C.Barnes Bristol Aircraft since 1910 (Putnam)
The Bristol Braemar, Pullman and Tramp
In the summer of 1917 dismay at the success of the Gotha raids on London led to an urgent demand for retaliatory bombing on German industrial targets and in October the 41st Wing R.F.C., or Independent Air Force, was formed for this purpose. Very large aircraft were needed for the long-range heavy bombing of Berlin itself, if necessary, and both the Handley Page and Bristol firms submitted suitable designs. Capt. Barnwell drafted his first layout, called B.1, in October 1917. It was a triplane with internal stowage of six 250 lb. bombs and a central engine-room for four engines in a fuselage of good streamline shape. The engines were geared in pairs to shafting so as to drive one large four-bladed tractor airscrew on each side of the fuselage. The B.1 had a four-wheeled landing gear with wheel brakes, a castoring tail wheel and folding wings and was to carry a crew of six, comprising two pilots, a wireless operator, an engineer and two gunners (one also acting as bomb-aimer) over a range of 1,000 miles.
This layout was passed to W. T. Reid for detailing and emerged as a less ambitious design having four engines disposed in tandem pairs on the centre wing. The fuselage had flat sides to facilitate construction, with spruce compression members locally reinforced with plywood and braced by swaged tie-rods. The design was accepted by the Air Board, a contract for three prototypes, Nos. 3751-3753 (C4296-C4298), being awarded on 26 February 1918. The Company had earlier investigated the possible production of large flying-boats for the Air Board, and had this project gone forward new hangars of adequate size would have been built. As things were, the only way of erecting the prototype bombers under cover was to occupy one bay of the Acceptance Park hangars; this was wide enough for the length of the bomber but not its full span. Consequently the bombers had to be assembled one at a time and slewed out sideways on trolleys running on rails out of the hangar door.
The first prototype, named Braemar Mark I, was completed in August 1918 with four 230 h.p. Siddeley Puma engines, substituted because the intended 360 h.p. Rolls-Royce Eagles were not available. F. P. Raynham made a successful first flight on 13 August and flew it to Martlesham Heath for acceptance trials on 13 September, having achieved the very creditable top speed of 106 m.p.h. at a gross weight of 16,200 lb. At Martlesham it was flown during October by Major R. H. Carr and Capt. G. Gathergood, who found the performance and handling generally satisfactory, but criticised the pilot's controls and view and complained of fuselage vibration during taxying. The method of bracing the top and bottom wings to the centre wing was thought to be responsible for tie-rod breakages, which occurred frequently in the outer bays. From Martlesham the Braemar I was sent to Farnborough, where it ended its days in 1920.
Most of the features criticised at Martlesham were improved in the second prototype, Braemar Mark II, for which 400 h.p. Liberty engines were available; it was first flown by Cyril Uwins on 18 February 1919 and its speed and climb with full load were better than predicted. On 17 April it was flown to Martlesham Heath, where it remained at least until February 1920. As late as November 1921 there was a proposal to fit a torpedo rack under the Braemar II's fuselage, but about this date it was wrecked when it swung during takeoff run and collided with a hangar at Martlesham Heath. In April 1919 the Air Board had agreed that the Company should finish the third prototype as a civil transport for 14 passengers, but Barnwell would not permit it to be flown with its enlarged fuselage until a model had been tested in a wind-tunnel.
The third Braemar, renamed Pullman, flew early in May 1920 and created a sensation at the International Aero Show at Olympia in July. It was the largest aeroplane ever seen inside Olympia and its interior decorations were greatly admired. After the show it went to Martlesham Heath, where it was purchased on 7 September, but no attempt was made to operate it as a passenger transport and it was finally dismantled. Although the enclosed crew cabin gave the pilots an unsurpassed view, it was not liked by service pilots, who made a point of carrying fireman's axes so as to be able to escape quickly in an emergency. The Pullman carried its original serial C4298 throughout its life, although it had been entered temporarily on the Civil Register as G-EASP from 14 April to 13 May 1920. The Pullman was not entered for the Air Ministry Civil Aircraft Competition in August 1920 because its landing speed was too high.
