Piper Seneca II stall characteristics

[Duffer2007]

Have searched for quite a bit and I'm just looking for a definitive answer on why the Piper seneca stalls at the root first. From what I can gather there are no root spoilers as such. Of course there are considerations such as wing planform but anyone out there that has a simple answer for me it would be much appreciated!

Thanks

[Mohit_C]

The Piper Seneca II has rectangular wings. Rectangular wings create strong wing tip vortices. The wing tip vortices have the effect of reducing the effective angle of attack at the wing tip, thust delaying tip stall. Therefore as the wing approaches the critical angle of attack, and given that the wing tip will always have a reduced effective angle of attack (which is what really creates the induced drag), it results that the wing root will stall first.

Let someone confirm this. This is the way I understand it though.

[adverse-bump]

like most light ac, does is not have washout?

[wheelbrace]

4 degree washout?

Something of that order at the wingtip, I was told when annoying the builders at Vero Beach.

However, by how much does this overcome any advantage at the root and inner wing from reduced AoA generated by prop wash? No root spoilers, maybe, but I have only seen Senecas with stall strips just outside the outer prop wash extremity.

Vortex generators ahead of ailerons on later models.

[John Farley]

Duffer2007

I know nothing about the Seneca stalling characteristics however I know a great deal about the airflow round the Seminole wing at the stall as I used to use one suitably tufted to teach such matters to Uni students in the 80s.

You ask for a simple answer as to what is going on with the Seneca. Therein lies the catch.

How a wing stalls is not a simple matter and depends on a combination of features and I would suggest the main ones are:

Aerofoil choice AND how this changes along the span.
Planform shape and aspect ratio.
Twist.
Presence of any fixed leading edge devices.

In the case of the Semiole as an example if you stand at the wingtip and look towards the root you will see :

An aerofoil that changes markedly from the root to the tip (and even includes a bit of LE droop near the tip)
A wing that has considerable twist

To me this wing just screams experience and extensive flight development on this or some other related design. It exhibits really classic root stall characteristics, ailerons that work well deep in the stall and stacks of natural warning. In short a GA dream. But there ain’t no simple reason for this!

JF

[On-MarkBob]

Hi,
I have done quite a bit of flying in the Seneca, the mark 1, 2 and 3. I have flight tested many and spoken to Piper on many occasions about various aircraft, from time to time. The type was conceived as the twin Cherokee six. The prototype crashed after shedding a wing panel in the VNE dive. I think it killed Piper's test pilot. It's along time ago now, so I can't remember the full story.

The Seneca's wing has quite a bit of wash-out, even though it might not look it. All Cherokee's were designed with wash-out after about number 70. The type originated from the Thorpe Sky Scooter.

The wash-out is there to make the root stall before the wing tip, and was increased a bit in the twin because of the prop wash. The wash-out is there to allow aileron control into the stall. Without it the aircraft had a vicious tendancy to end up inverted in a full stall. Pilots, it seems, have an instinctive reaction to control the roll with aileron, particularly approaching a stall that is 'unplanned' or unexpected. The use of aileron in the stall simply stalls the wing on the downgoing aileron side, as it further increases the angle of attack on that side, and causes the aircraft to roll in the oposite direction to aileron input. On the Seneca this was quite vicious and as I said, the aircraft would quickly be on its back. Most aircraft today are manufactured as best as possible so it will stall straight and stable, so unless it is an advanced aerobatic aircraft, the wings will wash out so as to stall after the wing root, which after stalling will pitch the nose down. Fly a Seneca today and this can be demonstated to very good effect. Stall the aircraft and do what you shouldn't and control the roll with aileron, you will be amazed that the aircraft has positive aileron control even during the stall.

[Centaurus]

The wash-out is there to allow aileron control into the stall. Without it the aircraft had a vicious tendancy to end up inverted in a full stall.

Its a long time ago but as a QFI on the Dakota, I was always a bit surprised at the viciousness of the wing drop when stalling the Dakota with flaps down and approach power (around 15 inches manifold pressure). It was instinctive to use instant aileron and rudder to stop further yaw and looking back I wonder if the initial fright at the rate of wing drop and thus using aileron without realising it for a few seconds, exacerbated the wing drop. I recall a height loss of at least 5-800 feet before level flight recovery was effected.

[frontlefthamster]

Stall the aircraft and do what you shouldn't and control the roll with aileron

...Bob, for the benefit of those reading here who believe what they see is correct, would you define to which aircraft (that is, which certification standards) your statement applies, or retract it?

You went on to say

do what you shouldn't and control the roll with aileron, you will be amazed that the aircraft has positive aileron control even during the stall

...and I would dare to say that you will only be amazed if you haven't been trained properly, and are not aware that any even vaguely modern aircraft must exhibit normal roll control characteristics at the stall.