Topic: Aerodynamically better fairings for sohc4 racers?

[gschuld]

I have been spending some time lately dealing with vintage road race fairings.  Having done some research on the subject, I have concluded that very measurable gains on the road race courses(especially the higher speed courses) could be had with more efficient fairings than are currently available and being used on our sohc4 racers, be it cb400, cb500/550, or cb750 racers.  Davies Motorsports, from my understanding, has made and produces two separate fairings specifically for the cb500/550 chassis that represent an example of an aerodynamic improvement over the original early designs. The first certainly appears to have been a modification of a TZ250/350 race fairing of the early 80s, the other (race numbers 14 and 6 below) was developed later in an attempt to improve the high speed aerodynamics and improve top speed.  Reports have suggested that it did indeed improve performance over the previous fairing, +/- 5mph(?) on the top end.

Brent Waller uses a copy of the original design fairing, first picture(Davies calls this fairing the "classic" fairing now), while the second photo shows the updated design. My understanding is that the Davies second design fairing isn't allowed in certain classic classes, presumably as the fairing isn't classic enough.  So I presume that they switch between the fairings depending on where they are racing and what is allowed.

This issue is what interests me, the hard to pin down variable.  There are quite a few separate classic road racing organizations in the US never mind the ones around the world that have their own independent rules and tech inspectors.  It's not a question of whether a better, faster fairing set could be made for ...say a cb750 racer.  It's totally doable, and the more leeway available to the designer/producer of the fairing the more potential for a performance increase.  At a certain point, more efficient fairings for vintage racers tend to start to resemble more modern fairings(for obvious reasons).  I wouldn't want a vintage road racer to carry fairings that looked like they came directly off this year's MotoGP racers, but pinning down the acceptable amount of modern aero thinking and incorporating it within a fast AND visually acceptable form is the key.  Davies Motorsport's cb500/cb550 fairings are the result of one companies interpretation of that dilemma.

Designing a fairing FROM SCRATCH, shaping it, prototyping it, testing it, and creating quality production molds is a challenging time consuming process.  For all that effort to be worthwhile, it ideally would be able to be used(within the rules restrictions) in as many vintage class associations as possible.  The pool of sohc4 racers around the world is already small enough...  and it would take quite a few fairings to justify the work involved to create a really good fairing.

So anyone who has insight into what is and has been allowed fairing wise in the various vintage classes(US and abroad), I'd like to hear about it.

Thanks,

George





 

     

[Sam Green Racing]

The ultimate for top speed, ask the guy in blue that sneaked into the picture. hahaha

[voxonda]

Fairing does nothing if rider doesn't fit. I do not fit my fairing but Tonny does.

[Old Scrambler]

Compared to a modern fairing, the '70 fairing was more useful as a number plate. I like the Davies design...........notice how its more forward and allows the front wheel to compress 'into' the fairing. Yes, get your knees behind the sides and use the smallest boots possible. Pay attention to drag such as the tail section and the angle of the riders back. Land-speed racers are sometimes known to 'raise their butts' to reduce drag. Also pay attention to recent factory development..........Honda increased the production speed of the CBR1000RR by allowing more air to pass THROUGH the front rather than pushing all of it around.

I don't know what is legal for your use...........but the required belly-pans should be designed to help........not hinder.  Also...........try and get your hands somewhat out of the air. Pay attention to the air-flow on your arms and body............if you feel a BREEZE on the outer parts of your arms and legs, GOOD.........that's laminar flow............if not, you have drag. If you feel air on your body or inner/upper arms........that means you have an air-brake

Other things that can help with top speed are inner-fenders that hug the rear tire (mounted to swing-arm) and good side-covers that minimize drag behind your legs. I've had several aerodynamics gurus tell me that after the initial shape of the nose..........have the widest point at 30% of overall length and don't reduce the size at angles of more than 7-degrees until you get to the tail. I see a lot of people pay too much attention to the sides when the hole you have opened in the air is tall versus wide.  Think about it............your trying to go faster than 150-mph.......that much wind force would blow your house down.....................because of drag  

[bwaller]

It's not voodoo but it does take tunnel testing, no science in "looks good" which is how I work! I imagine this work goes hand & hand with engine development when big money is involved. The rest of us take our best shot. I remember a few years back Rossi & Hayden mid season showed "bum up" action down any straights obviously after some recent testing. Like Denis the rear end is mucho important and I feel useless in understanding a good fix in vintage roadracing. Only some go fast enough I suppose!

On the way to round 2 right now. Worked until 1 am, left at 5, crazy #$%*. I wouldn't even be making this race without the help of our George here. Thanks bud, just awesome.

