250 GN, the 100 mph project - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

Grant-53 · 05-13-2012, 10:04 PM

The trick with an air cooled engine is getting air flow smoothly in and out of the fairing. A NACA inlet on either side of the dustbin ahead of the engine would work. The ideal exit point is near the rider's leg. If possible find a low pressure area behind the legs as the rear half of the fairing narrows. With the dustbin front you are looking at a long tail section to maintain aero stability. Consider an electric fan in front of the engine fins and a temperature gauge of some sort.

renault_megane_dci · 05-14-2012, 06:50 AM

Here is a pic of the carboard Kammback :

the start is a little smaller than my back and little lower than my shoulders then it goes to the end along a 15° angle

Funny story : the pics were taken by an unknown colleague making fun of it and forwarded to me by one of his colleagues ...

It was the first evolution.
Since then I also put an angle on the horizontal line.

renault_megane_dci · 05-14-2012, 06:57 AM

Quote:

Originally Posted by beatr911

If you are unsure which is better, please test three tanks of fuel with each set-up. Oh, and don't change anything else during those 6 tanks. Good testing takes time and conditions that isolate the change you are testing.

That would be a little over two month with the associated change in temperature from spring to summer !
So not really valuable on a testing POV.

The thing is I try to ride as less as possible.
After all, it is not only about MPG but also GPY : gallon per year

renault_megane_dci · 05-14-2012, 12:19 PM

IT WORKS !

Today's high speed attempt did show +200 rpm and relevant speed increase on the clock !

The context :
since fitting the 16*39 sprockets (up from 15*42 IIRC) the bike was not able to hit its peak power in 5th @ 8500 rpm.

Friday I got 8000 rpm (with the raised wind shield and tucking)

Today with the cardboard kammback and not tucked to make it work properly, I got 8200 rpm on the same slightly downhill.

The start of the hi speed attempt is consistent since it is a speed camera ...

Maybe the air was hotter / more dry allowing for a better mixture (I run pretty lean being on E10) and the wind was more still (I don't recall).

Now the bike clearly shows its limits in terms of hi speed handling being very short and light but I can go round that (see my pic of the 17" rear wheel on longer swingarm)

Anyway, I am very pleased !

renault_megane_dci · 05-15-2012, 12:17 PM

If weather allows, tomorrow is coast down test day to convince a colleague of mine that is rather skeptical.

I'll keep you posted !

renault_megane_dci · 05-16-2012, 10:53 AM

Today was coast down test day.

We rode to the "quiet back road" my colleague mentionned.
It was rather windy ...
So I went for a ride, trying to pass his parked car at 100 Km per hour, pulling the clutch and then cheking the speed at a distance, namely a sign on the side.

With the kammback : two attempt showed 62 ish Km per hour

Without the kammback, the bike was easier to maintain at speed (probably more throttle, maybe less wind) and I got a consistant 60 ish Km per hour.

Then I fitted the kammback back but we didn't do more attempts.

All in all : waste of gas ...

I don't know the distance from point A to point B either just the tiny difference in speed

Can I work out something out of it ?

janvos39 · 05-16-2012, 03:58 PM

The kinetic energy at 100 km/hr is 0.5*m*v*v and that is with a bike+rider of for instance 250 kg 0.5*250*27.77*27.77=96450 in both tests
This kinetic energy at 60 km/hr is 0.5*250*16.66*16.66=34722
So without the tail enengy consummed by air and roll resistance is 96450-34722=61728

Now with the tail. Energy left at 62 is 0.5-250*17.22*17.22=37076
So energy consummed in this case is 59374. (so approx. 4% less)