Departing Downwind

[Little Red 22]

This is a scenario my local pilots have been hammering lately. We fly R22s and 44s.

 

"Your destination is in the downwind direction from your departure point. You take off into the wind. At what speed and altitude do/should you make your turn to your destination? The goal is to be safe, but also get on course to your destination."

 

Some of the options are as follows. Any others? What's best?

Take off downwind

Turn downwind after reaching ETL

Turn downwind after reaching Vy

Turn downwind after getting to an altitude where a 180 auto is feasible

 

Thanks!

[apiaguy]

What's best doesn't mean the others are bad... but they do involve varying risk.

turning after climbing to an altitude where the auto back into the wind is the "best"

I do all of the choices at different times.

[Whistler]

correct answer is obviously to take off backward into the wind and at altitude apply forward cyclic and not bother with that silly turning.

[Hotdogs]

...or say screw it and request a present position departure at my own risk, into the winds, maintaining an altitude restriction below the local pattern. Works every time.

[eagle5]

On a phone interview a couple months ago one complaint my interviewer had was the lack of downwind experience, takeoffs/landings/hovering,etc..that we Robbie pilots exhibit. Do it downwind for a change and see what its like.

[Gomer Pylot]

The safest option would be to turn downwind only after reaching an altitude and airspeed that allows a 180 degree autorotation. We are prohibited from turning downwind until reaching 300' and 60 kts. There are circumstances that require a downwind takeoff, but doing it when you're at max gross weight isn't a good idea, and we usually are close to it. But you need to plan that downwind takeoff, because you may go from being in translational lift to being below it, and that takes more power than you might think. It's something that needs to be practiced, but preferably when light and with a low DA. I've done many of them, know what to expect, and I only do it if I absolutely have to.

[aeroscout]

With a long enough run (like on a runway) a downwind takeoff is no different than an upwind takeoff.

When your groundspeed on a downwind takeoff is equal to the tailwind component, you are in essence hovering in no wind. from then on aerodynamically the downwind takeoff is no different aerodynamically than a no wind takeoff. The only difference is the takeoff ground run distance.

[apacheguy]

It really depends on the wind speed. If you're taking off at NTC into a steady 40 knot wind you'd be crazy to turn downwind until you get some altitude and airspeed. Normal conditions I'd probably get it above ETL and make a shallow turn, depending on how big of a hurry I'm in.

[Nearly Retired]

As with all things in aviation, the answer to this question is, "It depends."

 

Mostly, it depends on how good you think you are at downwind autos. When will the engine quit? At the worst possible time, of course.

 

I'm with Gomer (because I worked at the same company he does). But I'll take it a step further. During Recurrent Training one year, I asked my instructor if we could do a simulated EOL from 300' agl, downwind with takeoff power pulled. He said okay, so we set it up. The resulting auto to the water runway (206 on fixed-floats) ended up being a scary, aerobatic maneuver. I almost did not make it, seriously. We plopped down and let the ship just bob there on the water while our heart rates returned to normal. Jimmy Poulson, I'll never forget him, good man. We sat there for a while and he finally said, very, very quietly, "Let's not do that again."

 

Convinced me that if you're at 300' agl when the engine quits you WILL land straight ahead. If you're downwind, you're just not going to flip it over on it's back in a crazy, low-level Split-S to get back around into the wind. Okay, so again, how good are you at downwind autos? Me, not so good I don't think and I don't want to find out.

 

But what about a takeoff from an airport? You're up at a corner of the field at which an into-the-wind departure puts you over a residential or industrial area with not very many good forced landing areas. In this case, take the downwind departure and just realize that if it quits you're going to run it on downwind. I'd at least see if I could take off into some form of crosswind rather than a direct tailwind. There's a reason you never see birds taking off and landing downwind. We're subject to the same aerodynamic rules they are. And remember, gravity is not just a suggestion- IT'S THE LAW, baby!

