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Base to final, cross wind stall

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Base to final, cross wind stall

Old 10-28-2014, 03:26 PM
  #76  
Rob2160
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Originally Posted by Boomerang1
Hi Rob, yep I can see where you are coming from.

To answer the first half of your question:

Travelling north - AS -100kts, GS - 40 kts

east - AS - 100kts, GS - a bit tricky to calculate. Assuming you are going with the flow (pun intended!) & not cranking in full rudder & a heap of aileron trying
to maintain course (that's why we don't fly 152's in 60 kt winds!) and ignoring the fact that the ground speed is constantly changing through the turn, at the point
when the plane is pointing east the ground speed would be 100kts from west to east but the plane would also be drifting north to south at a speed of 60 kts
(the wind speed). The course over the ground would be an angle, NW to SE.

South - AS 100kts, GS - 160 kts

West - AS 100 kts, GS - same situation as east but drifting from NE to SW.

The second half of your question.

Yep, of course the plane could complete it's 360 deg turn although (and your from Sydney)
if you started the turn (assuming constant rate of turn) over Sydney CBD, you would finish
your turn over the airport as the plane would be drifting south.

BUT (it's a big but) that would be a gentle turn. A 30 deg bank in a full size aircraft is not a gentle turn, it's an I want to go over there now turn. (not quite a watch
the wings don't pull off turn though). In a TIGHT turn from into wind to cross wind I believe the airspeed would drop until the plane regains it's equilibrium (probably the first time I've typed that word) with the moving mass of air.



Al brings up a good point about the airflow being 'straight from the front'. The key words are coordinated flight. Full size gliders usually have a length of wool taped to the canopy.
It's not a Christmas decoration, it's there to tell the direction of airflow relative to the glider. The name of the game is to do a turn while keeping the wool pointing straight back along the canopy. It's difficult until you get the technique correct. Start hooking into careless turns & the airflow over the canopy (and the wings) will be anything but the right direction.

My last ride in an open cockpit biplane was an AgCat on floats. I think most of the wind was from the 450 HP Pratt & it was certainly coming from the front!

John.
Hi John, You raise some good points and I'll add comments.

Yes the airspeed does reduce in a steep turn - not due to the wind though, it is usually due to increased induced drag from the higher "G" - adding power in the turn helps but very few light aircraft can sustain a high g turn and also maintain airspeed.

The point about the string on the glider, The primary reason for this is to help you fly in balance, Aileron deflection gives you adverse yaw which can be corrected with rudder. The string shows any imbalance in your flight very accurately. Adverse yaw is more pronounced in gliders due to the generally greater wing span (force x distance)

I agree with your comments on the speeds throughout the turn, that was my point and you are right, the aircraft will drift with the wind while flying an even circle.

RobinLeblond - that is a good article. I read through it and it covers just about everything on the topic.

The downwind turn problem myth originated when people started to confuse "steady state - unchanging winds" with what actually happens in the real world. As others have pointed out, there is usually a wind gradient near the ground, it can be calm on the ground and blowing 30 Kts at 1000 feet.

Take off in nil wind, then climb into this 30 Kts of wind, your airspeed will change - no question about it. If you happen to be turning and climbing and the 30 Kts is a tail wind then your airspeed will drop.

Also flying downwind, with a 30 kt tailwind..then you turn base and on final descend out of the 30 kt wind you will quickly lose indicated airspeed as you drop into nil wind.

These are very real scenarios that can and do occur and cause accidents and crashes in RC planes.

Separating it to pure theory, in a steady state unchanging wind, there will be no effect on the airspeed as the aircraft completes a 360 degree turn.

Bevar, cool rating to have at 18!. I had 500' waiver at 23 but rarely used it.

All theory aside. If your plane stalls, or begins to stall, immediately relax the elevator. Pulling too much elevator is the only thing that causes the stall. Reducing the elevator will allow it to recover. Adding power helps.

Safe flying guys, I wish you all no crashes, over and out.

Last edited by Rob2160; 10-28-2014 at 08:35 PM.
Old 10-28-2014, 03:44 PM
  #77  
mr_matt
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Originally Posted by RobinLeblond
Matt, I really didn’t want to create or feed such a monster; I just found this article by “educating myself” and thought that some of you may have interest in it…
Sorry Robin I was not singling out your post, I did not even read it until now, it is quite good. I actually have learned a lot from downwind turn threads over the years (most of it relating to group psychology). I was just stating that this thread went in that direction almost immediately.

I like the comments about elevator stick position, angle of attack and stalling, I think this is a big help in teaching,

The other stuff about airspeed, groundspeed, momentum, turbulence, bees on a train (or in a jar), well not a lot of new ground to cover their (no pun intended)
Old 11-01-2014, 09:33 AM
  #78  
David Gladwin
 
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Here is an extract from some notes I wrote for RCJI some months ago on handling crosswinds. It may help some.
In the circuit.

