Duncan, any pictures? Did you use the XS oil cooler or the classic's?
Thanks Erich
<ami@mcfadyean.freeserve.co.uk> writes:
> Also for what its worth, testing of the Lo-mcfadyean-sti XS cowls has
> just
> been completed. These are comprised XS cowls with the underslung
> portacabin
> removed. The radiator sits in a new duct under the cowls. The duct
> is much
> slimmer and curvier, set further back from prop blade interference
> and has
> about half of the inlet area of the XS. The oil cooler is removed
> from
> behind the water radiator and is now smaller and placed behind the
> port
> nostril.
>
> In terms of cooling, it all works rather well.
> In terms of aesthetics, it looks loads better (IMHO).
> In terms of overall drag, I have no idea whether they are any better
> or
> not. A throttle -closed VNE dive with the former BMW cowls (not too
> dissimilar to the Std. XS) lost about 4000fpm; now its about 3000
> fpm
> (although to confuse matters, prop pitch is now coarser).
>
> For good measure and to reduce wetted area(!) the cowls were also
> reduced
> in length by about 2" (because the Classic engine mount has been
> used). The
> secret to the cooling success is a new outlet duct at the base of
> the
> firewall through the area that the monowheel likes to occupy (or is
> occupied by the nose gear stuff on the Tri). The inlet duct is also
> "properly" dimensioned and shaped so that it isn't running in a
> stalled or
> 'vena-contracta' condition. You too can make this mod., but you may
> first
> have to change to fixed conventional gear to create the opportunity
> for
> the additional exit duct.
>
> Duncan McFadyean
>
> PS does anyone have a NACA duct splash mold I could borrow?
>
>
>
>
> On Saturday, May 18, 2002 9:40 PM, Fred Fillinger
> [SMTP:fillinger@ameritech.net] wrote:
> >> FWIW, on the aerodynamics aspect, the substance in Hoerner's
> "Fluid
> > Dynamic Drag" re cowlings is this. Once you have the problem of a
> > propeller, aerodynamics aren't much more than the least wetted
> area,
> > limited by "practical considerations" of what's inside. The shape
> is
> > a transition to the fuselage with curves of decreasing radii.
> Thus,
> > whether an alternator "bump" is worse than a larger cowling is a
> > matter of experimentation, or just aesthetics at a possible price.
> >
> > Biggest issue is cooling drag, meaning smallest, most efficient
> inlets
> > to still do the job. Whether a NACA scoop is better for the
> > intercooler, or larger central duct and split the flow, or totally
> new
> > arrangement would involve expert opinion. But I suspect it still
> > reduces to trial and error even for Lopresti. It's curious also
> that
> > Lopresti obtains the biggest gains on the faster aircraft, which I
> > guess is the "velocity squared" phenomenon: only 5 MPH on the
> Arrow
> > and no cowl kit for the slower but bigger market PA-28 fixed-gear
> > versions. In comparison, the XS cowl appears to have the type of
> > cleanups the aftermarket guys do.
> >
> > For landing lights, I have small halogens, 35W to 75W with
> narrow-beam
> > reflectors that are tiny and only $4 each, to play with. Besides
> room
> > to fit, having 2 small lamps means less heat each to deal with the
> > heat issues, and more focused light pattern to maybe make up for
> the
> > lower candlepower compared to the short-life aircraft lamp.
> >
> > Regards,
> > Fred F.
> >
> > The Europa Forum is supported by Aviators Network UK
> <info@avnet.co.uk>
> The Europa Forum is supported by Aviators Network UK
> <info@avnet.co.uk>
|