Canopy aerodynamics

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There are pressure diagrams of some canopies either on a previous thread here or on YouTube. As I recall, the was a bubble canopy P-51 and either an earlier P-51 or a P-57 razorback.

Angular windscreens will see tremendous turbulence at the edges where the airflow spills over the side or the top. I haven't seen a pressure map, but I expect that the Bf109 is terrible. Curved surfaces allow something along the lines of laminar flow. Even curving the forward corners is far better.
 
It doesn't get much worse than this:View attachment 776663 Blackburn Skua
I think that the Brits wanted an optically flat windscreen exactly perpendicular to the pilot's line of sight to eliminate distortion while dive bombing. I've spent a lot of time studying the Skua and it's the only thing that makes sense.

Keep in mind that the Skua was a dive bomber with a secondary role as a fighter.
 
One thing that's often overlooked is that the top of the canopy, where the curve reverses from up to down, is often a contributor to critical Mach number, even on propeller planes. In the process of going up and over and back down, the local airflow undergoes quite a bit of acceleration and compression shock waves can form there. It's an interesting subject to read up on.
 
Would that be the reason for presumable dive instability in late P47's vs the razorbacks?
 
Unfortunately, Hathitrust doesn't have all of them. It looks like someone got tired of scanning and started saying "not scanned because of copyright issues". I don't find any beyond R&M 2169

I have a colleague digging some of the missing ones out of the University of Michigan library for me.
 
It might have been removed since I looked through there a few years ago. I found report 13 (1918) to report 84 (1951). Roughly R&M 360 to R&M 3127.
PM me if you need any between those.
Edit: Found the report I was missing.
 
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R&M 2175 seems to be the upper limit. For the ones beyond this, I see: This item is not available online Limited - search only — due to copyright restrictions.

Also, 2126-2150 is blocked.

Where did you find the ones further in the series?
 
Remember that it was difficult to make curved glass/perspex that was optically flat
Thanks - I wrote it!

I though your profile pic looked familiar - probably what triggered the memory of the paper.

Ever given any thoughts of updating it? I frequent F1 forums and the aero chaps/chappettes they are all fired up about the open-source aerodynamics analysis tools that have been developed in the last 5-10 years.
 
Thanks - I wrote it!

Read that paper with pleasure. Found the analysis on the Spitfire's too steep windscreen especially interesting.

Another thing that interests me with regards to canopies is the leakage factor: AFAIK, the Bf-109 got a substantial gain in speed when they experimented with reducing the leakage in the engine cowling.

Given the pressure differences between the inside and outside on the canopies of typical WW2 fighters with sliding canopies, I would assume that that would have an impact here as well?

This would of course have shown up in the testing NACA did in the full-scale tunnels but is lost in wind tunnel modelling and I suspect also in CFD? Or is there a good way to account for it?
 

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