 

Generally, I take off into the wind and climb at 60 knots to 300' agl BEFORE DOING ANYTHING. I mean, what's the rush? You absolutely gotta save that 30 seconds or so? And then as I make my turn I keep climbing so I'm not cruising at 300'. I hate that. I hate pilots that do that. You fly over somebody's house at 300' agl while they're watching afternoon reruns of "Matlock" and you've just made an enemy for life. And he'll *really* be an enemy if you crash into his house during your downwind auto, ya putz.

 

I see a lot of pilots who start their takeoff into the wind and then immediately begin a turn on-course. I always think to myself, "Meh- lousy pilot there. Probably had pretty bad training." Or, "Meh- it's probably Avnut - he don't give a crap anymore. Didn't he teach Larry Bell how to fly?" Or maybe, "Wow, whoever it is is sure better than me. Heyyyy, maybe it *is* Avnut!"

 

So I guess the question remains: How good do you think you are? I'm pretty damn good, but I'm not *that* good, and downwind departures are something I avoid unless there is absolutely no other way. Hey, call me old-fashioned.

[Hand_Grenade_Pilot]

This is a scenario my local pilots have been hammering lately. We fly R22s and 44s.

 

"Your destination is in the downwind direction from your departure point. You take off into the wind. At what speed and altitude do/should you make your turn to your destination? The goal is to be safe, but also get on course to your destination."

 

Some of the options are as follows. Any others? What's best?

Take off downwind

Turn downwind after reaching ETL

Turn downwind after reaching Vy

Turn downwind after getting to an altitude where a 180 auto is feasible

 

Thanks!

 

Before we talk about each scenario, lets briefly go over the disadvantages of taking off downwind.

 

1.) Decreased stability (during the initial transition into forward flight) due to the aircraft's tendency to weather-vane into the relative wind.

2.) Increased distance required to reach ETL, as a result of your rotorwash being blown into your take-off path.

3.) Decreased angle of climb, due to increased ground speed.

4.) More distance required to perform a quick-stop or decelerate during the flare in an autorotation (also a result of having a higher ground speed).

 

Now, despite those disadvantages, there are sometimes legitimate reasons to takeoff down wind. For example, departing a spot where there is only one entry/exit path due to obstructions.

 

Whether a downwind takeoff should be performed depends on the specifics of the situation; pilot proficiency, wind velocity and aircraft performance (DA vs weight).

 

If wind velocity is low (5kts or less) and aircraft performance is high (low weight and low DA) taking off with a tailwind shouldn't create much of a problem.

 

However, trying to depart downwind with no or little additional power available (high weight and/or high DA) or with a strong wind can create some very significant risks.

 

Immediately turning downwind after reaching ETL results in a sudden loss of lift. If the pilot is anticipating it, and there is additional power available you can increase collective while continuing to accelerate with cyclic. If the pilot is unprepared (or is at the aircraft's power limit) they are likely to begin settling or exceed a power limitation.

 

Turning downwind at Vy (best rate-of-climb speed) is more much conservative, but still carries the risk of not having enough altitude to turn back into the wind if you find yourself being forced to auto rotate.

 

Waiting to turn downwind until you are at an altitude that allows for a 180 degree autorotation (about 300'-500'AGL) is certainly the most conservative take-off profile and is what I use whenever possible. That being said, it is not always practical or possible to take-off this way.

 

To keep it simple; the higher the wind component, weight, and DA the more weary you should be of departing downwind. Unless a significant power reserve is available, don't immediately turn downwind after reaching ETL. And always take-off (and land) in the most conservative way possible within the constraints of the situation.

 

*Edit: And to Nearly Retired's point, 300'AGL is hardly enough to make it a full 180 degrees, especially in a situation where you are caught by surprise. Realistically, at 300'AGL, you're giving yourself enough altitude to terminate an autorotation with a crosswind rather than having the wind behind you.

[bqmassey]

Great post, Hand Grenade. One thing, though.

