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Date: Fri, 01 Oct 2010 10:10:27 -0400
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: simple dyno
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Why would it need to be wood?

Not that wood would be lacking.  A typical prop is. . .what?. . .3"x8" at=
 the hub, for a total cross-section of 18sq.".=20
  A 5"x5" beam would give you 25sq.", and the typical prop is quickly nar=
rowed down to a very flat section.  And your=20
not worried about weight, so you could use something strong but heavy, li=
ke oak or hickory.

But, you could also use an aluminum bar.  McMaster-Carr has a 5"x5"x6' 60=
61 aluminum bar for $700=20
(http://www.mcmaster.com/#aluminum/=3D933sgh).  A 4"x4" of 6061 is $450, =
and a 4"x4" of 2024 is $1060. Kind of expensive,=20
but $700 won't buy much dyno time either.  Package (crate?) it correctly,=
 have it validated against a standard dyno, and=20
it could be rented out to other builders.

A composite bar could be built in a few days.  Again, since weight is not=
 a concern, you could make it a solid layup,=20
but you'd probably want to limit the wall thickness to something simply r=
idiculous like 1/2", rather than going batsh!7=20
crazy, just to save materials.  Either way, it would probably hold the we=
ight of a dump truck without blinking.


Bill Bradburry wrote:
> Over my head!
>=20
> A 75 inch log that is 5 inches square swinging at 7000 rpm???  If 191 H=
P=20
> can do that I will be surprised, but would not want to be close enough =

> to witness it!  [:<O
>=20
> =20
>=20
> Bill B
>=20
> =20
>=20
> -----------------------------------------------------------------------=
-
>=20
> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] =

> *On Behalf Of *Andrew Martin
> *Sent:* Saturday, September 25, 2010 11:56 AM
> *To:* Rotary motors in aircraft
> *Subject:* [FlyRotary] simple dyno
>=20
> =20
>=20
> Whilst researching propellers, I came across this gem of info from=20
> www.jcpropellerdesign.com <http://www.jcpropellerdesign.com>
>=20
>=20
> Gustave Eiffel (1832-1923) came up with a simple solution for measuring=
=20
> HP without complex apparatus, By using a /balanced /wood bar instead of=
=20
> a propeller with a square cross section of 1/15th of the length of the =

> bar, you can measure the rpm and calculate the HP available.
>=20
> Power in HP =3D 0.0532 (diameter/450)5 (RPM/1000)3
>=20
> =20
>=20
> As I need a load on the engine when I run it I=92m going to give this a=
=20
> go, 1350 x 90mm at 7000 rpm will give me 191hp, that=92ll do if I can g=
et it.
> --=20
> Regards
>=20
> Andrew Martin
> Renesis RD1c
>=20
> West Australia
>=20