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BGRing
3rd Apr 2007, 04:19
Ever heard of Wikipedia.
I Edited the Retreating blade stall article. to now include;

"It should be noted that at the onset of RBS. It is the tip of the Blade (Where Relative Airspeed is Higher) that stalls entirely. it has been noted that the tip will start to stall at around the 10 O'clock and be at greatest effect at 9 O'Clock and be unstalled by the 7 O'Clock position. It seems almost unlikly that this should happen due to the AoA being less at the tip from built in washout, but non the less, as you increase speed for an Airfoil such as comonly used in Heli, the Stall angel reduces. thus the tip is in stall. So the Root of the retreating blade is not stalled but in a very low lift condition."

Found here (http://en.wikipedia.org/wiki/Retreating_blade_stall#Causes_of_retreating_blade_stall)
under section Failure.

Should i change deleate or Dont give a .. feel free to Edit yourself. if You could make it clearer :} sure most of you could :)

Thanks.

PS if no one interested. just let this Thread Sink.:(

3rd Apr 2007, 06:02
Apart from spelling (unlikly, Stall angel, non the less) etc most of that section is wrong - especially the bit about needing an exceptional pilot to recover from RBS. Even the most basic textbook will tell you that reducing the severity of the manoeuvre, or just lowering the lever in level flight will help - to get the aircraft inverted would require active aggravation of the manoeuvre by the pilot.

The relative speed is at its LOWEST on the retreating side and as V squared reduces, lift reduces and the blade flaps down, increasing the AoA and leading to the stall.

The article doesn't mention the increase in vibration which is usually a precursor to RBS and lets the pilot know he needs to slow down.

BGring - I suggest you let someone like Nick Lappos or Shawn Coyle write for Wikepedia - leave it to someone who knows the subject properly.

BGRing
3rd Apr 2007, 09:17
what you see in my Post is what I added. If it is not in my post #1. It was not added by Me.

Do you disagree with what I added ?

PS thanks for the Spelling Check on My addition.

The relative speed is at its LOWEST on the retreating side(Highest at the Tip On that side eh) and as V squared reduces, lift reduces and the blade flaps down, increasing the AoA and leading to the stall.
Thanks for that.

I could have also added that;

"Due to Pilot corection of Dissymmetry of lift, coupled with the retreating blade flaping down (Increasing AoA) and overall Colective near max"

But i didnt. I only wished to confirm that when the tip stalls it is Failure. Untill then. it is Dissymmetry of lift. (Not counting Reverse Flow as this adds to Dissymmetry of Lift)

Thanks again.
Look forward to Nick and shawn adding to what I also Found to be incomplete. (see paragraph 5 of Analysis here (http://en.wikipedia.org/wiki/Dissymmetry_of_lift))

Here is an edit of my addition..

Comments please. Always redy to learn some thing new..


"It should be noted that at the onset of RBS. It is the tip of the Blade (Where Relative Airspeed is Higher on that side) that stalls entirely. It has been noted that the tip will start to stall at around the 10 O'clock and be at greatest effect at 9 O'clock and be un-stalled by the 7 O'clock position. It seems almost unlikely that this should happen due to the AoA being less at the tip from built in washout, and also having a Higher Relative Airspeed than the section of blade at the Root, but, as you increase speed with an Airfoil such as commonly used on Helicopters, the AoA at which stall Occurs becomes less.
failure is when the tip has finally stalled. not just the reverse airflow or low lift area near the center on the retreating side"

3rd Apr 2007, 19:10
BGring - a vital point you have left out is that the root of the retreating blade is not producing useful lift at all - it is in an area of reverse flow. Therefore the remaining area of the blade on the retreating stall has to operate at higher angles of attack to equalise the lift across the rotor disc.
You imply that the tip stalls first - contrary to what you would expect - this is not so because the root and inboard section have already ceased to produce lift and are in varying degrees of stall; this causes the blade to flap down and increase the AoA to a point where eventually the tip stalls. At this point there is very little of the blade producing anything but drag and vibration and the classic 'pitch up and roll towards the retreating side' occurs.
The stall angle of the aerofoil may well change at higher speeds but we are talking about the low speed side of the disc so that argument is inapplicable. More modern helicopters use aerofoil sections other than the 'standard' symmetrical aerofoil section and some have different sections along the length of the blade to reduce pitching moments and improve performance.
Quite why you see RBS as a 'failure', I don't understand, as no system or component on the helo has failed - it has just reached an environmental operating limit - change the environment and normal service is resumed on the rotor.
The language used in the article is not 'explanation friendly' and uses some inappropriate words and phrases more likely to be found in an academic or engineering book than a flight manual.
The quoted source is an FAA Basic Helicopter Handbook but I would be surprised if it says exactly (or even close to) what has been put in the RBS article.

