Hey guys,

Quick question on turns in ground effect. I mostly fly a 150 so ground effect is definitely my friend. Our strip has a little dogleg that necessitates a slight turn, but a turn nonetheless. It's a one way out strip for me so the turn is always to the right. What is the best/most efficient way to make this turn. Usually I just feed in a little right rudder, but It seems like it takes a bit longer to to gain some airspeed doing that vs a small co-ordinated turn. It's subtle for sure, but seems to be that way. Could totally be in my head though. Any thoughts?

Thanks,

Pete

Pete,

The energy difference in six inches over six feet is tremendous. If you are high enough to make a coordinated turn without putting a wing into terrain, you are well out of the really efficient low ground effect.

You are near gross in the 150 by yourself. It will fly in six inches ground effect much slower than in six feet ground effect. Getting it into ground effect sooner means more seconds of low ground effect energy. By the time you get to the turn point you will be flying faster than you have been. It will require quite a bit of rudder pressure to turn and opposite aileron to keep the wing level.

Practice low ground effect on a long, wide runway. Move to right side and then left side of runway while staying in low ground effect.

You are correct that the energy difference is minimal in high ground effect. Low ground effect takes time to find. When found and made full use of, it is well worth it.

Jim

The rudder pressure to turn and opposite aileron to keep the wing level is what makes me uncomfortable.
When I practiced spins this is exactly how we did it.
Rudder and opposite aileron, but power off.

Why is not dangerous in this scenario?

Motoadve,

My experience, with students practicing low ground effect, is their reluctance to get the mains off as soon as it will fly in low ground effect. I think this is because gross for /aft dynamic proactive elevator movement is necessary in learning how to stay in low ground effect.

A stall /spin at six inches is a not as dangerous, I think. But it would be preceded by a mush down, I think. The reason I don't really know is because the student tries to roll on the mains long enough to be able to fly smoothly into high ground effect. Much energy is lost this way. Once too high and too slow, I require a return to low ground effect before any rudder turns.

Thanks for the question. It was a good one.

Contact

I can say that contact's e-book has kept me safe with an under powered plane at high DA (C85 at 9500+DA) if it was not for low ground effect and working the terrain I would never be able to get anywhere. I have done rudder turns basically at or just above what the book stall speed is and it has not been much of an issue, granted the more speed the better, but the plane will tell you what is going on with it you just have to be willing to listen to what it's saying.

motoadve wrote:The rudder pressure to turn and opposite aileron to keep the wing level is what makes me uncomfortable.
When I practiced spins this is exactly how we did it.
Rudder and opposite aileron, but power off.

Why is not dangerous in this scenario?

I don't think stall/spin is likely scenario in an established, level, low ground effect rudder turn. But I still wouldn't stand on it. Now if you start pulling, load the wing up way behind the curve and get crossed up, the outcome might be different. I think it's managing energy. I know I will go around in low ground effect with rudder way before I will try to stagger over something. Probably takes awhile to get comfortable and competent. Ease into it and don't put yourself in a place that you're uneasy in.

Opinion.

Contact,

Thanks! So, a couple more questions/info. Currently I am flying with the mains around 2' off the ground. Too high sounds like. It's a downhill take off so once in the air the ground falls away for about 100 yards or so before flattening out so it's a bit tough to keep it low initially. I will work on staying 6" or so the entire way. On a flat paved runway I have no problem staying just off the ground. Currently with 10 degrees of flaps I am taking off around 42 - 45 MPH. I have tried different flap settings and I am off the ground sooner with 15 - 20 degrees, but very little difference in take off speed and extremely sluggish acceleration. I have though about taking off and milking the flaps out, but with my experience/comfort level (A smidge over 300 hrs) and a tree lined runway it doesn't seem like a good idea with electric flaps. So, do those speeds seem reasonable or should I be off the ground slower & sooner?

Pete

Pete,

2' is not bad but quite a bit less energy than 1' or 6'. Ten degree flaps is fine, but you will need to find a sight, feel, and sound that indicates it will just fly at six inches to a foot. The airspeed indicator is not accurate enough and you need a contact sight picture anyway. I would pay attention to the airspeed when a pilot is working on them, but that just wouldn't be accurate. Weight, conditions, weather, DA, etc., etc. is just too variable. The airplane will tell you when it will just barely fly in low ground effect. Stiff arm it up and then get dynamic and proactive on the control wheel to stay just up. With the flaps set, regardless of setting, you will have to horse it off to get it to fly when it will just fly in low ground effect. It will be a wild ride at first. The control movement (not pressure) to get up can be too much, it doesn't matter. The control movement (not pressure) fore/aft to level the nose in low ground effect and keep it there is what matters. It is hard to push the nose down when it is just barely flying and getting worse all the time. Getting worse all the time is why we have to push the nose down a lot. Push the nose down a lot and immediately pull back quite a bit.

A big problem in learning something new is the need to look professional. Mid school kids want to make high school moves. High school kids want to make college moves. College kids want to make pro moves.

Contact wants his pilots to make gross dynamic/proactive toddler moves to start with. It takes a whole lot less time that way. Once you have bracketed level in low ground effect grossly, fine tuning takes little practice.

Good luck,

Jim

FWIW, I find it a whole lot easier to stay in low ground effect (less than 2' AGL) if I have some nose down trim, and use back pressure to keep the airplane from descending. The reason for this is that as speed builds in low ground effect, the airplane wants to climb, right out of low ground effect. I find it to be much more difficult to push the yoke/nose down to stay in low ground effect, rather than pull the yoke/nose to keep from descending back to the ground.

