Doors opening at speed

Doug S.

The protoplasm may be 72, but the spirit is 32!
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At first it appeared to be only the "passenger" side...but around 2:15 it became much more obvious that it was both of them.

Dean's work is always first class...perhaps Fran can offer some advice?

Cheers!!

Doug
 
That doesn't seem right - my upper door edges vibrate around but i've never seen my door try to open itself. At first I thought the doors in the video were just vibrating around, part way through wow, sure sems like the whole door on both sides is trying to open.
 
Hmm, just tried bending my doors that much by hand, and it takes about 25# to bend it up so far. I don't see how there could be THAT much air entering cockpit to generate the type of airflow needed to do that from inside. You would have a 40mph wind going across your face
I am guessing it is a low pressure above. Would not take much separation to generate the force needed based on slow moving cockpit air on inside. It is a concern I have had while doing my stuff, if the air held tight to the roof after the windshield.

How much would ya charge Fran to bust out the cfd and flush out hinge, remove roof scoop and add a some vortex generators to top of windshield or leading edge of roof body work? My concern is the engine cover I made and the ability to feed motor from scoops. If the slip stream is going over or not. Would be a big help if you wanted to work with me on some of the stuff I am making.
 
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Ever wondered why the top on a convertible rag top will rise at speed? Same as the doors... Bernoulli's equation. Pressure is inversely proportional to velocity. As speed increases pressure reduces. This low pressure over the top causes the door to rise... It also allows an aircraft to fly. That is all I remember from my physics class.

Actually, l also remember what angle is best to have a projectile travel the farthest.
 
I'm not so much concerned about the how as much as I am about the why. Is this common to all SLCs? I don't really want my doors cracking open at speed. Do I need to strengthen the door frame or add a secondary latch to prevent this from occurring?

I don't know how fast the SLC in the video was going but I'm pretty sure I could shove my hand in through the gap that was evident in some parts of that video!
 
Some of us have messed around with light aircraft and may remember that most, if not all, low wing (Bonanza, Cherokee) etc incorporate a second, top of door, latch to prevent the door from gapping. As Michael said, we have to thank Mr Bernoulli.
 
I seen this happen on an earlier video of an SLC, The owner never had the roof scoop closed to the back in you could stick your hand out the hole at the back of the doors, its pulling in a lot of air, once the cab pressures up it has to go some where.
I had 63 Chevy II 1/4 mile drag car the hood would bow an 1" in the middle at speed from the air being pulled in by the scoop.
 
"Doors opening at speed" isn't an issue for the car in general. How do we know that? Because very fast SL-Cs, like Sharkey's old car that now does 178 MPH in the half aren't doing that, because the original car that did a reported 194 MPH at Daytona didn't do it, because the later Raver car doesn't do it, the factory 01 race car didn't do it, and so forth.

But the one in the video clearly was, so there is something going on, obviously.

My guess is that it's something simple, most likely loose lower hinges. I don't think the door is actually warping- because none of the other cars are doing that. In other words, I doubt that this door is the only one that warps at speed. What seems most likely to me is that the door is actually somewhat loose in the opening. That could easily cause the door to misalign at speed like the one in the video. Even a door that seems to open and close easily could be loose at the lower hinge. And as the owners who have some miles on the car know, the hinge bolts sometimes work loose- you have to really tighten them down, and use Loctite to keep them in place. And if the car was built without stiffeners at the hinge, that probably aggravates the problem.

Another possibility is a loose pin where the door latches to the body. It takes some time to get the pin exactly in place, and if it isn't tightened correctly, using the right kind of washers and nuts, for example, if could allow the door to lift slightly open as seen in the video.

Whether the forces on the door are internal (pressure from an open roof vent) or external (negative pressure from air over the roof and door edge) doesn't matter much, IMO, as we know from experience with many cars at very high speeds that doors seem to stay sealed at speed, including those who have air ducted into the cockpit from an open roof vent.

That's why I think the most likely cause of this is a lower hinge that needs tightening. And/or a loose pin (or latch?) on the other end.

That's what I think, anyway.
 
Thanks Will - that seems reasonable. The video doesn't show the lower portion of the door very well, it looks very much like it's all door deflection. That particular video is so jarring I was really caught off by it. Based on other videos where the door structure is visible it doesn't seem like there's actually much material in the upper portion of the door - basically a sheet of fiberglass. Made me start to second guess my passing on the door skins.
 
The difference is closed window to open window of the race cars. Open window will allow the pressure to equal. Closed window not, as seen in the video.
I have already removed the roof scoop, and planned to flush hinges anyways, but hoping some vortex generators can help keep the air a little tighter to roof. The concern for me comes from trying to pull engine air from the same exact area. My only hope is that the low pressure out the back will be greater than what is being seen on the roof line at speed so that air will actually be entering the scoops. No rear bonnet scoops, no problem. I will just need to be a little more creative to help keep air in contact with roof line, or change scoop design/location. The engine itself would be creating a little low pressure in the scoops, it would just suck if that area gets starved and engine runs lean, at speed.
Once my body is atleast formed, still plan to scan and check it out to make sure nothing goofy is happening.
 
Ditto on Scotts post #14 above, just scrolled thru pic thread and most if not all actual race car pics have only partial or no door windows which would really change airflow pressure over the cockpit.
 
Ditto on Scotts post #14 above, just scrolled thru pic thread and most if not all actual race car pics have only partial or no door windows which would really change airflow pressure over the cockpit.

The 01 car ran with both windows in and out, depending on what the rules interpretations were at the time. That car never had a problem with the door edges lifting.

That's actual experience.
 
If I remember correctly Fran has a air flow simulation picture showing high / low pressures on the car. I was thinking about putting snorkels in the front clam but it being a huge wing I didn't want to mess with the Aero of the car. My 911 didn't start to handle till you got over the 100 mph the front end had a lot to do with that being a big wing as well.
Fran was mentioning the angle of the radiator made a difference with pressures, as well as getting venting into the wheel wells. The Dodge Daytona a lot of people thought the wing was so high because the rules stated the trunk had to open which was not the case it was to get it into the clean air. Oh the fun of physics, keep the front pointy, the back flat, tires sticky and drive it like you stole it :)
 
For nearly everyone, it really isn't a big deal. My only concern is for me and that I am trying to pull air from that area. So I will make a few changes to try holding air closer to roof line.
My focus is already starting to change. Before going full blown perfect show car, at the end of mock up, I will do some time trial stuff with the car.
 
Changing the glass windscreen for the compound curve race poly screen makes a massive difference to the air staying attached to the roof line.... And subsequently the rest of the rear of the car
 
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Thanks for answering that. I was looking online for glass builders to possibly make a new laminated windscreen to lessen the intersecting angle, but ya, capabilities seem to be limited to single axis bends.
Will pick up the curved one as I get closer to done, and run it during my track driving.

Would you mind sharing the best wing height you have found to take advantage of the air heading downward off roof? Very speed dependant obviously, but have you found a happy medium? I am needing to design wing integration very soon. Just from pics I am seeing a common height about 6" down from top of roof.
 
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