Mid-Air Helicopter Dynamics + Landing Help Needed

[MTBS3D]

Hi All!

I need some helicopter guidance. I’ve completed the training sessions, and got “A” grades through most of them - undeservedly so I believe. There are some helicopter behaviors I’m struggling with, and I don’t think I’m improving.

The first behavior I don’t understand is mid-air hover getting sudden out of control spinning. Imagine flying a Bell 407. Counter-torque pedals are controlled - no problem. Altitude is steady, no problem. If I’m in motion, I’m in good shape. As I’m approaching zero speed for a hover, my helicopter suddenly goes crazy spinning wildly - so wildly, that my anti-torque pedals have no effect. The only solution is to reduce collective to zero which somehow lets me recover my control. What has changed in the dynamic that my helicopter is spinning like crazy when it hits zero speed in the air? What do I need to watch out for to prevent this?

My second issue is landing. I know I’m supposed to get to a 2 - 8 foot hover and then land. If I do an approach, I get closer and closer, but it always falls apart in the end. The moment I’m within ground effect, my helicopter feels uncontrollable and it easily bounces on the ground and slips left, right, and especially backwards (like a drop of oil on water). If I try to do a consistent torque / power reading, it’s useless because the numbers bounce around with every adjustment I make (e.g. let’s say my power is at 75% for a hover. If I’m having to compensate the helicopter position, it could jump up to 90% without me touching the collective so I guess every movement / adjustment adds to the sum). It just seems like way too many adjustments going on at once.

In connection to the second issue, I’ve tried a vertical landing. Can I gradually bring my helicopter down, hit a hover, and land? But that too feels impossible because the moment I hear my rotors vibrate, the vertical speed going down is too high and it’s near impossible to find a collective balance that brings me down safely.

I’m using a VKBsim Gladiator NXT Premium with a Thrustmaster TWCS throttle (the throttle is my collective). I’m not using any assists. All help appreciated!

[MTBS3D]

OK! I think I found the landing solution for those who are struggling like me.

In one of the instructional videos I watched, they commented that the collective determines how big the “swallows of air” are as they are being gobbled by your helicopter. Thinking in these terms helps.

The behavior of your helicopter changes as it loses altitude because (I believe) air is thicker closer to the ground than up high. With this in mind, when landing, you can drop that collective to zero and pull back the stick to bring your airspeed to zero (or near zero) above your landing target.

The copter will drop pretty fast, but not fall out of the sky. Watching the behavior, it will drop fast, and then have a sudden slowdown while approaching the ground. Even if you crash for practice purposes, watch the behavior of how the helicopter approaches the ground (the vertical speed in particular).

In my experience, you just have to raise the collective a bit to balance it out once the air thickens up (you will get a feel for when that happens with practice). It doesn’t have to be a crazy full collective compensation - just a moderate touch and the copter will respond pretty fast.

Get to a hover situation (like an air cushion under your copter) and then land by bringing the collective to zero.

I’m not using any assists., and so far, I’ve changed my crashes to quiet landings or at worst, embarrassing thuds. Now I know why my copilot looks so lifeless…he has seen too much.

Good luck!

[cowreth]

Hello

I’ve seen your second post. Congratz on finding the solution for your landing.

I’ve no magical solutions for the first part, but there’s one point I can bring to your own thinking, if I may.

It comes in one sentence :
When hovering, be it near the ground or higher in the air, there is not air moving though your blades.

When your up and fast, let’s say 100kt, then there’s a 100kt wind coming in your blade. This adds a lot to your lift. And during these phases, the collective becomes “less important” (kind of) because natural airflow will help your heli to fly. That’s the principle of autorotation. With such an exercice, you can feel and see how much this airflow counts.

When you’re hovering, there’s sometimes wind coming from the front. This is the best situation, but it will generally be less than 30kt of wind, which is insufiicient. More would put you in great danger for hovering. Sometimes, there no wind; or worse : wind coming from behind. The “lifting wind” is then inexistent. Even worse : wind can change; or an air mass can go through your position, changing the lift ability of your aircraft in the current context.

Then, only your collective will decide if your heli flies. Your reaction time must be on top, and your moves on the collective must be of more amplitude, because you have to react to these changes. Things get worse near the ground because of ground effect.

All these things apply to your landing. Hovering 2-8ft before landing is a point (but if you use an heli with wheels, you might want to use the wheels). But also “do that in a timely manner” is also very important. Timing is important, because aerodynamics of an heli relies on momentum and inertia, which decrease over time.

I hope it help. One last thing I would like to hint you at : vortex. That’s an other matter, but I do feel that by watching videos about VRS, you’ll have an even better grab at how heli’s aerodynamics work, and you’ll become an even better heli pilot. I said “an even better” because, based on your posts, I’m enclined to say that you’re doing great. And so, last but not least :

@MTBS3D

undeservedly so I believe

I respectfully disagree

Enjoy
Seb

[JasonMuc2112]

I guess the keyword here is “effective translational lift”. Unlike fixed wing planes, helicopters need more power when going slower, because the rotor is less effective in the self-induced downdraft. Read more about this and a lot of other interesting things here: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook

Edit: details on ETL are in chapter 2, page 22

[MTBS3D]

I respectfully disagree

The dead eyes of my copilots say otherwise.

This might explain my wild hover spin too. If my collector is aggressive and is capturing big swallows of air at a time, the moment I’m in a hover, the force of the main rudder could far outweigh the force of my tail rudder which is why my copter is spinning out of control no matter what I do with the torque pedal controls. This may be why I have to bring the collector down to zero to regain control of the helicopter when I"m in this wild spin.

The research continues!

[MTBS3D]

I will read this. Thanks for sharing!