Of course, that also means staying really cognizant of what the airplane is doing and where you are--not good to let up on the back pressure and descend right into the terrain after you've passed the end of the strip!

Seriously, though, give that a try, a little nose down trim instead of normal take off trim. Unless you really over-do it, you'll find that when the airplane is getting pretty close to Vy, there's very little remaining nose down effect, and by then you're ready to climb on out.

As for dog-legging while in low ground effect, and whether to use a flat rudder turn with opposite aileron to stay level or use a coordinated turn, if the dog leg isn't too much of a turn, you probably don't need to bank very much at that slow a speed to make a coordinated turn. With a high wing, you can actually bank quite far, close to 20 degrees at 2' AGL, before there's any danger of striking a wing tip. So it's not necessary to do a dramatic cross controlled turn to keep the wings level.

As you've found out, a dramatic cross controlled turn adds a lot of drag, much like a forward slip does in a landing. So most of the time with a low powered airplane, you want to use as little cross controlling as is necessary to get the job done.

As for those times when you must use a flat rudder turn, as long as you're enough above stall speed, there's no danger. Remember, we regularly use cross-controls when landing in crosswinds without any danger, because an airplane won't spin unless it first stalls.

Cary

I think Cary is right about the nose down or at least level trim. I never think of trim because I haven't used it since leaving spraying where a lot of trim was necessary to help hold the nose up in an overloaded Pawnee. Because I never went over 200 feet on pipeline, I left Cessna trim at cruise. That just happens to be the same as for full flaps in your airplane.

I have always thought neutral trim to be safest in maneuvering flight, including takeoff and landing. When the need to maneuver aggressively comes, I like receiving honest feedback from the airplane.

I usually have a bit of nose down trim when taking off, but maybe a bit more would be better. I'll fiddle with that too.

Thanks.

Ground effect is most pronounced when flying on the left side of the lift/drag max curve due to significant reduction in induced drag. When flying at a speed on the right side of the lift/drag max curve, ground effect Is decreasing with increased speed and has actually hardly any measurable effect.

How safe is a couple of hundred feet altitude at Vx, at Vy, at cruise speed? At which airspeed would we be more able to maneuver in case of engine failure? How many engine failures have you had at or below 200 '? I have had several and have found cruise airspeed to be more beneficial than the 200 '. Also I have found maneuvering at high DA and with heavy loads to be much more comfortable well above either Vx or Vy.

Rapid transition to cruise airspeed or slow transition to 1,000' is our choice on every takeoff. Excess engine thrust for climb to 1,000' is not guaranteed, however.

contactflying wrote:How safe is a couple of hundred feet altitude at Vx, at Vy, at cruise speed? At which airspeed would we be more able to maneuver in case of engine failure? How many engine failures have you had at or below 200 '? I have had several and have found cruise airspeed to be more beneficial than the 200 '. Also I have found maneuvering at high DA and with heavy loads to be much more comfortable well above either Vx or Vy.

Rapid transition to cruise airspeed or slow transition to 1,000' is our choice on every takeoff. Excess engine thrust for climb to 1,000' is not guaranteed, however.

How safe? It all depends on the individual situation and pilot skills. Having an engine failure at cruise speed in ground effect with not much space left in front of you or a unprepared surface probably proves equally unsafe, even fatal. It all depends on many factors, no situation is equal.

The more altitude you have when experiencing an engine failure the safer the situation is in general as it buys you time to maneuver and think. Statistically the more time a pilot has to think and act in an emergency situation the more favorable is the outcome.

I faintly recall one of your many anecdotes crashing an airplane and as I recall you described that if you would have had more time/altitude the outcome would have been different.

Of course the transition from take-off to altitude is the most critical phase of flight in case of an engine failure. However it really doesn't mean necessarily it is I less safe when flying at Vx or Vy and experiencing an engine failure as long as the pilot recognizes the need to lower the nose to maintain proper airspeed.

All I am saying is that there is no aerodynamic benefit to stay in ground effect after a certain speed. The only benefit really is accelerating to cruise speed in level flight, as you preach, and then exchange speed for altitude.

That might be practical in certain situations or for low powered aircraft like a J3, however for the large majority of GA flying this is absolutely irrelevant.











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Airspeed is altitude and altitude is airspeed. Our preference in the takeoff phase,I think, has more to do with orientation and indoctrination. My experience has caused me to prefer airspeed.

Your math concerning the extent of the extra energy available in low ground effect is better than mine, I'm sure. The low ground effect boat guys have a lot of data. My thoughts are based on experience. 50 thousand or so iterations. I really did it that way every time for years and found it to be useful.

I've had a flameout at Vx on takeoff. Lucky there was 10,000' in front of me, it was a wimpy Decathlon, and I still had young reaction time. I now accelerate in ground effect. Right or wrong I guess is all opinion.

Also watched a young Ag pilot collect a wire in the mains one day.
First reaction was to trade all that energy for altitude with a healthy pitch upwards. It worked fine for him and I heard later that he was able to tow several hundred feet of wire home successfully.

Sorry to wonder off of turns.

Pusher's concerns are valid. We need justify tthe value of any techniques we use/teach. Many of us have experienced good results with low ground effect until need to climb. That makes rudder turns down there sometimes necessary. FAA has gone as far as recommending ground effect to Vx or Vy as appropriate. Yet, they haven't recommended staying there until need to climb. We who find that also useful need keep talking about it and even teaching it. Things happen slowly in the FAA and big airplanes drive the equation.