Skidding and Slipping Departures from Controlled Flight in an RV
VIDEOS UPDATED. Added higher resolution videos, if available and added some additional examples of cross-controlled stalls in my RV-4.
Here are some clips showing what happens if you stall the airplane in a skid. In a skid, the airplane rapidly departs controlled flight "underneath" when the critical angle of attack is exceeded. There is very limited aerodynamic warning in the form of buffet and nose slice visual cues. The fastest recovery (minimum altitude loss) is to actually keep the roll going after the initial snap roll to an inverted position:
https://drive.google.com/file/d/0B8EIT6g2n8o_dDJWWG90MkhhRXM/view?usp=sharing
During the first demo above, altitude loss is about 400 feet; but that's based on initial entry conditions (level turn) and the fact that I know what's going to happen--much different than accidentally encountering a similar condition in a descending turn. If you read the captions, you'll note I can't do math in public as regards the altitude loss (no excuse)...The bottom line is that a loss-of-control at or below traffic pattern altitude makes recovery problematic at best, which means avoidance is critical (as other folks have wisely pointed out in this thread). Here are a couple more examples. The standby altimeter is visible to the right of the top EFIS, so altitude loss during the maneuver can be noted...but again, the maneuver is begun from a level turn and I’m anticipating auto-rotation:
https://youtu.be/h5OFuQaYs1o
https://youtu.be/tGItkZzTLUE
The next clip shows the view out the rear during a skidding departure in high resolution:
https://youtu.be/4BHcBmQ0aoo
It's an aviation urban legend that you can't depart controlled flight if you stall in a slip--of course you can, but you have to ignore significant aerodynamic warning to do so. In this case, the airplane wratchets as limited dihedral effect starts to roll the airplane at high AOA, warning you that something bad is about to happen with all of that counter aileron applied. In the first example, a sustained wing-rock begins and the airplane eventually rolls counter to direction of the intended turn. In the second and third examples, the airplane fully departs after extensive aerodynamic warning:
https://youtu.be/SD-EiHg2nBk
https://youtu.be/uMEVEZMUDXY
https://youtu.be/RtwS_vXQukk
Here's some high resolution rear cockpit views of a slipping deep stall...
In this example, the airplane departs "over-the-top" after a sustained wing rock develops:
https://youtu.be/aqJTLEpE8sY
In this example, the airplane does not depart but remains in a sustained wing-rock/deep stall with full slip input:
https://youtu.be/TL8isXld-oU
If you pay attention to the horizontal stabilizer and elevator in the last two clips, you'll notice the slipping deep-stall and departure induces a noticeable buffeting of the horizontal stabilizer. This has the potential to induce fatigue damage to the structure. This buffet characteristic may be unique to the RV-4, or simply unique to my RV-4; but is the reason that I address this phenomenon in the transition training manual when discussing this type of departure. Cross-controlled stalls are discussed on pp. 336-337. I only fly this maneuver (intentional slipping departure) for test and training demonstration purposes due to the buffet characteristic.
Fly Safe,
Vac