inverted wings & things

[velocity200]

Greetings from Australia......Gentlemen, I have been involved long term at an amateur level in a motorsport termed "landspeed racing" also known as time trials, the aim of this sport is to design a vehicle and race against the clock with the aim of achieving the highest average speed over a timed mile distance.
I have embarked on a new project who's goals are to exceed 500kph on a modified motorcycle, among the many challenges involved in achieving this is traction or in this case a distinct lack of it, the racing surface is salt( a large salt lake ) where the coefficient of friction ranges between 0.4 to 0.6. The solution for many is to simply add weight to increase the traction, but due to several constraints this is not feasible ( tyre load ratings and physical limits space to house the weight (lead)) so I am looking at using aerodynamic down force to achieve the needed traction.
Searching the literature and web I have found that it is considered possible at least in theory but there are very few examples of it having been performed in practice.
So gentlemen I require assistance in ascertaining how one should proceed in applying inverted wings and /or ground effects to a motorcycle. Caveat the vehicle will be maintaining a straight line of acceleration so no corners or leaning involved except for small roll and yaw movements due to relative wind speed and direction.

Cheers

 

[3DDave]

Almost all racing cars use this - they are the wings on the rear end of race cars and dragsters.

Perhaps it isn't often used on motorcycles?

I would think a limiting factor is that as the lift goes up, so does the drag, which will act at the wing. On a typical motorcycle the obvious place for a wing is above and to the rear of the rider, which then tends to lift the front wheel. You'll notice that most vehicles that use wings place them very close to the ground. Figure on 10% drag to lift ratio and see how much you'll be dealing with.

If you are limited by tyre capacity using lead, you'll be limited by tyre capacity using wings.

It may be more worthwhile to look at drag reduction as a way to limit the amount of traction you need.

Either way, I'd suggest building or finding a wind tunnel and getting some books on wind tunnel testing. It is a well-established method that is easy (low technology easy, not lift-a-finger easy) to use. Perhaps find a college and make a class project for them and get your results cheap(er).

 

[GregLocock]

get

http://www.amazon.com/Race-Car-Aerodynamics-Engineering-Performance/dp/0837601428

There is no inherent problem in using aerodynamic downforce for straight line motorcycles, but since it is a path not often trod it is going to be full of traps.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[velocity200]

3DDAVE...Thanks ...maybe I should clarify re tyres the motorcycle based tyres are unsuitable for the loads to be encountered, presently there is some experimentation being conducted using some high speed auto tyres ( goodyear landspeed ), so far with mixed results but as these are the only game in town I will persist with them. the physical space required to add weight is limited at least in the amount needed as well maintaining a CoG ahead of the CoP becomes an issue to.
The aerodynamics of the bodywork is well defined already and limited by rules......there may be some gains to be had with wind tunnel testing and tuning but not of the magnitude required ....the 500kph barrier has already been exceeded by a motorcycle using a custom tyre and running on a tarmac runway in the USA, where they are distance limited not traction limited, the opposite is true for the salt.
I understand that there is a drag penalty using aerodynamic down force, this can be countered by extra power which is not an insurmountable problem, the major concern is getting that torque to hook up. To date speeds of up to 270mph have been achieved on the salt But tyres and traction issues are severely limiting any further progress, ergo perusing the least trodden path.

Thanks Greg for your input

PS. Can pics be added to posts ?

 

[MikeHalloran]

You have to get the DVD of "World's Fastest Indian", starring Sir Anthony Hopkins as Burt Munro. Your issues are not new. ... and it's a pretty good flick. Give the wife the night off and crank up the speakers.

Assuming you are starting with the usual cigar tube shaped streamliner, it would seem the simplest way to get downforce is by changing its angle of attack, ever so slightly, by e.g. shimming the rear suspension up a mm or two at a time.

I first thought of strakes along the side, tilted up at the rear just a little of course, but fitting them to the body without gaps would be fairly difficult, especially if you want them adjustable. ... and if they're too far back they'll lift the front wheel, but if you run them much forward of the rear wheel, they'll interfere with the rider's legs at awkward times.
... maybe they could be integrated with whatever outriggers you use for low speed stability, but then they'd have to carry gravity loads in addition to aero loads, assuming they form short low-mounted wings from which the outriggers extend, but then they'd also cause extra drag that you don't want.

Have you considered a vertical wedge in front of the front wheel, to push the boundary layer out of the way?


