Utility category

[Alfredson007]

Manual says that spins are allowed if in utility category. Entry speed is "slow deceleration". Does that mean that entry should be done stalling it slowly rather than doing accelerated stall? But in utility category spins are ok dispate the placard on the cockpit saying no intentional spins?

Also why the G limit is raised to 4.4G in utility cat? It is the same air frame... ? Should not the G limit stay the same regardless of weight?

Thanks

[Oracle427]

Correct, spins should be entered with a entry into a stall at the aircraft's unaccelerated stall airspeed. During spin recovery in a 172, you will very quickly go into the yellow arc as you pull out of the dive. It is impressive how quickly the airspeed builds up and I mean impressive in a not so pleasant sort of way.

The G limit is a function of the stress that the airframe can handle before being damaged or suffering an outright failure. As you lighten the aircraft, the load factor is increased by the G's, but as the overall load at 1G decrease, the airframe is exposed to less stress as the load is multiplied.

In other words, a 100lb weight at 1G is 440lb at 4.4G. If the airframe would begin to be damaged when the weight reaches 380 lbs, then the G limit would be 3.8G as any weight above 380 would begin to overstress the airframe.

If you decrease the weight at 1G to 86lbs, then the weight at 4.4G would now be 380lbs therefore allowing the additional load factor in the utility category.

This is also one of the reasons why the maneuvering speed decreases as the aircraft gets lighter. At a lighter weight and a higher airspeed, the wing will not reach the critical AoA before overstress occurs.

This does not mean that any aircraft can merely be lightened up and suddenly it can start pulling high Gs and doing maneuvers it wouldn't be permitted to do in the normal category. The control surfaces may not be designed for this regime and there are many parts of the aircraft that remain at their original weight and can be causing local stresses even if the weight of the passengers and fuel is significantly decreased.

Also check the very useful Vg diagram.

http://learntoflyblog.com/2016/01/04/ae ... g-diagram/

[Alfredson007]

Great answer oracle, thanks.

I saw a video where extra 300 spinned faster if fwd stick was applied before rudder. The standard method calls for forward stick after rudder but should not inherently stable aircraft break the stall just by not touching the stick after the spin has been corrected with opposite rudder? If incorrectly timed stick forward can aggravate the spin and maybe cause overspeed after the spin has been corrected would not it be safer just not to touch stick until recovering from the dive?

[Oracle427]

I've only spun 3 aircraft and not an Extra. I have done inverted and accelerated stall to spin entries and each one is quite different visually and certainly touches every sense including smell. When the smell of exhaust fills the cabin you know that you aren't going the correct direction.

A spinning aircraft starts to act like the rotor of a helicopter is autorotation. The effect of the control inputs are not operating on a fully stalled aircraft and also a large gyroscope.

In an upright spin to the right, forward stick input will increasing the roll to the right and intensify the spin due to gyroscopic precession. Spinning faster does not equate to higher airspeed or rate of descent.

Rudder is the only control surface that acts directly against the yaw of the spin. By applying opposite rudder, you are going to slow the rate of yaw and roll and the effect of gyroscopic precession will be reduced when applying forward elevator to break the stall. If you apply forward elevator first you may overcome the ability of the rudder to stop the spin due to the additional rate of rotation.

In some aircraft opposite rudder is all you need to stop the spin. In the very limited upset recovery training I did, I found that the C172 and DA20 stopped rotation immediately when pro-spin inputs where removed and the aircraft entered a spiral dive, they did not remain in a spin after 1-2 turns. The Z242 recovered all anti-spin inputs to be made and held before it would recover after 2-3 turns.

