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180 turn back to the runway video
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by0ung(at)brigham.net
Guest

Posted: Wed Apr 28, 2010 7:08 am Post subject: 180 turn back to the runway video

Hello Boyd,



Again, a descending (power off) turn at constant air speed is a 1G maneuver.



Jason



 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>>>>>>>>


	


Jason

Just visited a cfi,  and I asked the question  "could you remain in 1 g

during a descending turn at a constant air speed"   his reply was "you could

for a short while,    but it would be the start of a death spiral."

Straight flight at a constant speed and power setting,   is considered 1g.

If 1 g  is lifting the aircraft and you put it into a turn, You will

require additional energy to cause the plane to change direction,  I.e.

TURN 180   Energy is needed to stop the plane from traveling in one

direction, and accelerate it into another direction. Thus more energy/lift

is required from the wings, to make the direction change and also lift the

aircraft.   I guess it could be argued that there is still only 1g apposing

gravity,   but additional lift is required to cause the change of direction.

Thus 1 PLUS g maneuver,   the greater the bank angle the greater the PLUS. 



Boyd

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Wed Apr 28, 2010 11:13 am Post subject: Re: 180 turn back to the runway video

Any turn of an airplane will require acceleration to change its direction, you can not turn the direction of any moving object without putting force on it, its a law of physics that can not be broken.  What can be done is that the  turning forces can be temporarily kept near one G by initiating a descent, and using more of the lift component for the turn, and less for lifting against gravity, TEMPORARILY.  But any descent incurred by this will have to be arrested sooner or later by additional lift from the wings, additional G loading somewhere before hitting the ground.  You can not change the laws of physics by being a good pilot.



What a good pilot can do is manage these forces so gradually, and smoothly that any increase in G loading is minimal and not noticed by the humans inside the plane.  This is very good and important technique, as the return to airport would be done at minimal airspeed with no power...   Horsing the plane around and being abrupt with the controls and the resulting G forces could cause an accelerated stall and be disastrous in this situation.  So while you can not change the laws of physics, you can manage them so smoothly as to give yourself every  chance of completing this maneuver without stalling.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Apr 29, 2010 4:49 am Post subject: Re: 180 turn back to the runway video

....Here is a very good video about the "Impossible Turn" as performed by two guys in a C172. 

http://www.aerobats.com/seminar_02-07.html 



Richard Pike 

MKIII N420P (420ldPoops).....



Richard,



Thanks for posting the "impossible turn" video. Very good indeed. It was missing only two things to complete the picture. An AOA gauge and and G-meter.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Apr 29, 2010 4:56 am Post subject: Re: 180 turn back to the runway video

Ooops!



Actually there is a third thing missing in this video. The engine was running at idle power. With idle power the relative effects of various degrees of bank on turn time and altitude loss are correct but what is missing is the effect of stopped prop. But still a very good informative video.... just not complete.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Jason Omelchuck

Joined: 07 May 2009
Posts: 120
Location: Portland Oregon

Posted: Thu Apr 29, 2010 6:43 am Post subject: Re: 180 turn back to the runway video

Hello Tom,



I have a clutch on my engine so the prop windmills (and my airplane behaves) with the engine at idle just like it would with the engine stopped.



Regards

Jason



 	  Thom Riddle wrote: 	
		  Ooops!



Actually there is a third thing missing in this video. The engine was running at idle power. With idle power the relative effects of various degrees of bank on turn time and altitude loss are correct but what is missing is the effect of stopped prop. But still a very good informative video.... just not complete.

by0ung(at)brigham.net
Guest

Posted: Thu Apr 29, 2010 4:00 pm Post subject: 180 turn back to the runway video

Tom and the gang:



Ok    I don't think we are really that far apart.   What I think we need now

is a definition of terms.   Example:  is a 1 g turn anything between .7 and

1.3      or .8 and 1.2......    give me your definition of 1 g maneuver.  



I had given an example of a steep bank turn to emphasize the situation.

And my definition of 1 g plus   is 1.01g and above.   I am probably taking

things to literally.     



Any time you turn a plane there is going to be more energy required.  And

you can trade the energy needed to turn by unloading the wings momentarily

and remain at a literal 1g .   But as soon as the plane returns to a steady

state and you remain in a turn,  greater than 1g will be required.   In a

shallow bank turn it may be as small as 1.05g total.   In my definition that

is 1 plus g.   If that is a 1 g maneuver by your definition,  then we are

still on the same page.   



When given the terms power off descending turn.  It left the parameters a

bit too open.   Now I had mentioned that I had not seen the video.  So maybe

everyone else had a better idea of the parameters used.



Sorry if I misled anyone.