[gschuld]

I'm fairly comfortable with the concepts regarding improved aerodynamics, but less so regarding what vintage classes would allow better aero fairings as they start looking more modern.  Brent, has anyone given you grief on the tech and rules front regarding your fairing, since it's design was based very heavily on an early 80 road racer fairing?

It is impressive what some teams have been able to gain through seemingly small alterations in the fairings and body positioning when tested in a wind tunnel.  I am not at all suprised by a raising of the lower backside on the high speed straights.  Delayed separation of the over the top airflow was the goal I imagine.

There has been some testing done that looks favorably toward rather large seat and tail fairings, assuming the airflow is ...fairly ...clean up to that point.  The most efficient aerodynamics solution doesn't always make the best looking fairings. ...unfortunately.

Just curious what classes wouldn't, for example, allow the Davies early (classic) fairing like Brent runs, and what classes would not allow the second more modern looking design.

George

[teebee67]

I understand that the CRMC will not allow the later fairing and, as virtually all club classic racing in England runs to CRMC rules, it would not be legal for any of their races (though rule implementation is usually much slacker at most club meetings). I think it has been OK'd for the IOM so the classic TT, Manx GP, etc (which I believe is what John had it made for) will be OK.

[bwaller]

George, believe the rules state period appearance or some such. No issues with Davies classic.

[gschuld]

George, believe the rules state period appearance or some such. No issues with Davies classic.

I'm curious though whether your VRRA tech would be OK with the more modern 2nd design cb500rr Davies fairing though.  CRMC allows the early Davies fairing(like yours) but does NOT allow the later more modern looking one.

George

 

[bwaller]

Not sure George, I'll ask & get back.

Raining cats & dogs here. Not good conditions to learn a new bike. The 550 is under wraps!!

[gschuld]

Raining cats & dogs here. The 550 is under wraps!!

Life is funny like that.... LOL.

Yeah, if you have a few minutes to ask the powers that be during the rain, PLEASE do and report back.  It's an important issue... 

Hopefully the weather will dry up and your racer can stretch her legs again. Fingers crossed.

BTW, do you have any kind of data logger that will record your speeds throughout the race course.  That could come in very handy for documenting improvements in performance as you improve your racer.  And you will improve going forward.

George

[HondaFreak]

I follow the live timing at the Classic TT for John Davies, because the speed trap times are indeed live and disappear after the race. Last year's speed trap times were up to 5mph higher at Sulby, over the previous year and there hadn't been any significant power output improvements between the two years. The average lap speeds increased too. Possibly more significantly Alan Oversby always wanted a larger screen with the 'classic' fairing but has made no such requests with the more 'modern' looking fairing. The photo is of William Dunlop tucked in 'behind the bubble' and gives you some idea of the profile coverage by the new fairing. I truly wish we had the resources to quantify the changes in the wind tunnel, however....

[HondaFreak]

I will have a look back at some old Facebook postings I made and see if I can find the back to back figures. Interestingly John Davies has a book on Vostok racers that used a pointed front and small screen in the 60's. It looks like a precursor to the current MotoGP top fairings. See attached photo to give you some idea of their style. It looks surprisingly modern.

[gschuld]

Yes, exactly what I was talking about.

Damn, I meant to modify my message as I managed to inserted the wrong image.  I managed to delete the thing instead. Hopefully this one is the right one.

1973 Cycle Rider magazine in house project.  Kawasaki 500, just under 150mph on the salt with modest engine mods.

George
 

[70CB750]

1969 Jawa

[gschuld]

Nice.  keep them coming...  Any up and aft sloping upper fairing photos from the 60s and 70s would be good to have.

Actually, any photos of outside the box design fairings that have had successful use on the track would be interesting.  I'm a history fan... 

George

[HondaFreak]

I have the 500/4 clocked at 136.4mph last year through the speed trap. That is with about 67-68bhp. The Paton clocks about 145 through the same trap but is putting out 80bhp by all accounts. I think you are right; pushing the air up and over rather than round is the key and also dragging it out of the engine/side panels so the airflow through the bike is better. It is not for aesthetics that MotoGP bikes have such big cut outs in their side fairings. That would be acceptable in classic racing as it wouldn't alter the profile :-)

[gschuld]

I think you are right; pushing the air up and over rather than round is the key and also dragging it out of the engine/side panels so the airflow through the bike is better. It is not for aesthetics that MotoGP bikes have such big cut outs in their side fairings. That would be acceptable in classic racing as it wouldn't alter the profile :-)

I'm VERY glad that you mentioned the side panel exits.  That is a big factor in aero efficiency.  Modern water cooled GP engines have huge radiators in front to cool them, this requires a significant opening up front, but exit ducts just behind the radiators on the side panels not only allow the airflow a place to go out and around the rider, but increases the cooling efficiency as well. 

