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In-Depth – De Havilland DH-88 Comet

May 7, 2010 2 comments

Hi! Welcome to this new category of this blog. Here, i’ll go in-depth on several interesting models, always looking to focus on the less common ones but surely attractive either from a history, flight characteristics, peculiarity, difficulty, style, appearance or symbolism perspective. In most cases, i’m sure a bit of all of these will apply.

To start it off in a nice way, i’ll talk about one of my all-time favorite aircrafts. Don’t ask me why, but the Comet really stands out from every other plane when i compare it with others. It’s style, unique appearance, flight challenge and twin low engine just adds to the pack!

De Havilland DH-88 Comet
De Havilland DH-88 Comet

Specs

  • Crew – 2
  • Propulsion – 1 piston engine
  • Engine model – de Havilland Gipsy Six R
  • Engine power – 172 kW / 230 H.P.
  • Max speed – 206 kts / 237 mph / 382 km/h
  • Cruise speed – 191 kts / 220 mph / 322 km/h
  • Service ceiling – 19.000 ft / 5.791 m
  • Rate of climb – 1200 ft/min / 366 m/min
  • Range – 2.542 NM / 2.925 mi / 4.708 km
  • Empty weight – 2.840 lbs / 1.288 kg
  • Max takeoff weight – 5.320 lbs / 2.413 kg
  • Wingspan – 44,0 ft / 13,41 m
  • Wing area – 212 sq ft / 19,7 sq m
  • Length – 29,0 ft / 8,84 m
  • Height – 10,0 ft / 3,05 m
  • First flight – 08.09.1934
  • Total production – 5 units

History

The de Havilland DH-88 Comet was a twin-engined British aircraft that won the 1934 MacRobertson Air Race, a challenge for which it was specifically designed. It set many aviation records during the race and afterwards as a pioneer mail plane.

Despite previous British air racing successes, culminating in 1931 in the outright win of the Schneider Trophy, there was no British plane capable of putting up a challenge over the MacPherson course with its long overland stages. The de Havilland company stepped into the breach by offering to produce a limited run of 200 mph (322 km/h) racers if three were ordered by February 1934. The sale price of £5,000 each would by no means cover the development costs. In 1935, de Havilland suggested a high-speed bomber version of the DH-88 to the RAF, but the suggestion was rejected. (De Havilland later developed the de Havilland Mosquito along similar lines as the DH-88 for the high-speed bomber role.)

Three orders were indeed received, and de Havilland set to work. The airframe consisted of a wooden skeleton clad with spruce plywood, with a final fabric covering on the wings. A long streamlined nose held the main fuel tanks, with the low set central two-seat cockpit forming an unbroken line to the tail. The engines were essentially the standard Gipsy Six used on the Express and Dragon Rapide passenger planes, tuned for best performance with a higher compression ratio. The propellers were two-position variable pitch, manually set to fine before takeoff and changed automatically to coarse by a pressure sensor. The main undercarriage retracted upwards and backwards into the engine nacelles. The DH-88 could maintain altitude up to 4,000 ft (1,200 m) on one engine.

De Havillands managed to meet their challenging schedule and testing of the DH-88 began six weeks before the start date of the race. On the day of the race, the three distinctively coloured planes took their places among 17 other entrants ranging from a new Douglas DC-2 airliner to two converted Fairey Fox bombers.

The first of the aircraft to fly was registered G-ACSP, named “Black Magic” and was bought by Jim and Amy Mollison (nee Johnson) who were both independently recognised as world record holders in their own right. This combination started the race as favorite. The “Black Magic” was the first of a great new generation of British aircraft that flew with all three of the now commonplace technical features: retractable undercarriage, variable pitch propellors and flaps.

De Havilland DH-88 Comet "Black Magic"
De Havilland DH-88 Comet “Black Magic”

The three Comets were painted in distinctive colours – the Mollisons’ G-ACSP Black Magic was black and gold; Bernard Rubins’ nameless G-ACSR was green and flown by Owen Cathcart Jones and Ken Waller; while G-ACSS, flown by C.W.A. Scott and Tom Campbell Black, was resplendent in red and white and named Grosvenor House.