Boyd Young

jbhart(at)onlyinternet.ne
Guest

Posted: Sun May 02, 2010 6:49 pm Post subject: 180 turn back to the runway video

Kolbers,



Riding the mower mid-week, I had some time to think about constant velocity 

and 1g turns, and so when the rain started, I started running some numbers.  

I picked numbers that were suitable for the FireFly and looked at constant 

level turns and descending turns.  I did not discover a one g power off 

descending turn.  But I found that increasing the rate of descent while 

keeping the same speed, did decrease wing and g loads and stall speed.  This 

may not be practical in that it may require a device to increase the drag.  

I don't know if flaperons will do the trick.  The numbers indicate that if I 

keep the FireFly over 40 mph in a coordinated level and/or descending turns, 

there is no danger of a stall.  If I increase the margin to 50 mph there is 

little chance of stall due to an uncoordinated turn.



What follow is my attempt at non-powered flight dynamics.  It will be 

interesting to get back into the air and to check out some these 

calculations.  More rain coming tomorrow.



Jack B. Hart FF004

Winchester, IN

-------------------------------------------------------------------------

Sailplane Aerodynamics



Centrifugal Force ->  F = WV^2 or R = WV^2   

                          gcR         gcF

Where:

W = FireFly gross Weight = 500 pounds

gc = gravitational constant 32.2 ft/sec2    

F = centrifugal force in lbf

V = Velocity in ft/sec

^ -> indicates the number trailing is an exponent

R = radius of turn in feet



F = W x tan(Ø)



Where:

Ø = angle of bank in degrees



Substituting into:



R = WV^2 = WV^2    =    V^2 

    gcF   gcW tan(Ø)  gc tan(Ø)



Constant G-Load = 1/cos(Ø)



Find new stall speeds



Given L = CV2 or C = L/V^2  and V = (L/C)^0.5  



Where:

C = coefficent of lift

L = Lift in pounds

V = Velocity in mph



Solve for C at FireFly stall in level flight



C = 500/(27)^2 = 0.686

    

Using this value of C, calculate the new stall speeds for banking turns.



Turn Radius in Feet While Maintaining Altitude

                                     

Bank    _________Air Speed______  Constant  New  FireFly  Stall

Angle  |mph->| 40   | 50  |  60 | Altitude  Wing  Stall   Speed

(deg)  |fps->|58.7  |73.3 | 88.0|  G-Load   Load  (mph)  Increase

             |  radius in feet  |          (lbf)

   0         |  ---infinite---  |  1.00     500   27.0     0%

             |      |     |     |  

  15         | 399  | 623 | 898 |  1.04     518   27.5    1.9%

             |      |     |     |               

  30         | 185  | 289 | 417 |  1.15     577   29.0    7.4%

             |      |     |     |               

  45         | 107  | 167 | 240 |  1.41     707   32.1   18.9%

             |      |     |     | 

  60         |  62  |  96 | 138 |  2.00   1,000   38.2   41.5%

Time to Turn 180 Degrees in Seconds



T = ?r/V



Where:

T = time is in seconds

? = pi = 3.1416

V = velocity is in feet per sec



Bank            Air Speed 

Angle   mph-> 40    50    60    

(deg)   fps->58.7  73.3  88.0    

  15         21.4  26.7  32.1

  30          9.9  12.4  14.9  

  45          5.7   7.2   8.6  

  60          3.3   4.1   4.9  



Turn Rate in Degrees/Second



Turn rate = 180/T in degrees/second



Bank             Air Speed 

Angle   mph-> 40    50    60 

(deg)   fps->58.7  73.3  88.0    

  15          8.4   6.7   5.6

  30         18.2  14.5  12.1

  45         31.6  25.0  20.9

  60         54.5  43.9  36.7



Now what happens if one lowers the nose, reduces power and flies at 50 mph 

with 500, 1,000, 1,500 fpm or 8.33, 16.67, 25.00 fps rates of descent.



If one lowers the nose and flies at the same speed and constant velocity in 

a circular spiral path, the time to turn 180 degrees increases with the 

increase in descent rate.  This is because the total distance flown will 

increase to complete the turn.  This in turn lowers the centrifugal force as 

the distance traveled to complete the turn increases.  This change in 

centrifugal force can be found by calculating the path length for 360 degree 

turn and from this determine the effective radius that generates the 

centrifugal force.  Or by finding the new velocity vector component in the 

horizontal plane and applying it to original radius of turn.  Calculating 

for a 50 mph coordinated(?) turn.  I don't know if these assumptions lead to 

coordinated turns or not.