[Pistonpilot]

I did my primary flight training in a 172R and found it very difficult to achieve a stable spin of more then 3 or so turns; it very much wants to enter a spiral dive (increasing airspeed, rapid roll, low nose) even with pro spin inputs. The instructors and I used to try and see who could get the most turns! At the time, the logic/research we'd done pointed to Cessna extending the vertical tail in an attempt to make the airplane more appealing/safe for flight school use. I am not sure which 172 models brought about the change in vertical fin length, but all subsequent models (including the R) exhibited nice self-recovery; if you let go of the controls, it probably would recover after just one turn...but it would recover to a very nose low dive, so the pilot should still know what to do! =)

-Ian C

Sent from my SM-G900V using Tapatalk

[AKar]

Yeah, the spin dynamics are rather complicated - one reason for any plane to spin faster when the nose is lowered during the rotation is that the mass of the engine (and that of the aft fuselage and the empennage) is brought closer to the axis of rotation. Because the angular momentum is conserved, the spin must speed up.

Rudder is the only control surface that acts directly against the yaw of the spin.

As a sidenote, there are some interesting spin recovery techniques used in some fighters, which due to their planform, block the rudder(s) from being effective during the spin. In those, the adverse yaw is used counter the yaw rate, by giving "stick into the spin".

I did my primary flight training in a 172R and found it very difficult to achieve a stable spin of more then 3 or so turns

In glider world, a much-used basic trainer, the ASK21, is notoriously impossible to spin or even stall properly. Just about only way to get it even drop the nose is to pitch way up, and when the airspeed drops, force some pitch-up rate by full-aft stick, which is held through the stall. In such planes, a "spin kit" is sometimes used, which includes some additional weights that are installed to the empennage. In Cessnas, the good old 150/152 spins nicely.

-Esa

[Great Ozzie]

Rudder is the only control surface that acts directly against the yaw of the spin.

As a sidenote, there are some interesting spin recovery techniques used in some fighters, which due to their planform, block the rudder(s) from being effective during the spin. In those, the adverse yaw is used counter the yaw rate, by giving "stick into the spin".

I'm not so sure if that is due to rudder blanking as much as it is due to "how the mass is distributed".

As the mass of an airplane is spun through the air, the airplane behaves like a gyroscope. The combined spinning masses of the fuselage and wings, as they rotate about their respective axes, interact with one another to produce either pro-spin or anti-spin forces. How the mass is distributed will determine this effect.

Airplanes with an equal mass distribution along the fuselage and wings are said to have a "zero loading" and respond best to the rudder during a spin recovery. The average general aviation lightplane is a good example of an airplane with this mass distribution. For a fuselage-heavy loading, the aileron is the primary recovery control. Fighter aircraft with short wings and long, heavy fuselages respond best to this control. However, these airplanes present their own set of spin problems. They develop combined aerodynamic and inertial problems that are interesting.

Long fuselages not only produce inertial characteristics just mentioned, but also create aerodynamic reactions that are unfavorable for spinning. With so much aerodynamic area ahead of the c.g., the airplane can become directionally and longitudinally unstable at high angles of attack. An airplane with these characteristics is almost certain to display poor spin and recovery traits. The F-5, for example, has a flat, non-recoverable spin, and it is not the only fighter airplane with spin problems. Stalls, Spins, and Safety by Sammy Mason (a nice illustration of this on a NASA Stall / Spin Research page).

In Cessnas, the good old 150/152 spins nicely.

Yeah you got to stay on top of the ball when doing power-on stalls with those. Kershner used a C152 Aerobat in his aerobatic school. Used the Aerobat in his "Basic Aerobatic Manual" too.

[AKar]

I'm not so sure if that is due to rudder blanking as much as it is due to "how the mass is distributed".

That's how it's quoted. The mass distribution certainly has a significant effect also. A long fuselage helps with spin characteristics aerodynamically, but it works against us mass-wise. Anyways, to me it sounds correct in physical sense to note the aileron effect is most effective with such airplanes. If any anti-spin roll effort is induced to a long, heavy fuselage, the nose tends to continue by its momentum, resulting in reduced AoA. However, that requires anti-spin lateral control (as is required in for instance, the F-18, but it uses its own set of anti-spin FCS logic), opposed to the stick-to-the-spin control required by some others. Now that this came up, I must search for the specific types!