While the Braemars were under test by the R.A.F. several ambitious projects for civil transports derived from them were proposed, and in February 1919 Capt. Barnwell had discussed the use of flying boats as ancillaries to ocean liners with the Royal Mail Steam Packet Co., who had pressed strongly for a steam turbine power unit if feasible. It was hoped that the Air Ministry might support such a project and the Company intended to start with a civil transport derived from the Braemar, but with a central engine-room. This would be powered at first with four petrol engines designed as a unit which could be replaced later by a steam turbine power plant of equivalent power. As a first step, W. T. Reid laid out a Pullman for 50 passengers, powered by four 500 h.p. Siddeley Tiger engines. Enquiries were made into the feasibility of a steam plant comprising a pair of 1,500 h.p. turbines, and it was proposed at one stage to use the Braemar I as a steam turbine test-bed. Fraser and Chalmers of Erith undertook to design a turbine of the Ljungstrom type, and the Bonecourt Waste Heat Company offered to design a high pressure flash boiler, but their quotation was considered too high. In May, Reid reduced the number of passenger seats to 40 and recommended that a similar flying boat should be designed by Major Vernon, who had joined the drawing office staff from Felixstowe, where he had been assistant to Major Rennie, John Porte's chief designer. In July the 40-passenger project was dropped because the Air Ministry would not support it, but discussions continued on a smaller test-bed triplane. Eventually a contract was awarded for the design and construction oftwo prototypes, equivocally described as 'spares carriers', powered by four Siddeley Pumas in a central engine room, with gear-boxes and transmission shafts supplied by Siddeley-Deasy. The contract price for each of these triplanes, named Tramp, was ?23,000, of which ?7,500 was Siddeley's price for a set of four engines and transmission gears. A flying boat of similar size with a Porte type hull, the Tramp Boat, was laid out by Major Vernon. It was found difficult to scale down the steam turbines to a maximum output of 750 h.p. each, which was all the Tramp could safely accommodate, and the condenser and boiler posed still more severe problems; in the end the difficulties of making a reliable lightweight high-pressure closed-circuit system proved insuperable.
The two Tramps, Nos. 5871 and 5872 (J6912 and J6913), were not completed until the end of 1921, and even then neither of them ever flew, because the transmission system, particularly the clutches, gave continual trouble. Work on them at Filton was stopped in February 1922 when both of them were transported to Farnborough for development and experiment by the R.A.E. as ground rigs. Quite a large 'greenhouse' grew up round J6913, which remained in use for a year, during which a working party from Filton carried out further modifications to the flight deck and engine controls.
Had it been feasible to produce a safe, reliable and economic steam plant within the permissible weight limits, flying boat passengers in the 1920's might have enjoyed the speed, silence and comfort so vividly pictured by Squadron Commander Hallam, a former Felixstowe pilot, in the last chapter of The Spider Web, which he wrote under the pseudonym 'PIX'. That ideal was not to be realised for 25 years, when the Saro Princess took the air powered by Bristol Proteus gas-turbines, and by then the flying boat was already extinct as a commercial proposition.
SPECIFICATIONS AND DATA
Types: Braemar, Pullman and Tramp
The British & Colonial Aeroplane Co. Ltd., Filton, Bristol
The Bristol Aeroplane Co. Ltd., Filton, Bristol
Type Braemar I Braemar II Pullman Pullman 40 Tramp
Power Plant Four Four Four Four Four
230 hp 400 hp 400 hp 500 hp 230 hp
Siddeley Liberty 12 Liberty 12 Siddeley Siddeley
Puma Tiger Puma
Span 81 ft 8 in 81 ft 8 in 81 ft 8 in 122 ft 96 ft
Length 51 ft 6 in 51 ft 6 in 52 ft 76 ft 6 in 60 ft
Height 20 ft 20 ft 20 ft 32 ft 6 in 20 ft
Wing Area 1,905 sq ft 1,905 sq ft 1,905 sq ft - 2,284 sq ft
Empty Weight 10,650 lb 10,650 lb 11,000 lb - 12,809 lb
All-up Weight 16,500 lb 18,000 lb 17,750 lb - 18,795 lb
Max. Speed 106 mph 125 mph 135 mph - -
Absolute Ceiling 14,000 ft 17,000 ft 15,000 ft - -
Accommodation 4 4 2 crew 3 crew 3
14 passengers 40 passengers
Production 1 1 1 nil 2
Sequence Nos. 3751 3752 3753 nil 5871 5872
F.Manson British Bomber Since 1914 (Putnam)
Bristol Types 24/25 Braemar
Capt Frank Barnwell, chief designer of the British & Colonial Aeroplane Company, submitted proposals for his B.1 heavy bomber to the War Office late in 1917, in which the performance estimates, based on the use of four 365hp Rolls-Royce Eagles, suggested that it would be capable of reaching Berlin with a small load of bombs. Because the project was not formally prepared to conform to a specific Air Board requirement, Barnwell was informed that Eagle engines would not be made available for the bomber; however, the War Office expressed sufficient interest in the aircraft to issue a contract, signed on 11 December 1917, for three prototypes (C4296-C4298).
