Hey hey and welcome back, Jacob here and this is Helicopter Lessons in 10 minutes or less. Today's topic is going to be effective translational lift. Now prior to watching this video I'd recommend watching my other videos on the symmetry of lift, transverse flow effect, and airflow at a hover to discuss some of that. aerodynamic principles that tie into this one.
But I'll put those links in the description of this video. That said, let's get started. So, effective translational lift. What is it? Well, it is going to be when the main rotor system completely outruns the recirculation of old old vortices and begins to work in a relatively clean and undisturbed air environment, thus becoming more efficient.
So I've got three diagrams here drawn out and this is going to show the progression from a stationary hover all the way up to effective translational lift. So stationary hover, looking at zero knots, and call that truly stationary, no air velocity. So we talked about this in our airflow at a hover video, where this airflow is coming in to the rotor system vertically. and starting to get pushed away from the rotor system.
And also, we're going to have these wingtip vortices on the tips of the rotor blades. So, that's what we're looking like, truly stationary hover. Now let's start to transition into forward flight.
So as soon as we have any kind of movement or airspeed, we're going to get into translational lift. And so what's happening here is now we're getting a little bit of airflow towards the helicopter. We're still having our wingtip vortices on the tips, but now this airflow is starting to enter the helicopter like this. But these vortices are continuing to get pushed back.
So we're getting a little bit more efficient, but we still have these vortices that are interfering with how the airflow comes over the helicopter. Now once we get to a point, we're going to actually outrun these vortices and be operating in a clean air environment. So where that happens is around 16 to 24 knots. We're going to go through effective translational lift.
Now this 16 to 24 knots depends on the blade size, the area, the RPM of the rotor system. But effectively, what it looks like is this. Air flow is now coming through your system, through your rotor system, at a rate where the wingtip vortices are all being left here behind the rotor system and no longer disturbing the air that's going through the rotor system.
Now as we move forward and get more and more efficient, it's actually going to improve efficiency all the way up to our best climb, our max rate of climb air speed when the total drag is least on the aircraft. We'll talk about that later on a total drag. drag video, I'll make that one.
But just keep in mind we're getting more efficient as we transition into forward flight and we outrun these vortices. So what are you going to see as you do this? Well, we talked about this earlier in the symmetry of lift video.
So if this is a top down look at the helicopter, we're moving forward. This advancing side is advancing into the relative wind and gaining more lift than the retreating side. And we talked about because of gyroscopic precession, there's There's a 90 degree delay, so all of this effectively rotates 90 degrees to the front half of the disc. So what's going to happen?
The nose is going to want to pitch up. We call this blowback. We call that effective translational lift, where the nose pitches up. And as a pilot, I need to know to push forward cyclic in order to compensate for this.
Alright, now we talked about in another video about transverse flow and I really want to kind of take this time to clarify the difference between transverse flow and effective translational lift. Transverse flow, obviously it's going to happen between 10 to 20 knots, so it's going to be... in between this transition to ETL. So at some point in between here and here, we're going to go through transverse flow.
Transverse flow is the difference in airflow from a horizontal on the front half to vertical on the aft half. That's what we're talking about, the difference in airflow between horizontal and horizontal. and vertical.
Effective translational lift is talking about the outrunning of these vortices. So I'll combine those in a video soon, but just to clarify transverse flow is the difference in airflow, whereas effective translational lift is going to be these outrunning of the vortices. Alright, so another thing to consider about effective translational lift is as we begin to accelerate into forward flight, the rotor system becomes more efficient so I require less power to maintain lift.
Also my tail rotor is is actually going to be outrunning its own vortices, making the tail rotor more efficient, and my vertical fin is starting to take some of the load that was required for that anti-torque. So with all three of those combined, I'm actually in an environment where I don't need as much left pedal, so I'm going to have to give it right pedal as I get more efficient to maintain my heading. All right, last thing to cover for all this is everything is reversed when you land.
So when you're on approach, you're on short flannel and you start descending below 16 to 24. knots you're gonna be getting into an environment where you require more main rotor and tail rotor thrust to keep your same alignment with the runway. So if you don't pull in collective you're gonna start to under arc through the approach and if you pull in collective and you don't give it that left pedal you're gonna start yawing to the right. So as you slow down between 16 to 24 knots you're gonna have to increase collective and give a little bit left pedal to maintain heading and the same angle for the approach.
That wraps up Effective Translational Lift. I hope you liked the video. Click like below if you did and put something in the comment section if you have anything to let me know how I can improve this video. Thanks much for watching. Have a good day.