Airspeed vs. Angle of Attack
- Thread starter Pilot121
- Start date
Pilot121
Well-Known Member
Do most planes have an an AOA indicator now? The 172 I fly doesn't.It's a reference point, but there are many variables in arriving at that value.
Also, the stock 1956 Cessna 172 didn't have an AOA indicator.
deadstick
Well-Known Member
No. I was trying to make a funny. What I was trying to say is that there isn't an indicator (discounting the kazoo) in the aircraft that will tell the pilot where they are relative to the critical angle of attack. They publish the airspeeds so the pilot can have a picture of his/her relative position to hitting the stall. I mentioned variables earlier. My current aircraft has published speeds for different configurations and bank angles, but two constants are the weights (MTOW) and power settings (idle). This is great for abnormal and to just get the idea of what the plane will stall at when maneuvering for an approach (i.e. With partial flaps).
This would be a great time to get into the maneuvering speed discussion, but it's past my bed time.
There is a push to get low-cost AOA devices in GA aircraft, but I don't any OEMs provide them. I've read posts by several who have installed them in their planes (single pistons to twin turboprops) and swear by them.
drunkenbeagle
Gang Member
The Cessna 172 stalls at 48 KIAS in un-accelerated flight. The numbers are correct, so long as the aircraft is not climbing/descending/turning.
The numbers exist for 3 reasons. In level flight, you won't stall the aircraft above the stall speed, and AOA indicators weren't common when these aircraft were built, and the FARs require them to be flight tested/published.
drunkenbeagle
Gang Member
Good news, that seems to be changing these days.
USMCmech
Well-Known Member
AOA indicators were not practical back in the 20s or 30s when certification standards were established. Airspeed has a fairly reliable relation to AOA and was used as a stand in.
Same reason we use Manifold Pressure to determine throttle position in complex engines.
Vy or Vx is also an imperfect solution from a time where attitude indicators were impractical. What Vy or Vx really is, is a best pitch angle for climb with a given thrust (typically full power) which results in a particular airspeed.
Flyinthrew
Well-Known Member
This has been a topic where I'm from. There being no AOA gauge in modern GA aircraft is a little weird Once you have one you have no idea why anybody would go without. It's a pretty simple device, too.
Of course, the same can be said for not having ILS in 30 million dollar jets.
Of course, the same can be said for not having ILS in 30 million dollar jets.
lightspeed
Well-Known Member
So is an airspeed indicator. So is the C172 stall warning horn.
Roger Roger
Bottom of the list
Never change.
Pilot121
Well-Known Member
Has this topic been discussed before? I couldn't seem to find any threads about it."PLEASE GOD NO! Not this thread again!!!"
///AMG
Well-Known Member
If being serious, read the thread on the Akron, OH Hawker crash. Don't worry, you didn't miss much. It was just 20+ pages of arguing between two broad camps of people experienced in two different ways of flying, a few words taken out of context (standard), and nobody convincing anyone else they were wrong (also standard).
z987k
Well-Known Member
But it's usually wrong.
ppragman
FLIPY FLAPS!
It really depends on the amount of position error, if you look through part 23, you'll notice that the requirements for stall speeds are based off of KCAS rather than for KIAS. Incidentally, if you look at the Caravan EX, you'll find that the position error between indicated and calibrated at Vso is pretty extreme:
@inigo88 is going to have the nitty-gritty details, but it has a big deal to do with crashworthiness, 15 KCAS is a lot of energy to get rid of through an accident.