Jump to content

what is tail rotor breakaway


Recommended Posts

My instructor gave me a study guide for my commercial add-on and used the term "tail rotor breakway" It is in reference to the aerodynamics of the tail rotor. Any ideas what this means. I can't seem to find it in my books. I can't contact my instructor as he gone for a while. Thanks Also if you could give me a reference to find this information I would appreciate it.

Link to comment
Share on other sites

Tail Rotor Breakaway: Occurs when a tail rotor enters vortex ring state during sideward flight. For most US helicopters this would happen in left sideward flight.

I didn't know that could happen. I assume we're talking about something different than just generic LTE, which I think of (perhaps not correctly) as any condition when there's not enough tail rotor thrust.

 

I'm guessing that you'd have to be flying sideways pretty fast to get into a vortex ring state. Would that be correct?

Link to comment
Share on other sites

I didn't know that could happen. I assume we're talking about something different than just generic LTE, which I think of (perhaps not correctly) as any condition when there's not enough tail rotor thrust.

 

I'm guessing that you'd have to be flying sideways pretty fast to get into a vortex ring state. Would that be correct?

 

 

Lack of tail rotor thrust is generally considered lack of T/R authority, :huh: which will more than likely lead to LTE :( in either T/R vortex ring state or more commonly Main rotor vortex interference.

 

As for the speed required in left side ward flight, considering the pedal required (right pedal), and the resulting lower pitch angle and consequently lower "down wash", the easier it is to match the velocities and create a vortex ring state, so you wouldn't necessarily need to be going too fast at all. :o

Link to comment
Share on other sites

Never heard of tail rotor break away. Loss of tail rotor authority (LTA) is often related to drooping the main rotor. A aircraft operating at high gross weight in thin air (high DA) would be susceptible to this. Loss of tail rotor effectiveness (LTE) is a Bell product issue. The B206 series has a tail rotor that is not adequate for the task. BB

Link to comment
Share on other sites

"LTE an issue of Bell products" yes, I heard that too, but it sounds as if you mean that LTE is an exclusive issue of Bell, which is not true.

 

Chris (C of G) you fly currently the A109 Power right? I believe you know Dave T. (DPE) fairly well too? He told me at my CFi checkride he encountered LTE in his 109 twice (or three times if I'm not mistaken) on ONE day! :o

Since your ship has the best power/weight ratio in its class, I would presume they would build the tailrotor a little "stronger" (if you know what I mean)?

Any experiences from your side?

 

Philip

 

 

PS.: To refresh your memory Chris: last time we met was for a cold one on a beautiful Titusville afternoon on the Irish Pub's deck... Your former student from france - I forgot his name, I'm afraid - and Francois were there too.

I hope youre doing good! I'm now up here in PA - temps are more bearable up here! ;)

Link to comment
Share on other sites

Never heard of tail rotor break away. Loss of tail rotor authority (LTA) is often related to drooping the main rotor. A aircraft operating at high gross weight in thin air (high DA) would be susceptible to this. Loss of tail rotor effectiveness (LTE) is a Bell product issue. The B206 series has a tail rotor that is not adequate for the task. BB
If you want to go completely nuts on this subject, head on over to PPRuNe.

 

Let's keep it simple. You can have an array of things happen to cause an unwanted yaw, or allow one to continue.

 

One is just that you don't have enough pedal applied. Lets call this LTP - Lack of Tail rotor Pedal.

 

(From here, the unwanted yaw becomes "uncommanded yaw", since the aforementioned is really under your control)

 

So in the "uncommanded" realm:

Your helicopter (for a variety of possible reasons) may be unable to create enough tail rotor thrust to match main-rotor torque - the tail rotor is functioning fine, and is suffering no aerodynamic issues. Call this LTA - Lack of Tail rotor Authority. B206 series helicopters are somewhat notorious for this, especially the A-model. On the other hand, the R44 has a bias the other way - the tail rotor will, under (almost) all curcumstances be able to handle all the torque the main rotor can put out. In any helicopter you can head yourself into LTA by reducing/drooping the rotor RPM - for instance, at max gross in calm wind, a Schweizer 300CB will just hold heading with close to full left pedal at 2000 engine RPM.

 

(You can of course break something, and the tail rotor stops pushing - loss of thrust or loss of control. Let's leave this one aside.)

 

Next up are the aerodynamic reasons why yaw might begin or continue - main rotor interferance, tail rotor vortex, weathercock, the increased pitch angle requirements of the "congruent" crosswind. Note that none of these can be sustained individually, but they can happen in succession at the hover or in slow flight. All tail rotor-equipped helicopters are susceptable to these effects. - these are the things the FAA Rotorcraft Flying Handbook groups and labels LTE - Loss of Tail rotor Effectiveness. The FAA AC says, in essence, that LTE is an uncommanded yaw which does not subside on its own, and if left uncorrected can lead to loss of control of the aircraft.

 

So you might pull too much pitch in an Aircrane, get hit by a wind gust in a Schweizer, hover at too high DA in a 206A, or just be slow on the pedal at the end of a steep approach in your Enstrom. In each case you get a yaw you didn't want, and if you don't apply the proper corrective action (pedal first, airspeed up and power down as able and required), the yaw may continue and accelerate, at which point you probably won't be ruminating on whether you have LTA or LTE...

Link to comment
Share on other sites

:(

If you want to go completely nuts on this subject, head on over to PPRuNe.

