Friday, March 23, 2007

Airspeed - Test Pilot: You

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Many of us think of test pilots as leather-faced guys in Nomex flight suits with eyes permanently reduced to slits by squinting into the sun across Rogers Dry Lake Bed at Edwards Air Force Base. And there are some of those.

But today we're going to talk about some test pilots who look a lot more like you and me. In fact, they are you and me.

Now I'm not suggesting that you go strap some JATO rockets to your RV-4 and push the big red button. What I'm talking about is systematically exploring the operating characteristics of the aircraft you fly and yourself as the pilot.

Here's an example. I've always wondered just how much altitude I would need to have before I'd consider trying to turn around and land on the departure runway if I lost the engine shortly after takeoff. There's even a great article about that very subject in AOPA pilot from four or five years ago. But I wanted to know what the numbers would be for the aircraft that I regularly fly and especially for me personally as the pilot in command.

So I decided to go play test pilot.

I set up a profile for the test in advance of the flight. I briefed it on the ground with the instructor and then briefed it again in the air right before the maneuvers. This isn't something you want to pull out of your ear while in flight. You won't have the test fully thought-out and you'll be distracted to boot.

So here's the test:

1. Establish a full-power climb at 79 knots (which is Vy - or best rate of climb - for this aircraft).

2. At a known altitude, pull the throttle to idle.

3. Wait for five seconds. This pause is to simulate the amount of time that it would likely take for a pilot to realize that he had an engine-out, evacuate his bowels, and initiate action.

4. Initiate a turn at 65 knots (which is the best glide speed for this aircraft) and up to 45 degrees of bank.

5. After 210 degrees of turn (180 degrees to reverse direction and another 30 degrees to point back at the runway), level out and note the altitude loss.

Because I'm already recording this for the podcast using an MP3 recorder plugged into the intercom, I don't have to worry about capturing data on paper or remembering it. I can just call out the data as it happens. Everything I'm calling out is something that I'd have to monitor anyway as a part of flying the airplane, so I'm not worried about being distracted. The only additional workload beyond that required to fly the plane in the first place is saying the instrument readings out loud so I can record them. Being that I'm preparing for my instrument checkride concurrently, I’m already doing my John King call-outs, so this isn't much of a departure from normal procedure.

After putting together this rough outline of the test, I thought about what, if anything, might approach the operating envelope of either the aircraft or the pilot.

As far as the aircraft is concerned, the only thing I could think of that would approach the edge of the envelope would be being banked over pretty far and flying pretty slow. Any slow-speed maneuver necessarily makes one think about possible stalls and spins. So I looked at the pilot's operating handbook to verify that I'd have enough of a margin above a stall during the turn. The POH says that, in the clean configuration and with the weight and balance we had for that flight, the stall speed with 45 degrees of bank is 53 knots indicated. Plenty of room.

How about the pilot? I'm pretty good at slow flight and my steep turns are great. But I can't say that I'm good – or current – at doing both simultaneously. So I'll practice both separately before we do the test and I'll have a high-time CFII in the right seat and close to the controls as a safety measure.

There is perhaps some benefit to not being very current with slow steep turns. It might be a good proxy for being surprised or stressed. Additionally, low-speed, steeply-banked turns are not something that it’s likely that I’ll end up practicing that often anyway, so not being current is a great proxy for not being current, too!

So, all that said, ace flight instructor Jamie Willis and I got into the plane on a beautiful severe-clear Thursday morning and went up to see what we could find out.

I hadn’t been up in months, so we went through some VFR basics to warm up. The steep turns were like the airplane was on rails. A nice little burble at the end of each one to tell me that I had flown through my own wake turbulence from the start of the turn. Slow flight and stalls were also all fine.

So we set up to do the test. Three iterations with the same procedure each time.

Here’s the first one.

[Audio 1]

The airspeed was all over the map. As expected, I had a lot of trouble nailing the airspeed while rolling into the turn and then getting her around those 210 degrees. So we tried it again. This time, I asked Jamie to really ride me about the airspeed and he obliged.

[Audio 2]

Guys, this podcast is the real deal. Who else would let more than a thousand people sit in the back seat while he got dope-slapped by his instructor for chasing the airspeed needle up and down the dial? I’m learning stuff here. But I’m also not going to let it go at that. This needs another try, so here we go.

[Audio 3]

Much better. I’m a little happier with that one.

So that’s the test run. We proceeded to knock off the rest of the VFR rust on that flight and I’m pleased to say that I greased all four landings after not having flown since September. I didn’t hurt that the wind was dead calm, but I’ll take at least some credit for pilot skill.

Like any good test pilot, my debriefing included a frank discussion of the shortcomings of the test. Here's what I identified.

· The five-count may or may not be a good proxy for the amount of time that I might need to identify an engine-out and make the decision to turn back. I've never had an engine out, so I really don't know how I'd react.

· Accomplishing a 210-degree turn is not the same as getting back to a runway. Depending on the wind and any number of other factors, even a 210-degree turn might leave you a long way laterally off the runway and needing to glide back to the centerline – and then turn back that 30 degrees to align the aircraft with the centerline. If you're at, say, Willow Run airport with lots and lots of flat real estate even if not all of it is paved, that's less of a problem. Grass is okay by me in a pinch and I'll even take out a marker if I have to. But if you're at Troy Executive Airport with shopping centers, industrial buildings, and power lines hemming in the runway, that's an issue. Shopping centers are harder to land on than grass. I took a handheld GPS up on the flight with the intention of analyzing the vertical and horizontal track so that I could correct for winds at altitude (the preflight briefing called for winds at 320 at 33 at that altitude), but it turned out to be too complicated to work out in time for this episode. Maybe again on a day where the winds at altitude are closer to what you'd expect on the surface.

· The data I got would all go out the window if I don't pre-brief the procedure on every takeoff. That includes wind and turn direction. It also includes situational awareness of what's going on other runways, especially if the wind is such that your best turn direction is toward a parallel runway. The offset is good because you have less lateral distance to travel back to a runway (assuming that you're going to land on the parallel), but, if you're not sure that the parallel is clear, you could risk eating Learjet. Learjets are sometimes worse to land on than shopping centers. And they usually cost more.

· I need to work on my ability to establish and maintain pitch for a given airspeed when in steeply-banked turns. I was all over the map on two of the three trials and even the last trial had me behind the airplane a little. I think I’ll make this maneuver a consistent part of my periodic VFR training.

Long story short, I now know that, if I’ve pre-briefed the procedure before taking off and I’m a little better than I have been at maintaining the best-glide speed of 65 knots while banked over 45 degrees, I could get probably get the plane turned 210 degrees within four hundred feet. What I don’t know is what kind of lateral position I’d be in after the turn and whether I’d be in a position to make it to the runway from there. Before I turn this into an actual operating procedure, I’m going to have to figure out how to get event data out of the GPS and figure out the lateral part – and the remaining horizontal part – of the situation.

But that’s what’s good about going out and – within reason – being a test pilot. You add to what you know and you figure out what you don’t know. Done well within the flight envelope of the airplane and the pilot in command, and with appropriate safety precautions (and seasoned flight instructors who have had upset training tend to be good safety precautions), you’ll be a better, safer, and more thoughtful pilot.

Long-time listeners won’t be surprised by the following disclaimers. I am by no means suggesting that you go out and do risky stuff. All of the maneuvers that I'm talking about are well within the normal operating envelope of the aircraft involved.

I have well over 100 hours in C-172s and probably 20 hours in this particular airplane. I went up with a 900-hour CFII who has hundreds of hours more than I do in C-172s and who has had training in unusual attitude and upset recoveries. The CFII had the seat forward and was close to the controls the whole time. It was a severe clear day over known territory. And we had flight following from Flint Approach the whole time for traffic advisories and in case we needed to talk to someone immediately in an emergency.

Nothing in what you've heard here is flight instruction or a recommendation about aircraft operations. Consult a qualified flight instructor before attempting anything you hear about on Airspeed.

Different aircraft do different things at different airspeeds and in different configurations and even the characteristics of the same model of aircraft will vary from specific aircraft to specific aircraft.

Don’t integrate anything you heard on this episode into your operating procedures. As you can tell from my commentary, I’ve only figured out about half of what I need to know before even thinking about making any firm decisions about what I’d do at any particular altitude or situation. And bear in mind that my personal flight skills and biases are inseparable from the results that I got. None of this is transferable to your particular situation because you’re probably not flying the same aircraft and you’re definitely not me (the latter of which will probably come as a relief to many of you).

Remember your training, observe the limitations in the pilot's operating handbook, and - above all - fly the airplane. But you knew that.

See also:

ASF Safety Advisor – Would You Make It?


Jack Hodgson said...

Hey Steve, emails to you have been bouncing for a couple weeks. What's up? -- Jack

Roger Halstead said...

Hi Steve, I'm the bald headed guy sho shot photos of you hanging out of the Ford Tri-motor at Midland Barstow a couple years back. (watch for line wrap)

Over the past couple thousand hours I've had two engine outs. One shortly after rotation at 50 feet and 100 MPH. The other about a mile from the pattern just a bit above the pattern and accelerating.

The second one (in the Debonair) more approximates what you are talking about, other than with the wheels up it has almost twice the glide ratio of a 172. On closing the cowl flaps I immediately became aware of a strong oil smoke odor. I instinctively rolled into a tight turn back toward the airport. From slightly above the pattern altitude a mile out, I knew I could make any point on the airport. While in the turn I checked the gauges and saw the oil pressure was on the peg. I immediately pulled the engine to idle and hoped if I needed a shot of power it *might* still be there.
I was already at best glide and only slightly under pattern altitude so I chose to glide all the way around and land on the same runway from which I'd departed. I knew that should I find myself running out of altitude I could turn into the airport at any time. With a close in down wind and base being a close in U-turn from down wind to the runway I hit the gear down switch and pushed the flap switch to full as best glide is 120 and I normally land at 80 MPH minus 1 mph for each 100# under gross. Those big flaps and gear down add a lot of drag to the Deb. I still used a good half of the 3800 foot runway.

BTW you eventually learn the "feel" of the yoke and with an engine failure you just ease the yoke forward to maintain the same feel. So you sort of recognize and react as if you are on auto-pilot.

Regards and keep enjoying that primary training.


Lieutenant Don said...

Great post on "the impossible turn". Has anyone worked out the math for that situation with multiple runways. I've thought that if I lost an engine above 500 or so AGL on DPA 20R, I'd try to make the turn and land on 2R. That would cut a lot out of the turn and potentially simplify the maneuver.