Introduction & Cross wind solutions to motorcycle Streamliners?

[PeterS]

A whole coil ? or perhaps a 50 mm high protrusion .

The question remains , why does it work if the lift is generated aft the greatest curve ?

[sendler]

If it works it will be as shown in post 3.
.
http://ecomodder.com/forum/412846-post3.html
.

[PeterS]

As usual I probably don't understand but from the illustration ....



would we be well advised to put two strips, separated by say 6", on the nose , one left, one right. Being that the air that worries me is not the clean consistent side wind on the open road but the left/right buffeting near heavy vehicles on the highway. That comes in impossible to anticipate gusts as big trucks pass or are passed.

[P-hack]

two stall strips on different sides of the nose would be perpetually in "stall" and increase drag.

Remember that in the motorcycle case, the "wing" is vertical, and folks are putting a, more or less, vertical stall strip all along the nose.

This reduces the lift (which has a sideways force on a bike) generated when there is a change in the wind direction, regardless of what caused the change in wind direction. You still have side pressure (which is where cross ventilation or step-through is helpful), but you don't have induced "lift". I put lift in quotes in case it isn't obvious that this lift is acting sideways to try and lay the bike down, and not trying to lift the bike.

the nose strip makes it act more like a flat-plate airfoil instead of an actual airfoil when the wind isn't straight on.

an airfoil can generate a much greater coefficient of lift at smaller angles of attack than a flat plate




We want the low drag of an airfoil without the "lift" ideally.

[PeterS]

Originally Posted by P-hack

two stall strips on different sides of the nose would be perpetually in "stall" and increase drag.

Remember that in the motorcycle case, the "wing" is vertical, and folks are putting a, more or less, vertical stall strip all along the nose.

.

Exactly, my thinking is that if the lift of the foil can be "spoiled" by two raised edges it may be possible to reduce the side vent area and that vent area must be a source of a LOT of drag.

[P-hack]

oh, it is. I saw someone computed a .4cd for an open fairing. Which is a notable improvement over a naked bike, but a very long way from streamlined. A single nose strip is sufficient to minimize the airfoil properties and not reduce straight ahead drag. It wont help with pressure differential due to angle of attack, and two strips will only ruin any straight ahead streamlining (and do nothing for pressure differential).

[PeterS]

Originally Posted by P-hack

oh, it is. I saw someone computed a .4cd for an open fairing. Which is a notable improvement over a naked bike, but a very long way from streamlined. A single nose strip is sufficient to minimize the airfoil properties and not reduce straight ahead drag. It wont help with pressure differential due to angle of attack, and two strips will only ruin any straight ahead streamlining (and do nothing for pressure differential).

OK, thanks for clearing up that bit of misunderstanding on my behalf ,
Cheers.

.4 would be a pretty good starting point and it should be possible to have closing ''doors'' for the open road far from traffic .

[Teri_TX]

Originally Posted by sendler

I offered an answer and further reading to correct the other poster's misconception that the Ecomobile was somehow flying into cross winds because of it's shape. It is not. Motorcycle steering dynamics is fundamentally tied to this discussion.

You are refering to post #104 by godscountry. He acknowleged his confusion and I missed the misconception he had and replied as I thought he didn't understand my thesis of reducing lateral lift.

Originally Posted by sendler

Well I didn't really want to sit and type for hours but your hesitance to read and study other good threads has compelled me.

I HAVE READ THE THREADS YOU KEEP REFERRING TO. They are notable for the wandering undisiplined thread drift which is very confusing to the normal person trying to read them. I spent a lot of time deciphering the contradictory messages. Please start your own thread.

Originally Posted by sendler

I would link some excellent threads Aerohead has written about the rapidly diminishing returns of Kamm tails but you don't like links so let's skip it.

YOU MISQUOTED ME. I SAID TO POST A PERMALINK IF SOMETHING IS RELAVANT. and not hijack the thread.