G-ACSP "Black Magic", the first of the Comets, flown  by Jim and Amy Mollison
G-ACSP “Black Magic”, the first of the Comets, flown by Jim and Amy Mollison
G-ACSR - the green one - landing in Baghdad on its  way to Australia
G-ACSR – the green one – landing in Baghdad on its way to Australia
G-ACSS "Grosvenor House", winner  of the MacRobertson Trophy
G-ACSS “Grosvenor House”, winner of the MacRobertson Trophy

Grosvenor House

“Grosvenor House” went to Martlesham for RAF trials in 1935 and, painted all white as K5084, was a memorable feature of the 1936 Hendon display. It was subsequently damaged when landing with a full load and disposed of as scrap. F.E.Tasker then acquired it and Essex Aero Ltd rebuilt it at Gravesend with Gypsy Six series II engines driving DH variable pitch airscrews. In pale blue and renamed The Orphan, G-ACSS was flown into fourth place in the 1937 Marseilles-Damascus-Paris race by Flg Off A.F Clouston and George Nelson.

Bearing a third name, “The Burberry”, the aircraft left Croydon on November 14th 1937 piloted by Clouston and Mrs Kirby Green, who succeeded in lowering the out-and-home record to the Cape to 15 days 17 hours. Carrying its final name, Australian Anniversary, it left Gravesend on February 6th 1938, but broke no records after the undercarriage collapsed in Cyprus. The last historic flight by ‘SS was one of its greatest. Flown by Clouston and Victor Ricketts, it took off from Gravesend on March 15th 1938, reached Sydney in 80 hours 56 minutes, crossed the Tasman Sea to Blenheim, New Zealand, in 7½ hours, stopped overnight, then returned to Croydon on March 26th. The 26,450 miles had been covered in 10 days 21 hours 22 minutes to set a record which still stands. The Comet then returned to Gravesend where it remained under tarpaulins until rediscovered in 1951. The DH Technical School then restored it to its original MacRobertson condition for display at the Festival of Britain Exhibition, after which it was preserved by the makers at Leavesden until handed over to the Shuttleworth Trust in 1965.

Flights and Records

On December 20th G-ACSR, suitably renamed Reine Astrid, left Evere, Brussels, piloted by Ken Waller and Maurice Franchomme, to carry the Christmas mail to Leopoldville in the Congo, arriving back on December 28th. It was then sold to the French government as F-ANPY and lowered the Croydon-Le Bourget record to 52 minutes during delivery by Hubert Broad on July 5th 1935. In the course of experimental work for a projected South Atlantic mail service, Jean Mermoz made Paris-Casablanca and Paris-Algiers high-speed proving flights in this machine in the following August and September.

A fourth Comet, registered as F-ANPZ, was built for the French government with a mail compartment in the nose. In their experiments with high-speed aircraft providing a mail service to far-flung colonies, the French also produced the Caudron C641 Typhon, an aeroplane that bore an uncanny resemblance to the Comet.

The Portuguese government had similar mail-carrying ideas, and acquired the Mollisons’ Black Magic for a projected flight from Lisbon to Rio de Janeiro. Renamed Salazar and re-registered as CS-AAJ, it was ferried from Hatfield to Lisbon on February 25th 1935 by Senor Carlos Bleck and Lt Costa Macedo, who covered the 1,010 miles nonstop in six hours five minutes. A return trip was made in the following September, and in 1937 Macedo again brought the aircraft back to Hatfield for overhaul; he made an outstanding return flight to Lisbon in five hours 17 minutes in July of that year. Shortly after being sold to Portugal, the “Black Magic” disappeared for a number of decades until it was found languishing on a portuguese farm and recovered to the UK. After passing through a number of owners, “Black Magic” now resides in a safe and secure environment with her own workshop. G-ACSP “Black Magic” is now in the process of a complete restoration to airworthy condition by the Comet Racer Project Group. Although a number of years away she will one day make her second “maiden” flight from the safety of her new home at Derby Airfield.

The last Comet

A fifth and final Comet named “Boomerang” was built to the order of Cyril Nicholson, who planned a series of attempts on the major long-distance records. Piloted by Tom Campbell Black and J.C.McArthur it made a record Hatfield-Cairo non-stop flight of 2,240 miles in 11 hours 18 minutes on August 8th 1935 during the first stage of an attempt on the Cape record. This was abandoned because of oil trouble, and the machine returned non-stop in 12 hours 15 minutes and established a new out-and-home record to Cairo. Although entered in the round-Britain King’s Cup Race of September 7th 1935, “Boomerang” was a non-starter and left a fortnight later for a second attempt on the Cape record; airscrew trouble over the Sudan on September 22nd compelled the crew to abandon the aircraft by parachute.

Radio Control Scale versions

To spice up your apetite, here’s an amazing 1/4th scale (3.35m wingspan!) radio controlled DH-88 Comet flight video. This awesome scale version can be powered up by two O.S. 160-200 size engines (2 or 4 stroke) for an amazing realism. Enjoy!

