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By: - 17th May 2018 at 20:52 Permalink - Edited 1st January 1970 at 01:00
I'd say to provide a clear view for landing. A curved approach, as well as using a sideslip to adjust height on final, was more common in those days. So it wasn't a totally useless feature.
By: - 17th May 2018 at 21:03 Permalink - Edited 1st January 1970 at 01:00
Yes I would also say that they would be fitted for landing in the case of severe icing/condensation.
Also useful on the ground to be able to see groundcrew during heavy rain on a/c without wipers/rain clearance.
On the fishbowl canopy Canberras the DV panels were also opened up when the a/c was returning to the parking bay to signify to the see in crew that the cockpit was depressurised and that therefore it was safe to open the cockpit door!
By: - 17th May 2018 at 21:07 Permalink - Edited 1st January 1970 at 01:00
Yes - DV window open + thumbs-up used often to indicate a/c depressurized. However it was still sensible to let the crew open the door first!
By: - 17th May 2018 at 21:13 Permalink - Edited 1st January 1970 at 01:00
On the OCU in the early/mid 70's it was normal for the see in crew to open the door after first checking the DV panel was open.
We always put a shoulder against the door as we turned the Handle 'just in case' :D
Different units had slightly different procedures and they were forever being changed with the passage of time.
By: - 17th May 2018 at 22:36 Permalink - Edited 1st January 1970 at 01:00
A shoulder against the door won't do much except provide a firm launch, even with just a few psi...
By: - 17th May 2018 at 23:01 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 17th May 2018 at 23:58 Permalink - Edited 1st January 1970 at 01:00
Why would there be any positive pressure at ground level?
By: - 18th May 2018 at 08:18 Permalink - Edited 1st January 1970 at 01:00
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'
By: - 18th May 2018 at 08:53 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 18th May 2018 at 11:31 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 18th May 2018 at 20:41 Permalink - Edited 1st January 1970 at 01:00
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?
By: - 18th May 2018 at 21:38 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 18th May 2018 at 22:00 Permalink - Edited 1st January 1970 at 01:00
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 :D
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
By: - 19th May 2018 at 06:33 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 24th May 2018 at 11:44 Permalink - Edited 1st January 1970 at 01:00
Bazv and exbrat, thanks for answering my question :)
By: - 24th May 2018 at 12:26 Permalink - Edited 1st January 1970 at 01:00
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.
By: - 24th May 2018 at 15:37 Permalink - Edited 1st January 1970 at 01:00
They are on the left because the pilot sits on the left.
By: - 24th May 2018 at 16:11 Permalink - Edited 1st January 1970 at 01:00
Unless its a helicopter :D
By: - 24th May 2018 at 16:13 Permalink - Edited 1st January 1970 at 01:00
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
By: - 24th May 2018 at 16:14 Permalink - Edited 1st January 1970 at 01:00
Originally posted by Graham BoakThey 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)
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By: merlin70 - 17th May 2018 at 19:55
DV or direct vision panels are found in many a/c canopies. Yes I get the idea that when open they provided direct vision to the outside world but only to the beam of the a/c.
A canopy misted with condensation could cause obvious problems but the DV panel provides little comfort unless you can side slip your way in to land.
In WWII you could perhaps take aim at your foe through the DV panel provided the Hun was happy to fly along side whilst you took aim!
So what is the purpose of a DV panel?