Turnback
Posted: Thu Jan 20, 2011 1:53 pm
Today I was doing some advanced training in a 172 (I know, ignore the implicit oxymoron there) and the guy gave me such a good takeoff briefing that I couldn't resist pulling the throttle on him at 500 feet.
"I have control". 59.9 degrees of bank, and 80 and ball centered, 80 and ball centered through the turn. Main challenge was the lateral displacement from the runway. S-turn and we were down on the 4000 foot runway.
If you're an airshow pilot, pretty tame. The aircraft is perfectly capable of the turnback - if you have the knowledge, training and experience to perform it.
Background: 172 has 57 mph stall speed at max gross, flaps up. We weren't at max gross, more likely 2000 lbs. Using square root formula:
sqrt(2000/2300) x 57 = 53 mph
At 2 G, we know that the stall speed is
sqrt(2) x 53 = 75 mph
I could fly a level, co-ordinated steep turn at 60 DOB at 80 mph and not stall.
But I was NOT. I was letting the nose fall during the turn - I was NOT trying to maintain altitude, so I didn't need to produce the same lift. I wasn't pulling 2G at all - perhaps 1G, which means that my stall speed was still 53 mph
Plenty of margin with 80 mph.
Bottom line: don't confuse what an airplane is capable of, with what any random pilot is capable of. Precious few pilots are capable of making an aircraft do everything it can do, without breaking it or stalling it. Your name probably isn't Bob Hoover.
See the Vg diagram aka "envelope" that you hear so much about:

"I have control". 59.9 degrees of bank, and 80 and ball centered, 80 and ball centered through the turn. Main challenge was the lateral displacement from the runway. S-turn and we were down on the 4000 foot runway.
If you're an airshow pilot, pretty tame. The aircraft is perfectly capable of the turnback - if you have the knowledge, training and experience to perform it.
Background: 172 has 57 mph stall speed at max gross, flaps up. We weren't at max gross, more likely 2000 lbs. Using square root formula:
sqrt(2000/2300) x 57 = 53 mph
At 2 G, we know that the stall speed is
sqrt(2) x 53 = 75 mph
I could fly a level, co-ordinated steep turn at 60 DOB at 80 mph and not stall.
But I was NOT. I was letting the nose fall during the turn - I was NOT trying to maintain altitude, so I didn't need to produce the same lift. I wasn't pulling 2G at all - perhaps 1G, which means that my stall speed was still 53 mph
Plenty of margin with 80 mph.
Bottom line: don't confuse what an airplane is capable of, with what any random pilot is capable of. Precious few pilots are capable of making an aircraft do everything it can do, without breaking it or stalling it. Your name probably isn't Bob Hoover.
See the Vg diagram aka "envelope" that you hear so much about:
