After 10 days on no flying (thanks crappy Colorado weather patterns) I got back into that ‘beat-to-shit’ cheap Cessna crap that I’m flying and went back up into the wild blue. Since I am now complete with what Jeppesen refers to as ‘Stage One’ I was ready to take it up a notch and start learning some real stuff. Today we did short field takeoffs and obstacle clearance.
The short field does not refer to the field that the “special people” use. Although most pilots that I know are, point of fact, “special people.” The short field is a runway that is small. What defines a short runway? Well I don’t know and I have not been able to find out. In my experience, any runway less than 10,000 feet long and less than 300 feet wide is just too damn small for me. But in the tiny little baby airplanes that I’m flying now, there are runways here that less than 4,000 feet and around 40 feet wide. That’s small. It’s not aircraft carrier small, but it’s still damn small. Perhaps the 15,000 foot runway at Edwards AFB and the 37 miles of lakebed runway on Rogers Dry Lake have spoiled me.
Short fields also generally assume that there is a 50 foot obstacle (usually trees or power lines) at the ends of the really short ass runway. In order to clear those obstacles in the least amount of runway we need to increase our available lift and utilize our maximum angle of climb. Normally we climb at the best RATE of climb, but in this case we’re going to switch to the best ANGLE of climb. That’s right, the objective of a short field takeoff is to get to best angle of climb airspeed as fast as possible. In our particular 210-hp C-172E the best rate of climb is 95mph while the best angle of climb is 70mph.
You are mostly concerned with the distance to the obstacle at the end of the runway. It doesn’t do you any good to get airborne early if, in the process of getting there, you have so much drag that you are just flying in nose-high ground effect and getting closer and closer to those obstacles without actually climbing. While it might be a little back-ass-wards in your head, trying to climb the second your wheels are off the ground is the wrong thing to do when trying to clear an obstacle. First you need the right speed, then you get the right climb. In order to get that speed, I needed to reduce drag.
The first way to minimize drag is to get your little wheel off the runway as soon as you can. For us, that means assuming that takeoff attitude at 60mph. When I see 60 on the airpseed, I’m going to pull that nose off the concrete and wait. The next criminal in the drag crime is Flaps. Now, everyone will tell you that flaps cause drag. They do. But they also generate lift. In most aerodynamic designs the magic place in flaps is around 15 degrees. More than 15 and your flaps are a drag device (which when you’re landing is a good thing, but not here.) Our aircraft wants 10 degrees of flaps to maximize our lift without adding too much drag. For our normal takeoffs, we don’t use any flaps and that’s because we have oodles of runway and no real obstacles to deal with. Not anymore.
Once you’re airborne you need to get to that best angle of climb speed as soon as possible, that’s the whole goal remember? So as soon as the airplane is off the ground with a positive rate of climb, you’re supposed to lower the nose back down to the horizon. You get that? You are now flying right at those obstacles you need to get over. It doesn’t make sense on the first glance, but if you think about the physics behind it, it all works. We need to use the available distance to build up the speed needed to clear that obstacle. So nose it over, build up speed, then capture that best angle of climb airspeed and up you go.
I had seen something remotely similar before when we would do a maximum performance climb in a supersonic jet fighter. In those cases, we takeoff as normal, pull the gear up and then keep the airplane at about 50 to 100 feet and accelerate down the runway in full after-burner. When you hit something like 400 knots, the sadistic pilot in front seat would reward you with a 6-G pull to the vertical and then fly straight up to around 10,000 feet. Sounds fun, right? Well, it’s not. It’s cool to say you’ve done it, but once that box is checked there’s no need to repeat.
Trust me, in a C-172 it does NOT look like this.
On the first takeoff, I did just as I described. I lined up on runway centerline and stopped. I held the brakes while advancing the throttle to maximum power. I ensured that the engine was good and then let go of the brakes and accelerated down the runway trying in vain to remain relatively close to centerline. At 60mph I put the engine cowling on the horizon and waited until the aircraft left he ground. Then I nosed it over to fly down the runway in ground effect, essentially staying about 20 feet over the runway until the airspeed got up to 70mph. Once it was there, I pulled the nose back and attempted to maintain 70mph in the climb.
At least that’s how it went in my head. Reality is much more interesting. At 60mph I pulled back way too damn much and yanked the airplane off the runway and was rewarded by the stall warning horn. Hearing that thing go off when you are literally 2 feet off the ground is definitely disconcerting. To say the least, it freaked me out, so I nosed it over to get some airspeed which had the effect of freaking out my instructor. As I would explain later, it had the added effect of actually increasing our airspeed so, hello, it worked. Was I a bit too low… probably. Was in ground effect… yes. So I’d say that the objective was achieved. Sure there was a little danger of prop strike, but these things happen. Once I saw the airspeed pass through 70mph I pulled back in an attempt to capture that speed. But the speed kept increasing, so I kept pulling. As my attention was diverted from the airspeed gauge to the attitude indicator I was again rewarded with the stall warning horn. I pulled way… way… way too much. This is where I nosed it back over and regained as much airspeed as I thought was healthy. Needless to say, it was not quite the smooth takeoff I was looking for. A Thunderbird, I am not.
Eventually I executed the maneuver within evaluation standards and received kudos from my instructor. But that was after 8 attempts. Yeah, for me, 8 times is the charm.
The moral of this story is: Big Runways are your friends. Short runways suck.