[to be continued… check back later]
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Mibojets A-10 Warthog Twin Turbine scale

This spectacular large Mibo Jets A-10 scale model is powered by twin turbines. Built and piloted by Billy Edwards, this aircraft even features an opening canopy. Shot on location at Apollo Field in Van Nuys, CA.

Specs

Scale: 1: 5,8
Wingspan: 3,00 m (118 inches)
Fuselage length: 2,75 m (108 inches)
Wing area: 133,9 dm2 (2100 square inches)
Turbines: 2 x 70N – 120N
RC functions: Rudder, elevator, ailerons, throttle, flaps, landing gear, brakes

Beginners’ Guide

April 30, 2010 Leave a comment

First Model

Some people consider a glider as the obvious choice for the first model. Although a glider normally flies slower and is supposed to be more forgiving, I think that’s just a matter of taste. Being a skilled glider pilot doesn’t necessarily mean being also a skilled powered aircraft pilot and vice-versa.

Assuming that a powered model was chosen, the beginner is advised to start with a so-called trainer. This type is usually a high wing aircraft model with nearly flat bottom airfoil that produces high lift, permitting slow landing speeds without stalling. It also has some dihedral angle to give a good lateral stability.

However, a flat bottom high wing with dihedral is more sensitive to crosswind gusts, so the first flights should be done during calm weather. A beginner should avoid wings with too sharp leading edges, as it will worsen the stall characteristics.  A well-rounded leading edge is therefore preferable, as it better conveys the airflow onto the upper wing surface allowing higher angle of attack at low speed.

A trainer model should not be too small, as it would be difficult to assemble and maintain and would be more sensitive to strong winds.  It should not be too large either,  as it would be difficult to transport, require a larger flying field and
would be more expensive. A reasonable size is about 150cm wingspan (60 in) with a high aspect ratio, which means the wingspan being about 5.5 times the wing chord. A square wing is advisable, as it distributes the weight of the aircraft evenly over the entire surface of the wing. In order to allow a reasonable low landing speed without stalling, the wing
loading
should not be greater than about 60g/sq.dm (19-oz/sq. ft). Wing loading is the aircraft’s weight divided by the wing area. Some degree of wing washout also improves the stall characteristics.

The basic parts of a trainer model:

Engine – provides the power to rotate the propeller.
Propeller – (also Prop) is attached to the engine’s shaft to convert rotational motion into thrust and speed, which depends on the Prop’s diameter, pitch and the Engine’s power.
Spinner – streamlined part that covers the end of the Prop shaft.
Fin – (also Vertical Stabiliser) provides directional stability (stability in yaw).
Rudder – movable part fitted to the Fin’s trailing edge, is used to change the aircraft’s direction.
Stabiliser – (also Horizontal Stabiliser or Stab) provides longitudinal stability (stability in pitch).
Elevator – movable part fitted to the Horizontal Stabiliser’s trailing edge, is used to make the aircraft climb or dive.
Ailerons – movable parts on both sides of the wing, are used to make the aircraft roll about its fore – aft axis. When one aileron moves up the other moves down.
Wing – provides the aircraft’s main lifting force.

One may build a model aircraft based on drawings (plans). This requires some building skills and also time and effort to find out and gather the materials needed for the construction. An easier approach (albeit more expensive) is buying a kit of parts. There are many kits on the market with different levels of prefabrication depending on their price.
The cheaper kits have most of parts included, but some pieces come either pre-cut or printed on sheets of wood, so the builder is expected to do some extensive job, such as to cut out the fuselage formers and wing ribs, glue the parts together, apply the covering material, etc.
For those who are not so keen on construction, there are almost ready to fly (ARF) kits with an extensive re-fabrication, requiring one or two evenings to assemble. There are also ready to fly (RTF), which normally come complete with the power plant and some of them even with the radio pre-installed.

First Flight

It’s highly recommended to have an experienced instructor beside you during your first flight. However, it is not impossible to get succeed by doing it alone. Maximum wind speed recommended is 5-8 Km/h (3-5 mph) including gusts.

Check your plane’s CG location with empty fuel tank (if you are using a combustion model) or with batteries (if using an electric model) by supporting the model with your fingertips underneath the wings. Find the position where the fuselage gets level or its nose is pointed slightly downwards. Remember a golden rule: a plane with a CG a bit forward to it’s ideal location will fly badly, but a plane with a CG aft it’s ideal location will fly once… So, if you are not sure about how to exactly put your CG, just make sure it is more forward than aft. Within the first flights when you try to fly leveled you will notice by it’s flight characteristics and you can make small corrections on each new flight.

