Tunnel aerofoil design

[drumzzzz]

I've been starting a winter time boat project in cad,

was curious if anyone ever tried a tunnel design with a further rearward aerodynamic center?

By moving the lift back would it be less sensitive to blowovers?



The AOA of the foil at approximate plane is just 3 to 4 degrees, as well as a shortened tunnel length

to contribute minimal lift.

 

[ZIonOB75]

I've been starting a winter time boat project in cad,

was curious if anyone ever tried a tunnel design with a further rearward aerodynamic center?

By moving the lift back would it be less sensitive to blowovers?

View attachment 4607

The AOA of the foil at approximate plane is just 3 to 4 degrees, as well as a shortened tunnel length

to contribute minimal lift.

my understanding with this is that the total lift should be equal to drag or resistance to prevent blowover.too much lift will blowover to much drag will submarine,,, were lift is compose of c.g., a.c., angle of attack, airfoil aerodynamic, hyrodynamic, prop set-up, while drag is the surface area, hull design, power, etc.. there is a formula for this and u can determine where to position ur a.c.....i would say the a.c. is one of the factor to consider...goodluck and good start..hope i know how to use CAD...

 

[Slideblues]

Lots of info here:

http://boatdesign.net/articles/tunnel-hull-design/

Scroll down for the formula's

Gener B)

 

[Chris Wittrig]

Lots of boats that are running out there right now that have a true deck crown to generate lift have that crown too far forward resulting in a center of lift that is ahead of the center of gravity. This setup actually worked when the speeds were lower than they are now. How do we fix this? Weight, trim, etc. Would it be nice to see a boat that had a center of lift closer to the CG? You bet! Don't forget, though, the effect of tunnel compression so getting the tunnel right is pretty much as important as getting the airfoil right.

 

[drumzzzz]

aeromarine research says:

LA = [½ ρAV2 SA CLA]

where:

LA = air lift

ρA = density of air

V = velocity

SA = surface area

CLA = lift coefficient

man I havent seen equations like this since highschool!

anyone got a slide rule? :lol:

Did anyone see the National Geographic documentary on powerboating?

it had tunnelhull blowover and submarining video galore,

aeromarine research had a bit to do with the information as well.

They had a bit showing how the dynamic CG is on them, and how they

counter with trim.

Is it all these forces- hydrodynamic,aerodynamic ect. that make up this dynamic CG,

completely seperate from the static/weight based CG?

(It makes sense how improperly adding steps can screw up stability as well now)

 

[james irwin]

I've been starting a winter time boat project in cad,

was curious if anyone ever tried a tunnel design with a further rearward aerodynamic center?

By moving the lift back would it be less sensitive to blowovers?

View attachment 4607

The AOA of the foil at approximate plane is just 3 to 4 degrees, as well as a shortened tunnel length

to contribute minimal lift.

THE BEST WE CAN DO IS , KEEP ALL LIFT AT A BARE MIN. WE HAVE FOUND , THAT ANY LIFT AT ALL . THAT IS FORWARD OF THE TRANSOME WILL CREATE LIFT ON THE NOSE ; ONE THING YOU MUST REMMBER , ALLTUNNEL BOATS WILL RIDE WITH A 3 OR 4 DGREE ANGLE WHEN THEY ARE AT SPEED ,

 

[drumzzzz]

just an offbeat thought- some airplane aerofoils have AOA stall points, I wonder if something similar could be designed into a tunnel?

 

[ZIonOB75]

just an offbeat thought- some airplane aerofoils have AOA stall points, I wonder if something similar could be designed into a tunnel?

i believe plane and boat are using the same airfoils design, so it has angle of attack stall point, u need to determine what kind of boat design ur using and pick from the the recommended airfoil, let say a glider plane uses airfoil that create a lot of lift in a low speed and power, while jet plane uses airfoil create lift with high speed and power, now to apply this to rc tunnel u need to know first ur engine power rate and how fast it will go coz u need a certain speed to gain this lift, since tunnel mostly running 40-60 mph which is a little contribution to total lift, so its kinda not the main factor for a rc tunnel but it's helpful when u know ur airfoil, AOA, AC,..i would say the hydrodynamic is more important than aerodynamic here,,,hope this help..

btw, i'm getting a tunnel boat but i'm buying the hull...wish i had all the access in making my own hull just like u...looking forward to ur tunnel design.

