RunRyder RC
 6  Topic Subscribe
WATCH
 2 pages [ <<    <     1     ( 2 )    >    >> ] 1443 views POST REPLY
Scorpion Power Scorpion Power
HelicopterMain Discussion › dissymmetry of lift question
12-01-2007 11:42 PM  9 years agoPost 21
Bad Karma

rrVeteran

UK

My Posts: All  Forum  Topic

So, I'd like to know what makes you think that dysymmetry of lift will miraculously vanish simply by increasing HS?
It doesnt disappear, but its effect does get lower as you up the headspeed, or at least it gets delayed.

What you effectivly are doing is reducing the pitch necessary to give you the lift you want, as you decrease the pitch the difference between the lift generated on one side of the disk to the other decreases, imagine an infinite headspeed, it would have zero pitch all the way round, and as such its lift is equal all the way round (just an approximation)

Regarding RBS because you have a higher headspeed, but the max airspeed of the heli isnt going to really change, the lower speed (retreating) side of the disk is going to stall at a higher airspeed than before because the AoA of the blades is going to be closer than at the lower headspeed, closer to the helis top speed.
Surely Helicopter design companies would simply beef up the head, shorten the blades, and jack up the HS and be done with all of this blade flapping nonsense...
Its never quite that simple unfortunatly, its highly subjective, from one heli design and intended use to the next.

There are problems with just shortening the blades and beefing up the head too much, the extra load of running higher head speeds, means the whole rotor system needs beefing up, and this means weight, including the blades, blade grips etc etc.

Using shorter blades, but more of them, and reducing the RPM is often more desirable in certain cases, for example in miltary helicopters, more blades means lower headspeeds, longer endurance, and lower noise, and more lifting power available at the top end of the collective due to more blade area (as long as the engine power is there to support it).

Increasing the number of blades but keeping the same blade length allows you to run lower headspeeds, which can mean the heli can actually weigh less even with more blades, due to the rotorhead etc not having to be as strong compared to with higher headspeeds, the gain in weight of the blade can sometimes be more than offset by the loss in weight from the structure of the head, grips, spindles, and blades themselves.

Add on to that the advantages of running at a lower headspeed where more of the blade is going to be in laminar flow compared to at high headspeeds, laminar flow causing less drag compared to turbulent, so the more laminar the better.

PM  EMAIL  Attn:RR  Quote
12-01-2007 11:47 PM  9 years agoPost 22
#55

rrVeteran

Red Bluff, CA

My Posts: All  Forum  Topic

I hate these posts..........after going (and still going) through flight-school (in the Army) we have learned about ALL of these aerodynamic factors soooooooo far in-depth that is just amazes me on how many people will post WRONG information trying to act like they know stuff...

( NOT refering to the post directly above^)

here goes my explanation (in a TOTAL nutshell) I will use "DOF" for short.

DOF can ONLY occur when the helicopter has relative airspeed...or could occur at a hover IF there is a Wind of some degree.

DOF...occurs when the advancing half of the rotor disc produces more lift than the retreating half....AND that happens becuase the Relative wind is ADDED to the advancing blade and Subtracted from the retreating blade....

well THAT cause the advancing blade to flap UP and the retreating blade to flap DOWN...

so now throw in phase lag.......and you have maximum up-flap over the nose and Max Down-flap over the tail..

causing the helicopter to pitch up..... it really is that simple

so then from there throw in transverse flow effect and you will notice that the helicopter will pitch up and roll right on take-off.....or, going through ETL. (roll LEFT on our models)

Check!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 02:12 AM  9 years agoPost 23
Divot

rrVeteran

Mesa, AZ

My Posts: All  Forum  Topic

I hate these posts..........after going (and still going) through flight-school (in the Army) we have learned about ALL of these aerodynamic factors soooooooo far in-depth that is just amazes me on how many people will post WRONG information trying to act like they know stuff...
Attention
Son you have disrespected this forum, America, and the Army.
Now drop and give me twenty.....one...two....three................
are you trying to make love to the ground son...faster, faster, faster.

well gooooll leee

PM  EMAIL  Attn:RR  Quote
12-02-2007 11:22 AM  9 years agoPost 24
Bad Karma

rrVeteran

UK

My Posts: All  Forum  Topic

Out of order, that post didnt disrespect anything.