-Esa

[DHenriques_]

Rudder is the only control surface that acts directly against the yaw of the spin.

As a sidenote, there are some interesting spin recovery techniques used in some fighters, which due to their planform, block the rudder(s) from being effective during the spin. In those, the adverse yaw is used counter the yaw rate, by giving "stick into the spin".

I'm not so sure if that is due to rudder blanking as much as it is due to "how the mass is distributed".

As the mass of an airplane is spun through the air, the airplane behaves like a gyroscope. The combined spinning masses of the fuselage and wings, as they rotate about their respective axes, interact with one another to produce either pro-spin or anti-spin forces. How the mass is distributed will determine this effect.

Airplanes with an equal mass distribution along the fuselage and wings are said to have a "zero loading" and respond best to the rudder during a spin recovery. The average general aviation lightplane is a good example of an airplane with this mass distribution. For a fuselage-heavy loading, the aileron is the primary recovery control. Fighter aircraft with short wings and long, heavy fuselages respond best to this control. However, these airplanes present their own set of spin problems. They develop combined aerodynamic and inertial problems that are interesting.

Long fuselages not only produce inertial characteristics just mentioned, but also create aerodynamic reactions that are unfavorable for spinning. With so much aerodynamic area ahead of the c.g., the airplane can become directionally and longitudinally unstable at high angles of attack. An airplane with these characteristics is almost certain to display poor spin and recovery traits. The F-5, for example, has a flat, non-recoverable spin, and it is not the only fighter airplane with spin problems. Stalls, Spins, and Safety by Sammy Mason (a nice illustration of this on a NASA Stall / Spin Research page).

In Cessnas, the good old 150/152 spins nicely.

Yeah you got to stay on top of the ball when doing power-on stalls with those. Kershner used a C152 Aerobat in his aerobatic school. Used the Aerobat in his "Basic Aerobatic Manual" too.

If I can add a bit here;

Getting into high performance aircraft spin recovery means taking a whole new look at the the issue.
Since I'm familiar with T38 departure I'll approach things from this perspective.

Mass distribution is REALLY important in determining spin recovery procedure in aircraft like the T38.
MD can be expressed as an inertia yawing moment parameter or for the short of that, the IYMP. If roll inertia (the Ix) is greater than the pitch inertia (Iy) you are wing loaded. (Your normal everyday airplane like a 152). This constitutes a positive IYMP and can be considered as wing loaded.
For aircraft like a T38 for example, the pitch inertia (Iy) is greater than the roll inertia (Ix) the reverse is true. The IYMP is then negative making a T38 fuselage loaded.
For spin recovery if you try and use "regular" control inputs such as PARE, you'll screw the bird right on into the ground.
Naturally we all know that with your standard 152, to recover from a spin we use rudder against the spin and forward yoke to increase AOA. (Basics here, not expanded of course). On the other hand in a high performance fuselage loaded airplane like the 38 the procedure is slightly different. Keep in mind I'm talking upright erect here so no need to get fancy
In the 38, the use of rudder to control the yaw rate and effect recovery will depend on the effectiveness of the rudder while the 38 is in the spin. At very high alpha and yaw rates the rudder effectiveness might be reduced leaving you with no option but to introduce additional anti-spin moments to recover the airplane. Here is where we get into inertia cross coupling which in essence is what is required to recover these high performance fuselage loaded airplanes like the T38. Actually the F105 requires the same method. It's rudder against, aileron with, and elevator aft.
The primary control for spin recovery in these birds are the AILERONS! In an erect spin you deflect aileron into the spin. For an inverted spin opposite aileron is used. The aileron deflection causes the airplane to roll even faster in the direction of the spin if you are upright and slower if inverted. We're still talking upright here.
This in turn causes the airplane to precess. The precession produced causes a yaw moment OPPOSITE the spin direction helping to stop the yaw rate of the airplane. When this happens you can reduce angle of attack and recover the airplane.
The big rub in all this is that these inputs seem unnatural and you have to deliberately make them or you won't recover the airplane at all.
It's a whole new world flying high performance airplanes ! )))))
Hope all this helps a bit.
Dudley Henriques

[Great Ozzie]

Yes it does... thanks for the post Dudley.

