|
|
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
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
|
|