MetroMPG's Honda Insight boat tail extension (cardboard) tuft video; ABA test +9.7%

[freebeard]

I understand the use of a serrated trailing edge from the B-2 bomber and high-bypass turbo-fan engines; They sort of mimic bird's feathers. But wouldn't the serrated leading edge be problematic?

[aerohead]

Originally Posted by freebeard

I understand the use of a serrated trailing edge from the B-2 bomber and high-bypass turbo-fan engines; They sort of mimic bird's feathers. But wouldn't the serrated leading edge be problematic?

I believe that for the lading edges,the tape acts as a turbulator,inducing more energy down into the boundary layer to help forestall separation.
Some wing/gear struts are not 'fine' enough to present the lowest drag and the tape is meant to help here.
Same for the blades of the prop.
Pima Air Museum has a formerly-classified aircraft from Vietnam service which could fly undetected at 100-feet AGL.I eagerly await it's renovation so I can see it's propeller.I suspect it's the lineal parent of the Q-tip prop and may have other 'tricks.'
It's anechoic!

[freebeard]

Pima Air Museum has a formerly-classified aircraft from Vietnam service which could fly undetected at 100-feet AGL.I eagerly await it's renovation so I can see it's propeller.I suspect it's the lineal parent of the Q-tip prop and may have other 'tricks.'
It's anechoic!

I'd like to see that too.

[sendler]

Is the serrated trailing edge beneficial only where there is a step in the middle of a panel or would you also incorporate it into the the trailing edge of a Kamm such as at the truncation of his tail? I have read that vortex inducers are more beneficial when located in the middle of a panel in order to form a vortex which is attached to the panel and has momentum to follow the same line after leaving the back rather than curling in. Are serrations at the trailing edge more for noise reduction at the expense of increased drag?

[freebeard]

Are serrations at the trailing edge more for noise reduction at the expense of increased drag?

I think that's pretty perceptive, but why would the drag increase? Extreme aero-modding seems to have that side effect. I wonder how much energy is turned into noise, it may be negligible. But a quiet car is a happy car.

...in order to form a vortex which is attached to the panel and has momentum to follow the same line

There's something else I wonder about. Are vortexes contained within the hole the car punches in the air (its maximum cross-section) or do they expand outside of it?

[sendler]

Originally Posted by freebeard

why would the drag increase?

Vortex generators increase the energy in the air at the expense of drag. The question always is, does the reduction in turbulence and vacuum acting on the the rear panel of a car outweigh the the energy loss that was used to create the vortices.

[ChazInMT]

Something to keep in mind everyone, the volume of air affected by a vehicle moving through it goes out to 6 feet or more, this is the sand box we're in. It isn't a 1/4" layer stuck to the skin of our cars/trucks. Skin friction is not the enemy here, it is the bluff body and associated pressure drag it creates. Airplanes may be affected by these zig zag things because they play in a different world where skin drag and subtle pressure changes over and already insanely tuned shape will have an effect.

None of you are flying through free air, we hope, and if you are, it is about to end badly for you, and how much drag you're generating is probably the last thing on your mind, ever, if you're indeed thinking about it at that point.
None of you are driving an insanely tuned aero dynamic vehicle (I've yet to hear of anyone driving a VW XL1 here yet)
None of you are cruising at speeds of 120MPH or more.

So quit trying to say "If it works on an airplane it must work on a car too."

It doesn't.

[freebeard]

Originally Posted by sendler

Vortex generators increase the energy in the air at the expense of drag.

I think the vortex generator and the serrated trailing edge act differently, and that a trailing edge and a blunt body with base pressure act differently.

An example of a car with a serrated trailing edge:

None of you are driving an insanely tuned aero dynamic vehicle (I've yet to hear of anyone driving a VW XL1 here yet)

I suspect that basjoos and 3-wheeler are at that end of the scale.

[ChazInMT]

Originally Posted by aerohead

Same for the blades of the prop.
Pima Air Museum has a formerly-classified aircraft from Vietnam service which could fly undetected at 100-feet AGL.I eagerly await it's renovation so I can see it's propeller.I suspect it's the lineal parent of the Q-tip prop and may have other 'tricks.'
It's anechoic!

It appears as though there are more ways than one to make a shhhhhhhpeller.

Google Search of "YO-3A Propeller"

6 Bladed Seeds





And 3 Bladed Meat Cleavers







By the way: Wasn't Ana Choic in the movie "Up in the Air" with George Clooney and Vera Faminga?

[moorecomp]

Originally Posted by MetroMPG

Coincidentally... started painting the tail this weekend with some leftover oil based paint I found in the garage... and it's light brown. Almost the same as the cardboard!

(Nothing photo worthy.)

Probably a couple of days to do 2 coats inside and out, then wrap it all in a plastic skin. I still have to look around Home Depot to see what options they have for something a bit sturdier than trash bag plastic, which is what I used to cover the Flea's test tail .

Look for rolls of plastic film that is self adhesive and put down on new carpet to protect during construction.