R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 11-17-2014, 05:47 PM   #16
Tech Elite
 
Join Date: Mar 2014
Posts: 2,353
Trader Rating: 92 (99%+)
Default

So on which side of the wing would the gurney flap be attached to? The side with the pressure yes, so would it be coming back toward the roof of the car?
thecaptain is offline   Reply With Quote
Old 11-17-2014, 06:01 PM   #17
Tech Elite
 
DesertRat's Avatar
R/C Tech Elite Subscriber
 
Join Date: Mar 2011
Location: Sniffin the 'Sauce Fumes
Posts: 2,552
Trader Rating: 1 (100%+)
Default

Gurney flaps stick UP from the trailing edge of the wing. Gives downforce with only a tiny amount of drag added. They're not sure why it works so well.
__________________
I race toy cars for fun. If I need to explain, you'll never understand.
Current rides: Diggity DC4 Chassis #10. Losi JRX-S Type R. CRC Xi (retired), CRC Altered Ego Aluminum Chassis. Associated B4 based dirt oval late model.
WTB: Carpet racing in Arizona.
DesertRat is offline   Reply With Quote
Old 11-17-2014, 06:05 PM   #18
Tech Elite
 
Join Date: Mar 2014
Posts: 2,353
Trader Rating: 92 (99%+)
Default

Yes normally at a 90 Degree angle but in which direction would it be facing.
thecaptain is offline   Reply With Quote
Old 11-17-2014, 06:13 PM   #19
Tech Elite
 
DesertRat's Avatar
R/C Tech Elite Subscriber
 
Join Date: Mar 2011
Location: Sniffin the 'Sauce Fumes
Posts: 2,552
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by DesertRat View Post
UP.
Quote:
Originally Posted by thecaptain View Post
Yes normally at a 90 Degree angle but in which direction would it be facing.
Up.
__________________
I race toy cars for fun. If I need to explain, you'll never understand.
Current rides: Diggity DC4 Chassis #10. Losi JRX-S Type R. CRC Xi (retired), CRC Altered Ego Aluminum Chassis. Associated B4 based dirt oval late model.
WTB: Carpet racing in Arizona.
DesertRat is offline   Reply With Quote
Old 11-17-2014, 06:37 PM   #20
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,757
Trader Rating: 23 (100%+)
Default

Down would be a Hanford device. Not what you want on a car if you can help it.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is offline   Reply With Quote
Old 11-17-2014, 09:44 PM   #21
Tech Elite
 
Join Date: Nov 2008
Posts: 2,132
Trader Rating: 7 (100%+)
Default

since most of "our" rear wings on sedans and such end up at around 90 degrees or really close to that. i doubt this would have any effect. am i right? A lot of the body also creates down force. now would a small gurney flap or spoiler at the trailing edge of the body be effective? say a few mm? or is that legal per (um dare i say as per current events) roar rules?
dragonracing is offline   Reply With Quote
Old 11-18-2014, 06:45 AM   #22
Tech Initiate
 
Join Date: Sep 2014
Posts: 24
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by DesertRat View Post
Gurney flaps stick UP from the trailing edge of the wing. Gives downforce with only a tiny amount of drag added. They're not sure why it works so well.
Actually, they're quite sure why...on a symmetrical airfoil (the first application), the trailing edge vortices alternate; these turbulate the airflow at any angle of attack, but they're MUCH more pronounced at higher alpha. This turbulation causes laminar separation as far as 45-50% of chord length ahead of the trailing edge. This separation is seen as lost lift and increased drag.

The Gurney Flap (or Wickerbill or Zaparka Micro Flap, as patented in 1935) simply pulls the turbulation to one side of the airfoil (high pressure side) and stabilizes the airflow ahead on the opposite side (low pressure side).

There are many flap systems in use in the aviation world; almost all have complex linkages and tracks. The beauty of the Gurney flap is in it's simplicity.

There is a small penalty in drag at low speed; it is more than outweighed by the advantages at high speed.

