and electrics are on a panel below the flight and engine instruments, select master on and leave the rest off. Pump up fuel pressure, and push nine strokes of prime (the feed goes only to the top five cylinders). Toggle the switch to energize the inertia starter, and after about twenty seconds ? once the groaning tone has risen to a whine ? move it across to engage, let the prop kick round a couple of blades and select mags to both.
The Pratt will cough into life with a pleasing sound and a few puffs of smoke: hold the starter engaged until it is definitely running, watch fuel pressure and give an occasional slow pump until the needle comes up. Oil pressure comes up quickly, the pitch lever can be moved forward and the engine settles into a smooth idle at around 1,000rpm. Generator on, radio on, and settle back to wait until the oil temperature comes up ? which can take a while on a cold day.
There is time to go around the cockpit again, and get comfortable while you wait. It is a roomy and comfortable place to be, with low sides and good vision except for straight ahead. Flaps are usually set at twenty degrees for takeoff, and trims at neutral. Run-ups are done once oil temperature reaches thirty, after which the temperature will be above forty and you are right to fly.
The BT is easier to taxi than a T-6: the tailwheel steers with the rudder until you ask for a tight turn, at which point it unlocks, locking in again once you are pointed ahead. Looking from side to side helps you to keep straight, and S turns allow you to clear the taxiway ahead. Review takeoff numbers and options before you get to the runway, roll onto the centreline, wiggle the pedals to ensure the tail wheel is engaged, then open the throttle slowly.
SOUNDS GOOD, FEELS GOOD
The deepening roar of a radial gathering power is one of the rewards of flying this type of aeroplane, particularly with the canopy part-open. It sounds good and it feels good as you accelerate strongly. The BT tends to keep straight and, once the tail comes up, forward vision is fine. Maximum power is 36 inches manifold pressure, but expect to lift off at about sixty knots before you get the manifold pressure much past thirty. Establish eighty knots, wind up the flaps, get power back to 30in and 2,000rpm and you will be climbing at a good thousand feet a minute.
The aeroplane is very stable and little trim change is needed. All-round vision is excellent and you can sit back and enjoy the ride, remembering to add a little throttle occasionally to maintain thirty inches. If you are going from A to B, set cruise power at around 26/1,800, which is about 65 per cent, and you will get around 120kt. The cockpit is comfortable, reasonably quiet with the canopy shut, and practical with two map/storage cases in the front and one in the back: factor in the baggage capacity, and the BT is an efficient tourer. On climb, you burn about 34 US gallons or 130 litres per hour, in cruise about 80 lph ? and with maximum useable fuel calculated at 100 gallons or 380 litres you have four hours endurance. You are burning about fifty per cent more fuel than a C182, and you get fifty per cent more fun via the radial soundtrack, the all-round view and the ability to open both canopies for fresh air and sharp photos.
If you intend to do much manoeuvring, it is best to get some height, as the BT is unlike the GA singles we usually fly. Sink rates of 3,000 to 4,000 feet per minute are common: it takes time to mentally adjust to this, it takes time to convert that descent back into upward motion, and it takes time to learn the input pressures required ? which is why the learning is done at altitude. The WWII manual stipulates aerobatics above 5,000ft, and power at 28/2,000. G limits are just over +5/-2, but you are unlikely to get near that (a good thing, as those limits were set seventy years ago when the airframe was new).
MILTARY TRAINING SEQUENCE
It is interesting to follow the military training sequence, which involves increasing inputs progressively from all controls. Start flying in a straight line, then roll into a level turn through about 45º to the left with a course reversal 45º to the right; repeat several times, with bank angle increasing from about thirty degrees up to about sixty. You soon learn what the rudder is for, and there are constantly varying loads on the stick to keep the nose on the horizon and to change direction.
Vertical exercises move from high-performance climbing turns to wingovers and lazy eights, and speed ranges from 120kt at the start, back to 70/80 at the high point to 140 descending. It all keeps you busy, you will feel the g loads and it takes time to learn how to keep it all flowing and in balance, but it is fun to do. A basic aileron roll requires 140kt and a nose-high attitude before you introduce aileron, as you will be nose-low on the way out. The BT-13 rolls quite slowly, quicker than a Stearman but a bit slower than a Harvard ? 42 feet of wing takes a bit of moving. Loops use the same speed, although a little extra doesn’t hurt. There is no G meter but you will pull a bit over three. The BT is responsive in all axes, with only small rudder inputs required to keep the ball in the centre. Elevator loads are quite light courtesy of a long stick, and ailerons are firm rather than heavy ? more so than I expected with those servo tabs.
NO SPINS TODAY
The aircraft is today placarded against intentional spins, which is surprising given its original role. Stalls are predictable, the nominal stall speed at max weight is 65 knots, but the aeroplane will usually continue to fly all the way back to sixty knots or less before the nose falls and a wing drops. It recovers promptly once you unload, provided the ball is near the centre, but it takes a few seconds and some height; it would be hazardous at circuit height. Stall warning is clear, with sloppy controls and some shaking, but there is nothing to justify the ‘Vibrator’ nickname from World War Two ? I guess everything had to be called something!
Descent is usually done with power back around twenty inches, which will see the speed back inside the 100 knot flap range once you level off. Crank in twenty degrees of flap on downwind, and you will be back around 85kt which is a good speed to hold onto base; power back to fifteen inches, crank in another ten degrees and you will have eighty knots turning final, ten more degrees and you will be coming back to the seventy you want at the threshold. Slower is okay in stable air, with care and power, and the full sixty degrees of flap can be used with an attention-getting nose down attitude.
A GOOD COMPROMISE
For most circuit operations, thirty degrees of flap is a good compromise as it allows a touch and go with only a small amount of forward trim required for the go part. The aircraft is quite happy to arrive flapless, but the speed is greater, the forward vision poorer, and it will float.
The BT is very predictable after touchdown, more so than a T-6: perhaps because the whole fin and rudder sit in clean air above the fuselage, perhaps because of better undercarriage geometry, or perhaps it is my imagination, but it feels more trustworthy. It is similar to a Chipmunk: arrive at the correct speed, pointed straight, and things will usually work out well. It naturally three-points, but is happy to ‘wheel on’ at a slightly higher speed. It remains a taildragger, and a heavy one, and if you get complacent or careless it will bite you; it can be bounced and adrenalin shots do occur.
It is best to leave all the post-landing housekeeping until the aeroplane is clear of the runway and at walking pace; lots of BTs have been ground looped, we don’t have many left and these small tasks can be a distraction from keeping straight. Canopy open, flaps up, reset trims; the taxi back to the hangar is a pleasant wind down after the flight, the only task remaining being to run the engine back up to around 1,500 revs and pull the prop back into coarse pitch before cutting the mixture.
Radials are rare these days, and it is not unusual for the rumble of the arrival to attract an audience. That is when the Harvard question is most likely to be asked: the BT has lived in the shadow of the T-6 since North American beat Vultee for the Basic Combat contract in 1938. Taking the time to answer is payback for the privilege of flying one: you create awareness of an almost forgotten veteran, and perhaps motivate people to learn a little more about the aeroplane and the history it represents.