Sopwith Camel "tail heavy"

[TomVrille]

The Center of Gravity on the Camel depended on the fuel status. In the course of a normal patrol of perhaps 2½ hours, the CG would move forward as fuel was expended. The aircraft was rigged to be tail heavy at takeoff with full fuel tanks, but slightly nose heavy at landing when the fuel was almost exhausted. This made the Camel slightly unstable at takeff, neutrally stable during the central part of the mission, and stable at landing when any extreme control sensitivity would be most unwelcome.

[RAF56_Ball]

TomVrille (et al),

Were they designed this way (varying CG) on purpose, or was it a serendipitous outcome due to compromises reached due to space constraints? You can only put so much fuel in front of the pilot in a Camel, and no one was doning wing tanks back then (at least in scouts).
I am asking only because I have seen people make similar statements, but have never seen reference to supporting desing documents, letters or eyewitness accounts from other members of design teams. Mind you, I have very little in the way of reference material about design ideas, and rather less access to it, so I was asking, not challenging what may have been established in other threads.

[gipsymoth236k]

FYI, both the main and aux fuel tanks in the Sopwith Camel were located BEHIND the pilot's seat.

Regards,
Gary Sewall

[Leif Ohlsson]

Originally Posted by DamianL

Can anyone advise if the vertical position of the tailplane leading edge in the gap was adjustable?

Is this then how the pitch was trimmed as described, by adjustment of the tailplane leading edge, and thus small adjustment in lift of tailplane?

I believe the quick answer should be no, the lift of the tailplane was adjusted by changing the trailing edge of the fixed part of the stabilizer, not the leading edge.

In effect, the mechanism was a screw. Turning the trim wheel made the screw mounted at the rear of the fuselage go up and down, raising or lowering the trailing edge of the fixed part of the stabilizer, which would be hinged at a convenient forward point, e.g. a spar.

The principle of lowering or raising the trailing edge - albeit not always by a screw mechanism - was retained as pretty much standard for generations of aircraft to follow. An example that I have detailed photos of is the Spirit of St. Louis.

Leif

Attached photos: First the Sopwith patent drawing of the stabilizer trim mechanism, then a replica of the Spirit of St. Louis, where you can see the wires for raising or lowering the trailing edge.

Note that the mechanism on the Spirit is not the Sopwith type screw, but a slider on the tail post affecting the rear stab struts, raising or lowering them, thus raising or lowering the trailing edge of the fixed section of the stab.

[DamianL]

Hi Leif

My understanding was that the screw jack with trim wheel in the cockpit was used on the Sopwith 1-1/2 Strutter, and on earlier production Pups, but it's use was discontinued during Pup production.

I don't think this device was used on the Camel. On the drawing I was looking at their was no adjustable jack as per your drawing, but I noted that there was some clearance between the stabilizer leading edge, fuselage longerons and bottom of fin.

Regards

Damian

[Leif Ohlsson]

Ooops. Totally misunderstood the issue at hand. My apologies for pontificating... -L.

[DamianL]

Hi Leif

No worries. It would be good to have a better understanding of the adjustable tailplane system, and whether this was to accommodate change in CG during a mission, &/or set to pilots preferences.

The Strutter was available in a single seat "long range" configuration, where a very large fuel tank was positioned where the rear seat would normally be. Presumably this aircraft would be subject to significant CG changes during a mission, maybe necessitating the adjustable taiplane.

Maybe they found that CG changes in the single seat scouts were manageable, without the need for the adjust-in-flight system?

Regards

Damian

[Leif Ohlsson]

All I can say is that I would hate to fly an aircraft without adjustable tail or trim elevator rudders, particularly if it was prone to the significant C/G changes during flight you describe.

If the C/G change was deemed tolerable in any particular type of aircraft, resulting in a stab design which was ground-adjustable only, I would think any adjustments made after that would be to accomodate individual pilots' preferences, or perhaps one should say the test pilot's evaluation of an individual aircraft - individual aircrafts of the same type must have come out with significantly different trims from the factory or assembly point.

- L.

[TomVrille]

Originally Posted by RAF56_Ball

Were they designed this way (varying CG) on purpose, or was it a serendipitous outcome due to compromises reached due to space constraints?

I seriously doubt that the CG shift of the Camel was a design goal, although I have never seen any discussion of this point in the literature. The Camel was designed to be highly maneuverable, well-armed, and inexpensive to produce. The various factors affecting stability were still not fully understood. When it was discovered that there were some stability problems with the Camel, the fact that the rigging could be adapted to manage the CG travel was most likely a bit of good luck.

[crankcase]

Originally Posted by gipsymoth236k

FYI, both the main and aux fuel tanks in the Sopwith Camel were located BEHIND the pilot's seat.
Regards,
Gary Sewall

Well spotted, Gary! Moving in front of the pilot, and assuming the ammunition was used up during a mission, how much weight difference would this make?
marc