The draft layout was delegated to Wilfrid T Reid for detail design. Nevertheless, despite its imposing bulk, the Bristol bomber was to be much smaller than the Handley Page V/1500. Obliged to use four 230hp Siddeley Puma engines the aircraft, which became the Type 24 Braemar, was probably doomed to obscurity from the outset as it scarcely represented any advance beyond the Handley Page O/400. Moreover, owing to the company's lack of suitable manufacturing space, only one Braemar could be assembled at a time.
The aircraft was a three-bay, folding biplane with the engines in tandem in fully-cowled nacelles on the centre wing, each engine driving a right-handed two-blade propeller; unlike those of the V/1500, the tractor and pusher propellers were of the same diameter. The two upper wings were of equal span, and the lower slightly shorter, with horn-balanced ailerons fitted to the two upper wings. The fuselage, constructed almost entirely of spruce with wire bracing, was ply-covered except for the nose section. The crew comprised two pilots, a wireless operator, a flight engineer and two gunners (in the nose and amidships). The bomb load, intended to amount to six 250 lb bombs, was carried in an internal fuselage bay. The four-wheel undercarriage featured pairs of tandem wheels, with a braking system, attached to mounting struts anchored to the lower fuselage longerons and the wing spars below the engines, this structure resulting in a very narrow track.
The first Braemar, C4296, was completed in August 1918 and flown by Fred Raynham on the 13th. The same pilot delivered the aircraft to Martlesham Heath exactly one month later. It was evaluated against the RAF Specification Type VIII which had been issued during its period of design and, with certain reservations, was considered to come close to the requirements, though it did not meet the load and endurance figures by fairly large margins. Some criticism was levelled at the flying controls, the ailerons being particularly heavy, and at the very poor field of vision from the pilots' cockpit. Doubt has been cast on a figure often quoted for this Braemar's maximum speed of 106 mph at a gross weight of 16,200 lb, for the highest corrected speed achieved by the aircraft at Martlesham was 102 mph at a weight of about 13,000 lb. C4296 was taken on RAF charge in May 1919, but was written off in a crash two months later.
From the outset it was obvious that the first prototype was underpowered and, once C4296 had left the factors, a second aircraft, the Type 25 Braemar II, C4297, powered by four 410hp Liberty 12A engines, was built, making its maiden flight on 18 February 1919. This aeroplane incorporated a number of improvements, including slight alterations to the nose profile to increase the pilots' field of view, and strengthening of wing tie rods; the undercarriage was also improved, though its narrow track remained unchanged. As far as is known the Braemar never carried its full intended bomb load, although in trials at Martlesham in 1919 C4297 recorded a speed of 122 mph at 5,600 feet while loaded with six 112 lb bombs. This aircraft was to be destroved in an accident when, taking off out of wind on 16 August 1921, it swung out of control and struck a building.
A third Braemar, C4298 (the Mark III), was flown in June 1919 but was almost immediately converted to a passenger-carrying aircraft and renamed the Type 26 Pullman. As such it was evaluated at Martlesham during September and October 1920, but its ultimate fate is not known.
Type; Four-engine, six-crew, three-bay triplane long-range heavy bomber.
Air Ministry Specification: RAF Type VIII.
Manufacturer: The British and Colonial Aeroplane Co Ltd., Filton, Bristol.
Powerplant: Mark I. Four 230hp Siddeley Puma six-cylinder water-cooled in-line engines, two driving two-blade tractor and two driving pusher propellers, and mounted in tandem in two nacelles mounted on the centre wing. Mark II. Four 410hp Lincoln-built Liberty 12A water-cooled in-line engines.
