Introduction & Cross wind solutions to motorcycle Streamliners?

[Teri_TX]

Hi Grant,

Originally Posted by Grant-53

Best solution for stability is down force from race car design. Shape laterally can be rounded to reduce lift and drag.

Tony Foale has an article on aerodynamics of motorcycles. He points out that a wing or similar on a motorcycle leaned over is not as effective as it is on a car which has a very low lean.

Cars have the advantage of being relatively level most of the time and much of the current thinking is to push as much of the air to the side as possible rather than over. Funny that McLaren thought that in his Mk1b race cars http://www.supercars.net/gallery/119513/1508/648060.jpg and passenger car designers are now just discovering this?

[PeterS]

Originally Posted by Teri_TX

I've had similar thoughts about manually deployed spoilers but Vetter lives in a place where it's an everyday problem. Where I live, the winds blow fairly consistently about 15-25 mph from the south and the roads are not very twisty. Vetter also experiences rapidly switching direction winds as well. Getting caught with your spoilers not deployed could be exciting (in a not good way!)


-- Teri

Riding in traffic cross winds are very variable, an 18 wheeler blocks it then moves on and the cross wind comes back, the same vehicle generate wind themselves and if your bike is sensitive to differential air pressure ... (please don't call it suction!) things can get very hairy. If I want to go the 160 km / 100 miles to my nearest city I'm on a freeway and right in the middle of 70mph traffic , heavy vehicles and lots of turbulent air .

Peter

[P-hack]

Well I commend Creasey for all the hard work (which is what this takes), but I wasn't sure how "streamlined" that design actually is. 80mpg@80mph isn't too shabby, but an 850cc engine should be able to go a lot faster than 125mph even on a naked bike, but it is open in the middle which helps move high to low pressure, and it seems comfy. Looks are not a concern though, streamlining results are. If someone won't drive something safe and efficient because of how it looks, they are part of the problem.

Lets approximate the flat sided/ blunt nose design as a flat airfoil, as you can see the worst case is a 45 degree angle of attack (say 45 mph crosswind @ 45 mph). prior to 45 degrees (going faster than the crosswind) there is more lift than drag.

I don't know what you can permanently attach to a flat plate airfoil to make it stall sooner, stalling is what they do best, but it is making more and more lift (and gobs of drag) all the way up to 45 degrees.



edit: comparison to naca 0018
per http://naca.central.cranfield.ac.uk/...report-647.pdf page 101 the cl increases much more dramatically up to 17 degrees (cl peak=1.3) then falls back towards looking like a sideways flat plate. it only has %30 more peak lift than the flat plate, but it comes on faster. The more streamlined, the more you have to deal w/crosswinds.



I'm leaning towards sharp leading edge/leading edge fence,splitter for a quick fix like sheepdog posted, but I am biased towards efficiency as being the reason for enclosing a motorcycle, since there are solutions for weather (and safety/not a helmet thread). But even then there are enough crosswinds in everyday driving that it will affect efficiency.

[P-hack]

Originally Posted by Grant-53

Best solution for stability is down force from race car design. Shape laterally can be rounded to reduce lift and drag.

well, I think that is the crux of it. motorcycles are inherently "unstable", down force cannot be applied directly over the traction points in a lean. If you cannot fairly completely cancel out sideways aerodynamic forces then it only gets more unstable and requires more skill to operate.

reading this, the 3 wheeled velomobiles appear to be much better in crosswinds:
Streamliners vs Velomobiles | Recumbent Aerodynamics Blog, and it seems worth the additional rolling resistance of a 3rd wheel in that case.

There are two wheeled streamliners, and the drivers keep them upright with mad skills. So like hypermiling, that is an option too.

[theo22]

Hi teri,

Here's how a stormstrip on a Quest velomobile looks like

The theory is (probably known but anyway) that air that flows sideways will become turbulent flowing over the stormstrip. And turbulant air can follow the shape longer, creation less underpressure and thus less sideforce on the vehicle.
Since a velomobile is a very light vehicle (35 Kg) with a relative big side-surface it is even more sensitive to sidewind than motorcycles.
I got blown off the road ones in a storm and use this strip since.
My 125cc Honda will get a strip too.

Greetings, Theo

Did you ever read articles on tony Foale's website TONY FOALE DESIGNS - Home page
Interesting stuff, take your time..

