John, I envy yoursophisticated tools! Once firmly on the ground then certainly
braking is important, but I guess it is bleeding off the speed from 60kts to
where
the wing is no longer adding major lift (say 30kts) that the prop pitch is
important.
Regards, David Joyce, G-XSDJ
Sent from my iPad
On 11 Jan 2012, at 12:32, "John Wighton" <john@wighton.net> wrote:
>
> David,
> Thanks for the reply/description. Having been an aeronautical engineer for 30
years l appreciate both the theoretical and practical analysis of a problem.
Clearly you have a heap more experience in the practical sense, especially
w.r.t.
Europa flying.
>
> I have at hand a bunch of tools (including Fluid-Dynamic Lift and Drag by
> Hoerner/Borst,
CFD programs, etc) from which l would happily spend hours/days/weeks
quantifying this discussion. But that will have to wait until l finish this
pesky A380 work on my desk right now.
>
> A rough calc (@50kt landing to standstill), along the lines of your
> suggestion,
reveals a flat plate drag load of about 96 lbf for the fine (zero degrees in
fact) pitched prop prop (4lbf for the feathered prop). This will reduce quickly
with the square of the speed (@25 kts max load is approx 24 lbf). The
proportion
of total drag during the ground run will depend on a heap of stuff (tyre
pressures, ground friction), etc.
>
> So unbraked l think you have a point. With normal (or higher) braking l think
the difference will be a lot less (as prop drag
>
> --------
> John Wighton
> Europa XS trigear G-IPOD
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> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=363034#363034
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