investigating Cannot aerobrake with full flaps. What I experienced, what I heard, and what I found. I'm not pointing fingers so please help me understand

[Dr. Anti-Vehicle]

Yes, I'm the guy who got downvoted like whirlpool on reddit for this post. The only purpose I brought this up is to learn and get to the bottom of it, not to say "ED this is bug so fix it". Then if it does turn out to be a bug, this can be reported. But people are very defensive yet little evidence is produced to prove otherwise. So here I am, looking for insights so I would really appreciate any feedback so that I can keep testing. Please, I need your help.

 

TLDR with my Youtube video: When landing with full flaps, nose drops down immediately upon touching down regardless of speed, AoA, or stick input. While in half flaps, nose keeps up until the jet slows down even without stick aft.

 

Reference of real life video. Nose does not crash down even with speed brakes extended.

 

Now, you might ask: why do you want to aerobrake anyway if Hornet is not supposed to flare landing? You are right, but this doesn't mean I cannot question it, right?

 

I notice it on day one with this module but I didn't think twice. Until last year someone told me "It's because the wheel friction is modeled abnormally high to prevent it from sliding on carrier deck" so I thought weird but ok. Then a few months ago someone else told me "It's because full flaps has reverse ground effect bug with wheels on the ground. If you try landing with half flaps, you will be able to aerobrake". Then I tried it, and he was right.

 

There were many possible explanations given by other players and here are my thoughts:

1. When on speed AoA with full flaps the elevator is already near its full effectiveness and can’t hold the nose up no matter what you do. My test: The stabs trim position is nowhere near max rotation.
2. Full flaps causes little airflow over stabs so it cannot hold nose up. My counter point: when plane is still in the air, stick aft can still bring nose up easily.
3. Full flaps introduces greater pitch down rotation force. My counter point: on speed AoA trim already compensates that force. So the downforce at the rear and pitch down force on the nose stay balanced.
4. Wheel friction is higher with full flaps. My thought: this is possible because speed drastically decreased upon touch down while speed maintains relatively steadier with half flaps. I don't think it's because full flaps has higher drag because again throttle input neutralizes that the force if you fly a butter landing which was the case in my example video.
5. Reverse ground effect with full flaps and wheels on the ground. My test: in order to test it, I figured to do a butter touch and go and compare landing speed and take off speed. Because my assumption, and I hope it makes sense to you too, is that if throttle input is smooth and steady, plane should touch and leave the ground at similar speed with the same configuration. And the results are surprising.

 

The result is: full flaps take off require 15 additional knots compared the moment before touch down, but half flaps land and take off at similar speed.

Screenshot 1: 130 kn moment before touching down with full flaps

Screenshot 2: 145 kn moment after wheels up with full flaps

Screenshot 3: 142 kn moment before touching down with half flaps

Screenshot 4: 144 kn moment after wheels up with half flaps

 

To better elaborate this: with flaps full, there is some kind of force that is preventing lift off that requires more speed and more lift. And once plane takes off, you can slow down and maintain 130 kn right above the ground just like the moment before touch down. But with half flaps, the energy states are almost the same the moment before touching down and wheels up.

 

In other words: flying on speed AoA with full flaps with wheels just barely touching ground required much more energy than flaying 1 inch above ground. In reality, the only additional force with wheels on the ground is friction

 

What I also don't understand is take off speed with half flaps is almost the same as full flaps. But AoA is different so I can't say anything about it for sure.

 

I encourage people are are interested in this to test it with as many configurations (weight, AoA, stick input) as possible and let me know your findings.

 

For people who think current flight model is accurate, my question would be: are you saying that there is absolutely no way to do a wheelie during touch down with flaps full, stick aft, and steady throttle input? I think this is hardly the case in real life.

 

As we know Hornet flight model review is still in progress. I don't know if this is something ED is also looking into, or if the updated model with change this behavior.

 

Tracks are attached. Please note: the tracks were used to take those 4 screenshots, not the same tracks that created comparison video in the beginning.

Full Landing & Take Off.trk Half Landing & Take Off.trk

Edited October 10, 2021 by Dr. Anti-Vehicle
Title

[BIGNEWY]

I have passed on your comments to the team and they will check it as part of the flight model review. I can not promise any change however your observations / feelings will need to be verified by the data and pilot feedback. 

 

thank you