I bet everyone who watched Top Gun: Maverick scoffed at the scene where Maverick sheds his stolen F-14’s nosewheel on a “50-foot obstacle” while attempting a short field takeoff… from a taxiway. In Mav’s defense, Tomcats don’t have an approved Short Field Takeoff procedure—that doesn’t involve a catapult. However, folks flying light GA aircraft don’t have that excuse. There’s lots of guidance out there designed to keep us out of trouble. Problems arise when we don’t comply with it, and the results can be catastrophic.
So, let’s do a shallow dive into what’s required to execute a successful “high performance” takeoff. We’ll explore issues and confusion surrounding aircraft performance speeds (“V-speeds”) and flap use during takeoffs. We’ll discuss why it’s important to know exactly what’s required for your plane, and why you should always read the fine print.
There are exceptions to everything in aviation. Obviously, not all airplanes have flaps; we’re not addressing them here.
For brevity: I’m using “Pilot Operating Handbook” (POH) to include all the various aircraft documents, including the Airplane Flight Manual, Pilot’s Information Manual, Owner’s Manual, etc.
Where to start?
When departing short, soft, and/or obstructed runways, there are two questions you must answer: What speeds do I fly, and are flaps required?
First, let’s review some definitions and generally accepted truths concerning V-speeds, flaps, and climb performance-related stuff:
- Vx is best angle-of-climb speed. It produces the greatest altitude gain in a given horizontal distance. Vx is a function of excess thrust: the IAS for Vx increases with altitude. Vx is typically flown in a clean, no-flap configuration (there are exceptions).
- Vy is best rate-of-climb speed. It produces the greatest altitude gain in a given time. Vy is a function of excess power: the IAS for Vy decreases with altitude. Vy is always flown in a clean, no-flap configuration.
- Some airplanes have a published obstacle clearance speed (OCS). This speed is usually slower than Vx and is flown with approved flap settings. One notable exception: Cessna 150.
- Even if the term “obstacle clearance speed” isn’t used, any speed other than Vx that’s directed for use until all obstacles are clear is an OCS.
- If a flap-equipped plane doesn’t have a published OCS, it’s because flaps use isn’t approved for takeoff. In that case, any OCS should be the same as Vx.
- Cessna usually publishes an OCS, along with a flaps-up Vx.
- Piper doesn’t publish a separate OCS. They use a flaps-down Vx, followed by a transition to a flaps-up Vx after the obstacle has been cleared.
- All flaps produce lift and drag. At some point, drag wins—usually around 10-20 degrees of extension (25 for Piper). The manufacturer will always specify the maximum flap setting approved, or recommended, for takeoff.
- Some airplanes use flaps for short field takeoffs; many don’t.
- All airplanes use flaps for soft field takeoffs—except Beechcraft.
It’s critical that pilots correctly interpret the manufacturer’s guidance on where, when, and how to transition through the various V-speeds. Using Vy—when airborne, clear of obstacles, cleaned up, and prior to establishing a cruise climb—isn’t that controversial. The confusion and creativity involve what happens from brake release up until that point.
Where to look?
In most POHs, V-speeds and flaps are addressed in at least two places: the takeoff and normal procedures sections. A third place to check is the takeoff performance charts; they may have asterisk items that aren’t covered elsewhere in the POH. For example, the Beechcraft C-23 Sundowner takeoff checklist just directs “flaps—set.” It only adds “flaps—up” as a note on the hard surface and grass runway takeoff performance charts, along with an “at 50 feet” speed of 74 KIAS. The C-23’s 69 KIAS Vx is never mentioned.
Apparently, Beechcraft doesn’t want you to takeoff unless you can fly a normal climb profile.
Published procedures may be based on climb speeds, configurations, and profiles that you’re not used to; and may include steps for transitioning from an OCS though Vx, to Vy, etc., that are different than expected. Sometimes you must figure these out yourself, based on whichever “standard scenario” you’re facing: Short or soft field with/without obstacles; or the most challenging—a short, soft field with an obstacle.
When is Vx not Vx? Obstacle clearance speed vs. Vx
Isn’t clearing an obstacle what Vx is for? Why have an OCS that is slower than Vx?
The reason is simple: flaps help get you airborne quicker, however, they create a significant amount of parasite drag and a lower speed is needed to minimize this. Continuing to climb unnecessarily at OCS, with flaps down, is self-defeating. Since drag quadruples as speed doubles, getting the flaps up as soon as they aren’t needed is critical. That means transitioning (i.e., accelerating) as soon as it’s safe, to Vx, Vy, or something even faster.
