Dan asked:
> Does anyone have any figures on how much difference > changing the pitch of the prop makes in cruise and climb? My observation on cruise speed and pitch with the C-85: All observations at 2400 rpm 7146 100 mph climb prop 7148 104 mph normal prop (per Ed and John) 7150 108 mph cruise prop (per Ed and John) 7150 112 mph theoretical - several heavy or draggy Coupes have shown they can only make it to 90 mph with miserable climb using this pitch. These correspond pretty well between my observations/measurements and Paul Prentice's information duplicated below. Sorry that I don't have good climb tables. Ed Burkhead http://edburkhead.com/Ercoupe/index.htm East Peoria, Illinois ed -at- edburk???head.??com (remove the ? marks and change -at- to @) Engine/Propeller efficiency Paul Prentice published tables in his 1991 book "Fly About Adventures and the Ercoupe." His tables have checked out pretty well, from my experience with measured speeds during in-flight observations. Ed Burkhead The following material is used by permission of the author and copyright holder, Paul Prentice. Paul may be contacted at [EMAIL PROTECTED] to request permission for any other use. All rights reserved. For each engine, these are at the "recommended cruising RPM according to the "Operators Manual" by Teledyne Continental Motors Form X30012 FAA approved Dec. 1980. All numbers @ 5.1 degrees Celsius @ 5,000 feet. C-75 @ RPM=2275 prop=CL7349 IAS=102 TAS=110 prop=ST7351 IAS=106 TAS=114 prop=CR7353 IAS=111 TAS=119 C-90 @ RPM=2350 prop=CL7150 IAS=106 TAS=114 prop=ST7152 IAS=110 TAS=118 prop=CR7153 IAS=114 TAS=123 C-85 @ RPM=2400 prop=CL7148 IAS=104 TAS=112 prop=ST7150 IAS=108 TAS=116 prop=CR7152 IAS=112 TAS=121 O-200 @ RPM=2500 prop=CL6948 IAS=103 TAS=111 prop=ST6950 IAS=108 TAS=116 prop=CR6952 IAS=112 TAS=121 For comparison: The C-85 with a 50 inch pitch prop. The 50 inch pitch means it would theoretically travel 50 inches forward during one turn. 113.6 miles/hour = (50 inches * 2400 rev/min * 60 min/hour ) / (12 inches/foot) / (5280 feet/mile) ENGINE PROP COUPE AVG CRUISE TIAS TAS MAX IAS TAS TYPE SIZE MODEL EFFICIENCY RPM SEA LVL 5000' RPM SEA LVL 5000' C-75 7351 C-D 97 2275 106 114 2275 106 114 C-85 7150 CD-to-G 95 2400 108 116 2575 116 125 C-90 7152 F1-F1A 95 2350 110 118 2475 116 125 C-90 7153 A2-A2A 97 2350 114 123 2475 120 129 O-200 6950 D-G 91 2500 108 116 2750 118 127 These are the best table I've seen.
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