Marc Zeitlin Posted January 27, 2004 Share Posted January 27, 2004 The question was asked "how high can a COZY go?". Jim Price has taken a normally aspirated 160 HP Long Eze to over 35,500 ft., and holds the altitude record for that weight class of single engine piston aircraft. Vance Atkinson has taken his 160 HP COZY III to 23K ft and performed a stall series there. His TAS was 152 KT at full throttle. Aerocad claims a Service Ceiling (100 fpm climb rate) of 25K ft. with a 200 HP engine. I have some vague recollection of Nat stating 26K ft. service ceiling for the COZY MKIV, although I can't find a reference. With respect to top speeds, the Roncz canard is suspected (by John Roncz, the designer) of having a critical Mach # of about 0.5. At that point, the canard will Mach stall, and the plane will become an uncontrollable lawn dart (per discussions with Richard Riley - one of the former principals in Berkut Aviation, the fastest homebuilt canard). 0.5 Mach is 380 mph TAS at sea level (we don't ever have to worry about getting there). However, at the altitudes that some people are talking about, say 25K ft, 0.5 Mach is 346 mph. Notwithstanding flutter considerations (which a simple web search, left to the reader as an exercise, will show is dependent both on TAS and IAS), this critical Mach # is one limit that you do not want to get near. Since 200 mph IAS is ~300 TAS at 25K ft., that's not far away from 346 mph - a short dive to change altitude, or a distraction and small stick bump could easily lead to a large speed change in a short period of time in these slippery aircraft. Mach stall is unrecoverable, unlike a short stint above Vne, or even a short stint with flutter. In either of the other two cases, throttle reduction and/or stick pressure will reduce speed and most likely eliminate the problem. Once Mach stall occurs, the nose drops, the speed builds, the Mach stall gets worse, and as RR has said, you tie the low altitude record while pointed straight down. RR believes that no aircraft using the Roncz canard should use a number higher than 300 mph TAS for Vne. Since no COZY's now exist that can reach this #, the 220 mph IAS Vne has proven acceptable - if people put substantially more speed capability into their aircraft, such as Greg Richter, or some of the posters here, Mach stall will become a large factor in their considerations. Just thought this might help some people in evaluating their options. Quote Marc J. ZeitlinBurnside Aerospacemarc_zeitlin@alum.mit.eduwww.cozybuilders.org copyright © 2023 Link to comment Share on other sites More sharing options...
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