Flying precisely is important, but…
Vx and Vy are usually far enough apart (10-12 KIAS +/-) that there’s a definite pitch change between the two. Sometimes OCS and Vx are also far enough apart (5-7 KIAS +/-) that a pitch change is required.
They can also be annoyingly close. The Cessna Skycatcher has a 55 KIAS OCS and 57 KIAS Vx. That 2 KIAS difference is difficult to fine tune even with its almost-too-accurate Garmin G300 digital airspeed indicator. The temptation to focus inside and nail it has to be balanced with the need to look outside—especially when you’re 12-15 degrees nose-high.
For short fields, the Skycatcher POH directs a climb at the flaps-down (one notch/10 degrees) OCS until clear of the obstacle, then retract the flaps when you’re faster than 60 KIAS. Confusion can set in because Vx is 57 KIAS… you’ve already blown through that, and in fact, operating at Vx is never mentioned anywhere else in the POH.
Conversely, the Cessna 150M POH directs a flaps-up 60 KIAS OCS, then states “If enroute terrains dictates the use of a steep climb angle, climb at a Vx of 56 KIAS with flaps up and full throttle.” In this case, OCS is faster than Vx, and both are flown clean—a rare case of slowing down after you’ve cleared the obstacle.
The concept of an “enroute Vx,” is unique to Cessna; other manufacturers address Vx in reference to takeoffs only. The 150M POH also refers to both a “climb speed” and OCS.
You’re supposed to decide whether climb speed means Vx or something else.
Climbing out at Vx: when is high enough high enough?
The 1975 Cessna 185’s Maximum Performance Takeoff checklist states: “Climb speed—64 MPH until all obstacles are clear,” then retract the 20 degrees of flaps and pick up either a normal climb (110-120 MPH), or a maximum performance climb (101 MPH at Sea Level, to 94 MPH at 10,000 feet).
Then in the Enroute Climb section it states: “If an obstruction ahead requires a steep climb angle, Vx should be used with flaps up and maximum power. This speed is 86 MPH at sea level, increasing to 88 MPH at 10,000 feet above Sea Level.”
But if there isn’t an actual obstacle out there, what kind of climb profile should you fly… especially if you’re burning 24 GPH at maximum power?
My Tacoma-area airport has a departure which takes you immediately over the very-cold Puget Sound. One local C-185 driver likes to climb using that Maximum Performance Takeoff checklist (I’m assuming; based on his pitch attitude, 20-degrees of flaps, and the scream of near-supersonic tip speeds) until he’s high enough to glide to Portland… 101 nm away. Now, I don’t own a 185, but I’m thinking that’s a bit excessive.
As we’ve seen, Cessna provides unequivocal guidance on using Vx for situations other than takeoff, including some discussion about the drawbacks of doing so. For example, a C-150M POH note says: “Steep climbs at low airspeed should be of short duration to allow improved engine cooling.” Unfortunately, this note doesn’t point to all the other reasons to avoid unnecessary, extended climb-outs at Vx: overall engine stress, higher fuel burn rates, reduced forward visibility, higher AOA, higher drag, slower airspeed, closer to stall… more annoyed, noise-sensitive neighbors.
But what about engine failures after takeoff?
Worried about that “impossible turn”? Most pilots could make it back to the field if they at least reach traffic pattern altitude (TPA) somewhere close to the airport. As advertised, Vy will get you there quicker, however, it takes you further from the runway. But how much further?
The horizontal distance traveled between Vx and Vy while climbing to a 1,000 ft. AGL TPA is negligible; it’s going to be hundreds of feet, not miles. However, if you can’t hold Vx or Vy within +/- 10 KIAS, all bets are off.
To convince yourself, take a look in William Kershner’s 2006 Flight Instructor Manual, 4th Edition. There’s a chart (Figure 11-10, p.170) for a “Fictitious Airplane” that illustrates the relatively minor differences when operating at Vx versus Vy.
It shows that a 74 KIAS Vx climb yields a rate of climb (ROC) of 1,250 fpm and a 90 KIAS Vy ROC of 1,380 fpm. That’s a difference of only 130 fpm. If Vx was faster and/or Vy was slower, the ROC gap would be smaller; that happens as altitude increases. In this case, if you climb straight ahead for one minute, you’d be roughly 130 feet higher using Vy, and a bit further from the runway. If you stopped at a 1,000 ft. TPA, instead of flying for one minute, the distance would be even smaller.
