lml@lancaironline.net Mailing List Archive

I was once told that the drag of a wind-milling prop is approx that of the drag of the prop disk flat plate area. That would be “relatively” huge for an otherwise slick Lancair – especially a IV or a legacy with the gear up. i.e. more than twice the drag you might otherwise anticipate, and thus a much greater sink rate (>2x).

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Paul Lipps
Sent: Wednesday, May 21, 2008 8:49 PM
To: lml@lancaironline.net
Subject: [LML] Lancair IV glide data

Lancair IV, 30.2' span, 98 sq.ft. area, 9.3:1 AR, 0.82 Oswald efficiency factor, 2000# empty, 360# 2 people, 240# fuel, 2.12 ft.sq. equivalent parasite drag area*.

All following values without regard to prop thrust or drag:

Best L/D is when drag area equals CDI X 98, 120 mph IAS, ROD 3000 ft./min. straight ahead.

45 deg. turn with induced loss equaling drag area for best turn L/D at 1.414G, 143 mph IAS, ROD 5050 ft./min., 542' turn radius, 8.2 sec/ 180 deg, 685' altitude loss / 180 deg.

45 deg. turn at 76% of best turn L/D, 109 mph IAS, ROD 4430 ft./min., 222' turn radius, 4.3 sec/ 180 deg., 323' altitude loss / 180 deg.

* Marty Hollman, Modern Aircraft Design, p.13. Marty did the design of much of the Lancair IV, and designed its high wing look-alike, the Stallion.