[Grant-53]

The basic fact that motorcycles lean makes fixed canards and wings difficult to use effectively. Some strakes at the nose could help but at a cost of drag. To complement the storm strip, a cross section where the top curvature is flatter than at the bottom could reduce lift. Most of us are wider at the shoulder than at the ankles, at least riding a bicycle. One advantage a cyclist has is greater ground clearance. The center of lateral pressure may need to be closer to the ground than the center of mass. Lots of work to do on stall aerodynamics and the effect of the Kamm tail on cross winds.

[Teri_TX]

Hi Theo,

Thank you for replying to the forum. I have been refering to the storm strips and your testimony of their effectiveness but I suspect that some on the forum thought I was making up stories. So, here it is "From the horse's mouth" (American slang, Theo I'm not sure you have heard this expression and meaning before)

Originally Posted by theo22

Hi teri,

Here's how a stormstrip on a Quest velomobile looks like

The theory is (probably known but anyway) that air that flows sideways will become turbulent flowing over the stormstrip. And turbulant air can follow the shape longer, creation less underpressure and thus less sideforce on the vehicle.
Since a velomobile is a very light vehicle (35 Kg) with a relative big side-surface it is even more sensitive to sidewind than motorcycles.
I got blown off the road ones in a storm and use this strip since.
My 125cc Honda will get a strip too.

Greetings, Theo

Did you ever read articles on tony Foale's website TONY FOALE DESIGNS - Home page
Interesting stuff, take your time..

I have read Tony Foale's writings and I will read them again.

-- Teri

[Teri_TX]

Hi Grant,

Originally Posted by Grant-53

The basic fact that motorcycles lean makes fixed canards and wings difficult to use effectively. Some strakes at the nose could help but at a cost of drag.

Are the "strakes" you propose like the ones on aircraft like the F-16 and FA-18? Would they be tilted downward for down force? Strake (aviation) - Wikipedia, the free encyclopedia

The strakes on the aircraft mentioned above are what the Wikipedia article calls "Leading edge root extensions (LERX)" Their function are "provides the same additional vortex lift at high AoA by leading edge suction" Unfortunately, the very low aspect ratio makes them very high drag compared to a high aspect ratio canards.

Even canards with a strong anhedral (inverted V) would not work in a severe bank as the windward canard would at that point add a lateral lift in the wrong direction. The leeward side would add a down force vector more normal to the road surface which is what we want.

Too bad there isn't a simple wing solution for motorcycles like 4 wheel race cars can use.

... To complement the storm strip, a cross section where the top curvature is flatter than at the bottom could reduce lift.

I'm not sure I follow. Are you suggesting an inverted wing-like profile in the elevation (looking horizontal from the side) view?

Lots of work to do on stall aerodynamics and the effect of the Kamm tail on cross winds .

Amen!

-- Teri

[Grant-53]

Yes, a nose strake at an angle to the ground was used on road racers such as the Lola T-70. As to the cross section, an aircraft or glider fuselage may have circular or elliptical shaped bulkheads. I am working on egg shaped bulkheads with the smaller end toward the ground. The overall shape of the body is based on a glider design shorted to a 3:1 ratio. (The SZD-9 bis Bocian 1E, nose to bulkhead #6). The bicycle builders at Specialized have settled on a design for their aero frame tubing as a truncated 5:1 shape that is also low drag in 15 degree cross winds.

[Teri_TX]

Hi Grant,

Originally Posted by Grant-53

Yes, a nose strake at an angle to the ground was used on road racers such as the Lola T-70.

Oh, those! Everyone back then just called them spoilers. Calling them "strakes" would confuse any race car enthusiast. Whatever.



Eric Broadley's Lola T-70 was one of the most beautiful race cars of that era. It even featured (in a short scene) in George Lucas's first big movie, THX-1138. Broadley designed the Lola GT which was the starting point for the Ford GT40. Heady stuff back then. Lola Cars - Wikipedia, the free encyclopedia

I understand there is a manufacturer still making authentic licensed copies.

As to the cross section, an aircraft or glider fuselage may have circular or elliptical shaped bulkheads. I am working on egg shaped bulkheads with the smaller end toward the ground. The overall shape of the body is based on a glider design shorted to a 3:1 ratio. (The SZD-9 bis Bocian 1E, nose to bulkhead #6). The bicycle builders at Specialized have settled on a design for their aero frame tubing as a truncated 5:1 shape that is also low drag in 15 degree cross winds.

Any references to the last statement? What does the truncated 5:1 shape look like?

-- Teri