Byrdman
MCKNBRD is offline   Reply With Quote
Old 11-18-2014, 10:12 AM   #23
Tech Addict
 
Join Date: May 2008
Location: Philippines
Posts: 572
Trader Rating: 5 (100%+)
Default

Quote:
Originally Posted by mschumi101 View Post
If you really want concrete numbers I'd say your best bet would be to create the bodies in Solidworks, autoCAD, NX etc and analyze them through the computers. While this only yields theoretical data it would probably be the best way to compare multiple bodies equally.

Flow Simulation of a Wing

A rather crude wing I did a few years back out of curiosity. It did gave me some values (like force, pressure and air velocity), but I was not satisfied with the results as I knew this is incomplete and inaccurate without the body. Sadly, I couldn't model the body close enough to be of use, and that's where I stopped.

This is with Solidworks btw.


Quote:
Originally Posted by J.Filipow View Post
A Gurney flap would be a simpler and more beneficial device to explore, as it can potentially increase rear downforce without sacrificing drag. For a standard 1/10th scale touring car, a proportional Gurney flap on the rear wing would be quite small, maybe only 2mm or so.
forces don't scale. it's not as simple as taking the proportional length of a real gurney flap then applying the same to our cars. ever wondered why wings for RCs are more angled or 'exaggerated', often approaching ~90degs? That's because we need to compensate for that discrepancy between the scaled, and real world physics. A real wing with that much angle of attack would just stall the airflow producing more drag and rendering it useless.
__________________
Tamiya - Awesomatix - Orca - Orion - LRP - Protoform - Sanwa - Futaba - NASA - Ride
Minami is offline   Reply With Quote
Old 11-18-2014, 10:35 AM   #24
Tech Elite
 
WheelNut's Avatar
 
Join Date: Jan 2003
Location: Edmonton, Ab
Posts: 3,208
Trader Rating: 5 (100%+)
Send a message via MSN to WheelNut
Default

One thing fr everyone to keep in mind when thinking about RC aero: We run scale cars in the same atmosphere as large cars. We don't scale don't the density of air particles. Our cars have the "scale" aerodynamics of a full size car running on mars, or at ultra high altitudes. That is why airfoil wings aren't used on RC cars, because there isn't enough volume of air particles travelling over the wing to generate much downforce. The speed isn't really the issue- it's the size.
__________________
•Brad Comis
WheelNut is offline   Reply With Quote
Old 11-18-2014, 11:32 AM   #25
Tech Initiate
 
Join Date: Sep 2014
Posts: 24
Trader Rating: 2 (100%+)
Default

If you're confused about the scaling concept, look up 'Reynolds Number'...and prepare for your eyes to roll back in your head with lots of physics, engineering, and other technical gobbledygook.

Byrdman
MCKNBRD is offline   Reply With Quote
Old 11-18-2014, 12:05 PM   #26
Tech Addict
 
Join Date: Nov 2003
Posts: 602
Default

Quote:
Originally Posted by WheelNut View Post
One thing fr everyone to keep in mind when thinking about RC aero: We run scale cars in the same atmosphere as large cars. We don't scale don't the density of air particles. Our cars have the "scale" aerodynamics of a full size car running on mars, or at ultra high altitudes. That is why airfoil wings aren't used on RC cars, because there isn't enough volume of air particles travelling over the wing to generate much downforce. The speed isn't really the issue- it's the size.
Dale - Protoform Race Bodies
Attached Thumbnails
Wind tunnel R&D-say-what-.jpg  
__________________
PROTOform Race Bodies
www.racePF.com // www.facebook.com/PROTOformRaceBodies // www.twitter.com/RacePF
daleepp is offline   Reply With Quote
Old 11-18-2014, 01:25 PM   #27
Tech Elite
 
Join Date: Mar 2011
Location: Houston
Posts: 2,513
Trader Rating: 1 (100%+)
Default

Quote:
Originally Posted by daleepp View Post
Dale - Protoform Race Bodies
Where's the question? He's correct. A molecule of air is the same size regardless of the wing size. A molecule of air is proportionately larger on a smaller wing.
__________________
Follow my rc products on Facebook at Raborn Racing Originals and the line of 3D printed parts at
http://www.shapeways.com/shops/rebellionrc
fredswain is offline   Reply With Quote
Old 11-18-2014, 01:48 PM   #28
Tech Rookie
 
Join Date: Oct 2014
Posts: 1
Default

Quote:
Originally Posted by fredswain View Post
Where's the question? He's correct. A molecule of air is the same size regardless of the wing size. A molecule of air is proportionately larger on a smaller wing.
Yah, but he got the effect backwards.

