Re: Nathan Peck's Quickie Q-Tour is uploaded to YouTube

David J. Gall



Your problems with the poor performance you’re getting with your Rotax are almost entirely traceable to your propeller. Your descriptions of your takeoff struggles and limited top speed at reduced throttle (and over-revving) are classic for a two-stroke engine that has a prop with too large diameter and not enough pitch. Mike Arnold went 213 mph on a (barely) 65 hp Rotax; I think you could easily be cruising at 150 mph with decent climb if you’d get a better prop, and I don’t think you need to have a variable pitch prop to get there. You could start by cutting down the diameter of your existing prop and increasing the pitch. The attached spreadsheet indicates that a 48” diameter should be maximum diameter for an airplane full-throttle top speed of 150mph if you’re using a 2.58:1 gear ratio. If you’re using 2:1 the maximum diameter shrinks to just 43 inches. (Assumes maximum engine RPM at 6800 rpm; you’d likely want an even smaller diameter in order to cruise at less than full throttle at 150 mph.)

I’ve attached the Sport Aviation article for reference – I’m not suggesting that you should  build your own prop, but the article explains what the spreadsheet is doing. I’d be happy to work with you on a custom prop design if you want.



David J. Gall


From: <> On Behalf Of Nathan Peck
Sent: Monday, May 10, 2021 11:13 AM
Subject: Re: [Q-List] Nathan Peck's Quickie Q-Tour is uploaded to YouTube


Thanks, Jim.  I wish I wouldn’t have sounded so negative toward the Rotax.  The are notable pro and cons to every power plant.  The Rotax is and has been fine, but is t perfect. 


On Sun, May 9, 2021 at 10:43 PM Jim Patillo <Logistics_engineering@...> wrote:

Nathan, thank you for the zoom meeting you did. Informative and like Sam said “what a history”. Sorry to hear you’ve had so many problems with the Rotax and Warp Drive. 

N46JP Q200

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