PM  EMAIL  Attn:RR  Quote
12-02-2007 02:09 PM  9 years agoPost 25
#55

rrVeteran

Red Bluff, CA

My Posts: All  Forum  Topic

Warrant Officers are usually not "dropped"....just one of the perks

Check!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 03:18 PM  9 years agoPost 26
Divot

rrVeteran

Mesa, AZ

My Posts: All  Forum  Topic

Warrant Officers are usually not "dropped"....just one of the perks
LOL...they probably just bench you from flying...that would be
so much worse then being "dropped"

PM  EMAIL  Attn:RR  Quote
12-02-2007 03:24 PM  9 years agoPost 27
SSN Pru

rrElite Veteran

Taxachusetts

My Posts: All  Forum  Topic

It doesnt disappear, but its effect does get lower as you up the headspeed, or at least it gets delayed.
Yep, in order for it to happen, the retreating blade needs to get close to or stall. That means a wind needs to be present or sufficient airspeed, in any direction. If you increase your headspeed, you increase the speed of the "wind" needed to stall the retreating blade.

Dysymmetry of lift won't ever disappear.

I can't wait to see how long this thread gets.

I DO think the original question was worded such that the poster thought they were thinking about settling with power and not dysymmetry of lift...

What say you?

Stupidity can be cured. Ignorance is for life!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 04:10 PM  9 years agoPost 28
Bad Karma

rrVeteran

UK

My Posts: All  Forum  Topic

It sounds like he's confusing two different things.

Settling with power or VRS can happen with a model, I've ran into them a few times, mainly with 400 class electrics, but they have so much of a power to weight ratio that they can actually get out of it on power alone, as can probably most model helis.

A large heavy scaler though may need to have some forward cyclic applied.

PM  EMAIL  Attn:RR  Quote
12-02-2007 04:21 PM  9 years agoPost 29
TachyonDriver

rrKey Veteran

Chipping, Lancs, UK

My Posts: All  Forum  Topic

Our models can get out of vortex ring/settling with power (same thing?) just by brute collective alone, but isn't it best to use a bit of cyclic too?

erm.... what does ETL mean, please?

Tach.

Little Spinning Bundle of Joy® DON'T DISS THE DINO!!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 04:27 PM  9 years agoPost 30
AirWolfRC

rrProfessor

42½ N, 83½ W

My Posts: All  Forum  Topic

Our models can get out of vortex ring/settling with power (same thing?)
Same as the thread title ? No, very different . . . . . In vortex ring state, the entire rotor disk has lifting problems, not just the retreating blade.

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-02-2007 05:18 PM  9 years agoPost 31
TachyonDriver

rrKey Veteran

Chipping, Lancs, UK

My Posts: All  Forum  Topic

Ah - so settling with power causes a pitch up due to procession?

Tach.

Little Spinning Bundle of Joy® DON'T DISS THE DINO!!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 06:16 PM  9 years agoPost 32
Billebob

rrVeteran

Tim-buck-2

My Posts: All  Forum  Topic

dissymmetry of lift question
can that come into play with our nitro helicopters? I remeber it from flight school but wasn't sure if it would come into play say on a slow approach with a 50?
That's one purpose of a swashplate. Think about it, the advancing blade gets it's pitch reduced over the side of the helicopter while the retreating blade is increased on the other side using the cyclic. If you don't have a swashplate then the head needs to be free to teeter and flap more to selectively dump equalising lift. Rotors pitch up and flap aft in forward flight if nothing is done.

