The Luton LA4a Minor by Air Commodore G.J.C. PAUL
Taken from “Popular Flying”, January-February 1976
(With some editorial correction on original typos, etc.)
In the September/October 1975 issue of Popular Flying (PF) there appeared the obituary notice of Cecil Latimer-Needham, written by his former colleague in Phoenix aircraft. Arthur Ord-Hume. In it he mentions the formation in 1935 of the Luton Aircraft Company and the design by Latimer-Needham of the Buzzard, the Luton Minor and the Luton Major. At a time when we are becoming increasingly aware of the costs of amateur flying it is perhaps of special interest that his Luton Minor is being built by enthusiasts today, and as the redesigned LA4a, the work of Arthur Ord-Hume, can hold its own with many more recent designs which have arrived since the first Latimer-Needham LA2 took the air 39 years ago.
In the same issue of PF Mike Vaisey in his Luton Squadron news records a formation by six Minors and the Duet at Sywell. A seventh was prevented from taking part by a fractured tailwheel and in the same issue again, there is news of the newest; G-BBEA by Hewitt and Stocks. The purpose of this article is to provide some general information about the design, and in particular to describe this Writer’s impression on how the Luton Minor performs in the air, with special thought for those who might like to know more about the air handling of the aircraft before they decide whether or not to build.
DESIGN AND CONSTRUCTION
The current post war Luton Minor LA4a is the redesign by Arthur Ord-Hume in conjunction with Latimer-Needham when they were Phoenix Aircraft Ltd. It is intended for the Aeronca JAP J.99 flat twin air-cooled engine developing a maximum of 37 HP. It is possible to fit other engines, for the airframe is stressed for power units up to 55 HP, and examples are flying with VW and Continental engines. This article relates to the Aeronca engined version.
It must also be stressed that it also relates to the two aircraft flown both of which have variations, not only from each other, but in minor details as well from the original plans. For example, though neither has it, the plans provide for a baggage space behind the pilot’s seat.
Possibly the carriage of much baggage with only the 37 HP engine would have undesirable effects on rate of climb; but with the more powerful engine a reasonable amount of kit can easily be carried.
The design is intended for easiest possible construction by amateurs having limited space and limited workshop facilities. Thus the mainplane is in two halves, reducing the space required for construction: and metal fittings are all simple parts made from mild steel sheet. The fuselage is of box construction with spruce longerons and bracing and plywood covering, except for the top deck aft of the cockpit, which is fabric.
Wings have two spars, each comprising top and bottom spruce booms, with ply web. Ailerons hinge directly from the rear spar. The two halves of the mainplane are mated by fittings on two steel tube pylons over the cockpit, and braced by a pair of parallel streamline steel tube struts from each side of the fuselage.
The tail unit is of similar wooden construction. All covering is by fabric, except for the leading edge of the mainplane which is ply covered. The undercarriage is of steel tube using rubber in compression shock absorber struts. The LA4 may have either tailskid or tailwheel and heel brakes may be fitted to the mainwheels.
POWERPLANT
The Aeronca JAP gives the builder and 0wner of G-AYDY a fuel consumption at economical cruising rpm of 2150 (57 Kts IAS) of 2 gallons per hour. The tank on this aircraft holds five gallons, so that a safe endurance of 2+ hours is available, giving a still air range of 117 nautical miles. Builder’s notes (from the PFA) state that the standard tank holds 6 gallons, and that a cruise speed of 70-75 m.p.h. (60-65 Kts.) is obtainable at a fuel consumption of 2 galls/hr. These figures seem optimistic for the JAP engined Minor. Power plant controls are the simplest, comprising fuel on/off cock; throttle; and magneto advance and retard. G-ASEA has the advance and retard mechanism linked to the throttle control, so that its handling is of no concern to the pilot in flying the aircraft, whereas G-AYDY has a separate lever in the cockpit, taking the place of the normal mixture control and this requires the pilot’s attention. In normal flight, the lever is kept at full advance. There are also differences in priming arrangements, for G-AYDY has a Ki-Gas doping system fitted for external operation by the man swinging the propeller, G-ASEA has a carburettor choke operated also by an external lever. The choke is so arranged that when the throttle is opened beyond the halfway point, the choke is returned to normal running. Fuel is gravity fed from the tank under the top of-the fuselage decking immediately aft of the engine bay, and the carburettor is fed permanently in hot air from a jacket surrounding the exhaust pipe. This arrangement shows clearly in the photographs. There is no record of this installation having suffered from carburettor icing.
