Leaning to right ?

[exhogflyer]

Yup, not me but the heli! I've noticed when my 450SEV2 is in a steady hover there is a distinct "lean" to the right. Being a noob I wasn't sure if something is not right but if I try and trim it out then I need to hold right stick so it doesn't walk left.Is this just equipment balance or due to tail rotor balancing the torque and causing a lean? Thanks guys!

[Khaag]

Tail rotor. In additon to countering the torque generated by the main rotor, it pushes your heli to the left. You have to lean right to counter this force.

[salrica]

http://truebloodengineering.com/modu...howpage&pid=10


http://www.rcheliwiki.com/Center_of_gravity

http://www.raptortechnique.com/cg.htm

[exhogflyer]

Thank you guys! I really love this site and the brain base here, without it us noobs would be smashin' stuff everywhere! Just a note I HAVE perfectly leveled my swash, she does hover without trim ( I was amazed how much of a diff it made!).

[helihaven]

A raised tail will eliminate hover lean https://www.helifreak.com/showthread.php?t=369598 towards the last half of the thread....

[extrapilot]

HH-
A raised tail that does what you say it will here will increase lean when inverted, waste rotor power, and create constantly changing torques in roll during flight. Seems more reasonable on net to accept a couple degrees of chassis lean…

[helihaven]

wow...not the findings i have seen from actual use of one...or others using it...wow im amazed...who woulda thunk it?

[extrapilot]

Aero engineers, helicopter designers, people who can add, those sorts of people.

[helihaven]

and not people who have actually DONE it and USED it...wow...i'll stick with the latter thank you!

[extrapilot]

Do or use whatever you want. The point is not to convince you of anything, but to inform the OP of the implications of that option.

[helihaven]

from things you have read but not personally experienced? nice advice.

[Luvmyhelis]

So basically you are calling the engineers of virtually almost every commuter helicopter and military precision flying attack versions with designed in raised tails that are designed to eliminate offset torque lean stupid????

I am speechless.

[extrapilot]

Having never thrown a wet giraffe from a floating canoe, I can tell you with 100% confidence that opposite/equal force still applies, and that both I and the canoe will accelerate opposite the (now angry) giraffe. That is the wonderful thing about physics- it applies consistently… to wet giraffes and to rotor systems…

I will make this as simple as I can. In upright hover in still air the thrust vector must cancel the translational force of the tail rotor. For a conventional 450, that means the tail rotor is blowing the helicopter to its left, and the main rotor must tilt right to offset this. The rotor is non-teetering, so the rotor tilt torques the airframe in right roll, so the chassis leans right. Great, we all get that. You mount your tail rotor higher (above the CG), so that its anti-yaw thrust produces an equal/opposite (LEFT roll) torque via the tail boom. Net result, less (or no) lean in the airframe in upright hover.

Problem: Inverted flight. Hard to visualize, so consider just upright hover into a negative punch with NO lateral motion. What changes in the scenario? Rotor rotational direction? Nope. Yaw torque direction? Nope. Translational thrust resulting from anti-torque? Nope. Arm/position of the tail system relative to the CG? Nope. One thing changes- the direction of flow through the main rotor. This has a very important implication; the rotor must now tilt LEFT to offset the translational thrust blowing the helicopter to its left. I hope that is clear?

If the rotor tilting right causes the airframe to torque right in roll, what do you suppose happens when that same system’s rotor tilts left? You guessed it- the airframe is torqued in left roll. But, nothing else has changed- your tail rotor is still applying torque in LEFT roll. So the setup that was helping to offset the chassis tilt in upright hover is now doing the opposite.

[extrapilot]

Originally Posted by Luvmyhelis

So basically you are calling the engineers of virtually almost every commuter helicopter and military precision flying attack versions with designed in raised tails that are designed to eliminate offset torque lean stupid????

I am speechless.

For the benefit of those who know the difference between ‘right’ and ‘write’, it might be better if you did remain speechless (well, writeless, to coin a forum term).

There are practical considerations for all machines- especially for ones that tend to chop off the heads/arms of passengers, or which carry cargo or operate from unprepared pads (read: obstacle clearance). You will find that where this stuff is mitigated via NOTAR or Fenstron, the countertorque is always at or near the CG- silly, low performance machines like the Comanche- for example. There are tens of other reasons for the placement of a rotor- all of which are WAY outside of our context (ie. noise from BVI, FOD avoidance, radar shadow, deck angle in flight vs hover, cost of re-engineering/certifying a new design, etc). Then there are design constraints, as with the Blackhawk- where a packaging requirement (C130) caused the designers headaches with longitudinal CG. They required additional lift at the tail, so a canted rotor was employed. That is difficult to implement IF you also want a vertical stabilizer, unless you put the rotor at the top of the tail. The canted rotor also happens to increase obstacle clearance height, etc.

