Hey Tracy, you’re doing better than theoretical …
6300 engine rpm / 2.17 = 2903.225 prop rpm
2903.225 prop rpm x 60 = 174193.548 prop rph (revs per hour)
174193.548 rph x 71 inch pitch = 12367741.935 inches of forward travel per hour
12367741.935” / 12 = 1030645.131 feet per hour
1030645.161 fph / 5280 = 195.2 mph
Your 209 mph appears to be better than best theoretical …
209 / 195.2 = 1.07;
1.07 x 2903.225 = 3108 prop rpm / or 1.07 x 71 = 75.97 inch pitch … the following table from Warp Drive gives same numbers.
210 mph at 2900 rpm requires 76” pitch; or conversely 210 mph at 71” pitch requires 3100 rpm.
Jeff
|
Prop RPM
|
|
Cruise Air Speed
|
2600
|
2700
|
2800
|
2900
|
3000
|
3100
|
3200
|
3300
|
3400
|
3500
|
3600
|
3700
|
3800
|
3900
|
4000
|
4100
|
4200
|
|
220
|
89
|
86
|
83
|
80
|
77
|
75
|
73
|
70
|
68
|
66
|
65
|
63
|
61
|
60
|
58
|
56
|
55
|
|
210
|
85
|
82
|
79
|
76
|
74
|
71
|
69
|
67
|
65
|
63
|
62
|
60
|
58
|
57
|
55
|
54
|
53
|
|
200
|
81
|
78
|
75
|
72
|
70
|
68
|
66
|
65
|
62
|
61
|
59
|
57
|
56
|
54
|
53
|
51
|
50
|
|
190
|
77
|
74
|
72
|
69
|
67
|
65
|
63
|
61
|
59
|
57
|
56
|
54
|
53
|
51
|
50
|
49
|
48
|
|
180
|
73
|
70
|
68
|
66
|
63
|
61
|
59
|
58
|
56
|
54
|
53
|
52
|
50
|
49
|
48
|
46
|
45
|
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Tracy Crook
Sent: Wednesday, February 10, 2010 8:35 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: rpm vs Power was : Throttle limits was Re: N.A. Renesis to turbo
Sun 100 flown at 500 ft.
Top speed on a normally aspirated aircraft is always best at sealevel. Best fuel economy is reached up high.
Tracy
On Tue, Feb 9, 2010 at 10:45 PM, Mike Wills <rv-4mike@cox.net> wrote:
When you guys put out these numbers (RPM, speed, etc...) would also be helpful to know at what altitude. I assume at or close to sea level? I havent yet made any speed runs at low altitude.
Sent: Tuesday, February 09, 2010 5:27 PM
Subject: [FlyRotary] Re: rpm vs Power was : Throttle limits
was Re: N.A. Renesis to turbo
Tracy, if you have the data could you give us the RPMs you saw at the 205 and 217.5 air speeds?
Dennis H.
Renesis RV-7A
Austin, Tx.
That was 209 and 217.5
the 209 mph speed was with the 2.176 drive turning a 68 - 71 prop with engine turning 6300 , mixture leaned to 17 gph. On other occasions I could push it to 6400 at best power mixture burning 20 gph.
The 217.5 mph was with a 2.85 drive turning a 74 - 88 prop with engine turning 7250. I didn't get a good read on the fuel flow but obviously it would have been higher. I remember requesting priority landing after the race due to low fuel.
Neither run was done at best power mixture but leaned a few gph less than max.
Tracy