Transmission range check should be performed on the ground before the flight. This is usually done with the Transmitter aerial collapsed (this is not applicable for 2.4Ghz radio systems). The control surfaces should respond without glitch at a distance of about 80 meters (263ft). This distance is only an approximately guide line, as the actual range may vary depending on the environment.
The effective range may only be half of this value if located at mountain bowl site or close to a public radio transmitter, radar station or similar. The range may suffer adverse effects if the receiver aerial is close to metal parts or model components reinforced with carbon fiber. Some transmitters allow the aerial to be totally collapsed inside a metal case (again not applicable to 2.4Ghz radio systems), which also may reduce the radiation. In this case the lower section of the aerial should be extended during the test. The check should be repeated with the power system running, alternating the throttle setting between idle and full-throttle.

The range will be much higher when the model is in the air, normally about 1Km or as far as one can see the model.

Take-off:

If you hand launch your model, throw it against the wind horizontally and straight ahead, not up.
If you take-off from the ground, taxi the model towards the wind and let the model gain ground speed before applying elevator. Once in the air try to climb at a very small angle, not abruptly upward, which would cause loss of airspeed and stall.

The model is more sensitive to the motor torque effect during the relatively low take-off speed and may begin to turn left (or right). Use the rudder or ailerons to prevent the model from turning during the climb stage, otherwise the model may initiate a spiral dive.

Don’t try any turns until the model has gained speed and reached a “safe altitude”. Be very gentle with the controls and practice gentle turns high in the air before you try to land. To prevent losing altitude when turning the model, just give little up elevator at same time you make a turn.

Try to keep the model in sight and do not fly too high or too far away. You may reduce the throttle while high in the air so you may get an idea how the model behaves at low speed – try to glide it while high and use just a bit of elevator to keep the nose leveled – even thought initially you will feel it is too slow and it may fall, just keep doing it so you have a real feel of how slow it can fly (as you have the model high in the air with slack to recover if something happens). This will give you an idea of the kind of speed you will use when approaching for a smooth landing (which will NOT happen on the first times… – you have been warned).

To prevent getting confused about which way to turn when the model flies towards you, turn your back to the model slightly while keeping watching it, so you can imagine “right” and “left” from the model’s point of view. At this stage, you should have already practiced with a good computer flight simulator and you should be already comfortable with this situation. If not, better to spend a few more hours on the simulator if you don’t want to crash your expensive plane.

Some trimming may be needed in order to reduce or eliminate roll, bank and/or pitch tendencies. A flat bottom wing often tends to “balloon” up into the sky, keeping climbing when full throttle is applied. This may be reduced during the flight by adjusting the elevator trim or by reducing the throttle. In worst cases it may be needed to increase the motor’s down-thrust angle and/or decrease the main wings incidence angle.

Landing:

Reduce throttle to about half or even less (depending on the power and torque of your power plant) so you have to slightly pull up the elevator to keep the altitude. Turn the model towards the wind and let the model sink gradually towards the landing area by easing the elevator.

During the last fifteen to twenty meters (45 to 60 feet) of descent, (which depends on the model’s characteristics) you should idle the throttle. The model will start sinking at a higher rate now. Try to keep the model in a shallow dive and don’t use the elevator to gain altitude or to prolong the flight at this stage, otherwise stall is likely to occur.
Just keep a slightly downward attitude throughout the final approach in order to maintain the airspeed.
The higher the wing loading, the steeper the approaching angle may be. However, it is not recommended approaching angles greater than 45 degrees.
If you notice that the model is sinking too fast or is too low to reach the landing field – just increase the throttle first before applying elevator to maintain or gain altitude to prolong the flight or to repeat the landing approach.
Pull up the elevator slightly about 30-60cm (1-2 ft) before the touch-down so that the propeller or nose gear don’t hit the ground.

Be prepared to repeat unsuccessful landings several times, since it’s often a matter of trial and error before one gets used with how the model behaves. If you are using a flying field with grass around the track (highly advisable), on the first tries just worry about the landing approach. Don’t try to land in a specific spot, avoid turns when the model is flying low or at low speed. Just let your model glide into the ground straight-ahead. With time and more experience, you will get better and better an soon will be landing exactly where you want. Even experienced pilots sometimes have hard landings, as this is the most difficult maneuver.

Avoid the proximity of buildings, roads and electric power lines. Don’t fly close to or towards people and animals.
The bigger the field for your first flight, the greater will be your chances for success. And remember, if the weather conditions are not adequate for your first experiences, control your excitement and come back later when the weather is better. This is a great way to prevent mistakes that will cost you a lot of money in repairs.

It’s also advisable to join the nearest model aircraft club there you may meet experienced fliers who can provide lots of useful tips and hints.

Good luck!