The 1979 model year was the first with the redesigned engine mount allowing the nose gear to fully retract and includes nose gear doors. N28067 has all the antennae external, but trues at book speeds plus a couple mph. I generally fly above 10,000 ft and see around 185 mph. I get 190 mph plus a little at lower altitudes. We carry O2 and routinely go as high as 14,000 ft to get over turbulence and still true about 180 mph.
Speeds at 6,000 ft. Four way square with speed and wind
direction on each leg measured to determine wind direction at altitude. Then, 10 mile runs directly into/with wind direction.
GS measured by Northstar Loran.
hdg pwr per gauge CAS mph TAS mph TAS kt GS kt wind
220 23.9/2500 177 197 174 147 220/25
040 23.9/2500 175 196 174 198 220/25
040 24.0/2400 173 193 171 192 220/25
220 24.0/2400 171 191 169 135 215/30
So, at 2500 rpm (76%), my average was 173 kt vs N281SV's 183 kt. At 2400 rpm (75%), my average was 164 kt versus N281SV's 180 kt. My test results were pretty close to the factory's top cruise of 178 kt in my POH. I mostly run 9,000+ ft at 2425 and the airspeed needle has been glued on 186 TAS at that altitude so long I almost forgot mine would run this fast!
[writeup to come...]
Fred Olson is the proud owner of a brand spanking new 2000 IO-550 powered Viking. Fred is rightly proud of his new bird and he and I have emailed each other with some informal flight speed test comparisons between his 2000 and my 1979 (Fred used to own a 1979 also, N28073). N281SV has narrower gear doors and all the antennae are internal, but otherwise aerodynamically is the same as mine. The following are from Fred's emails.
"Flew the airplane late Sunday PM to see what I could do as far as speed checks are concerned. Temp at 5000 ft. was 10 degrees C. I'd have been about 300 lbs under gross. I did my speed check runs east and west. Runs probably averaged seven or eight miles each way :
6000 @ 23.75/25 west 165 kts east 201 kts Avg 183 Best TAS 213 mph
6000 @ 23.75/24 west 164 kts east 196 kts Avg 180 Best TAS 211 mph
5000 @ 24.50/25 west 165 kts east 205 kts Avg 185 Best TAS 219 mph
BEST TAS=the highest indicated by the airspeed indicator in that run."
"I got the GPS formula for TAS from Tom. When I made my speed
checks, (I flew N/S/E/W) I was therefore able to correct my figures:
6000 @ 23.75/25 GPS kts N 171 W 165 S 195 (135331 = 367.87/184 kts)
6000 @ 23.75/24 GPS kts N 169 W 164 S 194 (133059 = 364.77/182 kts)
I know the speed spread (on my settings) should be a greater than this. I'll check them again and also get some higher altitude results. Seems as though you get about four knots more out of your '79 then I THOUGHT I got out of mine."
(Note, at 2500 rpm (76%), my average was 173 kt vs N281SV's 183 kt. At 2400 rpm (75%), my average was 164 kt versus N281SV's 180 kt. My test results were pretty close to the factory's top cruise of 178 kt in my POH.)