-Rob

[AKar]

Yes, thanks for your interesting post Dudley!

Just for curiosity, I browsed through upright spin recovery methods for a small random selection of jets. It is quite noteworthy how they may vary, and indeed can be quite counter-intuitive if not known in some cases.

F-86H

• Full opposite rudder, stick well forward, neutral aileron. If to no avail, trim forward and release controls.

F-100D, F

• Full opposite rudder, full aileron into spin, full aft stick.

T-33A

• Ailerons neutral, aft stick, opposite rudder.

F-15A-D

• Neutral controls. If to no avail, aileron into spin.

F-101F

• Neutral rudder and aileron, full forward stabilizer. From stabilized spin, an ejection is recommended, and by latest at 15000 ft.

F-4J

• Full-forward stick, full aileron into spin.

F-14D

• Varies depending on the yaw rate: from opposite rudder and forward stick to full aft stick, aileron into spin and opposite rudder.

F-106A

• Stick full forward and into spin.

F-18A-D

• SRM on if not automatically, full aileron into spin. When yaw rate stops, forward stick as required.

-Esa

[Alfredson007]

Just for curiosity, I browsed through upright spin recovery methods for a small random selection of jets. It is quite noteworthy how they may vary, and indeed can be quite counter-intuitive if not known in some cases.

I wonder how known these spin characterics were before any test pilot had actually taken off for the first spin tests. "Full opposite rudder, no, aileron, no, stick aft, no... eject.. yes"

[DHenriques_]

Just for curiosity, I browsed through upright spin recovery methods for a small random selection of jets. It is quite noteworthy how they may vary, and indeed can be quite counter-intuitive if not known in some cases.

I wonder how known these spin characterics were before any test pilot had actually taken off for the first spin tests. "Full opposite rudder, no, aileron, no, stick aft, no... eject.. yes"

The week after I flew the F14 at the Naval Test Center the same Tomcat (an F14A, the #619 engine test bed)
was involved in a spin test. The spin was erect, accelerated, and flat. It couldn't be recovered. Both the pilot (Cmdr DD Smith, and the RIO, (Pete Angelina) ejected. DD was -7g's in the front and had to use the lower handle to get out. Pete was at the spin axis and got out easily. Both survived.
The force of the seats ejecting broke the spin coupling and the pilotless aircraft recovered itself before impacting Chesapeake Bay.
Some lessons are learned the hard way.
Dudley Henriques

[Oracle427]

Dudley,

During these tests was a spin recovery chute added to the aircraft to aid in recovery? -7Gs!! That must have been some very serious rate of rotation. DD sounds very lucky to be alive to have overcome that force.

[DHenriques_]

Dudley,

During these tests was a spin recovery chute added to the aircraft to aid in recovery? -7Gs!! That must have been some very serious rate of rotation. DD sounds very lucky to be alive to have overcome that force.

DD sent us a photo of his face from the hospital taken a week after the ejection. He looked like he had gone 10 rounds with Mike Tyson. His eyes were completely shut with all the blood vessels broken and clotted. He was a royal mess. Pete didn't get a scratch.
I didn't get back to NTC until much later but to my knowledge drag chutes were never retrofitted to the Turkey as a departure recovery assist.
Departure recovery for the 14 was to neutralize the rudders and zero any lateral stick then ease the stick forward to gain 17 units AOA or less. The objective is to reduce alpha to under 30 units.

Dudley Henriques