BGRing
4th Apr 2007, 02:29
Hi Crab. Thanks again.
Listen. I have only Added a small portion to the entire Pre existing Section.
Please Elaborate on My particular Part.
here it is Again.
"It should be noted that at the onset of RBS. It is the tip of the Blade (Where Relative Airspeed is Higher on that side) that stalls entirely. It has been noted that the tip will start to stall at around the 10 O'clock and be at greatest effect at 9 O'clock and be un-stalled by the 7 O'clock position. It seems almost unlikely that this should happen due to the AoA being less at the tip from built in washout, and also having a Higher Relative Airspeed than the section of blade at the Root, but, as you increase speed with an Airfoil such as commonly used on Helicopters, the AoA at which stall Occurs becomes less.
failure is when the tip has finally stalled. not just the reverse airflow or low lift area near the center on the retreating side"

PS.

1/ reached an environmental operating limit not true. It has passed environmental operating limit and it is a failure if it Fails to produce enough lift to sustain level flight.

2/ BGring - a vital point you have left out is that the root of the retreating blade is not producing useful lift at all - it is in an area of reverse flow. Therefore the remaining area of the blade on the retreating stall has to operate at higher angles of attack to equalize the lift across the rotor disc.
this is in the appropriate section call Dissymmetry of lift. (Not created by me By the way, but I do wish to edit that section to. (see paragraph 5 of Analysis "http://en.wikipedia.org/wiki/Dissymmetry_of_lift", this paragraph is incomplete and misleading to me.

3/ You imply that the tip stalls first I was not Implying that. In fact I said that once the tip has stalled, it is Failure. this should imply that there are no other signs besides the effects of Complete RBS.

4/ The stall angle of the aerofoil may well change at higher speeds but we are talking about the low speed side of the disc so that argument is inapplicable. not true. Do the math at Vne. now look at your stall/AoA-V chart and revise. all blades have a stall angel. The argument is that if the pilot pushes the craft, IE forward cyclic to go past Vne, Then they are going to get an AoA sufficient to cause a Stall AoA on the retreating side. (Please don't mention why they blade reaches its stall angel, it is a variable. Crab, Ever heard of Flaping to Equality ? not a Pilot myself. but I have heard of it. hehe). The last part to stall will be the tip. and it will be tip to partially in and back to tip as the blade passes 10 to 9 to 7o'clock respectivly.

Thanks again Crab.
could I get you to re enlist me on to your team for a moment and review my post . Please take note to what I said I added. and what I will be willing to change.

PSS If you think there are other parts that need to be changed or added (That is parts i have not posted here but can be found at the link i provided here) you can do so yourself(I would be interested in you additions or edits). But for now. I am not changing anything that was already there, Not without solid feedback and Reputable Text reference and Total Edit being submited for Scrutiny, (Even then, Changing existint text is not what I feel comfortable with)As it is, I feel that the small addition that I did has not extracted from what was already there.

The language used in the article is not 'explanation friendly' and uses some inappropriate words and phrases more likely to be found in an academic or engineering book than a flight manual.
I found that if I read some sections fast I could get confused as to the meaning. (Due to Check and Self check of what was being conveyed) however the second time I read. I was able to get a better fly of the text and understand what was being conveyed. Some points I
disagree, and others, Like you you mentiond, I feel have been left out.

The quoted source is an FAA Basic Helicopter Handbook but I would be surprised if it says exactly (or even close to) what has been put in the RBS article.
Here is my addition.