Structure: Wire-braced, all-wood structure, the fuselage ply-covered, and the two-spar, folding wings, fabric-covered.
Dimensions: Span, 81ft 8in; length, 51ft 6in; height, 20ft 8in; wing area, 1,905 sq ft.
Weights (Mark II): Tare, 10,650 lb; all-up (max bomb load), 18,500 lb.
Performance (Mark II): Max speed, 125 mph at sea level, 110 mph at 10,000ft; climb to 10,000ft, 17 min 40 sec; absolute ceiling, 17,000ft.
Armament: Five 0.303in Lewis machine guns: two on nose gunner's cockpit with Scarff ring; two guns with pillar mountings on midships gunner's cockpit; and single gun on Scarff ring in floor of fuselage amidships. Max bomb load, six 230 lb bombs.
Prototypes: Three: C4296 (Mark I) and C4297 (Mark II); C4296 first flown by F P Raynham at Filton on 13 August 1918. No production. (Third aircraft, C4298, was converted to Bristol Type 26 Pullman commercial passenger aircraft, but not operated as such.)
P.Lewis British Bomber since 1914 (Putnam)
In the course of the closing months of the 1914-18 War a number of new advanced bomber aircraft were under construction as prototypes and were completed soon after the Armistice. In the West Country during October, 1917, Capt. F. S. Barnwell at Bristol spent some time on a scheme for a large triplane bomber with folding wings and a crew of six. The machine was designated B.l and was prepared to possess a minimum range of 1,000 miles to enable it to bomb Berlin. Its capacity was to be such that it would carry internally six bombs of 250 lb. each.
Technically, the design was of particular interest, as it envisaged the embodiment of a concept which had been considered a number of times previously by other designers, namely the use of a power plant situated in the main fuselage and coupled to wing-mounted propellers. In this case four engines were scheduled for installation in a central engine-room from which gears and shafts would drive a single tractor four-blade propeller on each side of the engine bay. Preoccupation with his fighter design work made it impossible for Barnwell to devote further time to the B.l, so the layout was transferred to W. T. Reid for development. The practicability of the original centralized power-plant scheme was never put to the test by Bristol, as, once on Reid’s drawing-board, considerable revision and simplification took place. The triplane wings were retained, the central planes acting as bearers of a pair of tandem engines on each side. The design was submitted soon to the Air Board, resulting in an order for three prototypes being placed on 26th February, 1918.
Once the project was accepted, construction of C4296 - the first Type 24 Braemar Mk.I - went ahead rapidly so that a successful initial flight was made by F. P. Raynham on 13th August, 1918. The shortage of 360 h.p. Rolls-Royce Eagle engines for which the four-seat Braemar was designed, meant that substitutes had to be found to fly the machine. Four 230 h.p. Siddeley Pumas were selected, but the total output was considerably lower than that with which the Mk. I was intended to show its paces. Nevertheless, the big 81 ft. 8 in. span triplane performed very creditably in its official trials at Martlesham during September, 1918.
Sweepback was incorporated in the three-bay wings outboard of the centresection, the cellules being mounted on a conventional fuselage with slab sides. The main undercarriage consisted of four wheels installed beneath the lower wings’ centre-section in tandem pairs. Horn-balanced ailerons were incorporated in the centre and upper planes, and the tail unit used biplane horizontal surfaces and triple fins and rudders.
The second Braemar to be built, the Type 25 Mk. II C4297, was completed early in the following year, making its maiden flight on 18th February, 1919, with Capt. C. F. Uwins at the controls. The Mk. II, fitted with four Liberty 12 engines giving 400 h.p. each, was able to reach a top speed of 125 m.p.h., nearly 20 m.p.h: faster than the Braemar Mk. I. Consideration was given to converting the Mk. II to carry a torpedo beneath its fuselage, but towards the end of 1921 the machine was written off following an accident at Martlesham prior to taking-off.
The third Braemar prototype was completed in the spring of 1920, not as a bomber but as the Pullman civil transport with a fuselage accommodating fourteen passengers. In its bomber form the Braemar was scheduled to carry six 230 lb. bombs and to be armed with five Lewis guns.