Our air cooled engines have somewhat different needs cooling wise.  We need good quality cooling air to flow through the head and cylinders, plus the all important oil cooler in Hipo engines.  Basically the airflow that we need is concentrated in the upper half of the frontal area of the engines.  Assuming a proper integral belly pan fairing like the Davies models, the unavoidable air running through the rest of the cowling trying to get out can help somewhat with oil pan cooling, exhaust pipe cooling, etc.  The side exit vents existed back in the 60s and 70s as well, but mostly for ducted airflow control with oil coolers such as with the Dick Mann CR750 below.  Some creative work regarding airflow control and exit ducting tailored for an air cooled engines could allow a significant reduction in the airflow needed into the cowl, which could have a positive effect on aero drag.  It would, obviously, create a more complicated fairing and become less and less cost effective to produce/reproduce.  I noticed that the second generation Davies fairing (below) has a pair of air exit ducts pretty far up and aft on the fairing side panels.  Based on the positioning of those exit ducts, it looks more like an exit for cylinder head/cylinder bank cooling air. If so I would expect some minimal ductwork directing the air from the aft ends of the head/cylinder bank sides to those exits.  Interesting if that's the case...  very nice

Getting the air up and over the rider as much as possible has clearly been shown as the way to go for the last 30+ years. Millions spent on wind tunnel time has proven this again and again.  Certainly some have done it before the mid 80s, but it was less common.  I applaud those that were ahead of their time.   

The 136.4mph is with the second generation Davies fairing correct?  And with the earlier "classic" fairing?  Thanks for the info.  Please keep it coming...

George 

 

[RAFster122s]

It doesn't take much for the air to flow through and out a side exit without any internal ducts.  The air will flow in a path of least resistance.  Depending upon the amount of air through the front you may have a negative pressure spot behind that duct exit. The key with any openings is to not introduce turbulent flow and induce drag.
tufts on wings and objects in the tunnel show the airflow and it is even used in flight testing sometimes in the real world.
I enjoy aero and rc aircraft.
I have a friend who is an aero engineer and now a professor, he has a doctorate degree and has worked for several big aero companies and even did wind tunnel testing for NASA starting out. He is in the UK this summer working there until fall classes resume and he returns.
Do you have specific questions that could be entertained through email?
David

[HondaFreak]

From memory, the top speed of the 500/4 in 2013 was 132-133mph. So 3-4 mph improvement in top speed. It doesn't sound a great deal but over 151miles and 4laps of the TT course it certainly makes a difference. If you consider that in 2013 William Dunlop lapped at 109mph, with only a top speed of 133mph, you can infer how much time is spent flat out. That average speed is 82% of top speed. It is roughly the same with the 350. I am not certain it makes such a difference on the short circuits, but on the roads, particularly on low powered bikes, the aerodynamics play a significant part in edging up the lap speeds.

[HondaFreak]

RAF122S - could you ask your friend what is the smallest scale for wind tunnel testing that the results still remain valid for - back to back tests, not absolute numbers - and aren't too much effected by scaling errors to make the tests worthless? 

Thanks,

Peter

[gschuld]

Great question.

From what I have come to assume, it is more cost effective, in both time and accuracy, to use a full size wind tunnel with the actual parts being used.  Much of the on the spot development during wind tunnel testing with motorcycles involves quick cut and tape on modifications, or swapping out premade test fairing sections, to the fairings and adjustments to the riders positions on the bike.  Hiding the rider from the air is as important as the air through and around the bike.  The rider is obviously an integral part of the overall aero equation.  To a point where any testing done without a rider, regardless of scale will offer only limited useful data.  Leading edge testing, ram air or cooling air intake duct testing, for example can generally be done without rider since it is so upstream of the rider itself.

Testing basic airfoil shapes is much easier to scale down, with the resulting data getting skewed as the scale reduces. 

Interesting subject, fascinating really if your into this kind of thing.

George

[RAFster122s]

Tim had replied the Reynolds Number needs to stay around 500000 to give consistent results but needs more information about the speed range. Are we looking at a large envelope such as between 100-180mph, 100-175, 100-160, 125-160?

Granted the areo package needs to work consistent with positive results from low speed up through top speed.

[gschuld]

Nice example of forward thinking upper fairing aero from 1970/1971.  Bottom two BSA Rocket 3, Dick Mann.

George

[voxonda]

The BSA/Triumph letterbox fairing is a very well designed fairing. Most interesting part, for me, is Dick's seat in 3rd pic. It shows that on the very fast circuits like Daytona, Talladega etc. the seat plays a major part in the aerodynamics. For making sure the low pressure area is situated away from the rear of the bike(s).