If remaining in, or joining, the circuit, then due allowance needs to be made to compensate for the track alterations created by the cross wind component. During the turn onto the downwind leg, the crosswind (using the example for take-off) will blow the model away from the runway so widening displacement from the runway. If the model is now flown with a heading parallel to the runway the track will be away from the runway, further increasing that displacement. As an example, if the crosswind component is 10 knots, the downwind turn takes 10 seconds and the downwind leg takes a further 20 seconds, the total displacement from the ideal downwind track is equal to 30 second of crosswind component. A 10 knot x/wind is about 15 feet per second so those 30 seconds of flight will result in displacement of 450 feet, or 3 runway widths, quite significant. To prevent that displacement the heading of the model must be altered towards the runway to compensate for both the crosswind and downwind leg displacement. With a crosswind blowing the model away from the runway the heading can be further altered into wind to anticipate the effect of the wind in the final turn.

That Finals Turn.

The final turn in crosswind has caused the demise of more than one model jet due to failure to anticipate the situation.

If the crosswind is blowing away from the runway then we have a safe condition. The crosswind will tend to tighten the turn radius for a given angle of bank meaning that in general a lesser bank angle is need than in still air for a given turn radius. However, if the crosswind is blowing towards the runway the effect of the wind is to increase the turn radius meaning that to achieve a still air turn radius more bank angle is needed and this is a potentially dangerous situation. If a tighter turn radius is required more bank will be needed and greater bank angles increase stalling speed. Stall speed increases with 30 degrees of bank by just a factor of about 10 % whereas a bank angle of 60 degrees the increase is almost 50 % more than in level flight. Add the illusion of a high flight speed due to what is now a tailwind and the higher bank angle needed to make the turn onto the center line, more than one jet has stalled, flicked and spun in ! So downwind heading corrections to anticipate the finals turn bank requirement can add considerably to safety when turning onto finals.

David G.
Old 11-01-2014, 02:02 PM
  #79  
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I can see what David is saying here but the second paragraph has me stumped.

With my interpretation of what's written this is the exact opposite of what I would expect,
a picture would say a thousand words and, judging by the second post on this thread, save
a lot of space!

The example using a '10 second turn' is interesting (perhaps reflecting his career in full size
aviation), at 80 mph almost 400 metres is covered in that time. To me a 3 second turn through
90 deg sounds like a nice, gentle turn with a model. We often just hook the model around much
faster than that. We dart around in that big, floating sea of air at RATES so high that models don't
get time to stabilise & 'go with the flow'.

The other stuff about airspeed, groundspeed, momentum, turbulence, bees on a train (or in a jar), well not a lot of new ground to cover their (no pun intended)
Strange Matt, you used the word that I believe has a lot to do with a lot of model crashes, momentum.

We dart around, upwind, downwind, changing direction up & down at RATES much faster than is possible
with full size aircraft until recently. Check out the video of the F-22 at around the 2 minute mark. As you
can see it's travelling vertically up, inverted, no forward speed, no VTOL thrust - nope, that points down.

Magic? A US classified anti gravity device? Bees in a jar?

http://www.youtube.com/watch?v=FUdt6ZSWUsI

I like the comments about elevator stick position, angle of attack and stalling, I think this is a big help in teaching,
On the F-22 it has enough control power & authority, it's strong enough so the wings don't pull off & the pilot has the necessary life
support systems to hold him together that he can force it into attitudes where momentum carries it to wherever it wants to go regardless
of what the laws of aerodynamics or gravity say.

I think it's the same with models. We have no feedback besides visual (and to a very much less degree, sound) but some of us ham fistedly
haul on the controls, the resulting aircraft attitude relative to the airflow (driven by momentum) leading to 'mysterious' stalls & crashes. We don't feel buffeting, the
stick forces don't get heavy, we don't have aids like stick shakers to tell us doom is approaching (although the guy I'm teaching to fly APPEARS
to have a stick shaker on HIS radio!), the powerful servos just drive the elevators to 45 deg deflection just as they are told to do.

Stall, snap, crash.

The message? Simple. Carry a little extra speed on approach & try to turn gently & steadily when you have no altitude to save you from mistakes.

John.

Last edited by Boomerang1; 11-01-2014 at 02:06 PM.
Old 11-01-2014, 04:52 PM
  #80  
rcpete347
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HI David, I agree with your last paragraph.
Also I was flying with flight mode in the flap switch. For mode 1, no flaps, I had 30 points of up elevator and 30 points of right aileron, for level flight. For mode 2 and 3, all was at 0( flaps down for landing.

Rcpete
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Old 11-02-2014, 12:02 AM
  #81  
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If the second para seems illogical to anyone they should remember that we are turning the aircraft from the downwind position to a fixed point on the ground, the touchdown aiming point. The greater the tailwind component in the turn ( a crosswind relative to the runway heading) the higher the ground speed which will increase your turn radius, relative to that fixed point, for a given angle of bank. The greater the crosswind, the more tailwind in the turn and if no allowance has been made and you are too close to the runway c/l the more bank will be required to obtain the turn radius to roll out on the centre line. The more bank used to increase the turning rate, if airspeed is not increased, the nearer to the stall you get !

