Relationship of PIO during landing with Onspeed AOA

[vitlyluvi]

Dear Sir,

I have heard that by following Onspeed AOA technique (constant AOA /Speed) on approach to landing, one gets protection to a large extent from PIO events during landing.

Could some explanation be provided. Does Onspeed AOA technique offer advantage over Reducing Speed / Increasing AOA approaches???

Thanks. Gp Capt LK Vitly. IAF. India.

[Genghis the Engineer]

Could you define what you mean by an "onspeed AoA approach" in a bit more detail?

G

[9 lives]

I have heard that by following Onspeed AOA technique (constant AOA /Speed) on approach to landing, one gets protection to a large extent from PIO events during landing.

In my opinion, these two are probably only related by the fact that a well flown approach has a better change of resulting in a non diverging flare and landing. (Simply; good approaches result in good landings).

The PIO which might result after flare will more be a product of the changing attitude of the aircraft as it comes into ground effect, or surface contact, not being managed by the pilot. The approach can be very stable, yet the pilot lets it get away from him in the very final moments.

The natural frequency of the aircraft in pitch will allow it to change pitch attitude rhythmically at a rate very close to the pilot's ability to react to that, and the pilot may apply control inputs to arrest the pitching at the exact wrong times, and make it worse. This is extra prevalent with flying boats, as the variable interaction of contact with the water vs the C of G, and center of lift fight each other. It is a vital part of flying boat pilot training to assure that pilots can prevent and get themselves out of this condition.

On the other hand, a constant approach on AoA is flown for a glassy water landing, or landing on a snow covered surface, where the altitude above the landing surface cannot be determined with precision. In this case, the approach is precisely flown on a fixed AoA, and descent rate to the point of surface contact. You could still get a PIO after that in some cases, if pitch control is not positively assured. It's different factors, not related to the approach at that point.

Does that help?

[LOMCEVAK]

vitlyluvi,

Firstly, are you referring to a roll or pitch PIO?

Secondly, during the decreasing speed/increasing AOA approach are you retrimming or maintaining a pull force? If not retrimming then the need to hold a progressively increasing puill force may make it more difficult to make small, precise control inputs and thus exacerbate any PIO tendency that exists. PIO tendencies can be mitigated to a greater or lesser extent, depending on the severity, by adopting an 'open loop' control strategy but this is very difficult to do if the aircraft is not in trim such that you can, effectively, release the controls.

[vitlyluvi]

Thanks sir for your helpful explanations. Pio was discussed in pitch during flare for touchdown....I heard that there exists some test results with tp schools and with calspan. ?..any document on this issue.....Thanks sir.

[LOMCEVAK]

I do not have any documents that would help you. Do you have a link to any documents that may have triggered your initial question?