Canopy DV Panels. Why?

Just to finish off about Canberra DV panels – it was of course a simple part of the a/c which gave us little trouble but I remember one little problem we had on the OCU back in the early 70’s
– On one of our a/c the knurled thumb nut which was used to latch the panel closed had fallen off (it was usually ‘retained’ so normally would not fall off).Somebody reported it to our chiefy (I cannot remember if the guilty party was Air or Groundcrew) – probably reported using a variation of ” It came off in me hand Chief ! ”.So we had to do an all trades loose article search after a quick look had failed to find the damn thing.
We spent the best part of 2 weeks delving into all the nooks and crannies of the cockpit,all just torch and mirror of course and perhaps an occasional trawl with a magnet (fibre optic shufti scopes were still a long way off 😀 ) – but no luck,none of us could find it.
So after almost 2 weeks we put the cockpit back together and the Boss (Sqn Ldr) took the a/c up for an inverted flight check,just as soon as he had rolled inverted – the knurled nut fell ‘up’ (down) into the fishbowl canopy and he caught it,relief all round and the job card could be cleared.But where had the nut been hiding ? one of life’s little mysteries !

And in the middle in a Rapide 😉

RH side on continental designs ?

And the helicopter pilot on the right was handy for not belting the bridge structure. 🙂

Originally posted by Graham Boak

They are on the left because the pilot sits on the left.

The DV panel on the left also handy for LH circuit flying (which was fairly standard istr)

They are also used on PA-28’s to empty your full bottle of wee out in flight and I know one rear seat passenger that will tell you it’s not a 100 % guaranteed operation……. enough said LOL

Unless its a helicopter 😀

They are on the left because the pilot sits on the left.

Canopy DV Panels. Why?

The correct answer being because of A.P.700, Ministry of Aircraft Production, Design Requirements for Aeroplanes.

Chapter 103, para.21 (paraphrased because of the Forum’s image loading problem):

“Direct vision.- draught proof direct vision openings (i.e. not through transparent material) shall be provided for approach and landing, and for use in bad visibility during flight. The openings shall be rainproof when open, and leakproof when closed. The view through these direct vision openings shall be as indicated by an asterisk in paras. 17.(I), 17.(II) and 17.(III). It shall be possible to open the panels against ice secretion.”

Paras. 17 (I), (II) and (III) dealt with Day fighters, Night fighters, and Bombers, G.R. landplanes and Flying boats respectively.

This is from a 1945 edition.

Bazv and exbrat, thanks for answering my question 🙂

Light aircraft and gliders have DV to provide a means to see the outside world in the event of canopy icing. It’s happened to me once when I passed through cloud; it was so quick and I couldn’t initially tell that I was in clear air. Once iced it stays so a side slip landing was required.

I guess the modern high performance aircraft have canopy anti icing systems of sufficient reliably they don’t need a DV or one fast period of the flight warms everything up enough by kinetic heating, to melt any ice build up. In a real emergency you can always jettison the canopy, certainly the slightly older fast jets (not sure about Typhoon) had to be qualified to fly as a cabriolet at the lower flying speeds.

Originally posted by smirky
Why would there be any positive pressure at ground level?

The various a/c I have worked on over the years – normally conditioning/pressurising air is being supplied from the engine compressor at all times,the actual cabin pressure is created by restricting the outflow via an outflow valve/cabin pressure valve.Even with the outflow valve fully open there can be a slight cabin pressure,with a large crew door such as on a fishbowl Canberra – even a slight positive pressure could ruin a see in crew’s day.
Also on a Canberra (and many other types) the cabin outflow valve/cabin pressure and or the Ram Air valve are partially closed/closed when the a/c lifts off the rwy,this is selected via the W.O.G/W.O.W/Squat Switch usually fitted to an U/C leg (weight on ground switch /weight on wheels switch/USA ) – as the weight comes off the U/C leg (ie the leg extends) either a micro switch or a proximity switch will tell the pressurisation system to start pressurising to its normal differential pressure.On a Canberra a/c – when the a/c returns with a low fuel load – usually the U/C legs stayed extended which meant that (1) The U/C could potentially be selected ‘up’ on the ground (the W.O.W switch would usually inhibit that) and (2) the cabin could still be pressurised.
During and after refuel on a Canberra one could often see 2 or 3 groundcrew jumping up and down on a wingtip to get the U/C legs to ‘settle’ – heavier groundcrew were popular to make this easier 😀
On a sliding/lifting canopy a/c this is not normally a problem because as soon as you select canopy open then the hood seal will deflate and disperse any residual cabin pressure

The Canberra T4 had a DV panel on both sides of the ‘fishbowl’ to cater for the QFI as well.
The Canberra DV panels were fitted/hinged/mounted from the inside of the canopy,they were fairly robust construction and I have not heard of any DV failures.
I would hazard a guess that on the more modern military jets the pressurisation/air conditioning (ECS) system is seen as reliable and much more efficient,any misting or icing which would cause vision problems is less likely and if it did happen then one would select ‘Flood Flow’ which gives unregulated warm/hot air to the screen to clear serious misting etc.

Interesting to hear about the Canberra’s but I still don’t have a clear understanding of why DV panels are on some types and not others. The only consistency I can see is they they are on the port side.
I have had first hand experience of canopies misting and using the DV panel to provide ventilation and help clear the view but is this really the only purpose?.
The use of DV panels does not seem to be confined to one a/c type or role.
Canberra’s being pressurized would seem to be at risk from the DV panel failing at altitude and thus proving an inherent weakness.
Modern gliders still have DV panels but not Hawks, Tornados or Typhoons.
Any other thoughts?

They were also important if you had an engine problem such as an oil leak on piston fighters that would cover the canopy obliterating fwd vision but with goggles you could sideslip down to a landing and any oil that sprayed on your goggles could be wiped away.

Never really saw the use of them until I had a canopy that was completely iced over on approach to landing. Very useful, a DV, to see where you are going, especially with a little sideslip. Also lovely to open in flight for extra ventilation on hot days.

Didn’t the Canberra gold-fish bowl have a habit if misting up during rapid altitude changes? Would make sense to have a small DV panel ‘just in case’

Why would there be any positive pressure at ground level?

Nevertheless it was our official procedure at that time – the idea of having a shoulder against the door was 2 fold – (1) so that if there was any residual cabin pressure then one would be propelled away from the door with ‘merely’ a sore arm/shoulder and (2) keeping the shoulder against the door then became ‘habit’ and one would be less likely to open the door facing the a/c – I certainly would not have liked a faceful of Canberra door to ‘improve’ my already ugly mug :D.
Having said all that – as long as the DV panel was open – realistically there was not going to be any cabin pressure.

A shoulder against the door won’t do much except provide a firm launch, even with just a few psi…