Bank  Descent Horz  Horz  Wing  New  FireFly  Stall   180    180

Angle  Rate   Vel   Turn   G    Wing  Stall   Speed   Turn Altitude

(deg)  (fpm) (fps)  Rad   Load  Load  (mph)  Increase Time   Loss

                    (ft)        (lbf)                 (sec)  (ft)

  15      0   73.3  623   1.04   518   27.5    1.9%   26.7     0

        500   72.8  627   1.03   517   27.5    1.9%   27.1   177

      1,000   71.4  639   1.03   515   27.4    1.5%   28.1   369

      1,500   68.9  662   1.02   512   27.3    1.1%   30.2   602

                                       

  30      0   73.3  289   1.15   577   29.0    7.4%   12.4     0

        500   72.8  291   1.15   574   28.9    7.0%   12.6    82

      1,000   71.4  297   1.13   567   28.7    6.3%   12.8   168

      1,500   68.9  307   1.11   555   28.4    5.2%   14.0   279

                                       

  45      0   73.3  167   1.41   707   32.1   18.9%    7.4     0

        500   72.8  168   1.40   700   31.9   18.1%    7.2    47

      1,000   71.4  171   1.36   681   31.5   16.7%    7.5    99

      1,500   68.9  178   1.30   649   30.8   14.1%    8.1   162



  60      0   73.3   96   2.00 1,000   38.2   41.5%    4.1     0

        500   72.8   97   1.97   985   37.9   40.4%    4.2    27

      1,000   71.4  100   1.87   936   36.9   36.7%    4.4    58

      1,500   68.9  102   1.76   879   35.8   32.6%    4.7    94



Conclusions:



1. If you react well, the FireFly should be able to return to the runway 

   with an engine out at 300 feet agl by dropping the nose and banking at 

   30 degrees or higher.

2. Drop the nose and fly at best glide speed -> 50 mph

3. Dropping the nose will lower the wing g-load and stall velocity in a 

   turn.

4. Make coordinated turns, but at 50 mph there is some built in margin of 

   safety.

5. Constant velocity flying is not such a bad idea.

6. Be gentle with the stick in pitch.

7. When in doubt push the stick forward, it increases ias and distance.

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon May 03, 2010 2:12 am Post subject: Re: 180 turn back to the runway video

Jack,



Thanks for the math. Looks like the math jibes well with my experience and that of others who have used this technique.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

R. Hankins

Joined: 18 Jan 2006
Posts: 185
Location: Grants Pass, Oregon

Posted: Sun May 09, 2010 1:59 pm Post subject: Re: 180 turn back to the runway video

I just finished up the annual on the KXP and took it out for a test flight.  Having read through this thread the other day, I decided to try a whole bunch of simulated departure engine failures with 180 turns back to the runway.  I tried steep and shallow, delayed and instant reaction to the power failure.  The worst I could do was a shallow turn after waiting for the stall to tell me I needed to react.  This took 400' of altitude.  



The best case was instant reaction and a tight turn.  This took  100 to 150'.  I couldn't believe it, so I did it 4 or five times.  The most I could lose with the tight turn back was 250' and that only by waiting for the departure stall with the stick back before initiating recovery and turn.  No comparison at all between shallow and steep turns.  The shallow turns took nearly twice the altitude every time.  The KXP is designed to be nimble at these slow speeds and does the 180 steep turn in 5 to 6 seconds. 



 I did several 360s and 720s in each direction at minimum controllable  airspeed, trying to force the accelerated stall and just about got dizzy.  Just look down the wing and watch the world go round.  I hadn't done these in a while.  What a hoot!

_________________
Roger in Oregon
1992 KXP 503 - N1782C

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun May 09, 2010 3:00 pm Post subject: 180 turn back to the runway video

I did several 360s and 720s in each direction at minimum controllable 

airspeed, trying to force the accelerated stall and just about got dizzy. 

Just look down the wing and watch the world go round.  I hadn't done these 

in a while.  What a hoot!



--------

Roger in Oregon

Roger H/Gang:



I agree with Roger's tests.



Kolbs are nimble little flyers.  Very difficult to get one into an 

accelerated stall.



Easy for a low time Kolb pilot to get one into a mush/stall in level flight 

and not realize they are no longer flying because the aircraft remains level 

until it smacks the earth.



Very easy to do this on approach to an unfamiliar grass strip.  Swear you 

were flying when he hit the earth, and can not understand how you tore up 

the Kolb so badly!!!



I've been flying these Kolbs for a while and I still use my air speed 

indicator to let me know how I stand as far as flying the airplane.  I know 

what my stall speed is.  As long as I stay above it, I'll keep on flying.



john hauck

mkIII

Titus, AL

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

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