Frameless windscreens

[kaiserbill]

I have always wondered why some manufacturers were early adopters of the Frameless windscreen, yet others seemed to drag their heels somewhat.
I specifically mean for fighter/attack jets that were supersonic, not trainers such as the Aermacchi MB326.

Grumman with their F11 Super Tiger and SAAB with their Draken seem to me to be the first to adopt it, with first flights in the mid/late 50's ...... with North Americans Vigilante and Northrop's F5A Freedom fighter following very closely.
SAAB followed on in the mid/ late 1960's with the Draken.

Yet, there were still manufacturers putting out new designs in the 1970's with framed windscreens. 2 that readily spring to mind are the Tornado and Mirage F1.
I know the F1 flew first in the mid 60's, but entered service in 1973.
The Tornado only flew first in 1973, and entered service in 1979.
The fighter version of the Tornado, the ADV, only entered service in 1986, still with a framed windscreen.

These days of course, a frameless windscreen is a given.

Why was this this case?
I am aware of high speed aircraft (interceptors, recce, test) that benefitted from sharper, framed windscreens, but aside from these aircraft, most of those jets named above were quite capable of Mach 2 with frameless windscreens.

Was it simple design inertia, or were there practical reasons, such as performance, expense, or manufacturing/maintenance costs?

EDIT: The above examples were not meant to be a definitive or exhaustive list, but were simply the ones that readily sprang to mind. Other examples are welcome.

 

[Hood]

I think it was probably the bird-strike issue that meant framed windscreens were retained by some aircraft, especially low-fliers like Tornado that would statistically spend most of their lives at low altitude (plus coastal environments with seabirds).

During the 1970s there was much discussion on this related to training aircraft with large single-piece canopies over stepped seating (such as Hawk and Harrier T.2). While the framed windscreen would protect the student, the instructor was looking through the main canopy and could get a bird in the face if it smashed through the thinner canopy. That was one reason why internal screens were retained between the two seats and it took tests to convince the designers that the canopy would hold and thicker materials led to MDC for safe ejection. For example this is why the BAC P.45 had a framed windscreen and a framed forward canopy section.

 

[kaiserbill]

I can see that, although in fairness, as designed the F11 Super Tiger would have spent almost all its time in a coastal/maritime environment, as would the Vigilante.
I had idly wondered if there was a heat issue, but the examples noted were all capable of Mach 2.
Perhaps it was simply easier/cheaper to manufacture?

 

[TomS]

I was going to suggest that technology is not always uniformly distributed. Frameless canopies do take some skill, and it's possible that not all manufacturers had it, or were confident in it, until later.

 

[Zoo Tycoon]

Subject to confirmation;- I understand the frame less canopies are polycarbonate, whereas the framed canopies are acrylic, of course with an angled laminated, toughened glass plate right at the front (indeed ballistic resistance) . For these two plastics there’s quite big differences in strength, hardness and in particular low temperature properties such as toughness.

These properties alternately trade better for one while worse for the other;- I’d imagine there’s considerable difference in lifecycle costs which maybe the deciding factor.

 

[robunos]

Another problem with frameless canopies is optical distortion, leading to problems with gun and weapons aiming.
For example, when the USAF adopted the Canberra as the B-57, the initial 'A' version retained the Canberra style bubble canopy. This proved to give unacceptable performance in the ground attack role, and the the B-57B switched to a separate framed windscreen and canopy, as did the UK developed B(I).8 Canberra version, for a similar mission.
IASTR that the McDonnell F3H Demon originally ha a frameless windshield, but changed to a framed one after a number of in-flight failures . . .
Also, regarding the Tornado, I've seen a quote from 'Roly' Beamont, I think in his book 'Testing Years', that the Tornado canopy 'had the worst glass to iron ratio', of any aircraft canopy he'd ever seen . . .

cheers,
Robin

 

[Zoo Tycoon]

F16 frame less canopy vs bird

View: https://m.youtube.com/watch?v=ibJ3aXrvaCs


A face full of HUD optics;- that’ll sting a bit
Post event, one had to wonder what the straight ahead optics are like. Obviously a laminated toughened glass plate would be fine.

F35 has a structural frame to prevent this;-

View: https://m.youtube.com/watch?v=hXsFmIqTHIE

 

[dan_inbox]

Frameless canopies weren't always such a success. See the MiG-21 which reverted to framed.

 

[robunos]

@Zoo Tycoon; I believe the F-16 canopy is specially made to remove optical distortions when complete, something about tailoring the thickness of the flat sheet before it's stretched and formed to shape . . .
@dan_inbox; Even the one piece MiG-21 canopy had a separate, flat windshield.
Image crop from source image HERE :-

cheers,
Robin.

