Introduction & Cross wind solutions to motorcycle Streamliners?

[Teri_TX]

Hi everyone,

I recently joined and have been lurking a while before making a fool of myself by posting :-)

I stumbled on to this site via a stumble on to Craig Vetter's site after stumbling on another site ... I forget what I was orginally looking for. That's the beauty of serendipity! Anyway, I'm a retired engineer (mechanical and electrical) with even more time now to ponder things. I have never had a motorcycle or ridden one (except once on my brother's dirt bike many moons ago) but I'm considering one (Honda CBR250R is my current choice) for high FE so I can putter around and explore the countryside. Having weather protection would extend the utility of the motorcycle instead of just being a joy riding toy.

Allert Jacob's velomobile is probably the most documented successful and beautiful aero bodied motorcycle/scooter (sorry Craig Vetter !) to date (in my opinion). He reports that side winds have minimal effects on the handling and this is without a long tail. After reading about many of the other similar projects I started wondering why his aeroshell is least affected by side winds.

Others have mentioned in passing that the side forces from side winds is from the lateral lift forces after a vector analysis of the apparent wind direction. This got to me to thinking of why and how minimize the lateral forces. Craig Vetter's "last Vetter Streamliner" had door fairing temporarily until he decided the side gusts were too much with them. He is also a veteran motorcyclist and probably prefers the open feeling of not having door fairings anyway.

The above ramblings got me to thinking that maybe the lateral lift is the real problem and I started Googling about wings and various lift and spoiler devices. Today, I stumbled across a "spoiler" type device called a stall strip which is just a simple triangular piece of metal (usually) placed at the stagnation point of the wing root to improve stall behavior. Even the U2 spy plane has a retractable stall strip to assist in landing since it simply just wants to keep flying which I found in my Googling..

After reading about "stall strips" I looked again at Allert's aeroshell to verify something I had just thought was simply a "styling" look he placed on the sides. The swoopy creases and resultant slight concavity probably cause any lateral lift to be ruined or minimized at least. I wonder if Allert deliberately put them there for aero reasons or that he just thought they "looked good". Anyone have an email address for Allert Jacob or other means to relay this question to him? Theo22? I'll PM him.

Back to Vetter's streamliner, I wonder if a stall strip or even a low vertical fence on the centerline of the nose section would serve a similar purpose to disturb the low pressure side airflow in a side wind gust condition and yet not have any perceptible parasitic drag in the forward direction? I hope Craig Vetter reads this or I may have to email him directly if he doesn't respond to this post.

On another thought, I did a search of the archives for "DIY wind tunnels" and many replies were rather negative, pointing out the Reynold numbers etc. The original posters were usually asking to determine Cd's and such to "compute" forces on their "finished" project. I was wondering if instead of the utility in studying flow conditions and "relative" forces between different designs. The operative term is "relative". I have a 42" shop fan which might be used as the fan for a modest wind tunnel. Of course, where I live, the wind blows rather hard most of the time from the south and I could probably just set up models outside.

Sorry for lengthy post and look forward to an intelligent discussion.

-- Teri

[Frank Lee]

Yeah, Allert initially reported good x-wind performance but a buddy of his posted later on that it wasn't so great.

[sheepdog 44]

Thats an interesting concept. Definitely worth looking in to.

[Teri_TX]

Thanks Sheepdog44,

I was looking for such a figure in my searches but I gathered enough info from the various text articles and small thumbnails. I don't have enough postings yet to quote your message.

As I said, I wonder if a simple fence along the vertical center line might not be even more effective as it would certainly cause airflow disruption of any airflow not dead on center. However, it might be too effective and cause drag for minor cross winds. So maybe the triangular shape might be best.

I'll PM Craig Vetter and Theo22 to see if they could test out the theory. Anyone else out there with a fairing game to try? A piece of 1/2" or so rope hot glued or taped on would probably work just as well. Wikipedia article on "Turbulators" was my earliest clue.

I wish I had a streamliner to test the theory out on ;-)

-- Teri

[Ironside]

Teri TX, it's interesting that you came up with that idea, if I understand it correctly it's almost exactly what Royce Creasy (of Voyager fame in the UK) seems to have discovered.
Take a look at a photo of his 'fat jogger' which has what appears to be rope or wire taped across the front of the fairing which he later incorporated into the bodywork, described as 'explicit separation features'. Specifically designed to disrupt the airflow to improve the 'indifference' to sidewinds.
Photo of 'fat jogger' -http://bikeweb.com/files/images/royce-578.preview.jpg

[Teri_TX]

Hi Ironside,

Very interesting.

Where on Royce's site is the discussion behind this image? I look at his site periodically but it is not well designed as far as back links are concerned. I finally found the image but there is no discussion with that image that I can find.