At the speeds a typical touring car travels the Reynolds number of an RC car will be about 1/20 to 1/30 of the equivalent full scale car. If we use the assumption that aero forces are proportional to square of speed and proportional to the body surface area, then an RC car going 1/2 as fast as a full scale car should generate (1/2)^2*(1/100) or 0.0025 times the downforce. If we factor the mass of the car which is about 0.001 times the full scale car then the scale downforce of an RC car is 2.5 times the full scale car.

Last edited by dpk241; 11-18-2014 at 02:36 PM.
dpk241 is offline   Reply With Quote
Old 11-18-2014, 02:25 PM   #29
Tech Addict
 
Join Date: Nov 2003
Posts: 602
Default

Quote:
Originally Posted by dpk241 View Post
Yah, but he got the effect backwards.

At the speeds a typical touring car travels the Reynolds number of an RC car will be about 1/20 to 1/30 of the equivalent full scale car. If we use the assumption that aero forces are proportional to square of speed and proportional to the body surface area, then an RC car going 1/2 as fast as a full scale car should generate (1/2)^2+(1/100) or 0.0025 times the downforce. If we factor the mass of the car which is about 0.001 times the full scale car then the scale downforce of an RC car is 2.5 times the full scale car.
dpk241;
Thanks for clarifying.

IMO we use the word "wing" pretty loosely here in the RC world. A true wing (airfoil) is configured in a cross sectional shape that
operates with Bernoulli's Principle - regarding high and low pressure zones. What we have on RC bodies are merely air deflectors
that are strategically placed. They're actually pretty rudimentary - but seem to get the job done - and are "tunable" in some situations.
https://www.youtube.com/watch?v=aFO4PBolwFg
Gurney flaps or wickerbills (or whatever you like to call them) are only effective when there is a true inverted wing profile involved.

My 2 cents.

Dale - Protoform
__________________
PROTOform Race Bodies
www.racePF.com // www.facebook.com/PROTOformRaceBodies // www.twitter.com/RacePF
daleepp is offline   Reply With Quote
Old 11-18-2014, 03:01 PM   #30
Tech Master
 
DS Motorsport's Avatar
 
Join Date: Aug 2005
Location: The Netherlands
Posts: 1,437
Trader Rating: 2 (100%+)
Default

Last year I started with researching aero with the idea that there is still a lot to be gained. Most bodies right now are either sculpted by hand or made in CAD, then a mold is made and after some initial testing 99% of the time the original model will be the one being sold.

To start gathering RC data I had all the populair 1/10 nitro bodies 3D scanned and started running CFD on them to see how they would compare. After sometime I had some numbers which matched the feel the bodies gave on track.

Protoform SRS-N before converting to a solid model:


A Gurney flap doesn't work on an RC car like it would work on a 1:1 car.
In RC we use bits of plastic which channel the air upwards causing the car to be pushed down a bit, the whole principle of a proper wing doesn't apply.

First I looked into building a windtunnel but as has been said above it needs to be pretty big in order to produce some reliable numbers.
A very basic tunnel doesn't have to cost a lot, but one which is reliable and can be used to really improve downforce will get expensive quite quickly.
Personally I don't have the space to build one so I will try to do as much as possible in CFD and then start having prototypes made.

This video by Sauber F1 gives a very nice insight into the construction of a windtunnel and basic aero stuff, also how it works with scaled models:

http://youtu.be/KC0E0wU6inU
__________________
P1-RC.com
DS Motorsport is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 11:51 AM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net