 

[kaiserbill]

Yes.
I was specifically meaning windshield, not canopy. After all, the P-51 Mustang, amongst others, had a "bubble canopy.
I suppose the F-16 uniquely managed to blur things a bit.
I had thought about the early Mig-21's, but didn't include them because of the heavy framing up front.

 

[BLACK_MAMBA]

To this day I still don't understand why the Tornado ADV kept a framed windscreen although I'm quite sure the bean counters are responsible.

I think technological capability is the reason. Many framed winscreen aircraft have been converted to frameless so birds/heat are less of an issue than what the manufacturers were capable of back then. Something newer technologies could overcome to meet the strength & distortion requirements.

 

[TomcatViP]

As hinted by @TomS, It's without doubt a matter of technology access.
Althout the gap, that initially started during WWII, has recessed today when dealing with structural challenges, the new demands for stealth have not been fully addressed equally by all actors around the world.

 

[Fluff]

To this day I still don't understand why the Tornado ADV kept a framed windscreen although I'm quite sure the bean counters are responsible.

I think technological capability is the reason. Many framed winscreen aircraft have been converted to frameless so birds/heat are less of an issue than what the manufacturers were capable of back then. Something newer technologies could overcome to meet the strength & distortion requirements.

Not really needed, ADV was not expected to mix it, just follow GCI, and launch on command, sorry that sounds like an advert for male performers.....

 

[BLACK_MAMBA]

To this day I still don't understand why the Tornado ADV kept a framed windscreen although I'm quite sure the bean counters are responsible.

I think technological capability is the reason. Many framed winscreen aircraft have been converted to frameless so birds/heat are less of an issue than what the manufacturers were capable of back then. Something newer technologies could overcome to meet the strength & distortion requirements.

Not really needed, ADV was not expected to mix it, just follow GCI, and launch on command, sorry that sounds like an advert for male performers.....

Which is exactly why I said the bean counters are behind it... "It intercepts so it isn't needed".

Even for interception a good clear view forward is always an bonus.

 

[kaiserbill]

Not really needed, ADV was not expected to mix it, just follow GCI, and launch on command, sorry that sounds like an advert for male performers.....

Which is exactly why I said the bean counters are behind it... "It intercepts so it isn't needed".

Even for interception a good clear view forward is always an bonus.

You both raised interesting points that jogged my memory on the original updated Mig-31.
The Mig-31M interceptor first flew in 1985, and had a new frameless windscreen as part of a deep modernisation. Clearly, MiG at least thought it a worthwhile feature in the interceptor role.
The end of the Cold War put an end to it obviously.
Pity..it was a beautiful, absolute beast of a plane.

 

[riggerrob]

Yes.
I was specifically meaning windshield, not canopy. After all, the P-51 Mustang, amongst others, had a "bubble canopy.
I suppose the F-16 uniquely managed to blur things a bit.
I had thought about the early Mig-21's, but didn't include them because of the heavy framing up front.

A secondary function of Mig-21's canopy is that it folds down in front of the pilot during ejection. Then the canopy protects the pilot against arm, flail, shrapnel in the face, leg flail, etc. at supersonic speeds.

 

[kaiserbill]

Folds up I think, rather than down?
I was under the impression it is hinged at the front, thus pivoting upwards and acting to screen the pilot from the slipstream.

 

[robunos]

Folds up I think, rather than down?
I was under the impression it is hinged at the front, thus pivoting upwards and acting to screen the pilot from the slipstream.

It's cleverer than that . . .
When the canopy is closed, the side rails of the canopy are attached to pivots on the seat. On ejection, the forward canopy hinge is released, and the seat, with the canopy attached, departs the aircraft. As this happens, the canopy pivots nose end down, to form a shield, protecting the pilot. once the seat has cleared the aircraft, the canopy is jettisoned, prior to pilot/seat separation.
From Wiki :-

"On variants prior to the MiG-21PFM, the cabin canopy is hinged at the front. When ejecting, the SK-1 ejection seat connects with the canopy to make a capsule that encloses the pilot. The capsule protects the pilot from the high-speed airflow encountered during high-speed ejections. After ejection, the capsule opens to allow the pilot to parachute to the ground. However, ejecting at low altitudes can cause the canopy to take too long to separate, sometimes resulting in pilot death. The minimum height for ejection in level flight was 110 m. Starting from the MiG-21PFM, the canopy is hinged on the right side of the cockpit."

cheers,
Robin.

 

[kaiserbill]

Ok, I did not know that sequence.
You learn something new every day.
Very clever indeed...I see now what riggerrob meant by "folding down".
Thanks.