From: "Charlie England ceengland7@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Ross Redrive se ex se
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
References: <list-982361@logan.com>
Message-ID: <cf5e0f47-2594-b0c8-7401-dd2b8e785aee@gmail.com>
Date: Thu, 26 Nov 2020 19:08:39 -0600
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I'd agree with you; if you limit the rotary to a 'sane' rpm for aviation 
use (say, 7000), and use a prop that's typically used on smaller 2 place 
homebuilts with Lycs (meaning 2700 rpm at the prop for 75% power at 
altitude), then somewhere around 2.6-1 makes sense. On the RVs, even the 
180 & 200 HP Lycs use constant speed props that are 74" dia. & turn 2700 
rpm.
https://shop.vansaircraft.com/cgi-bin/shop.cgi?ident=1606438205-166-687&browse=props&product=csprop-hartzell
Only reason to turn under 2700 in cruise is if you're highly motivated 
(self or legislated) to keep noise to a minimum.

Another motivator to keep rpms up is that a lot of prop carvers are in 
uncharted territory when you ask for a 2200 rpm prop. (Right, Sam H. ?) ;-)

When I ran numbers treating the Renesis as a 180 HP engine (~6000 rpm, 
supposedly the minimum bearing load rpm) and swinging the big 76" dia 
prop, I was wishing for a 2.4-1 ratio (~2500 prop rpm).

Charlie

On 11/26/2020 5:09 PM, Stephen Izett stephen.izett@gmail.com wrote:
> Why is that?
> Tracy made the comment that even the 2.85 which I have is only really useful for props >than 74”
> Which I understood to be about the tip speed being to low and inefficient with  smaller diameter.
> I dont want to spin my engine more than 7500 rpm.
>
> What am I missing?
>
> Steve
>
>
>> On 27 Nov 2020, at 7:03 am, Ernest Christley echristley@att.net <flyrotary@lancaironline.net> wrote:
>>
>> At 70 inches, you would want to go the other way.  The C4 gearset was 3.17, but the problem was the weak planetary gear carrier.  But, I just posted a link with a 6 planet carrier.
>>
>> On Thursday, November 26, 2020, 5:56:14 PM EST, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
>>
>>
>> On that note can I ask a gearbox question.
>> I’ve always understood we only really had the choice of 2.17 and 2.85 :1 gear ratio options if using the Ford planetary gears.
>>
>> Looking at our Glasair and I imagine some other aircraft with prop diameters of around 70 inches we would prefer a ration around 2.6:1
>> giving us I think a better prop rpm and tip speed.
>>
>> Are there other options?
>>
>> Steve Izett
>>
>>
>>
>>> On 27 Nov 2020, at 6:32 am, Ernest Christley echristley@att.net <flyrotary@lancaironline.net> wrote:
>>>
>>> Is that the 4 planet, C4 gear set?  If so, I've been made to understand that there aluminum body gets wallowed out by the planet gear's shaft.  I recently found that there is a performance shop selling a replacement unit with six planets.  I know nothing about them other than that.
>>>
>>> https://speedmaster79.com/Ford-C4-Transmission-Performance-6-Pinion-Planetary-Gear-Set
>>>
>>> On Thursday, November 26, 2020, 3:16:01 PM EST, Le Roux Breytenbach breytenbachleroux@gmail.com <flyrotary@lancaironline.net> wrote:
>>>
>>>
>>> Terry : Thanks Terry for the Ross Redrive the parcel arrived on Monday 23 Nov .
>>> Neil if you want some dimensions on the hollow propellor shaft your welcome.
>>> Regards
>>>
>>>
>>> Sent from my iPhone
>>> Le Roux Breytenbach--
>>> Homepage:  http://www.flyrotary.com/
>>> Archive and UnSub:  http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
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