Mushing in Helicopters

Welcome back to Helicopter Lessons in 10 Minutes or Less! I'm Jacob and this video covers Mushing.

If you’re interested in my eBook study guide, check it out here:

To be useful to the airfoil, airflow needs to impact inside the critical angle. That is, the Resultant Relative Wind (RRW) needs to be below the chordline and inside the critical angle to produce lift. Broken down further, there are 5 regions of the airfoil: Positive Lift, Positive Stall, Negative Lift, Negative Stall, and Reverse Flow. We need airflow specifically in the positive lift area of the airfoil for the blade to produce lift. Anything else and the helicopter doesn't produce lift and falls out of the sky.

In straight and level flight, the rotor system is predominately operating in the positive lift region. The combined effects of forward airspeed, induced flow, and angle of incidence put it there. The same holds true as a helicopter enters a dive profile. The aircraft is traveling towards the ground and the RRW is in the critical angle. But if I pull back aft cyclic too quickly or aggressively my profile changes but the helicopter's momentum still carries it in the same direction. The RRW shifts underneath and into the Positive Stall region of the airfoil. The aircraft is now mushing. You may feel feedback in the flight controls and the aircraft continues its descent despite a pitch-up attitude.

This was talked about heavily by WW2 fighter pilots during strafing runs in their planes who barely recovered in time or witnessed others not so lucky. The same holds true today for planes and helicopters. Today the FAA uses the term CFIT (Controlled Flight into Terrain) to describe a flight conditions where aircraft strike the ground without any mechanical issue. Mushing is not a mechanical failure. Its an aerodynamic condition.

So how do you recover? The tendency is to clam up and apply more aft cyclic. But this prolongs the stall and can make it worse. The only way to get out of mushing is to apply forward cyclic and rotate the RRW back into the positive lift region of the airfoil. You should start to feel more authority with the cyclic and begin to slowly reapply aft cyclic as needed to recover. But the best fix is prevention. To avoid mushing, use a slower, more progressive aft cyclic in dive recoveries. Since its the speed of aft cyclic application, just avoid the rapid, aggressive nature. All that goes to say you should always allow enough altitude to recover from any maneuver. Keep in mind that at higher airspeeds and Pressure/Density altitudes, recovery from a dive increases in both time and altitude required. Think ahead. The worst time to realize you can't recovery is while you're trying to recover.

That wraps up mushing. It is a temporary stall condition predominately experienced during aggressive dive recoveries. Thank you for watching. Be sure to hit like, subscribe, and leave a comment.

As always, I'm Jacob. Safe flying.

[billbryant]

From a former Mi-24 / HIND scientific & technical intelligence analyst for the US Army Foreign Science & Technology Center [ FSTC ], now the National Ground Intelligence Center [ NGIC ] in Charlottesville, VA. I was the principal technical analyst on the Mi-24 / HIND during the 1970s, and the sponsor of the Catch 24 Conference at FSTC in 1976 addressing the air-to-air combat potential of the Russian Mi-24 / HIND helicopter. This conference was well attended by US Air Force and US Marine aviators, both rotary & fixed wing.

This conference eventually culminated in the J Catch Trials in 1978 of the Mi-24 / HIND air combat potential against both rotary & fixed wing US aircraft - with & without complimentary ground based air defense support. The numero uno lesson learned in Tactical Air Combat Maneuvering [ TACM ] in a helicopter is to aggressively pull collective first, then apply aft cyclic to avoid mushing. Then, add a right or left turn to climb out.

Cheerz,
bb

[OculusQuestFun]

You know what I enjoy most about your delivery? You don't assume the viewer knows more than basics. In other words, understanding what you're getting across is easy because of how you lay out the information.

[bbjbnb]

An interesting story Jacob... 35 years ago when I was young and dumb (now I'm just dumb), I was goofing off in my Aeronca L-16A when landing one day. I was at or over gross weight as I had a large man in the back seat and at the time, I was over 250lbs... and I was making a very steep approach and pulled hard at about 50' above the runway at about 90mph. I definitely felt the wing, "let go" and all lift was lost and the plane was mushing toward the ground. Thank goodness for the big wing of the champ and when I let off the pressure on the stick, lift was regained about 5' from mushing into the runway, which based on the descent rate would have probably broken the airplane and our backs! Never did that again, but am just telling this story as it is not only fighters that can experience this effect. I guess some would call this a high speed stall, but I like the explanation of mushing and it certainly felt like that. Love your videos. Thanks for all your expertise and time.

[Oz_Gnarly_One]

Just when I thought I had a good understanding, from your previous videos, you add another one to remind me I still have more to learn. Thank you for these videos.

[glennwatson]

Definitely been finding your videos useful with converting from PPL fixed wing to helicopter. Felt instantly at home in a helicopter which never fully felt in the fixed wing. Thanks for making the videos.

[dudenameddylan]

Just passed the SIFT on Monday with a 58. As a prior medic its been tough learning all of this from scratch but your videos help a lot!

[steppaul]

It's like a really fast and aggressive settling with power situation. Great video, great explanation.

[Knewman]

I always thought mushing was when you were trying to recover from a dive and needed help from a team of Siberian Huskies to pull you through. 🤣🤣

Thanks for the awesome content.

[trespeacock]

Hey Jacob, it’s been a while. I just wanted to drop in and say THANKS. Your videos helped me immensely with passing the SIFT. Fast forward to now, I’m at Rucker in common core hold. I will continue using your videos to learn and refresh. You are doing great things for aviators and future aviators!

[ltauzzy]

Awesome to see you back! I missed your videos!

[Delatta]

Interesting topic and instruction. I was a Utility guy and I think this phenomenon should be taught to the Army UH population more often. An interesting rule of thumb is at high gross weight, 90 kts IAS, 60 degree bank angle, the aircraft doubles in weight and will loose altitude. It’s fatal at low altitudes.

[danteishbak]

Excellent posting, thanks for share it.

[simpleFnK]

Hey sir, great explanation! So what’s the difference between mushing and autorotation

[DeathPredator]

Is this not really simply a specific case of settling with power, wherein momentum is exceeding lift?

To be distinct from vortex ring state by not being characterized by disrupted airflow (for a period of time within the correction, anyway), though it threatens to rapidly become so.

[SkyBaum]

Think 💭 ahead! Key point in flight as well as many aspects in life!

[MitchG]

I'm sure you are familiar with the g loading chart in the -10. Do you know if the g loading chart is to prevent structure damage to the airframe or to prevent pilots from getting into mushing? (Positive G only) What happens if you exceed the positive g limits from the g loading chart?

[nighthunter]

What is the different between the mushing and jackstall?

[TrickyFitz]

You came back just when I finished watching all your old videos. Perfect timing!

[briankeith]

Is mushing ever a problem during an autorotation deceleration ?

[AeriaGloria]

The Mi-24 suffers bad from this becuase of its speed, weight, and it’s wing behind the rotor that stalls at similar AOA as when the rotor stalls. The manual mentions giving not only forward cyclic but decreasing collective 1-3 degrees.

It’s simulation in DCS seems to agree with this. Couldn’t reducing collective to un stall blades also be part of recovery for other helicopters?