Comet 4 / 4B / 4C - Overhead Panel

Comet 4 Cockpit.

In Fig.1 and Fig.2, the Comet 4 overhead panels are shown in blue, with the fire warning and control panel in orange. This had been a one-piece panel since the first Comet 1. However, pilots complained that the view through the windscreen was quite hooded, and tall pilots had to stoop to see the end of the runway on approach.


Fig.1: Comet 4 overhead panel (blue) and fire control panel (orange) — looking forwards.


Fig.2: Comet 4 overhead panel (blue) and fire control panel (orange) — looking up.


Comet 4B/4C Cockpit.

When the fuselage was lengthened to produce the Comet 4B and 4C, de Havilland took the opportunity to improve the design of the top section of the cockpit. The four central windscreens were made taller, rising to a peak in the middle, and an emergency escape hatch was added in the roof

Fig.3 and Fig.4 illustrate the changes to the windscreen. Taller glass pushed the top of the windscreen frame further up and further back, with less room for the fire warning and control panel, which had to be split into two sections.


Fig.3: Comet 4C overhead panel (blue) and control panels (orange) in two separate parts.


Fig.4: Comet 4C overhead panel (blue) and fire control panels (orange) — looking up.


Greater Detail

In the last version, I made the quilted lining form the inner skin, from edge to edge, with the radio controllers and other equipment floating there, as if by magic. Since then, I have become more confident at modelling. I made the inner aluminium skin, ribs and stringers, with proper radio racks, brackets and fasteners. It also allowed the quilted lining to be more realistic and drooping, stopping short of the radios, with pop fasteners or "Pull The Dot" eyelets.


Fig.5: Comet 4C overhead panel, showing the equipment racks and brackets fastened to ribs and stringers.

There is more detail on the hydraulic change-over levers, too: higher resolution handles, animated lock mechanisms, and some internal detail. Pulleys (but not cables and springs).


Fig.6: Hydraulic change-over levers and enclosures with improved detail.

As well as around the overhead panel, the quality of the quilted lining has been improved everywhere. Now there is an "aluminium" inner skin, the lining can end correctly, and be attached to the pilots auxiliary panels with pop studs.


Fig.7: Improved quilted lining throughout the cockpit.



Rapid Development of Radios (1958-1962)


In the short period the Comet Series 4 was in production, radios and radio navigational aids developed tremendously. This is reflected in the X-Plane Comet, too.

The Comet 4, as specified by B.O.A.C., had HF and VHF communication, and ADF and VOR navigation radios by Marconi. The transponder was by Cossar. The audio switch box (and cabin intercom) were by Ultra Electronics. These were fitted to the roof using the Marconi system, where the base of the controller box was mounted to rails or brackets attached to roof stringers.


Fig.8: Comet 4 overhead controllers.

Later Comet 4B/4C aircraft had HF and VHF communication, VOR navigation and audio intercom by STC (Standard Telephone & Cables) — a company better known for producing the iconic Trimphone for the GPO. The transponder was Cossar, and ADF navigation was by Marconi.

By this time, controllers were housed in more modern racks with Dzus rails, so the front fascia of the instrument held it in place, rather than the base of the enclosure box. This made it much easier to maintain, change out, or swap arrangements.

As it was, very few of these arrangements remained in tact. The only hard evidence I have is from the original de Havilland Comet Illustrated Parts Manual, which lists the equipment and their positions when the aircraft were originally built. This gave me the precise model and part numbers for radios, controllers and racks, and over the last two years, I have tracked down detailed descriptions and illustrations or drawings of the radios themselves.

In fact there were even more permuations and combinations — pretty much one for each operator — but based around these types of equipment. Some operators preferred radios in different positions. For X-Plane, I have condensed these to three basic overhead configurations:

Comet 4
Comet 4B / 4C
Comet 4C (RAF)

As air traffic increased, there was a need for more useable frequencies for VHF (COM) radios, and this was done by reducing channel spacing.

VHF Airband Channel Spacing
YearRangeSpacingChannels
up to 1947118-132 MHz200 KHz70
1947118-132 MHz100 KHz140
1954118-135.95 MHz50 KHz360
1972118-135.95 MHz25 KHz720
1990118-136.95 MHz25 KHz760
2012 (EU)118-136.95 MHz8.33 KHz2280*


*Theoretically — less because the emergency channel (121.5 MHz) preserves 100 MHz spacing. There are no other channels between 121.4 - 121.6 MHz.

As a result, it was a hunt to find pictures and descriptions for the STC VHF (COM) controller (bottom left).


Fig.9: Early Comet 4B/4C overhead controllers.

RAF Transport Command (216 Squadron) took one of the last batches of Comet 4Cs in 1962 (which the RAF renamed "Comet C Mk.4 C". The RAF specified Ultra intercom, Plessy UHF and Collins HF communications radios, Marconi ADF, and Elliott VHF and VOR radios (Bendix, made under license in Britain) with Bendix controllers. A conventional transponder is absent, being replaced with TACAN on the flight navigator's panel, which served both military and civilian functions.

X-Plane does not support HF or UHF communications, but the controllers I have modelled are animated, and I will write a plug-in to make them respond, in case Laminar (or a third party) adds HF or UHF in future.


Fig.10: Late Comet 4C (RAF) overhead controllers.

All this new work is modelled, unwrapped and textured, but not shaded. It is mostly animated, but some animations are waiting for custom datarefs in a plug-in before they will respond in X-Plane. Lighting effects will be made once everything is in place.

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GMM-P
03/01/2018

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