H.King Armament of British Aircraft (Putnam)
Braemar. The Braemar four-engined triplane bomber of 1918/19 had internal cells for six 230 250-lb or twelve 112-lb - five 40-lb bombs, aimed from the nose by the front gunner, who had a Scarff ring-mounting for twin Lewis guns. For these there were six ammunition drums. Doubtless dictated by the width of the fuselage was the fitting in the dorsal position of two transversely-moving pillar mountings for one Lewis gun each. (Later large bombers, as will be seen, had laterally-sliding Scarff ring-mountings.) For this second station there were six ammunition drums. There was, additionally, a ventral position with an inverted-bow mounting for a fifth Lewis gun, and for this there were eight drums, four on each side, disposed horizontally. As the Braemar was intended for the bombing of Berlin, it is probable that the carrying of a single 3.300-lb bomb was in view, and certainly a scheme was prepared late in 1921 for fitting a torpedo-carrier under the fuselage. This installation would have placed the Braemar in the category of the Blackburn Cubaroo and Avro Ava.
A point of special note is that one contemporary document mentioned a gyro bombsight. This was said to be mounted to the rear of the pilot's seat, together with other instruments 'for bomb dropping'. In the forward compartment was a High Altitude sight.
A.Jackson British Civil Aircraft since 1919 vol.1 (Putnam)
BRISTOL TYPE 26 PULLMAN TRIPLANE
After the 1918 Armistice the unfinished airframe of the third Bristol Braemar four-engined heavy bomber was completed as the Pullman Triplane with cabin accommodation for two crew and 14 passengers. One aircraft only: C4298, c/n 3753, powered by four 400-h.p. Liberty engines, allotted the civil registration G-EASP for one month from 14.4.20. Type number 26 allotted in 1923. Span, 81 ft. 8 in. Length, 52 ft. Tare wt., 11,000 lb. A.U.W., 17,750 lb. Max. speed, 135 m.p.h. Cruise, 100 m.p.h.
Jane's All The World Aircraft 1919
The Bristol " Braemar " was originally designed as a long, distance bomber, but owing to the Armistice coming when it did the machine was never used on active service. It is now being slightly modified to do duty as a passenger-carrier and commercial machine.
It is a four-engined triplane with a single fuselage and with the four engines fixed in pairs tandem-wise driving two tractors and two pushers on either side of the fuselage.
In its original form the fuselage had accommodation for one gunner in the nose, two pilots just in advance of the main planes and another gunner's cockpit midway between the planes and the tail unit. The tail is a biplane with triple rudders.
The main planes are slightly swept hack and ailerons are fitted to the two upper planes only.
The main planes are made to fold.
Type of machine Four-engined Triplane.
Name or type No. of machine Braemar Mk. 2.
Purpose for which intended Bomber or Passenger Carrier.
Span Top 81 ft. 8 in.,
centre 81 ft. 8 in.,
bottom 78 ft. 3 in.
Gap 7 ft. 2 1/2 in.
Overall length 51 ft. 6 in.
Maximum height 20 ft.8 in.
Chord 8 ft. 6 In.
Total surface of wings 1,905 sq. ft.
Total area of tail Top 51.5 sq. ft.,
bottom 45 sq. ft.
Area of elevators Top 42.5 sq. ft.
bottom 42.5 sq. ft.
Area of rudder 25 sq. ft.
Area of fin 28.2 sq. ft.
Engine type and h.p. Four Liberty engines, 1,640 h.p. (total).
Airscrew, diam., pitch and revs. Front (two) 10 ft. 2 In. dia.,
rear (two) 9 ft. 2 in. dia.,
front (two) 6 ft. 11 in. pitch.
rear (two) 7 ft. 5 in. pitch,
Weight of machine empty 10,650 lbs.
Load per sq. ft. 8.6 lbs.
Weight per h.p. 10 lbs.
Petrol tank capacity in gallons 450 gallons.
Oil tank capacity in gallons 40 gallons.
Speed low down 125 m.p.h,
Speed at 5,000 feet 122 m.p.h.
Speed at 10,000 feet 113 m.p.h.
Landing speed 55 m.p.h.
To 5,000 feet 6 minutes.
To 10,000 feet 13 minutes.
Disposable load apart from fuel 1,940 lbs
Total weight of machine loaded 16,500 lbs
Flight, January 23, 1919.
The Bristol Triplane.
