# Can airspeed in ground effect be used to estimate climb performance?

A very interesting crash video (in which everyone survived) shows a Stinson which takes off but is unable to climb out of ground effect.[*]

Watching the video, it seems that the pilot had ample time to put the plane back down in a controlled manner, but was likely stuck in a mindset that "the plane took off and is climbing, we only need a hundred feet more and we're safe". The reality was that the plane was unable to climb out of ground effect, which is why over the 2 1/2 minute flight it never rose above tree height.

Since ground effect enhances lift, it also means that the plane can accelerate and fly faster in ground effect, since less thrust is being used to overcome the induced drag. Stating the obvious, there is, therefore, some kind of concrete, observable relationship between ground effect performance and climb rate.

The trick is how to quickly recognize in situ that the plane isn't able to climb out of ground effect.

• Is there any practical way for the pilot to eyeball estimate the climb rate from the plane's performance in ground effect?
• Is there a rule of thumb this pilot could have used to say "I am unable to go accelerate past XXX kts when 5ft from the ground and therefore I know I cannot climb beyond ground effect?"

[*] Google Maps shows that rising terrain was not a factor at the moment of the crash. The airport is at 6370 and the valley is very flat and doesn't rise above 6400' for 5-10 miles in the direction of takeoff.

• Proper density altitude and load calculations before takeoff could have saved a Stinson. Which is to say, this never should have gotten to "I'm off the ground but can't climb." Jun 22, 2021 at 14:28
• Absolutely, couldn't agree more. Jun 22, 2021 at 14:38

Not really. You don't really know until you work out the numbers, there being so many variables. Although experience and instinct gets you most of the way there if you have the experience.

He was out of ground effect but was effectively at or above the airplane's absolute ceiling . During his forever takeoff, he used ground effect to gain a bit of surplus energy to allow him to, more or less, zoom climb to about 50 ft, where he found himself with no surplus energy left, on the peak of the power curve, but slipping to the backside of the power curve. The rest of the flight was slowly consuming the speed margin on the back side of the power curve until he was about to stall and mushed into the trees. You can see his pitch attitude slowly increasing bit by bit during that whole phase. He didn't need rising terrain; he put himself into a trap whose only escape was to return to ground effect and eventually land.

The biggest red flag, beyond the sheer length of the ground run, is the part where he lifts off and settles back onto the ground. If that happens when you are at your normal liftoff speed, the airplane is screaming at you to give up. If he had lots of hours in that Stinson, the instinct that comes from familiarity should have been sufficient to recognize the red flags.

The final red flag is simply the lack of acceleration from thrust above 20 feet or so; instead of zooming to 50 feet on surplus energy, you should feel the plane pulling you faster.

Aside from those clues, the other obvious one is doing the little bit of performance math where he could have determined that he was already at his absolute ceiling in those conditions and needed to wait until a time when the air was cooler. But discarding all that, the skipping takeoff and sluggish acceleration should have been enough warning.

When I was bush flying on floats, in a not-very-rocket-like Cessna 180, there were many times I would be taking off with a very heavy load, on a very hot day, where the performance was marginal even at 1500 ft asl (density alt maybe 4 or 5000 ft, enough to make a float equipped 180 pretty doggy). I'm on a lake whose length I can only estimate, and I can only estimate my all up weight (coming back from a pickup from a camp).

I would set a reject point, usually about half way down the water run using a shore line landmark. If the airplane had the performance reserve, you could tell right away as it would come off the water and you could feel it accelerate smartly once clear and would immediately start to climb. Too much of sluggishness there, and I'd fly along in ground effect to see if it improved and put it back down right away (with the shore line looming) if it wasn't accelerating once at about 30 feet or so. Then back to the dock to off load that outboard motor they insisted they bring along.

Sometimes a customer would insist I take all his stuff, and I knew it was way too much, but sometimes you have to find a tactful way to say no, so I would say "let's try it", and go step taxi down the lake with the power reduced (the customer can't tell that you're only at 23" of MP) until the opposite shoreline was looming, say "we won't make it; you don't want us to crash into the opposite shore do you?" Back to the dock to off-load non-essentials, and no complaints to the boss.

• I have watched that video many times but never have I read as concise and useful an explanation as yours here. Kudos sir! Glad I was not aboard. BTW during my time in Winslow, AZ there were two fatal crashes on takeoff in which both planes apparently zoom-climbed out of ground effect and then quickly stalled just off the end of the runway... hot & high. - NN Jun 22, 2021 at 20:30
• @nielsnielsen thanks! For the ultimate zoom climb into the back side of the power curve catastrophe, read the NTSB report on the famous CRJ200 incident where they took the empty airplane to its service ceiling by zoom climbing the last several thousand feet to its 41000 ft service ceiling using the autopilot's Vertical Speed mode, instead of letting it take its time by flying in Mach mode, and finding themselves on the back side with no way out ntsb.gov/investigations/AccidentReports/Reports/AAR0701.pdf Almost the same thing in a way, except at FL410, and with even worse results. Jun 22, 2021 at 23:52
• that's awful! glad I wasn't on board that one either! Jun 23, 2021 at 0:18
• I knew the accident investigator that went on site. The plane hit a meth lab in an out building behind one of the houses, which caused a big fire. It took GE a while to admit that core lock and poor windmilling ability (due to low ram effect into the compressor inlet) was a problem on the CF-34. The production flight test procedures had to have a core lock test procedure added to the normal in-flight shutdown/relight tests as a result of this accident. It also led to an industry wide change in training procedures to add high altitude stall recovery in the sim. Jun 23, 2021 at 2:07
• this is ghastly, thanks for sharing this info. i had no idea it was possible to get behind the curve at high altitude. When I was working for HP, I got to fly a couple of times in their rockwell sabreliners (mod 45 and 60 stretch) and once we got an expedited climb profile at low gross weight out of SJO, climbed at like 20 degrees to 41K and then went screaming off to Corvallis. my only cabin mate had a gas problem and I was sitting next to the emergency window exit which leaked like a sieve at 41K so he would let loose with a big one and I would suffer the consequences! Jun 23, 2021 at 6:26