One of our glider club's tow plane is a '66 235 with constant speed prop. We suspect that at typical tow speeds, 65-70 kts, that the ASI is reading 5-10 kts low. That is, CAS is less than IAS at high angles of attack. Suspicion based on comparison with glider IAS and GPS runs where we tried to compensate for wind. Around 115 kts and no glider GPS indicates no obvious airspeed difference.
Our POH has no plot or table of CAS vs IAS. Does any one have this info for a 60s era PA28-235 like ours? We're concerned because the sign of the CAS vs IAS difference seems wrong to us, suggesting some malfunction. In all the other planes we've flown CAS is greater than IAS at low air speeds.
Thanks,
Larry
Northern California Soaring Association
Our POH has no plot or table of CAS vs IAS. Does any one have this info for a 60s era PA28-235 like ours? We're concerned because the sign of the CAS vs IAS difference seems wrong to us, suggesting some malfunction. In all the other planes we've flown CAS is greater than IAS at low air speeds.
Thanks,
Larry
Northern California Soaring Association