Originally Posted by sendler

Streamlining a motorcycle turns it into a vertical airfoil which generates horizontal lift when sidewinds combine with the headwind of forward motion to create an angle of attack. This increases the force beyond what a normal bike would see.

At least we agree on something which was my original thesis in message #1.

Originally Posted by sendler

The greatest lift of an airfoil is located just behind the max thickness. So "spoiling" with a fence along the top and back section of the tail isn't going to help anything.

You are referring to the picture of Craig Vetter's fence on the tail of his streamliner in JeffM's post #52. I never suggested anything like that. Vetter said it was at the suggestion of Tom Finch 2013 Vetter Streamliner-Chap 68-redesigning Terry Hershner's-Zero in a private email. Blame him, not me. I have no idea why he made the suggestion to Vetter or his reasoning. I do not know how JeffM got the same picture Vetter privately sent me.

Originally Posted by sendler

Venting the max pressure differential from one side of the wing to the other across the engine bay or the riders lap is the easiest way to make the increased side lift of a streamliner a complete non issue.

That is one way of only minimizing lateral lift at the expense of extra drag. A crude solution which Vetter alludes is only partially effective.

Originally Posted by sendler

Top speed runs on salt flats are an extreme case where the rear tire is completely at the limit of traction and so the vehicle is essentially flying as it skips along the ground.

The HPV speed runs are done on a special smooth section of asphalt road in Nevada. Videos of them crashing from a cross wind is solely attributable to cross winds and not loss of traction from bouncing wheels. I can't really comment on the various land speed record runs on salt flats. They appear to carve a groove in the salt from the solid aluminum wheels. Calling them cars is a stretch. More like jets or rockets without large wings flying at ground level.

Originally Posted by sendler

In lieu of venting which still could be done even if the rider is fully enclosed,

So how would you do this? Still sounds like a higher drag "minimizing solution".

Originally Posted by sendler

Spoiling on either side of the nose could also reduce the side lift at a slight compromise of cd if the spoilers are carefully run along the lines of flow. They will have to be much larger than a piece of rope. More like Sheepdog's design at the early part of the thread (no photo) but two of them and moved part way around to the side of the nose.

Sheepdog in message #3 linked a picture from http://www.langleyflyingschool.com/I...l%20Strips.gif

You apparently don't understand how stall strips function. I thought the image was self explanatory. See the Wikipedia article Stall strips - Wikipedia, the free encyclopedia on stall strips. The critical explanation is: "Here it acts to trip the boundary layer air flow at higher angles of attack, causing turbulent flow and air flow separation. " which is the next to last sentence in the article. Two strips are not stall strips but turbulators Turbulator - Wikipedia, the free encyclopedia

Ironside's experience in message #78 with a mere single 7mm diameter rope centered on the fairing speaks for itself. His piece of rope behaves as a stall strip even though it is not the usual triangular shape section on aircraft in the Wikipedia article.

[sendler]

Originally Posted by P-hack

two stall strips on different sides of the nose would be perpetually in "stall" and increase drag.

Not necessarily. This is not a long, straight wing shape. It is more of a meld of a wing with a steep rake, and a missile. On a streamliner like Vetter's that has a low, pointed nose, there will be lines of laminar flow which start at the point of the nose and move upward. And outward. One line will obviously flow straight up and over the top of the windshield. But if you were to go out and ride in the rain with talc powder on the front of the bike you would see that there are other lines just to the side of the nose point that start off straight up, but then begin to curve out toward the mirrors for example. They would also be invisible (other than the slight increase in skin area) to the steady head wind flow just as the straight up foiler is. But they might have more effect for any given amount of protrusion since they are closer to the area of max lift, there will be less time for the air to reattach. It would be more work to get them on just right so they are not in perpetual stall but the bike would look really high tech with two or three foilers.

[PeterS]

A question ..

What if the ^ section / flow detacher/ turburlator was at the point of maximum lift along the side of the body ? Would that reduce the lift by allowing a detached area of air under the flow ?