While for her largest machines Italy has to a great extent pinned her faith in the triplane, as instanced by the large Caproni triplane bombers, there has been in this country a tendency, rightly or wrongly, to adhere to the biplane type, even for very large machines. That excellent results may be obtained by the biplane form has been amply demonstrated by the large four engined Handley Pages, but it may be doubted whether the triplane form has been as extensively tested as it deserves. The object of the Bristol Bomber was to provide a high-speed machine for bombing or passenger carrying, capable of lifting a considerable load in addition to the weight of crew and fuel. The "Braemar," as the Bristol Bomber is called, is driven by four Siddeley-Deasy "Puma" engines, developing a total of 1,000 h.p. at 1,500 ft. The manner of mounting the engines will be clear from the illustrations. Two drive tractors while the other two drive pushers, after the manner of the large Handley Page. The two tractors have a diameter of 9 ft. 10 in. and a mean pitch of 6 ft. 11 in., while the diameter of the pushers is 9 ft. 2 in., and the pitch 7 ft. 2 1/2 in. The two pilots' seats are placed side by side in the fore part of the body, some distance ahead of the leading edge of the planes, while the extreme nose of the fuselage is occupied by a gunner. Well aft in the body is another cockpit with two guns mounted on a turntable, while a fourth gun is mounted on another gun ring in the floor of the fuselage. The machine is thus well capable of looking after herself as regards defensive gun arrangements. The weight of the machine empty is 9,300 lbs., and she carries 400 gallons of petrol, 40 of oil, and 30 gallons of water. After allowing 360 lbs. for two pilots, the machine is still capable of lifting another 3,000 lbs., bringing the total loaded weight up to 16,200 lbs. The wing loading, it will be seen, is fairly high, 8 1/2 lbs. per sq. ft., and the load per horse-power is 16.2 lbs. The speed at ground level is 106 m.p.h., which is not bad for such a large machine, and the climb to 10,000 ft. only takes 35 minutes. Naturally the performance cannot compare with that of the smaller machines, but for a weight lifter it is not by any means poor, and the machine might make a good commercial aeroplane for carrying large loads.
Flight, December 18, 1919.
THE PARIS AERO SHOW 1919
PRELIMINARY REPORT ON BRITISH SECTION
The British and Colonial Aeroplane Co., Ltd.
From the very first days of flying and of aero shows, the British and Colonial Aeroplane Co., of Filton, Bristol, have made it a rule to exhibit at the Paris Aero Salons. With the excellent workmanship for which Bristol machines were ever famous, it is not too much to say that this firm's stand has always been one of the attractions of the show, and on more than one occasion the Bristols have been the only British machines to be exhibited. This year, as usual, the Bristols are to be shown in Paris, and although the representation of Britain is not left solely to this firm, their stand will, nevertheless, be a conspicuous one, no less than three complete machines being shown, while a fourth, the Bristol Pullman, is so large as to prevent the actual machine from being exhibited. An excellent scale model of it will, however, be on view, and should, in conjunction with illustrations, enable visitors to form a very good picture of the luxurious "Pullman."
The Bristol "Pullman"
As already mentioned, there will be exhibited on the Bristol stand a very fine scale-model of the Bristol "Pullman." This large triplane is provided with a most luxurious cabin, seating 14 passengers, who obtain an excellent view of the country over which the machine is passing, through Triplex windows in the side. One of our photographs gives a very good idea of the comfort and spaciousness of the cabin, which has a height of 7 ft., and is heated and lighted by electricity.
Fitted with four 410 h.p. Liberty engines, placed on the wings, the machine is capable of a maximum speed of 125 m.p.h., while the economical speed is 100 to 105 m.p.h. In addition to the two pilots (or pilot and engineer) the Pullman has a lifting capacity of 2,700 lbs., with a fuel capacity of five hours' flight, or 4,000 lbs. with fuel for two and a half hours' flight. These figures are based on an economical speed of 100 to 105 m.p.h., i.e. at three-quarter throttle, giving a sufficient reserve of power to reach a maximum speed of 125 m.p.h. if necessary. If desired, the seats may be removed and the machine used for carrying mails and cargo, the space available being then 570 cub. ft. The machine has an overall length of 52 ft. and a wing span of 81 ft. 8 ins. The weight empty is 11,000 lbs., and fully loaded 17,750 lbs. Climb to 5,000 ft. in 5 mins., and to 10,000 ft in 12 mins. The ceiling is about 15,000 ft. with full load.