PROPELLERS
The propeller fitted to G-A YDY is 63 inches diameter and 32.4 inches pitch, and gives a satisfactory performance. The instruction manual for building issued from the P.F.A. office says that the propeller should be 60 inches diameter, and 34.8 inches pitch. The propeller fitted to G-ASEA at the time of our check flight was one intended for the Aeronca monoplane when fitted with the Aeronca-JAP engine; this is marked DRG DA 1O RHT JAP D 55 P 23.3 whereas the markings on the hub of the propeller mentioned in the instruction book shows it to be TYPE Z.5931. The resulting differences in performance are considerable, and are mentioned later.
ACCOMMODATION
Accommodation is not really the right word, for it suggests a large and commodious place. In the Luton Minor it is the pilot’s cockpit: and one's first approach to it. Crouching under the mainplane and inserting oneself between the lower ends of the lift strut cross bracing wires gives the impression of a very small closet from which the outlook, once seated, is likely to be severely restricted, especially by the wing overhead.
Entrance has to be learned. It is accomplished from the port side by placing one’s left foot on the top horizontal strut of the undercarriage, gripping a front section strut and. with one’s head well forward alongside the port side of the engine cowling, placing one’s right foot on the centre of the pilot’s seat. Move two is to transfer head and shoulders through the cockpit opening over to the starboard side - which enables you to get the left foot into the seat, and then to insert the lower half of oneself into the cockpit. The top half follows.
At this point one is seated, and discovers astonishingly, that not only is it comfortable, but that the outlook in all directions except immediately upward is good, and the feeling of impending claustrophobia vanishes. This is important, because, having been mainly accustomed to low wing monoplanes, this pilot has always been allergic to a wing immediately overhead, and been put off by this feature of the Luton Minor.
I personally have undergone a distinct change of viewpoint as a result of experiencing the Luton Minor, and although one needs to fly one’s airfield circuit in a manner such as to ensure that one never turns towards a spot in the sky that has not first been scrutinized, this can be done, and the overall outlook from the cockpit is, in practice just as good, if not better for example than from a Tipsy Nipper.
The cockpit can best be described as snug. When comfortably seated this pilot’s eyes were 16 inches from the nearest instrument, considerably less than the ideal of 28 inches, and less even than the Chipmunk which at 17 inches is one of the closest ever accepted into the R.A.F. Legroom however is ample, and the width of the cockpit at seat level is 23 inches, allowing Cockpit plenty of room for the well dressed pilot standing up to six feet, and weighing up to 180-190 lbs. in flying kit. The view over the nose straight ahead is good and there is no need to weave from side to side when taxying. On a not very cold day (OA T at 1000 ft. 7 degrees C) the cockpit was found warm enough to be comfortable without gloves, and by leaning slightly forward towards the windshield, it was possible to get into a position where there was little or no draft. Neither G-ASEA nor G-AYOY have map pockets or baggage space, so that any personal items as well as maps and so on have to be stowed in one’s pockets, or strapped to one’s person. G-ASEA has a car type bucket seat fitted, which is 15 inches wide and 17 inches from front to rear. On either side of this are metal fairings, which protect the control runs beneath them.
HANDLlNG
G-A YOY is fitted with an Aeronca JAP engine, which one was interested to hear was once the property of Latimer-Needham himself.
