Aerodynamic aspects of an old GoOne 3 velomobile

[freebeard]

Cites Mair (1969) so I see where it's coming from. The part about rectangular sections is opaque to my monolingual brain.

aerohead's favorite Template is a strict half-body. I struggled with the question at Why does The Template have to be a half body of revolution?. It covers superellipeses, etc.

[aerohead]

Originally Posted by freebeard

Cites Mair (1969) so I see where it's coming from. The part about rectangular sections is opaque to my monolingual brain.

aerohead's favorite Template is a strict half-body. I struggled with the question at Why does The Template have to be a half body of revolution?. It covers superellipeses, etc.

For 'practical' purposes, Paul Jaray morphed his 1922 streamline half body, from semicircular, to rectangular, and then back to semicircular, in order to accommodate passengers.
It doesn't really matter what one does to a body cross-section, as long as the local area does not vary any more than that of ideal semicircular section.
A look at a local sheet-metal shop which does work for heating and cooling system contractors will reveal their 'square-to-round', and 'round-to-square' duct transitions, which follow the same rules.

[aerohead]

Originally Posted by beate

And that's the reason why i would like to try elliptical cross sections of the back. There are some remarks (examples!) in the textbook of Hucho that these maybe at least not worse than the tipped tails. If done right, of course. Does anyone have links to more systematic research on such tails - the 2 dimensional case might be even more interesting for a velomobile than the (rotationally symmetric) 3D-case.

A truncated tail is not necessarily that bad - see for example the Quest velomobile.

Both, Sighard Hoerner's book, AERODYNAMIC DRAG, and Freiherr Reinhard von Fachsenfeld's 1951, Aerodynamik des Kraftfahrzeugs include data from empirical tests of 2D sections.
I published both years ago here at EcoModder. but haven't a clue how to find them.

[aerohead]

Sighard Hoerner's 'AERODYNAMIC DRAG,' also has material dedicated to various 'wing tips' and their respective drag coefficients that might be insightful.
Hoerner worked at Messerschmitt.
He personally aero-modded a 1935 DKW 'Reichs / Meisterklasse' two-door sedan, dropping the drag, from Cd 0.64, to Cd 0.25, using the Jaray 2D shapes you're working with.

[freebeard]

I published both years ago here at EcoModder. but haven't a clue how to find them.

Google found 'About 11 results (0.45 seconds)' searching on 'Aerodynamik des Kraftfahrzeugs'. First result:
https://ecomodder.com/forum/showthre...orm-28260.html

[aerohead]

Originally Posted by freebeard

Google found 'About 11 results (0.45 seconds)' searching on 'Aerodynamik des Kraftfahrzeugs'. First result:
https://ecomodder.com/forum/showthre...orm-28260.html

Thanks!'
I speed-scanned the thread, and unfortunately, I didn't post any 2D studies, except for the asymmetrical wing sections, as the 2D wouldn't be germane to passenger cars.
From the asymmetricals you CAN see how the Cd develops as the aft-body is increased in proportion to the 'nose.'
The same thing happens in 2d.
The FKFS demonstrated that the Cd goes asymptotic @ a thickness ration of 21.3% of cord*********************************.
Any additional 'fineness' would only increase drag again, on account of the added skin friction.
L/d = 4.694 = Cd 0.065.
Marchaj places the drag minimum for a 2D section @ L= 3.92X the thickness.

[beate]

Before i continue here my current plans:

- i could verify a small positive effect on drag.
- but in total some disadvantages seem to outweigh that gain ... i'm slower if there is wind from the back. And uphill the added weight is noticeable. Even on the ramps of small road bridges.
- in average there seems no gain.

I am going to give the tail a nicer color (RAL 1023, like the bike itself) and then observe it further. Maybe try to enclose the back wheel a 2nd time.

And then concentrate on other issues. Improve the fairings on the wheel cases. Further improve the brakes (!). Improve the stiffness. Add a few internal improvements like a box for the battery.
Maybe even try to make an improved canopy.

Quite a large program for the dark half of the year?

[freebeard]

Impending Fall Equinox.

It sounds like the 'low-hanging fruit' has been plucked. Is there an opportunity for weight savings with the new canopy?

[beate]

Not really. The easy options to save weight are already done. Maybe another 100 g or even slightly more with a new seat even lighter than the current one. Maybe a few grams by using ultra light pedals, and maybe a few grams by more lightweight and thinner steering rods. The remaining option with the largest potential - replacing the central aluminum frame by a stiffer and less heavy one from carbon fibre is expensive and fully out of my reach. And pretty ridiculous for that vehicle except to replace a broken frame (which hopefully will never happen).

But anyway - there is potential in a significantly more leightweight tailbox, and even in one with better aerodynamic performance. But before doing something like that i need to
a) learn and
b) improve the flow in the front parts of the velomobile.
c) retire (which i will at the end of the year)

Overall the performance of that velomobile has already improved quite a lot, and i am acutually quite satisfied by that.