Am I too fast; too slow?: When you find yourself flying without the numbers

Stable flying speed range just came up in a support topic, as it does now and then. This is just a comment on the common thread of safe flying speed, rather than a tutorial.

If you find yourself flying and you don’t have handy reference to all the airspeed numbers for your settings such as flaps, how else might you judge if you’re too fast, too slow, or somewhere roughly in range?

AoA (Angle of Attack). But rather than chasing a number for AoA, look at the “picture” on your HUD (see below).

If AoA is heading towards a double digit number, you’re likely too slow.

If it looks like AoA is going to go negative, you’re too fast (for current flap setting etc.).


Above, eyeball the angle from your nose mark to the FPV (small circle). Here it is 12 degrees or more - symptom of too slow for your current flap setting. This led directly to swaying/wing rocking, a stall and crash.


What might you guess the AoA here? It’s not double digit but it’s wider than the 5 degree mark spacing. It’s getting into the caution zone of too slow (controls more sluggish wing rocking and stall is closer).


Notice the arrow to the FPV is pointed up. So the AoA is negative. Way too fast (notice full flaps have been added at this speed). It shouldn’t ever be negative (aircraft was ballooning - not wanting to descend).

edit: The last two images are before and after screen shots of the same flight - before any flaps to full flaps. Note the IAS is the same 185kts. It was too slow for no flaps and too fast for full flaps. All judged with AoA

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that happens to me but it depends on your load but for me the slowest is 165

It’s a good point to bring up load.

It’s actually independent of your load. That’s why it is so useful - your load is “baked into” the safe AoA range.

So all you have to do is keep the AoA within a safe zone, and load is taken care of.

Example: you add, say, 20% more load. At a given airspeed your AoA will be higher from the increased load.

That higher angle you see as a sign to increase speed to put the AoA back more safely within the eyeballed range.

yes but it defends of flight and cargo i put it

Yes, so the more load you add: cargo, pax, fuel, the more it “stretches” your AoA into a bigger angle at a
given airspeed. This tells you to increase speed to make the AoA go back down some.

So instantly it’s telling you to increase speed to compensate for the higher load.

The AoA safe range tells you if you have added enough speed for the extra weight you’re carrying.

edit: Note the AoA is rather different than pitch. You can have an 8 degree AoA with your nose flat on the horizon or above or below the horizon .

Man you are smart!

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I was pretty much convinced I was dumb in math etc. as a kid, but I’ve kind of grown to appreciate that base feeling of working up from the bottom. Dropped out of primary school 3 times, but ended up engineering flight hardware for NASA. I never liked being talked down to by people (math teachers etc,), so I try to avoid doing it to others. Just try to talk straight, the way I want to be talked to.

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wow for NASA yea one of my family members are a nuclear engineer

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That’s impressive and also very inspirational. Every time I go to counter a point you make I make sure to double check my numbers because I know you’re probably ready to fire back with your own data lol.

Just wanted to add onto the post that you can also approximate AoA even without the FPV (for example, if you’re landing in cockpit view no HUD) by 1. checking your horizon compared to your VS (be your own FPV) and 2. assessing how sluggish the aircraft feels. You lose control authority at lower speeds, presumably because there is a lower volume of air acting upon your control surfaces. Therefore, if you fly enough to have a “baseline” on what certain planes should fly like, you’ll know if you’re approaching stall. This may be easier for certain aircraft like the DC10/MD11, where standard AoA is extremely high especially for final approach. The two of them feel like they have good control authority on short final even though their noses are jacked skyward.

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will bookmark for future reference

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Yeah, I think that’s an important point. As you said, one grows to always be cross checking various factors such as attitude, control response and speed (horizontal and vertical), power setting etc.

And a drawback with AoA using the FPV is that it bounces around until you’re in a somewhat stable orientation, as does VS. So, you’re controlling most directly by reference to attitude and feel (while looking at the numbers).

I definitely agree. The DC10 type aircraft are good examples like you said.

Most of the time I’m not flying by directly looking at AoA. But I tend to cross check it more when evaluating my climb limits (step climb assessment), setting flaps, judging approach speed and cross wind during landing.

Engineering is a cool profession.

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