Mike Halloran
Pembroke Pines, FL, USA

 

[velocity200]

If this works, these are examples of what is out there....

 

[velocity200]

ok lets try this

 

[velocity200]

The blue bike has exceeded 500 kph and the gun metal grey is the fastest on the salt at 270mph
Mike I have seen the worlds fastest indian and the bike is not a streamliner

 

[MikeHalloran]

I get a 404 on the first pair of pictures, but I can see the second pair.

Those are not streamliners, either, but they are fairly large, and there has to be a lot of parasitic drag associated with the unshelled space where the rider is.
I'm guessing that's in your rulebook.

I'm also guessing that your rulebook also prohibits 'dustbin fairings', which completely enclose the front wheel. They were banned from motorcycle roadracing decades ago, I think because of stability problems with the CP being forward, and possibly because of the speeds they allowed. The front fender on the blue bike is, I assume, as close as you can get within the rules.

All I can think of is ... make the fairing, and the rider, smaller. ;-)

Mike Halloran
Pembroke Pines, FL, USA

 

[velocity200]

Yes Mike the body aerodynamics are limited by rules no dustbin fairings either ......body shape is fixed, more power is available, traction not available to transmit extra power to the ground....exploring inverted wings to make up the shortfall

My thoughts are 2 wings each side of both front and rear wheels located at axel level and horizontal to the ground, gimballed so they maintain horizontal while the bike can roll as needed. this would place the down force over the contact patch. provision made for changing angle of attack....the option of the rear wing above the bodywork at the rear may not be possible as the rules state no part of the body work can be higher than 36" above the ground .....as there are no rules about wings or aerodynamic traction aids it could be possible to locate above rear wheel and high with its associated benefits.
Looking for comments for or against proceeding any further
cheers

 

[MikeHalloran]

Looking at the body in profile, it already resembles a wing.
... but not inverted.

Is it permissible to taper the bottom of the rear fairing upward, so that the muffler projects from a 'bottom' surface and not a 'side' surface?
Further to that, if the 'edge' between bottom and side surfaces were also a bit sharpish, perhaps you could trap trailing vortices there. I don't know if that would hurt or help, but it would be fun to try in a wind tunnel.

Mike Halloran
Pembroke Pines, FL, USA

 

[3DDave]

A link to rules would have been helpful. Without them suggestions are moot.

 

[velocity200]

wrt rules ....the class is called partial streamlined and the rules that affect streamlining as follows.

7.G.11 Partial Streamlining:
If a streamlined seat/tail section is used, it can not extend further to the rear than 10 in. beyond the rear
edge of the rear tire, or 1/3rd of the wheelbase and whichever is less. No part of the seat/tail section may
be closer than 4 in. from the ground, or over 40 in. from the ground with the rider seated.
It shall be possible to see all of the rider: completely from either side, except the hands and forearms. As
viewed from directly above it shall be possible to see all of the rider except the hands, forearms, legs and
feet. It is forbidden to use any transparent material to avoid the application of these rules. Fairings or
bodywork shall have a minimum of three (3) separate mounting points.
No part of the fairing ahead of the front axle may be lower than the top of the front rim at the axle vertical
centreline or be forward of the front edge of the rim. There shall be no streamlining forward of the front
edge of the front rim.
Front fender is optional, and if used shall comply with the following: front wheel and tire shall be visible
from either side for a continuous 180 deg. of their circumference. The front of the fender may not extend
lower than a horizontal line drawn through the front axle. The perimeter of the fender may not be further
than 1.750 in. from the tire tread. The sides of the fender may fair in the fork tubes or sliders, but must not
be over 2 in. wider overall than these parts. No part of the seat/tail section behind the rear axle may be
closer than 4 in from the ground with the rider seated.

there are no rules wrt. wings or other aerodynamic devices for motorcycles mainly because there is zero use of them so I have an open book except possibly the 40" rule if the scrutineers considered a wing a part of the body work...such is not the case for cars which have many rules regarding wings etc..

This was tried in the 1970's by a NZ racer in road racing until it was banned

 

[3DDave]

Banned cause it worked or banned cause it was dangerous?

Now that tires aren't a problem, is there a rule regarding width? A six foot wingspan should do nicely.

What are your current drag and overturning moment estimates? How much excess horsepower is there at speed? How much downforce is needed for propulsive traction and how much for steering traction? How much side-wind will stop your attempt?

