Simple underbody question.

[Conceptual]

I am working on a garage project, and I have read a few aero books before starting, but I have a question.

The books keep telling me that a 5degree inlet, flat throat, and 10 degree outlet are a good combination to work with. It also states that it is best to use flat surfaces for this, and sharp transitions.

My question is about using a corrugated material for the throat of the venturi.

Does increasing the surface area by using corrugated panels decrease pressure?
Does it increase the amount of downforce because of the increased surface area?
Is it worthwhile to use the corrugation on the inlet and outlet as well?

Any educated answers are appreciated. Any others may return to learn as I am.

THANKS!

[wesley123]

What is the project you talking about.

I mean, a book can tell you that, but if it isnt possible to do on the project you aint coming anywhere further.

[Conceptual]

Corrugated panels were attempted back during WW1 and into the 30's by Junkers and the Ford Trimotor. The corrugation was selected because it contributed strength, but added drag.

Thanks, this is what I was looking for!

Any specific reason that it induces more drag? Is it the increased surface area inducing more skin friction?

I appreciate any answers!

[Conceptual]

What is the project you talking about.

I mean, a book can tell you that, but if it isnt possible to do on the project you aint coming anywhere further.

Trust me, with this project, I can get away with anything that I want.

[kilcoo316]

My question is about using a corrugated material for the throat of the venturi.

Does increasing the surface area by using corrugated panels decrease pressure?
Does it increase the amount of downforce because of the increased surface area?
Is it worthwhile to use the corrugation on the inlet and outlet as well?

In turn:

1. No. Increased surface area will increase BL drag.
2. No, the corrugation is formed from surfaces non aligned to the vertical. The overall vertical component of these will equate to a simple flat surface.
3. No.

Corrugations are not the same as riblets...

Read - if your interested

[Conceptual]

My question is about using a corrugated material for the throat of the venturi.

Does increasing the surface area by using corrugated panels decrease pressure?
Does it increase the amount of downforce because of the increased surface area?
Is it worthwhile to use the corrugation on the inlet and outlet as well?

In turn:

1. No. Increased surface area will increase BL drag.
2. No, the corrugation is formed from surfaces non aligned to the vertical. The overall vertical component of these will equate to a simple flat surface.
3. No.

Corrugations are not the same as riblets...

Read - if your interested

As always, I appreciate your time and effort to educate.

I cannot see the book from that link, is the book worth buying for a garage built "car"?

Ebay search for this author: http://shop.ebay.com/i.html?_kw=Peter&_ ... m104.l1199

ALL religious books, no aero books...

I did pick up this one tho...

http://cgi.ebay.com/Road-Vehicle-Aerody ... .m20.l1116

[kilcoo316]

I cannot see the book from that link, is the book worth buying for a garage built "car"?

Oh no no!

Not worth buying.


Its just an article on riblets if your interested.


Some people may get confused between the two (riblets/corrugation), and I'm hoping that link will clear it up before it even starts.

[Conceptual]

I did see some of the pics after refreshing a few times...

With the way that I am manufacturing, actually making those would not be difficult at all. I guess the hard part for me would be the maths to make sure that I have the correct aspect ratio for my plan area.

I did not see however, if this would be used along the full length of the venturi, or just the throat to exhaust.

Care to educate me on where to best use these ribblets?

[Scotracer]

I did see some of the pics after refreshing a few times...

With the way that I am manufacturing, actually making those would not be difficult at all. I guess the hard part for me would be the maths to make sure that I have the correct aspect ratio for my plan area.

I did not see however, if this would be used along the full length of the venturi, or just the throat to exhaust.

Care to educate me on where to best use these ribblets?

Riblets (AFAIK) decrease the skin drag therefore it's best to use them on the largest area possible. Obviously, the further aft you are on any aerodynamic surface the more turbulent the regime, therefore they will be more useful in this scenario - riblets will not help if you are still in a laminar regime. If it were me I'd use them, if I were restricted in the amount I could use, on the rearward section of the flat floor.

I don't really know how you are going to be able to test your design however as these are typically used on aircraft wings (which have pre-defined limits on ground effect) which are only semi-relatable to the floor of a vehicle.

[Conceptual]

I am currently working on the molds for a project car. It will not be built in any conventional way, and it is not being made for anything but to see if it can be done the way that I have come up with.

I am obviously starting with the suspension, so I can define the pickup points that need to be built into the floor. The floor from front to back, including riblets will be a single, continuous piece. I was going to include the strakes that are common in diffusors already for the stiffening that they will give in my setup.

It will probably end up in the trash bin, but for the cost, I whouls be able to bin several dozen if I have too...lol

THANKS for all the info!

[PlatinumZealot]

I like the riblet technology. First time learning of it.

What order of size are these riblets? 1mm deep, 1cm deep? Or it depends on the boundary layer?

[riff_raff]

Corrugated panels were attempted back during WW1 and into the 30's by Junkers and the Ford Trimotor. The corrugation was selected because it contributed strength, but added drag.

Dave,

The skin corrugations were added for the same reason modern aircraft monocoque fuselage and wing structures use stringers, as well as F1 composite tubs using honeycomb cores. It provides increased buckling strength to the load bearing skins.

The designers of the Fokker and Ford airframes were more concerned about cost than drag. Using a corrugated skin was less expensive than a smooth skin with stringers, even though it had higher drag.

As for the corrugations increasing the effective surface area creating downforce, it has no net effect. Pressure forces always act normal to the local surface topography. So if the local surface is vertical (like a corrugation rib), then the local pressure force is sideways.

A ribbed underwing structure might be stiffer than a flat surfaced one, but it would also be slightly heavier and have slightly higher drag. But of course, the stiffer structure would also yield more consistent aero performance. So it's a trade-off.

Regards,
Terry