http://www.yoshine.com.tw/e-yx24.htm

Read down midway to invention of the swashplate.

bb

PM  EMAIL  Attn:RR  Quote
12-02-2007 06:39 PM  9 years agoPost 33
#55

rrVeteran

Red Bluff, CA

My Posts: All  Forum  Topic

ETL: effective translational lift

but that is a whole nother conversation....

have you ever ridden in a Helicopter? do you remember that "shudder" on take/off? It's the helicopter outrunning it's own rotor vorticies....

you can actually see it too....look down at the grass...you will see disturbed grass ahead of you and slowly work its way back towards the tail and then dissapear all togther. that's ETL.

oh ya.....( when refering to the main rotor) because "Vortex ring state" ALSO is acutally a wind region on the tail Rotor when talking about LTE. (loss of T/R effectivness) 210Deg to 330Deg 0-35kias

Vortex ring state....is a "stage" of settling with power... it's where the vorticie on each rotor tip develops into TWO vorticies swirling in opposite directions.....it caused by the helicopter inablity to delfect the air from the main rotor downward due to the LARGE amount of air being pushed UP through the rotor system.

If only you guys could get ahold of FM 1-203 ( the Army's Helicopter aerodynamics book) you could understand soooo much of why our models do what they do.

still learning this stuff though...only 19

Check!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 07:04 PM  9 years agoPost 34
SSN Pru

rrElite Veteran

Taxachusetts

My Posts: All  Forum  Topic

That's one purpose of a swashplate.
The swashplate has absolutely nothing to do with Disymmetry of lift or Settling with power.

Stupidity can be cured. Ignorance is for life!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 07:07 PM  9 years agoPost 35
#55

rrVeteran

Red Bluff, CA

My Posts: All  Forum  Topic

true^ lol....

Check!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 07:32 PM  9 years agoPost 36
AirWolfRC

rrProfessor

42½ N, 83½ W

My Posts: All  Forum  Topic

If only you guys could get ahold of FM 1-203 ( the Army's Helicopter aerodynamics book) you could understand soooo much of why our models do what they do.
The updated version of FM 1-203 is here,
http://AirWolfRC.com/FM3_04X203.pdf

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-02-2007 07:55 PM  9 years agoPost 37
#55

rrVeteran

Red Bluff, CA

My Posts: All  Forum  Topic

Great post! thanks! If you guys have got some free time and would Really like some GOOD anwsers to your questions ( Much better than mine) take a look at that link that "Airwolf" just posted...

so the next time someone asks you about Dyss of lift, or ETL, or Transverse flow effect, or settling with power, or LTE, or RBS, or phase lag, or gyroscopic presscion, or ground ressonace....YOU can explain it and have good Understanding yourself...Plus- you can then understand why our models do some of the things they do.

Great post- Guys, take a look at that!

Check!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 09:36 PM  9 years agoPost 38
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

My Posts: All  Forum  Topic

Our models can get out of vortex ring/settling with power (same thing?)
No, very different . . . . . In vortex ring state, the entire rotor disk has lifting problems, not just the retreating blade.
Vortex Ring Effect and Settling With Power are indeed the same thing.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

PM  EMAIL  GALLERY  Attn:RR  Quote
12-02-2007 10:50 PM  9 years agoPost 39
SSN Pru

rrElite Veteran

Taxachusetts

My Posts: All  Forum  Topic

Gimbal,

Good job, now you've awakened the Beligerant monster...

Stupidity can be cured. Ignorance is for life!

PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 2 pages [ <<    <     1     ( 2 )    >    >> ] 1443 views POST REPLY
Scorpion Power Scorpion Power
HelicopterMain Discussion › dissymmetry of lift question
 Print TOPIC  Make Suggestion 

 6  Topic Subscribe

Thursday, October 19 - 8:48 pm - Copyright © 2000-2017 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online