Canopy aerodynamics

[Aeroweanie]

Remember that it was difficult to make curved glass/perspex that was optically flat


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.

Yes, I am working on several new ones. I have one on laminar flow testing pretty far along and I have got a model built for one on the P-38 dive testing. I also have models of the F4F and P-47 being built.

 

[Aeroweanie]

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?

Yes, leakage is a big issue. One drag cleanup item we did on Rare Bear was to seal up a lot of leaks in the fuselage and wings.

 

[Simon Thomas]

Attached is R&M 2600, which is the index for 1909 to 1947.
It indicates R&Ms 2126-2150 are in technical reports 56, 58, 61, 63, 64, 65, 66, 67, 68 and 74.
R&M 2150 is an index report of the previous 100 reports.

Links to these reports:
56 : Technical report 56 1939.
58 : Technical report v.58 1941.
61 : Technical report v.61 1943.
63 : Technical report v.63 1944.
64 : Technical report v.64 1944.
65 : Technical report v.65 1945.
66 : https://babel.hathitrust.org/cgi/pt?id=mdp.39015022483419&seq=5
67 : https://babel.hathitrust.org/cgi/pt?id=mdp.39015022483427&seq=5
68 : https://babel.hathitrust.org/cgi/pt?id=mdp.39015022483435&seq=11
74 : https://babel.hathitrust.org/cgi/pt?id=mdp.39015022483492&seq=5

 

[Holtzauge]

Yes, leakage is a big issue. One drag cleanup item we did on Rare Bear was to seal up a lot of leaks in the fuselage and wings.

OK that's interesting. In addition, I see that the slope on the rear of the of the canopy on Rare Bear is longer than for a typical bubble canopy which makes sense.

As a sidenote on canopies, one of my colleagues in the Swedish defense industry once told me that one of the hills the aerodynamicists at SAAB were willing to die on was regarding the canopy, and while certainly providing an adequate view to the rear, you can still see that they carried the day with that one.

 

[MIflyer]

I love a bubble-top:

Note that on the P-47 especially there is a huge difference between the windscreens used on the Razorback and Bubbletop versions. It is obvious that the razorback windscreen seems more streamlined while the bubbletop must have better visibility out the front. You wonder if they found the flat front of the bubbletop was not very draggy or if they decided visibility was so important that that drag was not that important.

 

[MIflyer]

Note the early Ercoupe flat windshield in the top photo as compared to the later "bubble" windshield in the bottom one. What were they trying to do? Was it just for looks? Rumors have it that the old style flat one produces less drag or at least less turbulence with the canopy open, but I do not know.

 

[Aeroweanie]

Note that on the P-47 especially there is a huge difference between the windscreens used on the Razorback and Bubbletop versions. It is obvious that the razorback windscreen seems more streamlined while the bubbletop must have better visibility out the front. You wonder if they found the flat front of the bubbletop was not very draggy or if they decided visibility was so important that that drag was not that important.

View attachment 781580View attachment 781579

Thanks - I have never noticed that difference. The model I'm having built is a P-47D, but I think I'll also have a P-47C built too.

When I was in college, my parents moved to Evansville IN. The first time I flew down to visit them, as we were leaving the airport my father pointed out the then-Whirlpool factory and told me that Republic had built P-47s in that factory.

 

[bada]

Yes, I am working on several new ones. I have one on laminar flow testing pretty far along and I have got a model built for one on the P-38 dive testing. I also have models of the F4F and P-47 being built.

Hello Aeroweanie,
could you give some advice as with which one should we start as beginner and then move to which one once we have the basic knowledge under control?
Thanks.

Edit: VSP Aero looks like something to start with as it contains all the tools within.

 

[Aeroweanie]

Hello Aeroweanie,
could you give some advice as with which one should we start as beginner and then move to which one once we have the basic knowledge under control?
Thanks.

Edit: VSP Aero looks like something to start with as it contains all the tools within.

Its best to have a good background in aerodynamics before launching into running CFD. Several years ago, I taught the senior-level Applied Computational Aerodynamics course at Cal Poly. Starting from no experience, by the end of the three month course, everyone in the class meshed and ran Navier-Stokes CFD analyses of the F-86 and MiG-15. So, with the right background, it is possible to get up to speed quickly. The real challenge is then learning how to interpret the results you get and know what is real and what is a numerical artifact. I spent a lot of time in the class showing the students CFD results and helping them understand what they were looking at and what it meant.

I've never messed with VSP Aero, but at first glance it looks like a good place to start.