 

Immediately turning downwind after reaching ETL results in a sudden loss of lift.

 

There's isn't necessarily a loss of lift. Obviously, the amount of lift produced has nothing to do with ground speed (hence, wind); it has to due with relative wind—indicated airspeed for our purposes.

 

Turning upwind, downwind, crosswind, none of it will necessarily change your indicated airspeed, and, consequently, won't affect your lift.

 

I think that the "loss of lift" that we experience when turning downwind is due to our nature to fly visually and maintain a nicely carved out ground path, which does, in fact, require a change in airspeed.

 

Long story short, if you keep a constant bank angle, accept whatever ground track it gives you, and keep the nose down, you won't slow down and you won't have a loss of lift.

[manhattan]

Great post, Hand Grenade. One thing, though.

 

 

There's isn't necessarily a loss of lift. Obviously, the amount of lift produced has nothing to do with ground speed (hence, wind); it has to due with relative wind—indicated airspeed for our purposes.

 

Turning upwind, downwind, crosswind, none of it will necessarily change your indicated airspeed, and, consequently, won't affect your lift.

 

I think that the "loss of lift" that we experience when turning downwind is due to our nature to fly visually and maintain a nicely carved out ground path, which does, in fact, require a change in airspeed.

 

Long story short, if you keep a constant bank angle, accept whatever ground track it gives you, and keep the nose down, you won't slow down and you won't have a loss of lift.

How refreshing to know there are pilots that understand this.

 

One of the most misunderstood concepts pilots share (FW and Rotorcraft alike) is RELATIVE WIND.

 

We humans are so used to being "Ground Based". The aircraft knows nothing of ground track only what it is doing in respect to the relative wind. If you were to have a pitot tube that always weathervanes into the relative wind with an azimuth indication, you would see that cyclic control is the only control that will vary this (disregarding pedal and indirect power changes for simplicity's sake).

 

Example, Wind 180@30, T.O. RW 36. You would start of with heading 360 and a relative airspeed of 30@180 (RELATIVE!!) which is above ETL. As you accelerate and require more power in the initial TO run due to loss of relative airspeed you would eventually pass through 0 KIAS and back up to Vy. A much longer TO roll.

 

The only difference to this example on a calm wind day (although very impractical) would be to start off in backwards flight @ 30 KIAS, slowing down to 0 KIAS, and then flying a normal forward TO profile with the ONLY DIFFERENCE between the two examples being TRACK OVER THE GROUND.

 

I see this all the time with CFIs when conducting VRS demos. They claim that heading into the wind or downwind at altitude will affect the VRS demo! Ridiculous! A zero airspeed hover is a zero airspeed hover! Of course a pilot flying downwind at low altitude will bleed off his airspeed and increase his descent angle which is conducive to VRS. But at altitude this has absolutely no effect.

 

Thinking in terms of track through the air vs track over the ground is something that a lot of us pilots could use more of.

[Hand_Grenade_Pilot]

Great post, Hand Grenade. One thing, though.

 

 

There's isn't necessarily a loss of lift. Obviously, the amount of lift produced has nothing to do with ground speed (hence, wind); it has to due with relative wind—indicated airspeed for our purposes.

 

Turning upwind, downwind, crosswind, none of it will necessarily change your indicated airspeed, and, consequently, won't affect your lift.

 

I think that the "loss of lift" that we experience when turning downwind is due to our nature to fly visually and maintain a nicely carved out ground path, which does, in fact, require a change in airspeed.

 

Long story short, if you keep a constant bank angle, accept whatever ground track it gives you, and keep the nose down, you won't slow down and you won't have a loss of lift.

 

That's a really good point.

 

What I should have said is that if one is attempting to turn downwind very quickly (steep bank) while trying to maintain a constant ground speed the result can be a loss of ETL. This, combined with your resultant lift vector being less vertical (due to being in a banked attitude) can result in the aircraft settling w/out additional power being applied.