COZY: Approaching Deep Stall


kent ashton
 

Here’s how I “approach” it. Ballast the airplane for the first flight box. Go fly. Slow down cautiously maintaining level flight and eyes out of the cockpit and examine the canard reaction. If you reach full aft stick and the canard has not shown you any appreciable stall-unstall or bob (still maintaining level flight) you likely have too much ballast. Reduce ballast by say 15-20 pounds and fly again. Eventually you should reach a point where in level flight, the canard seems to bob or stall-unstall but you can maintain level flight. Actually, this is probably far enough for testing. That IAS, whatever it is, will give you a good pre-stall warning for situations where you are not watching your speed and get slow inadvertently. It will also give you a bit of a pad to catch a dropped-in landing where you might roundout high and need to arrest the descent rate or if you try to turn too hard.

Nevertheless if you reduce ballast and go further, I would expect to first see the canard bob, then pronounced stall-unstall (pitch buck) behavior. Be careful to maintain level flight and keep your head out. Be careful to make steady pitch inputs and not fight the canard by loading and unloading it. Canard bob may transition to more pronounced pitch-buck. If you reach full aft stick with pronounced canard stall-unstall or pitch buck, the airplane is pretty much maxed out. At some point during that pitch buck you might feel like the bottom has fallen out and you see the deck angle pitch up (with the same pitch input). This is incipient wing-stall. This is why it is important to keep your head out. If you have maintained a level velocity vector and react quickly, the airplane should pitch down and fly again.

If you allow the airplane to sink as you test it, the G load is less and the speeds will not be accurate.

In the case I can recall where a real wing stall was encountered, the pilot entered the wing-stall from a nose high attitude. He probably lost more energy as he tried to pitch the airplane over and could not unload the canard (and unload the wing) fast enough to avoid the wing stall. A level attitude should allow a rapid recovery.
-Kent

On Aug 24, 2022, at 4:17 PM, 'Andrew Anunson' via COZY Builders Mailing List <cozy_builders@...> wrote:

I have aft CG testing coming up soon. What are signs that I'm approaching a deep stall?

Thanks,
Andrew Anunson
Cozy MKVI #1273
Pound, VA

--
You received this message because you are subscribed to the Google Groups "COZY Builders Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cozy_builders+unsubscribe@....
To view this discussion on the web visit https://groups.google.com/d/msgid/cozy_builders/1818223298.1409395.1661372226394%40mail.yahoo.com.


Marc J. Zeitlin
 

Kent Ashton wrote:
 
If you allow the airplane to sink as you test it, the G load is less and the speeds will not be accurate...

You know better than that, Kent :-). A steady state VS (up or down) is a zero vertical acceleration condition, so the vertical "G" loading is still exactly "1". Only if the VS is changing as one climbs or descends is the "G" loading not "1".

Stall testing should be done engine out, engine power for level flight, and full power (which is an absurd nose up angle). This is because you can stall on approach (no throttle), climbout (full WOT), or in cruise.

--
Marc J. Zeitlin                      marc_zeitlin@...
                                            http://www.cozybuilders.org/
Copyright © 2022                     Burnside Aerospace


skybob8
 

If “VG,s” were to be placed on main wing and canard per supplied temples and instruction, do you feel that the stall characteristics (the bob) would be changed or should they be the same except at slower speeds.


Izzy
 

My son and I share ownership on an Aeronca Chief my Dad restored. He installed VG’s at one point and I learned a few things about them as a result.

Without VG’s the stall of the Aeronca wing is somewhat predictable and manageable. I can slow down to about 39-40 mph and continue to hold altitude, if the airspeed indicator is to be believed, before the plane starts to stall. The onset is a mush and a slow roll one one way or the other. 

With the VG’s installed, the plane can slow down to as low as 32 miles per hour. When the stall happens, it is violent, sudden and requires more time, power and altitude to recover before entering into a spin.

The thing I learned is, although VG’s can help you slow the speed at which the wing will stall, it doesn’t magically add more energy to the system. And as a result, when a stall does happen, much more energy needs to be added before return to controlled flight happens. Maybe it comes from trading altitude for airspeed (hard to do when just over the runway trying to land), or by adding lots of throttle (which takes a moment or two before it’s effect yields an increase in control). 

The reason my Dad installed them was to help the Aeronca get up on to the “Water Step” for a floats equipped takeoff, allowing for departure from smaller lakes and rivers. But the poor controllability at 32 miles per hour basically makes the plane a wheels-only landing Aeronca when there is any kind of gusting conditions when using the standard landing gear. 

Not sure if that anecdote helps at all, but felt it worthy of mentioning. I’d be curious if anyone who actually knows something about aerodynamics could comment. Maybe I just suck at landing Aeroncas :0

Izzy
(603)410-7277

On Aug 25, 2022, at 13:04, skybob8 <quickstrip@...> wrote:

If “VG,s” were to be placed on main wing and canard per supplied temples and instruction, do you feel that the stall characteristics (the bob) would be changed or should they be the same except at slower speeds.


Vance Atkinson
 

Apples and oranges... comparing a std. stall ( with or without VG's)  vs. aft cg constrants and stalling.

Vance Atkinson


On 8/25/2022 7:04 AM, skybob8 wrote:

If “VG,s” were to be placed on main wing and canard per supplied temples and instruction, do you feel that the stall characteristics (the bob) would be changed or should they be the same except at slower speeds.