You will also find- the primary issue with the raised-tail as an anti-lean strategy in RC acrobatic helis is that its intended effect is reversed when the main rotor flow is reversed. As there are no full scale machines presently capable of sustained inverted flight, it is not a concern for the designers, and due to the discomfort of inverted flight, I suspect the passengers wouldn’t care too much about a 5deg lean even if it was…

If you want to learn about high-performance tail designs, have a look at Shawn Coyle’s work. Or read anything Nick Lappos has written- you know, the aero engineers and test pilots who design the machines. Believe it or not, there are actually people in the world who know more about this subject than you, no matter how prolific your posts.

[helihaven]

Yup I'm certain you have never thrown a wet giraffe from a floating canoe...nor flown a raised tail either...You are just gonna argue a point to death even when others have seen the exact opposite of what you quote with their own eyes...just like in the tail slider thread...I had an ex-wife like that once...LMAO

[Luvmyhelis]

[nmdesertracer]

[cpmboy]

[helihaven]

Not to continue to beat a dead horse...or to throw any other large mammals from a floating canoe, the OP asked what caused the right side hover lean in a heli, and what he could do to compensate/correct or eliminate it. I told him his solution was an elevated/raised tail assembly, which i use on all of my helis, and have built for friends of mine for the same issue.

"extrapilot" posted HIS opinion on the matter, stating that it would do just that (thanks for at least stating that extrapilot, others have even argued THAT point) but that his perceived liabilities of the raised tail werent worth the effort of eliminating the lean in upright hover, and pretty much just live with the lean and deal with it. He has his opinion...and I have mine. His views, evidently from what he posted are based on everything OTHER than what I have experienced in actually FLYING with a raised tail.

I will agree that there may be limitations and downsides i have not experienced yet, but the ones he described have just not materialized as far as I am able to notice, as well as "lovemyhelis" who has 2 of my tails on his 450's and has asked me to make him one for his 600 as well. If they robbed power (how you come up with that one baffles me BTW) it is so miniscule an amount that i have not been able to measure it. I do admit one "downside" to them and that is extra weight, but all of my helis are stretched, larger motors, larger blades, higher cell counts/voltage than stock, so its really a benefit as I see it, but on just a stock heli it would require a heavier battery or well thought out all the way forward placement of all components possible.

To have worked at perfecting (and still not there) my tail assemblies, and have everyone who has one of them to continually tell me how well they perform, then have someone who HASNT had one, tell me everything i have done is for nothing is like me telling HIM that I have known plenty of people with an engineering degree, but that most engineers while being able to explain in graphic detail HOW a light bulb works are completely incapable of screwing one into a socket....

[extrapilot]

Everything stated was established in rotary aero/physics decades (or centuries) ago; no opinions involved. I realized there is a simpler way to think about this problem, however, so I thought I would post it while it is still in my mind-

For a conventional TRex-type machine: To remain in a stable hover in still air, the main rotor must dip in the direction the tail rotor is blowing. This holds for all orientations, upright and inverted, for any observer.

As the pilot, upright tail-in, the tail is blowing to your right, so the rotor must dip to your right. Inverted tail-in, the tail blows to your left, so the rotor must dip to your left. Since the chassis is closely tied to the rotor in our designs, it will naturally lean in the direction the rotor dips. This is the basis of the OP’s query.

For your raised tail approach- you placed the tail rotor above the CG, so its thrust also creates a roll torque. As before, upright and tail-in, the tail is blowing to your right, so the rotor is tilted right, so the chassis leans right. Your raised tail twists the chassis counterclockwise, reducing the (right) lean to near zero.

Inverted and tail-in, the tail is now blowing to your LEFT, so the rotor is tilted left, so the chassis leans left. Unfortunately, your tail design is STILL twisting the chassis counterclockwise- opposite the direction required to correct a LEFT lean.

That is as simple as I can make this. I don’t know why it seems complicated or magical. As one cannot prove a negative- perhaps you will send me the spec; I will machine a tail, and have a local pro pilot do the test flight.

And please, let’s limit the drama. I never anything like “everything you have done is for nothing.” None of this is personal mate- Im just relaying facts. If your goal was a level chassis in upright hover, you have achieved your goal, period. But, as I suggested to the OP, there are downsides to a raised tail that are significant, especially for an acrobatic heli. I can’t think of many factory 3D machines that ship with a raised tail; actually, Im not aware of any.

Regards,