Spin recovery versus CG location?  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> RC Airplanes >> Aerodynamics >> Spin recovery versus CG location?
Page: [1]

Login
Message << Older Topic   Newer Topic >>
Spin recovery versus CG location? - 4/4/2008 6:05:32 PM   
griesel


 

Posts: 51
Joined: 9/10/2006
From: Tucson, AZ, USA
Status: offline 		What is the relationship between spin recovery and CG location. First their are different types of spin
recovery. An Instructor friend demonstrated a hands off spin recovery on a GP Big Stik 60 with no
turn off of throttle. CG was at 10% of Mac. A Cessna 152 recovers nicely with controls at nuetral and
throttle set at idle. CG location unknown. I have heard some hanger tales of a Gruman trainer where
both occupents would have to unbuckle and move close to the front window to recover from a spin. I
have been setting my planes up around 25-27% of Mac and they fly OK but have not tried spin recovery.
I just got a world models Super Stunts 60 and they specify a CG of 6.1 inches from the leading edge
which would be 37% of Mac. I guess they want to sell a lot of replacement planes.
       Post #: 1

RE: Spin recovery versus CG location? - 4/4/2008 6:51:32 PM   
dick Hanson



Posts: 9924
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		Every setup is different
your past experience with higher wing loading --is pretty much the std setup - stay forward of 30% MAC!! On somevery lightly loaded 3Dstuff going aft of 33% is possible

_____________________________

I am watching you
Libby

(in reply to griesel)
       Post #: 2

RE: Spin recovery versus CG location? - 4/5/2008 11:27:29 AM   
pimmnz


 

Posts: 494
Joined: 11/9/2005
From: Auckland, NEW ZEALAND
Status: offline 		And the Grumman trainer is spin restricted cause the wing spar is a big tube, which you then fill with fuel as the fuel tank. Guess what happens when the autorotation starts? Fuel goes to wing tip, and you can't stop the autorotation. My instructor was real careful during stall recovery, 'Keep the (expletive deleted) ball in the centre, son'.
Evan, WB#12.

(in reply to dick Hanson)
       Post #: 3

RE: Spin recovery versus CG location? - 4/5/2008 4:49:53 PM   
Nathan King



Posts: 1458
Joined: 5/29/2007
From: Omaha, NE, USA
Status: offline
quote:

ORIGINAL: griesel

What is the relationship between spin recovery and CG location. First their are different types of spin
recovery. An Instructor friend demonstrated a hands off spin recovery on a GP Big Stik 60 with no
turn off of throttle. CG was at 10% of Mac. A Cessna 152 recovers nicely with controls at nuetral and
throttle set at idle. CG location unknown. I have heard some hanger tales of a Gruman trainer where
both occupents would have to unbuckle and move close to the front window to recover from a spin. I
have been setting my planes up around 25-27% of Mac and they fly OK but have not tried spin recovery.
I just got a world models Super Stunts 60 and they specify a CG of 6.1 inches from the leading edge
which would be 37% of Mac. I guess they want to sell a lot of replacement planes.


Good question! It sounds like you have a good instructor too. The further back the center of gravity is, the more likely the airplane is to spin from a stall. This relationship is not linear but is more exponential. That being said, if the airplane stalls in perfectly coordinated flight there is no way the airplane can possibly spin. Get your center of gravity far back enough and the pilot will not recover the airplane, no matter what he/she does. A spin actually has four phases: Entry, incipient, developed, and recovery. Entry is simply a matter of all ingredients for a spin being present (lack of coordination, stall, etc). The incipient phase is usually the first rotation, and the developed phase is when the spin is fully stabilized.

The acronym "PARE" (Power idle, Ailerons neutral, Rudder opposite the spin and held, and Elevator through neutral) is helpful for spin recovery because it helps you remember the elements of proper recovery technique and keeps them in their proper order of application. The first task is returning the throttle to idle. You will be descending rapidly and gaining speed, so idling is a good way to slow things down a bit (in full scale flight this also keeps the airplane below VNE). Keep the ailerons neutral and apply opposite rudder. Remember, you are in a stall so the last thing you want to do is continue to pull up. The only way to break the stall is to reduce angle of attack below the critical angle (which is a bit different for every airplane). After you are out of the spin resist the temptation to sharply pull up as this could cause you to enter a secondary stall. Remember, stalling has nothing to do with relative pitch or speed, it has to do with angle of attack - period.

< Message edited by Nathan King -- 4/5/2008 4:53:21 PM >


_____________________________

Nate,
WACO Brotherhood #99

(in reply to griesel)
       Post #: 4

RE: Spin recovery versus CG location? - 4/6/2008 11:12:53 PM   
feihu



Posts: 178
Joined: 11/17/2002
From: Sun City, AZ, USA
Status: offline
quote:

ORIGINAL: griesel

What is the relationship between spin recovery and CG location. First their are different types of spin
recovery. An Instructor friend demonstrated a hands off spin recovery on a GP Big Stik 60 with no
turn off of throttle. CG was at 10% of Mac. A Cessna 152 recovers nicely with controls at nuetral and
throttle set at idle. CG location unknown. I have heard some hanger tales of a Gruman trainer where
both occupents would have to unbuckle and move close to the front window to recover from a spin. I
have been setting my planes up around 25-27% of Mac and they fly OK but have not tried spin recovery.
I just got a world models Super Stunts 60 and they specify a CG of 6.1 inches from the leading edge
which would be 37% of Mac. I guess they want to sell a lot of replacement planes.


If you move the CG aft far enough, the airplane will become unstable and uncontrollable in pitch, and therefore unrecoverable from a spin. But most conventional airplanes with conventional CG locations can enter a spin intentionally or inadvertantly, and can be recovered using the standard spin recovery procedure.

You have just discovered that different airplanes have different spin characteristics, and some spins that are entered intentionally can generally be shown to to recover hands off, but especially those spins that are entered unintentionally usually require some help.

While spins are prohibited in the Grumman American Trainer, the handbook describes the standard spin recovery procedure in the event of an inadvertant spin. I think the hangar tale you heard about the Grumman trainer is just that and not a real life experience.

Aerobatic airplanes generally have the CG aft of "normal" to enhance the aerobatic characteristics of the airplane. A 37% mac is not out of the ordinary.

feihu

(in reply to griesel)
       Post #: 5

Page:   [1]
All Forums >> RC Airplanes >> Aerodynamics >> Spin recovery versus CG location?
Page: [1]





Jump to:


Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Member Video Posts | RCU Video Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

© 2001 - 2007 24-7 RC, LLC, all rights reserved.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America

Kaango.com Classifieds

0.547RCU1