 

Let's keep it simple. You can have an array of things happen to cause an unwanted yaw, or allow one to continue.

 

One is just that you don't have enough pedal applied. Lets call this LTP - Lack of Tail rotor Pedal.

 

(From here, the unwanted yaw becomes "uncommanded yaw", since the aforementioned is really under your control)

 

So in the "uncommanded" realm:

Your helicopter (for a variety of possible reasons) may be unable to create enough tail rotor thrust to match main-rotor torque - the tail rotor is functioning fine, and is suffering no aerodynamic issues. Call this LTA - Lack of Tail rotor Authority. B206 series helicopters are somewhat notorious for this, especially the A-model. On the other hand, the R44 has a bias the other way - the tail rotor will, under (almost) all curcumstances be able to handle all the torque the main rotor can put out. In any helicopter you can head yourself into LTA by reducing/drooping the rotor RPM - for instance, at max gross in calm wind, a Schweizer 300CB will just hold heading with close to full left pedal at 2000 engine RPM.

 

(You can of course break something, and the tail rotor stops pushing - loss of thrust or loss of control. Let's leave this one aside.)

 

Next up are the aerodynamic reasons why yaw might begin or continue - main rotor interferance, tail rotor vortex, weathercock, the increased pitch angle requirements of the "congruent" crosswind. Note that none of these can be sustained individually, but they can happen in succession at the hover or in slow flight. All tail rotor-equipped helicopters are susceptable to these effects. - these are the things the FAA Rotorcraft Flying Handbook groups and labels LTE - Loss of Tail rotor Effectiveness. The FAA AC says, in essence, that LTE is an uncommanded yaw which does not subside on its own, and if left uncorrected can lead to loss of control of the aircraft.

 

So you might pull too much pitch in an Aircrane, get hit by a wind gust in a Schweizer, hover at too high DA in a 206A, or just be slow on the pedal at the end of a steep approach in your Enstrom. In each case you get a yaw you didn't want, and if you don't apply the proper corrective action (pedal first, airspeed up and power down as able and required), the yaw may continue and accelerate, at which point you probably won't be ruminating on whether you have LTA or LTE...

 

 

John I agree that uncommanded yaw is a safe topic heading overall however a Bell Factory instructor told me LTE is a term Bell coined relating to the 206. Whether or not that is true I cannot confirm so I will stand corrected on that point. From what I recall the FAA calls uncommanded yaw vortex ring state (all of my theory books are packed as I am moving). BB

Link to comment
Share on other sites

I thought vortex ring state was a main rotor phenomenon (sp?)not tail rotor :blink:

 

 

Rotors, in any application, are subject to the same rules and regulations of aerodynamics. LTE, by FAA definition, can be T/R Vortex ring state, (which occurs when a t/r "downwash" velocity is overtaken by air acting in the opposite direction), Main Rotor vortex interference (when tip vortices disrupt the air flow of the T/R) and weather vane instability.

If you think about it, the t/r vortices can also rob the Main rotor of power, like in a tailwind, but the net effect is not as great.

Common misconceptions are what it takes to get vortex ring state. All helicopters get it at different configurations, and the same helicopter will get it with different airspeeds and ROD dependent on several factors, not the least of which are power applied and gross weight.

 

Can you think of a situation in which you can get main rotor vortex ring state with no rate of decent?

Link to comment
Share on other sites

Can you think of a situation in which you can get main rotor vortex ring state with no rate of decent?

 

How about hovering on a hillside with a strong updraft?

Link to comment
Share on other sites

Rotors, in any application, are subject to the same rules and regulations of aerodynamics. LTE, by FAA definition, can be T/R Vortex ring state, (which occurs when a t/r "downwash" velocity is overtaken by air acting in the opposite direction), Main Rotor vortex interference (when tip vortices disrupt the air flow of the T/R) and weather vane instability.

If you think about it, the t/r vortices can also rob the Main rotor of power, like in a tailwind, but the net effect is not as great.

Common misconceptions are what it takes to get vortex ring state. All helicopters get it at different configurations, and the same helicopter will get it with different airspeeds and ROD dependent on several factors, not the least of which are power applied and gross weight.

 

Can you think of a situation in which you can get main rotor vortex ring state with no rate of decent?

 

Landing behind a large aircraft (at the end of an approach)..?

Link to comment
Share on other sites

Can you think of a situation in which you can get main rotor vortex ring state with no rate of decent?

 

OGE above a mountain/hill or any other source of significant updraft.

 

Quick stop or flare downwind. You aren't in a decent, but the rotor is still "falling" into it's own downwash.

 

Those, or variations there of, are all I've got ATM.

Link to comment
Share on other sites

OGE above a mountain/hill or any other source of significant updraft.

 

Quick stop or flare downwind. You aren't in a decent, but the rotor is still "falling" into it's own downwash.

 

Those, or variations there of, are all I've got ATM.

 

 

Good suggestions, FauxZ, Bart and Bristol. However, I am not so sure you would get Vortex Ring State behind a heavy jet, but that doesn't mean you couldn't get caught in a Vortex. I wouldn't see that as the same thing, but a hazard never the less. And you don't necessarily need to be down wind to get it in a quick stop, either. Good to see the standard "low airspeed, High Rate of descent, and power applied" can be seen form outside the proverbial box. :P

 

Has anyone experienced Vortex Ring as a high speed phenomena? :huh:

Edited by C of G
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...