Graham et al,
I think you will find, if you do the vector diagrams at intervals along the
blade, that the faster the forward speed of the A/C, the more twist you need
in the blades for them to provide lift along the whole length of the blade.
Hence, the PV50 and 55 have much more twist than the Warp Drive. At slow
speeds i.e. at take-off, the inner section of blade will have too much AOA
but that is better than producing negative lift at high speed (as Fred has
already pointed out). The ideal prop would have adjustable blade twist as
well as variable pitch.
Regards,
William
----- Original Message -----
From: "Graham Singleton" <grahamsingleton@btinternet.com>
Sent: Monday, May 28, 2007 10:47 AM
Subject: Re: Europa-List: re:propeller optimization
> <grahamsingleton@btinternet.com>
>
> Fred,William Ira
> William and everyone
> I continue to be puzzled by the Warp Drive prop, which we all know was
> designed for slow microlight A/C. Jerry Davis once pointed out that you
> need less twist at hi speed, which can only mean that the Warp has the
> wrong twist at any speed! (Jerry is UK agent for Arplast)
> Thinking for a moment, at the root the blade angle should be nearly
> parallel with the direction of flight. At the tip it will be dependant on
> speed, diameter and rpm, (of the prop) With a VP prop it will only be
> optimised at one particular speed but should be a good compromise for the
> speed range.
> I haven't done any sums so more than that I won't say at this point.
> Graham
>
> William Mills wrote:
>> <william@wrmills.plus.com>
> the latest Arplast blades PV55 have a slim aerofoil with plenty of twist
> (hub to tip) to cope with cruise
>> speeds of 120 /130 Kts (about 24 degs is required) Regards,
>> William
>>
>
>
>
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