Spin question

[Diana]

How does increased weight aft of CG (two people instead of one) affect a spin and spin recovery in a tandem airplane like the Citabria? What would you expect to see different in the spin characteristics with two people instead of one? Would recovery take longer with more weight aft of CG? This is assuming that the W&B is within acceptable limits.

 

[gismo]

How does increased weight aft of CG (two people instead of one) affect a spin and spin recovery in a tandem airplane like the Citabria? What would you expect to see different in the spin characteristics with two people instead of one? Would recovery take longer with more weight aft of CG? This is assuming that the W&B is within acceptable limits.

A more aft CG decreased the rudder's effectiveness (shorter arm) as well as making a spin flatter (or more likely to become flat). Both effects will likely increase the time and rotation during spin recovery. For an example, I cannot keep my Porterfield in a spin when I solo from the front seat which gives a pretty far forward CG, but flying from the rear it will stay in a spin indefinitely with only a little effort.

 

[bbchien]

Cessna 140 is harder to get in, and a little more effort to get out of a spin with stuff in back of the seats....

 

[Diana]

So, would it make it turn tighter or quicker with a shorter arm? It would take longer to recover?

 

[bbchien]

So, would it make it turn tighter or quicker with a shorter arm? It would take longer to recover?

Turns a little quicker, takes longer to recover....

 

[Ryan Ferguson]

How does increased weight aft of CG (two people instead of one) affect a spin and spin recovery in a tandem airplane like the Citabria? What would you expect to see different in the spin characteristics with two people instead of one? Would recovery take longer with more weight aft of CG? This is assuming that the W&B is within acceptable limits.

In your airplane, you won't see much difference. If you crank the airplane into a fully developed spin (at least 4 turns), you'll see it flatten out and tighten up a bit more than if you were flying solo. Otherwise, it's pretty negligable.

 

[BruceAir]

From The Airplane Flying Handbook:

WEIGHT AND BALANCE REQUIREMENTS
With each airplane that is approved for spinning, the weight and balance requirements are important for safe performance and recovery from the spin maneuver.

Pilots must be aware that just minor weight or balance changes can affect the airplane’s spin recovery characteristics. Such changes can either alter or enhance the spin maneuver and/or recovery characteristics. For example, the addition of weight in the aft baggage compartment, or additional fuel, may still permit the airplane to be operated within CG, but could seriously affect the spin and recovery characteristics.

An airplane that may be difficult to spin intentionally in the Utility Category (restricted aft CG and reduced weight) could have less resistance to spin entry in the Normal Category (less restricted aft CG and increased weight). This situation is due to the airplane being able to generate a higher angle of attack and load factor. Furthermore, an airplane that is approved for spins in the Utility Category, but loaded in the Normal Category, may not recover from a spin that is allowed to progress beyond the incipient phase.

AC 61-67C "Stall and Spin Awareness Training" also contains excellent information.

You can find links to much more information about spins on my Web site at: http://www.bruceair.com/spins.htm. I especially recommend the articles by Rich Stowell, which you can find on his Web site.

 

[Skyport]

Diana-

First a reminder that there are different CG limits for Normal and Aerobatic Category ops.

Generally the further aft the CG the more difficult an aircraft is to recover from a stall, or spin, with the worst case being unrecoverability when well aft of the limit. In the case of a Citabria, flown within limits, stall and spin recovery is never a concern however you will find the Citabria will get slightly deeper into the stall when flown at the aft limit, and the spiral issue we discussed previously will not be a problem.

Once again a reminder that under the version of CAR 4 in effect when the 7AC was certified the Citabria is required to recover from a 6 turn spin "hands off" in 1.5 turns.

And the reason the 8KCAB was certified under a new TC was to get away from the stringent CAR 4 spin recovery requirement. Likewise the 8GCBC could expand the CG envelope at increased gross weights by certifying under Part 23 rather then CAR 4. The bottom line is that your GCAA has better spin recovery characteristics then most modren aircraft, when flown within limitations.

Tom-