Random Aerodynamic Oddity of the Day Thread

[Bicycle Bob]

Originally Posted by freebeard

It's got 40/60 weight distribution so I'm thinking yes. And with the cutaway wide body there may be an air curtain effect above them.

5mm aluminum belly pan. The exhaust is wrapped and the diffuser has a gold leaf finish to reflect the heat!

If it is tail-heavy, it would need fins at the back, not the front. However, off-road, things get ballistic, not air-borne when you need that much wheel travel.

[cRiPpLe_rOoStEr]

That's great for some sort of Baja Bug on steroids anyway.

[freebeard]

If it is tail-heavy, it would need fins at the back, not the front.

Maybe... the launch probably depends on the spring rates and rebound. Those front dive planes could hold the nose down to hold it level in the air and keep the trajectory flat. Longest imaginable lever arm on the light end. What could fins at the back do?

I think it's pretty genius to get downforce without the typical airdam and wings.

[Bicycle Bob]

Originally Posted by freebeard

Maybe... the launch probably depends on the spring rates and rebound. Those front dive planes could hold the nose down to hold it level in the air and keep the trajectory flat. Longest imaginable lever arm on the light end. What could fins at the back do?

I think it's pretty genius to get downforce without the typical airdam and wings.

With a lot more wing at the back, it might stay level. Flat things tumble in the air because the leading edge of a wing gets more lift than the back end. To get stability, you need the center of mass well forward, or more area at the back. To avoid flutter, the leading edge of a helicopter blade is heavily ballasted. Arrows avoid tumbling, but don't glide, falling nose-first. Paper airplanes are a good introduction to the art.

[kach22i]

Years ago when discussing Bob Windt's Wing In Ground Effect (WIG) hovercraft, it was said by others at the national hovercraft rally that an elevator either fore (canard) or aft (horizontal stabilizer) would work to control pitch. However human reaction time favored the aft location, a faster automated system would favor the canard and be more effective.

The flippers on the off-road Porsche work like front dive planes /strakes or fins do to keep the nose down, but once airborne they may help prevent flip over by acting as a vertical air brake.

Engineering Explained: 10 Aerodynamic Features Of Race Cars
https://www.carthrottle.com/post/eng...-of-race-cars/

2. Dive Planes

These fixtures are typically located on the right and left sides of the front bumper (see below), and are curved to redirect airflow at the front of the vehicle upward, thus creating downforce. They’re also used to alter the airflow along the sides of the vehicle, attempting to minimise the amount of high pressure air that enters underneath the car (which would create lift/minimise downforce).

[Bicycle Bob]

Originally Posted by kach22i

The flippers on the off-road Porsche work like front dive planes /strakes or fins do to keep the nose down, but once airborne they may help prevent flip over by acting as a vertical air brake.

If the car is nose-high and you brake the front, the back comes under it in a classic blowover. What matters is the angle of attack. Aircraft have no trouble flying upside down by adjusting that a few degrees.

[kach22i]

Originally Posted by Bicycle Bob

What matters is the angle of attack.

I agree that the angle of attack is of paramount concern.

Considering that we (I) have not seen such large dive planes on a Baja style racer before in competition I'm going to take a "wait and see" position on their effectiveness.

Thinking about the classic blow over at speed verses getting airborne via hump or ramp, we need to admit that these are two different, or we need to lump them into the same bed.

1. Classic blow over can be caused by a crest in the pavement or in some cases another vehicle disrupting it's ground effects. Either way, once a little air gets under, a lot of air wants to follow and rapidly.

2. Baja jump is just that a jump that follows an artillery type trajectory based on vector, mass and velocity - not so much aerodynamics. In a Baja racer jumps are at lower speeds (let's say 1/2) than a LeMans racer, and therefore lower aerodynamic forces/concerns.

#1 is a frisbee.

#2 is a cannon ball.

Now to bring this back home to my original explanation, examination and defense of prior comment about looking at vertical acceleration as a separate force being impended by the horizontal surface area of canard - dive plane.

This comment failed to mention forward motion that creates lift at positive angles of attack (post #605 second paragraph) because it was meant to say that angle would not be achieved to begin with and is a preventive measure not a countermeasure.

Indeed once a positive angle of attack on the flipper like dive planes is achieved there will me more not less lift.

Keep in mind this lift condition exists under the car body as well at positive angles, especially with it's flat floor plan of thick aluminum flying it like a kite over every jump.

There are preconditions, conditions, and post conditions for every airborne incident. Certainly thinking in time frames in lieu of static conditions is out of our normal discussions, usually we get as far a buffeting and call it a day.

This has been an enjoyable brain twister for me, and will certainly be eager to read a more expert analysis than what little I have been able to offer.

[freebeard]

This has been an enjoyable brain twister for me, and will certainly be eager to read a more expert analysis than what little I have been able to offer.

Same. I think it comes down to flattening the curve trajectory.

edit:

justacarguy.blogspot.com: Soap box, Los Angeles, 1946

This reminds me of Burt Munro's Indian.

[Bicycle Bob]

Originally Posted by freebeard

Same. I think it comes down to flattening the curve trajectory.

If the theory seems elusive, I recommend getting a rugged toy car, and some weights, cardboard and hot glue, and just playing for a while, to see how far you can toss it and have it land on the wheels. A standard launch catapult would be easy to build as well - for heavier models, pull back a calculated bit more.

[freebeard]

jULIANeDGAR would approve. It might make for a new pinewood derby race category.

I'd more likely use it as a means of learning the physics engine in Blender.