"It should be noted that at the onset of RBS. It is the tip of the Blade (Where Relative Airspeed is Higher on that side) that stalls entirely. It has been noted that the tip will start to stall at around the 10 O'clock and be at greatest effect at 9 O'clock and be un-stalled by the 7 O'clock position. It seems almost unlikely that this should happen due to the AoA being less at the tip from built in washout, and also having a Higher Relative Airspeed than the section of blade at the Root, but, as you increase speed with an Airfoil such as commonly used on Helicopters, the AoA at which stall Occurs becomes less.
failure is when Finaly the tip has stalled, not just Prelude and contributing factors to a Requirement to the Greater AoA on Retreating side such as the reverse airflow areas or low lift/stall area near the Root of the Blade on the retreating side, Please revise "http://en.wikipedia.org/wiki/Dissymmetry_of_lift" as it Preludes the final Onset of Tip stall"



less than .5% of people who have seen this Thread have Bothered to post. (Don't expect more than 2%, but even then that leaves room for 3 more to jump in and add to it) thanks again Crab.

:)

Arm out the window
4th Apr 2007, 02:50
BGRing, while it's a good aim to try and ensure information on sites like Wikipedia is right, your corrections as evidenced by the posts on this thread are going to be confusing and of dubious content, in my opinion.

Also, without trying to be nasty, your spelling and punctuation aren't very good if these posts are how you normally write, so my suggestion is to leave it alone. There are lots of good texts around that have well-considered explanations of phenomena like RBS, so if you really want to fix that Wikipedia entry, get hold of one of them and come up with a paraphrased article that is concise, clear, correct and reads well.

BGRing
4th Apr 2007, 03:08
Sounds Good. Wish I could literate better. Spelling can be fixed.
When one edits an article . there are disclaimers to the effect.
Do not copy text from other websites without permission. It will be deleted.
and

Content that violates any "http://en.wikipedia.org/wiki/Wikipedia:Copyrights" will be deleted. Encyclopedic content must be "http://en.wikipedia.org/wiki/Wikipedia:Attribution". You agree to license your contributions under the "http://en.wikipedia.org/w/index.php?title=Retreating_blade_stall&action=edit&section=4" \l "copyright".

So I put it back to my first post. where I mention
feel free to Edit yourself. if You could make it clearer :} sure most of you could:)
But only the parts I have said I added.


There are lots of good texts around that have well-considered explanations of phenomena like RBS, so if you really want to fix that Wikipedia entry, get hold of one of them and come up with a paraphrased article that is concise, clear, correct and reads well.
If you could come up with a link for my own use I would be Grateful. but as far as adding to WiKi is concerned. I would be forced to Rephrase in my own way. (God help us) unless I could get Permission.

Thank you for contributing. to this thread. and for your feedback.

PS give me a couple of days. I maybe able to edit each post to fix Spelling and Punctuation error’s. (Or not : )

My refference to the addition to Wiki;
http://www.actechbooks.com/principles_of_heli_flight.htm
page 136-137
Effect of Increasing Airspeed on Stall Angle.

Any other books you feel I should read? any you have found to be of non Dubious Origins? Let me know :) Links to online resources would be a Gold mine to me.

Thanks again "Crab" and "Arm Out The Window"

4th Apr 2007, 06:55
BGring - now I am convinced you are winding me up......I did wonder at your first post why someone who thinks they should edit wikipedia would have such a bad command of the English language - your further posts have confirmed my belief that you are just fishing by posting mostly gibberish on a site normally populated by pilots (not unusual but your gibberish isn't in aerospeak).

I know Engleesh - I learn him from a book! (apologies to Manuel from Fawlty Towers):)

BGRing
4th Apr 2007, 09:17
:D Well done. You outed me. :D

Me be nx trikm ia Wable woble stik in de >>> Fli be d Sonic in de Advan sid. not de Stall de Retard sid.

(Translated, Crab; Your coments on the tell tale signs of RBS may actualy be just a Wobble from Advanceing blade getting close to or in Sonic range) Depending on your load at the time it could be one first or the other. RBS stall first if you are heavy where you may not get enough FF flight before you get RBS. Or, If you are light, you may get Sonic vibrations before RBS.

This will depend on individual aircraft and Blade tip Designs, amongst other things Pressure altitude and Temp. lastly as mentioned in previous paragraph. Weight (Disk loading)

Crab. Please dont worry about me. I will get to the bottom on my recent Beleifs and well.

Me be ment to go good so me be go now.


Dumb topic i chose.:(

Addition to Wiki has now been removed.( back to the way it was)