I like the idea that cars at the Indianapolis 500 drive more than 1G of downforce. If the track had a twist the cars could operate inverted on the aerodynamics alone. Turn? Maybe not, but they'd stick upside down to a ceiling. The cars would be faster if IRL allowed them to use adaptive aerodynamics, but that's just money wasted on making the race take less time.

 

[rb1957]

expect a lot of experimentation (and several crashes) getting this right.

you'll have to be very careful about the balance, I'm guessing you want more downforce over the rear wheel, but not so much that you flip the bike ! so you'll have to provide some at the front (like the kiwi bike has).

remember lift is proportional to v^2 which isn't really what you want ... you want more downforce initially (to accelerate with) and less later (to reduce drag and increase max speed. could you have speed sensitive incidence ?

the kiwi rear wing is very high ... looking for clean airflow? I wonder about very low wings ... in ground effect ? (also the drag induced moment is lower)

Quando Omni Flunkus Moritati

 

[140Airpower]

There is only one factor that does not favor adding weight instead of aero downforce and that is the problem of accelerating up to speed in a limited acceleration distance. This is the drag racer problem. Otherwise for top speed running, adding air drag is a greater loss compared to adding weight. Note that the additional rolling resistance is greater from adding downforce since it has to also compensate for the greater aero drag.

The acceleration vs total drag problem can be calculated, but can only be proven empirically.

 

[velocity200]

TY for your replies to date ......3DDave this bike has not been built as yet, still in the design stage. Its a clean sheet project with no rule regulations wrt wings and the body regulations are posted above....some plug in data I can supply from the previous build and other existing LSR bikes .... drag will be in the 0.5 to 0.55 range ( from coast down testing) ....overturning moment ??? I suspect it will be closly related to the tyres im using and camber angle ....I am using this data as a starting point for calculations.
Air density =0.0691....Rolling resistance 0.0155 ( from coast down tests) ...Frontal area= 6.1 sq'....Target speed 300 mph....Weight balance 60% rear 40% front.....lift CL= 0.2 (guesstimate)...weight transfer due to lift 50% applied to rear tyre...Coefficient of friction for Salt surface 0.4 bad day 0.6 good day.....from these I calculate 558 HP to overcome drag...aero drag = 698lbs....HP to overcome rolling resistance = 55.... r.r = 69lbs...total hp required = 613.....weight required to achieve traction for this HP level = 2800 lbs....weight of bike when completed will be around 1000 to 1200 lbs. with rider ...shortfall to be supplied by down force.......tyres load rating 1700 lbs each @ 100 psig.....maximum side wind speed is up to 6 mph

RB1957...yes I would be great to have the lift at lower speeds and taper off the angle of attack at higher speeds ...there are no rules banning this....so the problem is an engineering one ..... I am hoping for wings in ground effect, two at the front and 2 at the rear horizontal to the ground each side of the bike mounted off the axels on gimbal bearings so as they stay horizontal the ground as the bike rolls as needed.

140 airpower certainly not distance limited course is 6 miles long .....mounting the weight needed is not possible while maintaining the body shape and frontal area .....though extending the wheel base is possible as that can be as long as needed.

cheers

 

[drawoh]

... The solution for many is to simply add weight to increase the traction, but due to several constraints this is not feasible ( tyre load ratings and physical limits space to house the weight (lead)) so I am looking at using aerodynamic down force to achieve the needed traction.

What is the difference between the force of gravity and the aerodynamic force of a wing? The only one I can see is that the wing will create drag.

You do need to keep this thing on the ground.

--
JHG

 

[btrueblood]

"mounted off the axels on gimbal bearings so as they stay horizontal the ground as the bike rolls as needed."

This seems like an unnecessary complication - will the bike really need to roll that much at speed? The downforce from the wings won't change much with even a 10-deg. bank angle. I'd think you would get more out of active aero surfaces (think ailerons) that could counteract stability problems, though that suggestion has so far been deemed too expensive by other speed teams (like hydroplanes).

 

[rb1957]

i think he has restricted envleop ... so he can't add enough weight.

weights are "better" 'cause they create a constant downforce, and don't add significantly to drag, but also i guess "dumber" (so probably a class weight restriction).

if we can have speed sensitive windscreen wipers, you should be able to design a speed sensitive wing incidence adjustor; downforce required at speed is less than that required at start, right? hadn't thought about wing clearance if the bike tilts; but this is for straight-line speed ... any tilt would "terminate" the run, no?

Quando Omni Flunkus Moritati