WWII Fighter question

[Thilo]

Hi group

I pilot friend had the luck to take a ride in a Spitfire.

He mentionned that the aircraft would roll very easily, with minimal effort on the stick. But when it came to pull the aircraft nose out of a dive, a large amount of force was required.

He speculated that it was the gyroscopic effect of the huge prop that could affect the movement along the pitch and yaw axis.
Or the relatively small tail surfaces...

This should probably affect most WW II fighter aircraft.

Does anybody the answer to the above?

Thanks,

Thilo

[Farmer 1]

In a word, Idon'tknowbutIdoubtit.

The gyroscopic effect you mention is called precession. If you attempt to turn a gyroscope around one axis, the effect is transferred ninety degrees in the direction of turn of the gyro, i.e. the propeller. This would (I think) tend to yaw the aircraft to the right, if the propeller turns clockwise.

It's an awful long time since I did this stuff, and the memory's like a - thingy - so I sit to be corrected.

[Saab Dastard]

Farmer 1 is correct - gyroscopic forces have nowt to do with it!

I suggest you read the excellent "Spitfire: A Test Pilot's Story" by Geoffrey Quill - there's an entire chapter on Longitudinal Stability!

SD

[effortless]

Rolling is usually easier than changing your direction of travel as the forces to overcome ar smaller. When you roll you are still going mostly in the same direction and not trying to overcome the huge forward momentum. The same is true to a greater or lesser extent in all aircraft.

[barit1]

Agreed - inertial forces are the dominant factor. The first experience I had with this was as a passenger in a Mustang. At 240 kt in a turn, a 60° bank duly induced its 2 G's, yet the nose barely crept around the horizon compared to the 100 kt airplanes I had been flying. A great physics lesson!

(And a hesitation roll emptied my shirt pocket - all the contents collected on the canopy - duh!)

[Milt]

Pitching Stick Force or Stick Force per g.

Aircraft designers and test pilots can arrange for any elevator stick force required by balancing control surfaces or using powered controls however for the standard man the range of stick forces need and must be within an acceptable range of the strength of his arm and wrist/hand.

Stich force per g is the normal measure and in the days of the Spitfire was probably determined using a spring balance similar to that which you might use to weigh the catch of a fish.

The safe strength of a Spitfire at max weight was probably about 7.0 g and the RAF would have been rather peeved if its pilots kept breaking them so there emerged a range of stick forces per g considered by the boffins and TPs to be acceptable for Pilot Officer Prune. The desired range for all speeds has evolved as being between 5 and 9 pounds per g for a single handed fighter stick and not less than 11 Pounds per g for heavies.

It was also desirable to have some "harmony" between elevator and roll control with the combination providing "the feel" for how you fly the aircraft. An additional source of feel was the extent to which the stick moved at various airspeeds.

This is all not dissimmilar to the control forces designed into the average motor vehicle.

Powered control surfaces and 'fly by wire" allow for acceptably precise pilot control using wrist forces only. Complications then arise with side stick control because your wrist has variable strengths in differing directions.. So now we have a developing generation of side sticks having asymmetric forces for roll and pitch control to enable the pilot to match his force and movement inputs with the resulting reactions of the aircraft/spaceship. Side Stick force per g for a highly manoeuverable aircraft is generally optimised at around 3 pounds which results in close to the maximum wrist pull of 27 pounds allowing the standard man to achieve 9 g. 9g happens to be about the maximum our standard man can withstand for short periods and stay visual/conscious when sitting in a lay back seat and equipped with a g suit.

[4Greens]

At higher altitudes and indicated airspeeds some compressibility effects come in. These are due to increasing Mach number and can lead to some airflow problems over the elevator.
Not much was known about this at the time.

[Thilo]

Thanks to all

By all your replies it definitely has (and had) nothing to do with the gyroscopic effect of the props.

Thanks for clarifying the matter.

Thilo