Of cours, the reverse is true if the finals crosswind is a headwind on base turn, the headwind effectively tightens the turn meaning less bank, (therefore less pitch rate , less increase in angle of attack, greater margin over stall point,) is required for a given radius relative to the TD point. Safer !

Full size gliders, which use speeds not dissimilar to ours are still crashing because they get this wrong, they find themselves too tight, maybe too low also, on the turn to final, use more bank than normal to tighten the turn, fail to lower the nose to conserve or increase speed, use a bit of rudder to "help" it round ( introducing the yaw element, essential for a spin) and off it goes into the spin, usually too low for any chance of recovery.

David.

Last edited by David Gladwin; 11-02-2014 at 12:36 AM.
Old 11-02-2014, 01:43 AM
  #82  
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Interesting points and I would say all of GA is susceptible on the overshoot to final in an abbreviated pattern.
Old 11-02-2014, 02:55 AM
  #83  
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Thank you David, that makes sense.

The terminology 'crosswind blowing away & towards the runway' had me confused.

John.
Old 11-02-2014, 07:27 AM
  #84  
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Originally Posted by Boomerang1
Thank you David, that makes sense.

The terminology 'crosswind blowing away & towards the runway' had me confused.

John.
Actually Tail Wind or Head wind on Base would have been better.

Any way there is another Thread I Believe where a gentleman is working on a Jet Telemetry system that reads out every thing U need to know about your plane to an IPhone or an Android. My contention is with Telemetry (which a lot of radio systems know have) one should be able to set up some kind of warning when a planes actual Air Speed (Not perceived Speed from the ground) Gets be below a set Air Speed the system gives, (Hopefully an oral warning) Like Air Speed Air Speed Air Speed. Just a thought.
Old 11-02-2014, 08:02 AM
  #85  
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Originally Posted by HoundDog
Actually Tail Wind or Head wind on Base would have been better.

Any way there is another Thread I Believe where a gentleman is working on a Jet Telemetry system that reads out every thing U need to know about your plane to an IPhone or an Android. My contention is with Telemetry (which a lot of radio systems know have) one should be able to set up some kind of warning when a planes actual Air Speed (Not perceived Speed from the ground) Gets be below a set Air Speed the system gives, (Hopefully an oral warning) Like Air Speed Air Speed Air Speed. Just a thought.
That would be useful, but you can stall at any airspeed. An AOA alarm might be even better. Or even a stall alarm, maybe with a horn, like the full-scale people have.

One attraction of an airspeed indicator for models would be that it might help lay this downwind-turn nonsense to rest. When people can turn into the wind, balloon up because they're still on the elevator, and see the airspeed dropping, rather than increasing, that ought to do it.
Old 11-02-2014, 09:56 PM
  #86  
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LOL, why all of the analysis? Just fly the damn thing. Wing down into the wind and land it.
Old 11-02-2014, 11:07 PM
  #87  
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iF YOU DON'T LEARN FROM YOUR MISTAKES, how do you get better.
Rcpete
Old 11-03-2014, 03:23 AM
  #88  
Ron Stahl
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Pete, it's very easy to remember ; wind in your face is working against you landing crosswind. You need to keep the speed up on the cross wind turn to final and start the turn wider, wind from your back just the opposite. The plane got too slow and it stalled. Nothing more nothing less. BV discussed this years ago on his site about guys getting too slow in a crosswind and crashing.
Old 11-03-2014, 05:47 AM
  #89  
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Originally Posted by AndyAndrews
LOL, why all of the analysis? Just fly the damn thing. Wing down into the wind and land it.
That's after U have turned to Final the Stall Spin happens in the turn from Base to Final with a tail wind on Base.


I Like Telemetry because I've gotten BORED with just flying. It's the same thing every time, start up taxi out take off go fast lend taxi back shut down Go sit with your buddy's and listen to every thing U did wrong. Any trained monkey can "GO FAST & GO HIGH", No Challenge, especially with Jets. Try it while watching the Telemetry read outs on your Radio, I've purchased over $1000 worth of HiTec telemetry equipment Just to see what's it all about.
But then that's just me. People should do what suits them best.

Top_Gunn
If some one made an AOA that worked with my Aurora system I'd probably have it.
Old 11-08-2014, 06:18 AM
  #90  
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U Jet Jockeys should Check this out"

RCU Forum on Android phone based Telemetry
http://www.rcuniverse.com/forum/rc-jets-120/11603664-new-android-based-telemetry-system-our-jets-other-flying-things-3.html


Telemetry for Jets. Includes Air Speed and Angle of Attack (AOA)
http://www.ultimate-jets.net/collect...en-assi-module

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