Those numbers may seem excessive to pilots who are used to 500-600 fpm ROCs, not 1,000+ fpm, and differences between Vx and Vy of 8-10 KIAS, not 16-18 KIAS. But the spatial/lateral relationships remain the same. Obviously, your mileage may vary; that’s why it’s important to have an idea of what they really are in your plane. Instead of drawing charts and doing actual trigonometry, conduct your own flight test.
Still concerned about an emergency return? A better tactic might be to climb at OCS or Vx until all obstacles are clear, then circle near the airport at Vy until you reach a comfortable cruising altitude.
Tactics, techniques and procedures
There is no universal short or soft field procedure that always works for ever airplane.
Defaulting to a one-size-fits-all technique of extending one notch of flaps, holding the brakes… or letting her roll, running her up to max power, releasing brakes, rotating as appropriate, pitching up to hit that speed at 50 feet… or to hold OCS… or Vx, until clear of the obstacle, retract the flaps, climb out at Vx… or Vy… might work great most of the time. Or you might end up bending something.
Taking off with the wrong flap setting, either too much or not enough, is self-critiquing.
I once went “a notch too far” with the Johnson bar in my 1953 C-170B while attempting a takeoff on skis from a Fairbanks-area strip. The extra flaps added enough drag that I could barely crawl out of ground effect. Fortunately, I figured it out just in time so that the spruce trees in my flight path only barely scraped my F. Atlee Dodge skis as I clawed for a few more feet.
If you’re operating out of real soft fields—mud, icy slush, loose gravel, sand, wet grass, hot asphalt, etc.—then you’re a test pilot. Manufacturers may offer soft field techniques, but they won’t provide any data that supports your decision to try it. Although they might provide data for a hard dry grass runway, it’s based on adjustments to their hard paved runway calculations. For example, in fine print at the bottom of the Cessna 185 takeoff data chart for Takeoff Distance w/20 Degrees Flaps from a Hard Surface Runway, is the following:
Note 2: For operations on a dry grass runway, increase distances (both “ground run”and “total to clear a 50 ft. obstacle”) by 6% of the “total to clear 50 ft obstacle” figure.
Manufacturer guidance on speeds, flaps, and piloting techniques is all over the map. Not just between companies, but among product lines—even for the same airplane, depending on model year. It can get confusing and dangerous if you don’t pay attention.
There are gotchas when flying different planes from the same builder. For older 172s (mid-50s through early 70s), Cessna states: “To climb over an obstacle after takeoff use the Best Angle of Climb Speed of 60 mph, with full throttle and flaps up.”
The 1975 Cessna Skyhawk Owner’s Manual directs a maximum performance takeoff configuration of “Wing Flaps—UP” and “Climb Speed—68 mph (until all obstacles are cleared).” It then states: “If 10 degrees of flaps are used for minimum ground runs, it’s preferable to leave them extended rather than retract them in the climb to the obstacle. In this case, use an obstacle clearance speed of 65 mph.” An actual Vx is never mentioned.
There are significant differences between a 1956 C-172 with a 145 hp O-300 and a 1975 Skyhawk with a 150 hp O-320; don’t assume they fly the same and get ambushed by muscle memory.
Even the illustration of a generic high wing aircraft doing a short field takeoff in the FAA Airplane Flying Handbook is misleading:
(Source: FAA-H-8083-3C; Figure 6-8)
In fact, newer Cessnas use OCS with flaps, then transition to a flaps-up Vx—maybe the FAA should have depicted a Piper instead?
On the other hand, if you fly PA-18-150 Super Cubs, the POH simply says, “FLAPS… Whatever.”
Before you shove the throttle forward and release brakes…
- Always read the fine print so you have all the info needed to engineer your departure.
- Fly airspeeds as accurately as possible, without staring inside at the airspeed indicator.
- Know exactly what you’re going to do with pitch, power, and flaps.
- Know what procedure is needed to clear that 50-foot obstacle off the end of the runway.
- Determine what actual ROC you’ll need to clear any obstacles, whether you fly OCS, Vx, or Vy.
- Finally, have an out in case it’s not looking good. I wouldn’t want “missed it by that much!” on my headstone.