For starting, the ignition advance/retard is set halfway forward, and the throttle lever set to match it. The starboard magneto only “ON" for swinging. As soon as the engine fires, the port mag. is placed “ON” and the throttle slightly closed, and the engine warmed up at 1000 rpm, taking something like five minutes for the well cooled oil to reach a temperature at which the engine can be run up. In fact, during the whole flight the oil temperature never rose beyond 55 degrees C and that after a series of climbs at full throttle and low speeds. Run up on the chocks gave 2150 rpm, with only little mag. drop, although until the engine was well warmed the mag. drop on the starboard side tended to be higher than was expected.
G-AYDY has a tailskid and no wheel brakes. Nevertheless taxying in a light wind (about 7 Kts.) was without problems, and any pilot who can handle a Tiger Moth on the ground is unlikely to experience any problems with a Luton Minor. The rather hard suspension was noticeable however, and a healthy reminder not to taxy too fast.
G-ASEA on the other hand has a remarkably effective pair of heel-operated brakes on the main wheels, and a tailwheel. The heel pedals are well placed, and the arrangement confers a degree of controllability on the ground, which is superior to G-AYDY, especially when proceeding across or down wind. Take off is straightforward with no significant tendency to Swing from the straight-ahead course. Rudder and elevator are effective immediately, and the long line of the nose makes it easy to judge correct attitude.
One does not expect a high wing aircraft to benefit from ground effect but there is no doubt that the take off run is remarkably short, even with the 1ow powered Aeronca JAP; ground run into the 7 knots wind was estimated at something of the order of one hundred yards on smooth grass, though no precise measurements were taken. The aircraft takes a few moments to attain its recommended best climbing speed of 42 knots (IAS) but as it accelerates it becomes “alive” in the way that a thoroughbred will, and one would be little troubled in flying the Luton Minor reasonably accurately without instruments, and relying only on feel. It is that sort of aeroplane.
In level flight, G-AYDY settled comfortably at 2150 rpm giving 47 knots IAS (interesting how often rpm on the chocks turns out to be the nicest cruise speed), and the general handling was explored. The first surprise was the almost entire absence of aileron drag. The remarkable lack of friction in the aileron control circuit of G-AYDY was especially noted, and is not only a tribute to the excellence of Bill Goldfinch’s construction, but also contributes much to the pleasant handling and responsiveness of the aircraft.
Turns in either direction are possible without touching the rudder, though it is beneficial to use a touch of rudder when entering a turn and in turns of over 30 degrees, proper co-ordination of all three controls is essential if a sloppy turn is to be avoided. The aircraft is directionally stable, and can be flown straight and level feet off indefinitely. The high wing also confers a good degree of lateral stability. There is, however, no fore and aft trim, so that it is not possible, unless weights and loadings are so arranged beforehand, to fly hands off.
This brings me to a point of personal preference, which I consider important. The design of G-AYDY is cleaned up by enclosing the elevator cables within the fin fairing: but as a result, there is only a single elevator control circuit, with no back up system. One has only once to experience the failure of an elevator control circuit to feel very strongly for evermore that ever aircraft, however light, must have either a duplicate elevator control circuit: as the Tiger Moth: or a pilot controlled elevator trim tab which is enough to get you home in an emergency. In addition, the latter confers the benefit of making it possible to fly an otherwise nicely trimmed aircraft like G-AYDY hands off whenever desired. One can do without rudder or ailerons if necessary but not elevator control. Controls are nicely harmonized, and whilst light throughout the speed range, as one would expect in such an aircraft, always have plenty of feel to tell the pilot just what the aircraft is doing.
Popular Flying quotes the stalling speed of the Luton Minor with JAP engine as 25 kts. The stall with the stick fully back on the stops was off the 20 kt clock on G-AYDY. The reading looked like about 17-18 knots, which, if the PF figures are correct, suggests the not unlikely position error of 7-9 knots at this attitude. From entering the straight level engine off stall to full recovery to normal flight without any particular haste lost only two hundred feet. There was a slight tendency each time for the port wing to drop at the stall, but so slight as to suggest that it might have been due to no more than the pilot leaning that way in the cockpit. The stall on each occasion was gentle and without vice, though there was no prior buffet or similar warning.