APS tail

[paso54]

We are coming to Speed week in 2014 and would very much like to run our bike the "Parny Express" in the form you can see in my Avatar. Now I have a copy of the 2013 rule book and it is looking like we cant run this in M/PS F as too long on tail and length could we run in A/PS F ? or we will mod if required. cheers p (in the uk)

[maj]

You would need more than just the tail length, to classify as A , wheelbase  , fuel tank size or  specialist bodywork are a few options
or shorten the tail to MPS or M

[wobblywalrus]

Not sure how an open or closed tail will help with wheel related turbulence loss.  Work on automatic transmissions tells me that contained turbulent fluid in an enclosed area around a rotating object can cause drag.  Engine vibration is best killed at the source by counterbalancers, and maybe the same philosophy applies to wheel turbulence.  My figuring is it might be best to enclose the rear wheel to make it less "fan like."

No empirical teasing to back this up.  Its just thinkin' while drinkin' a nice smooth Pilsner.     

[JimL]

That is the principal.  Reduce the entry space to strip away the volume of available air pulled around the wheel/tire.  Use the spat to cut away the high pressure air flow into the face of the tire.  That high pressure point is really dense air, and acts like a brake against that surface.

This will only be incremental gain, because we have really dirty air flowing around these bikes.

That means, in other words, "...make lots of horsepower!"

JimL