His rope is a "turbulator" (see Wikipedia subject "Turbulator", I can't post links yet) than a stall strip I referenced. The image Sheepdog helpfully provided explains the stall strip very well since it comes from a hidden link in a flight school training course. The end result may well be the same and complementary to a stall strip.

A stall strip only becomes "active" (turbulence producing) when the local airflow angle exceeds half the apex angle of the stall strip. It is normally placed at the stagnation point in normal flight so it is not drag producing. I can imagine somewhat more complex stall strip designs to produce varying degrees of turbulence. I'm sure the real aerodynamicists could tell us a lot more than us arm chair types.

In a private correspondence with Craig Vetter, he said a short fence on the tail of his streamliner was suggested by Tom Finch of Tailwind trailers which he reports has some effect in reducing side wind sensitivity. Craig said he was going to try it on the nose section at my suggestion. I have not heard from him yet.

A fence would be the extreme degenerative version of a stall strip. It would cause turbulence at any non-zero (direct head on) local airflow angle.

There is hope for decreasing side wind sensitivity for streamliners. I am awaiting more reasoned discussion on this subject. I'm not sure how this forum works in regard to renaming thread titles or if it can except by moderators.

-- Teri

[Ironside]

Hi Teri,
There is a link to Royce Creasey's articles on FF Web | Feet Forward people do it Feet First. Second paragraph, the link to 'read this first' will take you there.
I'm very close to testing my 'dustbin', only paint and screen to do. Its comforting to know that there are solutions to instability in crosswinds, this has always been a worry, especially as my creation weighs in at less tha 100Kg.

[Teri_TX]

Hi Ironside,

I'm afraid I can't see any direct link. In the past I did read most of Creasey's long discourse on his theories of FF design but I really don't care to spend the time again. His acerbic nature can be trying to the spirit.

Creasey's turbulator has the disadvantage of always adding drag even in a no side wind condition (calm air or perfectly head on into the wind). A stall strip can be designed to add no drag up to a defined non-axial apparent wind direction (the solution to the optimal angle is left up to the student :-) . In practice, a fence would behave like a turbulator as rarely is the apparent wind perfectly on axis (a transient condition at best).

I do believe there is a solution to cross wind stability but it will probably involve aero trickery like stall strips, fences, vortex generators, turbulators, et cetera. A fundamental design without add ons may be not be possible unfortunately. Even Dassault Aviation has resorted to winglets in spite of their chief designer's aversion to such band aids, as he believed in "doing it right" from the beginning. An admirable goal not always achievable.

-- Teri

[Ironside]

My mistake Teri, technical aspects of ff design at Technical aspects of FFs | FF Web. There's a menu that will take you to individual aspects you might be interested in.

[visionary]

Welcome to the club

Hi Teri, welcome to a very small club – people actively trying to understand the aerodynamics of full bodied motorcycles. My own research has shown there to be very little genuine high-quality study in this area and your last comment - “ I wish I had a streamliner to test the theory out on” may prove to be the only way to really know.

I doubt that there is any company or academic institution worldwide currently undertaking serious research on the fundamentals of motorcycle stability through aerodynamics. This is primarily because there are no true full-body motorcycles currently in production other than the monotracer.
Think of all the superscooters and cruisers, which sport significant portions of bodywork and the manufacturers of those products, you would think aero research would be a well-trodden path.
The reasons that it is not are many and varied, but put simply; those people most interested in the subject are blessed with the least resources. Conversely, companies blessed with adequate resources, like the big-four Japanese manufacturers seem oblivious to the opportunities for enclosed motorcycles.


I have evaluated the options (for research), just as you have, and my thoughts are: that the time and expense of building a small scale wind tunnel would not be justified as the accuracy of results are unlikely to provide clear answers. So realistically it means testing at full scale and real-world conditions, ie build one and play.

Of course this testing method is not without hazards, as explained by Roger Dunkley in his aerobike blog.
AeroBike Enclosed Motorcycle

Those brave souls who have tried this method are fewer even than the bike builders. When I recall pictures of Craig Vetter and his tuft testing, I think this represents the most scientific published information. Despite Royce Creasey’s writing and theory I have yet to see similar basic testing methods employed.

It occurs to me while writing this, that tuft testing of a superscooter (with tufts on rider and rear of machine) would advance our knowledge greatly. The ideal test would involve images taken at high degree of lean and during strong sidewinds (maybe simultaneously) as well as the more traditional straight-ahead shots.

Anyway, back to your original question about forms of separation device. I’m a few months away from my own road testing and would be happy to try some of these ideas on your behalf. However, I feel that quantifying the effect of a device is the biggest obstacle, after all the “feel” of a vehicle is a highly subjective subject.

Just like you, I hope a well-informed discussion of this topic results from your opening post.