 

[Slideblues]

Hey Guy's

The only piece of advice I could offer ya (Ben Dare Dun Dat) is to dont go to far to fast, build ya up a couple centers and some spoons try one thing and go test, Nutin better than on tha water testing, Note the results and then try something else.

We have a Way To Fast "Hall of Fame'r" and his running buddy that are board members,

Tommy Lee and Rod G, Also Jack Garcia of Bandit tunnels, Hopper of HTB, and others.

There here if ya run into problems,

Have fun and test,test,test,

Gener B)

 

[james irwin]

Hey Guy's

The only piece of advice I could offer ya (Ben Dare Dun Dat) is to dont go to far to fast, build ya up a couple centers and some spoons try one thing and go test, Nutin better than on tha water testing, Note the results and then try something else.

We have a Way To Fast "Hall of Fame'r" and his running buddy that are board members,

Tommy Lee and Rod G, Also Jack Garcia of Bandit tunnels, Hopper of HTB, and others.

There here if ya run into problems,

Have fun and test,test,test,

Gener B)

HEY YALL . GUESE WHAT I JUST FOUND , I WAS UPSTAIRS AND FOUND THE OL BOAT WE DESIGNED AT THE OL WIND TUNNEL , MAN I TELL YOU , BY TODAYS STANDARDS , IT STILL LOOKS GREAT . THIS ONE WILL STILL HANDEL TODAYS HOT RODS. THERE ARE NO SHARP CORNERS UP FRONT . 28 .5 LONG / 2INCH TRANS OFFSET FORWARD ,63/8 WIDE TUNNEL / WELL WELL WE JUST MAY PUT ONE IN GLASS . B) B) B) B) B) B) B) B) B) B) B) B) B) B) B) B)

 

[talonxracer]

Could we even take this a step further into aerodynamics, under camber, like the high speed glider airfoil the MG06. This airfoil uses ailerons that are 33% of the chord/fore and aft, Allowing slight movements of the ailerons in the same direction to change the airfoil shape. Seeing as we do not make the sharp turns of a true tunnel racer in both directions we could "alter" the center of lift instead of using engine trim, sorta like ailerons and flaps combined, flaperons, at the forward part of the tunnel between the cowl and sponsoons. Mix this function with the rudder and third channel remote needle.

Doug

 

[ZIonOB75]

Hey Guy's

The only piece of advice I could offer ya (Ben Dare Dun Dat) is to dont go to far to fast, build ya up a couple centers and some spoons try one thing and go test, Nutin better than on tha water testing, Note the results and then try something else.

We have a Way To Fast "Hall of Fame'r" and his running buddy that are board members,

Tommy Lee and Rod G, Also Jack Garcia of Bandit tunnels, Hopper of HTB, and others.

There here if ya run into problems,

Have fun and test,test,test,

Gener B)

HEY YALL . GUESE WHAT I JUST FOUND , I WAS UPSTAIRS AND FOUND THE OL BOAT WE DESIGNED AT THE OL WIND TUNNEL , MAN I TELL YOU , BY TODAYS STANDARDS , IT STILL LOOKS GREAT . THIS ONE WILL STILL HANDEL TODAYS HOT RODS. THERE ARE NO SHARP CORNERS UP FRONT . 28 .5 LONG / 2INCH TRANS OFFSET FORWARD ,63/8 WIDE TUNNEL / WELL WELL WE JUST MAY PUT ONE IN GLASS . B) B) B) B) B) B) B) B) B) B) B) B) B) B) B) B)

kinda interesting, post pic pls. i wanna see, i wanna see.... i'm in the process getting tunnel hull,,,hard to decide....

 

[jayt]

Could we even take this a step further into aerodynamics, under camber, like the high speed glider airfoil the MG06.

Guys, there is a big difference between a boat and an airplane - it's called ground effects - what works at 1000 feet may not work at 0.2 feet. Actually, I know it doesn't work the same. I used ground effect data when I designed my cat, the fastest non-rigger FE boat in the country - faster than any FE sport hydroplane at an official 74.3 mph. That may change this weekend though...