Stall Spin Characteristics of 4B

[Bissetg]

I was keen to further explore the stall and spin characteristics of the Bearhawk 4B. I loaded mine to what I would consider to be my normal backcountry configuration. That is a weight of approx 2000lbs and CoG 19.25 inches aft of datum.

The reason for the testing was to see what would happen if a pilot was overwhelmed by startle factor and applied a delayed, incorrect, or no recovery response in the event of an emergency.

The scenarios I specifically wanted to explore involved doing everything wrong, not checking forward when the aircraft stalled, not applying power to minimise height loss. These scenarios included;

1 What would happen In the event of a partial or complete power failure and for instance, trying to extend the glide and inadvertently stalling and not applying recovery inputs. I.E clean stall with partial or no power and stick held hard back.

2 In the approach configuration what would happen if you got too slow and didn’t apply correct recovery inputs.

Approach configuration on all testing was flap 3 and 11 MAP.

The results are specific to my B model fitted with a Lycoming IO 360, VGs at 6% of chord, 31 ABWs and AB baby bushwheel.

The basic stall with power off and no recovery input, the stick held on the backstop, produced a soft nodding stall that would pitch the nose up and then down, and then repeat in a pitching oscillation, (importantly this demonstrated the wing was stalling and it was not just a loss of elevator authority holding the wing at a high angle of attack and mushing) the ROD was high but there was no tendency to drop a wing.

Repeated with Partial power and no corrective rudder input resulted in a slight wingdrop and yaw to the right, no buffet or warning it was going to break, again holding the stick on the backstop produced a nodding recurring stall and recovery with directional control easily maintained with rudder, the ROD was about 1500ft/min.

The next step was to see if the aircraft would enter a spin.

To do this I intentionally did not initiate a wingdrop stall recovery but held full back stick and left the power on, this is the sort of thing you would really berate a student for!

The aircraft stalled, dropped the right wing and yawed right. With the stick held on the back stop and neutral aileron the aircraft continued a docile yaw right. By adding a little right rudder the aircraft quickly entered a spin.

As soon as the pro spin control inputs were released the aircraft recovered.

My conclusion is that my 4B will stall and indeed spin in my normal operating configuration, but only if it’s abused. It is very directionally controllable in the stall with the powerful rudder enabling you to hold a heading even while the aircraft is held with the stick hard back and a continued pitching oscillation.

It will only spin with pro spin control inputs and recover quickly when they are released.

In all scenarios tested, on release of back pressure on the stick the Bearhawk recovered, and with the application of power flew away from the stall with minimum height loss.

The testing I’ve done is different to the phase 1 testing I did where I stalled and did orthodox recovery’s which my Bearhawk 4B also does well and predictably.

I’m satisfied that my aircraft is exhibits great controllability and predictability throughout its envelope. I haven’t flown an aircraft with better stall characteristics.

[jaredyates]

Thank you for testing and sharing Grant, your experience matches mine in terms of how the stall develops at various CGs. I never did press it to the point of spinning.

[Ed.Meyer]

Great write-up. I also say thanks for sharing.

[Bissetg]

I would have to say that anyone wanting to do this needs to be conscious of retracting the flaps early in the recovery to avoid an over speed. The video of the spin recovery in the video I shot that Nev is putting on his Bearhawkblog.com site and I’ve emailed to Jared, shows the flap being retracted as part of the easing of pro spin control input.

Clearly, if this exercise was being done in anger the flap over speed and retraction would be the least of your worries.

My view is that the stall recovery is so positive and quick that it is very unlikely (but not impossible) that a spin would be encountered so I don’t see much need to explore this characteristic further.

[marcusofcotton]

...video of the spin recovery in the video I shot that Nev is putting on his Bearhawkblog.com site

Looking forward to seeing that when its up!

[Nev]

I"ve put together a short video narrating Grant's testing (Bearhawk 4B with VG's) and showing his video footage.

HERE'S a link (then scroll down).

The video link beside it is of Eric Newton and Lee Taylor doing their original spin testing. At about the 1:30 mark you can get a very good idea of the rate of spin.

[Bissetg]

I’ve had some queries made directly about this post so I’m aiming to clarify what was written to help anyone that hasn’t fully understood what I’ve tried to get across. I don’t mean this to come across as telling anyone how to suck eggs so please skip if you don’t need stalling 101.

1. ‘’Pro spin control inputs” means full aft stick and into turn (yaw) rudder. Ie. Skidding.

To break that down. The reason your wing(s) stall is because it has exceeded its critical angle of attack. The way to un stall it is to reduce the angle of attack by checking forward. The way to maintain directional control is to use rudder, only use aileron once you are un stalled. If you maintain aft stick and into yaw (skidding) rudder you will spin hence the term Pro Spin.

Your stall speed depends on your demand for lift, ie. at zero G you have zero demand for lift so your stall speed is zero. Conversely, a 75 degree banked turn at 4 G your stall speed will be double your basic stall speed. Typically you have high G in a turn or pull up/out. The answer to recover from the stall is to decrease the angle of attack and unload the G by checking forward, and sort it out from there.

2. Stalling in a turn Low level is a major cause of loss of control accidents. It’s important to understand that your stall speed has increased in the turn, but what has become clear to me is that the effect of slipping or skidding turns is not well understood by some folks.

My view is that unless you are intentionally doing a side slip you should have the ball in the middle. This is a basic pilot discipline thing that all pilots should strive to maintain.

If you stall in a slipping turn the aircrafts top(outer) wing will stall first, that tends to roll off the bank and the startled pilot usually checks forward and finds themselves recovered in a wings levelled or thereabouts position. On the other hand a skidding turn stall will result in the lower(inner) wing letting go resulting in the aircraft rolling further even inverted and diving into the ground. A skidding stall in a turn is pro spin and should be avoided at all costs, the worst thing to do is try and pick up the down going wing with aileron and not check forward.

The point I was trying to make in the original post is that while the Bearhawk exhibits excellent manners and benign stall characteristics, it will obey the laws of physics and spin if you make it. Fly it properly with the ball in the middle and below the critical angle of attack and it’s in its element. The powerful tail feathers mean excellent controllability at low speed which is where you need it most. Put another way, there will have been an awful lot of things happen that you should have picked up on and corrected before you find your Bearhawk in a spin.

If you’re unsure or worried about this, give Jared or one of the Bearhawk instructors a call and go and do some wing drop stalls and recoveries, but my experience is that if you are proficient in a C172 or any other training aircraft you will find the Bearhawk a breeze.