On Wed, 04 May 2005 16:30:56 -0600, RomeoMike
wrote:

I don't know anything about the relative stability of the P-51, Me 109
and Spitfire. Do you have some info on that? If the latter two planes
had the range of the P-51, would they be any more taxing to fly straight
and level on a long mission? If the P-51 really is more stable than the
other two, are you suggesting that the designers made it that way to
give the pilot a better ride? Maybe there is someone out there who has
flown at least 2 of the 3 planes and can comment.

There are numerous writings by pilots who have flown all three of the
above, and written about it. Eric Brown wrote "Duels in the Sky" in
which he describes flying and comparing a phenominal number of
airplanes. Leonard "Kit" Carson was another well known pilot who was
both an experienced fighter pilot and an aerodynamics engineer who
wrote about flying the Me 109 and compared it to the Mustang, which
was the airplane he fought in.

The more extensive comparison is from Carson, but besides Carson and
Brown, I've read numerous reports from other WWII pilots who had a
chance to compare the flight characteristics.

The Me 109 was head and shoulders above all competition when it first
flew, but it was designed in 1935 and was almost entirely all manual
in nearly all aspects. For instance, no version of the Me 109 ever
had a rudder trim. This meant that at only one airspeed did the pilot
not have to be pushing on the rudder to correct for yaw, and that
airspeed was below cruise. The faster the airplane went, the more
pressure required on the rudder bar. This could and did fatigue the
pilot to the point where turning in the direction of the tired leg
caused a notably slower response than turning in the opposite
direction.

But we were talking about stability. Almost to a man, the pilots of
P-51's who also flew the Me 109 commented on how unstable it was, how
it hunted constantly and would not hold it's flight path. The
instability was designed into the airframe. Fighters needed to be
able to change direction quickly so stability was necessarily
compromised for maneuverability. In those days there wasn't any
computer controlled fly-by-wire so the pilot just learned to be
constantly adjusting the controls in order to hold formation or fly in
a straight line.

Because the Me 109 was designed as a combat superiority weapon, a
fighter that followed the front closely, it wasn't designed for
extended range. Long range required lots of fuel and lots of fuel
compromised performance. Like the Spitfire, it originally had only a
fuselage fuel tank which gave it a pretty limited range. So flights
were relatively short and the pilots rested up between them.

The Mustang on the other hand, was redesigned from it's original
iteration as a low altitude fighter to a high altitude long range
escort fighter. The designers understood that in order to sit in the
cockpit for extended periods of up to 6 hours, the airplane would have
to be stable enough that the pilots did not have to be constantly
correcting the flight controls. On the other hand, it was a fighter.
It's job was to fly with the bombers to the target, outfight the enemy
fighters and return to base. That was a tall order. The Mustang
pilots kind of got lucky.

By the time of the Mustang's combat debut, the Luftwaffe had been
increasingly devoting it's efforts at stopping the daylight heavy
bombing formations. It had had more than a year to develop tactics
and modify their fighters into bomber destroyers. And they were
getting pretty good at destroying bombers with their fighters. But
this was coming at a cost: The fighters were heavily loaded down with
large caliber cannon and in many cases, rockets. They were also
sending up the twin engined fighters and even ordering the night
fighters up on daylight interceptions. Some Me 109's even carried
bombs up above the bomber and dropped them into the formations hoping
that the timed explosion would occur in the middle of the formation
either destroying bombers or greatly disrupting the formation. They
also carried a lot of armor plate. All this had a decidedly negative
effect on performance. It didn't matter much in terms of attacking
the bombers because the bombers were plodding along at 150 to 160 mph
and flying in obligingly straight lines, albeit packed tightly
together for mutual protection. But the Mustangs were a different
opponent altogether.

They showed up lean and clean and stripped for action. The original
model B had only four heavy machine guns and was blindingly fast
compared to either the Focke Wulf 190 or the Me 109G. They were some
40 to 50 mph faster which allowed them to dictate combat terms.

In addition, and this is a bit of an unknown, the German fighter
pilots were under orders to ignor the fighter escort, whenever
possible, to concentrate on destroying the bombers. That meant that
they were not normally supposed to seek out combat with the escorting
fighters. Fighter pilots being normally aggressive, they often did
anyway but their orders were to hit the bombers first. This allowed
the escorting Mustangs to intercede, sometimes with smaller numbers,
and survive.

But we were talking about stability. The first Mustangs, the A model,
were designed as a low to medium altitude fighter. They had more
range than Spitfires or any single engine German fighter, but not as
much as the later models B, C and D had. This is because they were
not thought of as escorts, but as a better P-40. In their original
configuration they were a delight to fly according to those who flew
them. One pilot mentioned putting his pointing finger on top of the
stick and being able to aileron roll it, so light and easy were the
controls.

That all changed with the introduction of the model B. The B got the
Packard built version of the Rolls Royce Merlin instead of the Allison
V12 and the designers added bob weights to the control cables to
increase stability. They also added a fuselage mounted fuel tank
which was behind the pilot. When this was full, the Mustang was
treacherously aft weighted. I'm not positive, but it may be that the
bob weights were installed to counter the difficulty pilots would have
handling the fighter when the fuselage tank was full. Even with them,
when the fuselage tank was full, the Mustang was very sensitive. The
information I have is that this tank was selected first during the
form up and climb to escort altitude, then they switched to the drop
tanks. The Luftwaffe actually attempted to negate the use of the drop
tanks, at least once or twice, by attacking the Mustangs early causing
them to drop the external tanks and fight. This reduced their range
leaving the bombers unescorted over the target. But there were too
many Allied fighters (including Thunderbolts and Spitfires) and too
few German fighters for this tactic to be repeated too often.

Whatever the real reason, once that fuselage tank was empty, the bob
weights contributed towards a strong positive stability.

When the model D Mustang was initially introduced, pilots complained
about it being more unstable than the B. That was because the
fuselage had been cut down and a bubble canopy installed instead of
the earlier turtledeck. This changed fuselage actually diminished top
speed somewhat and caused some instability. The engineers then added
the dorsal fin to the front of the rudder which is now considered one
of the signal visual characteristics of the model D.

If you look at the famous photo of the four fighter formation
featuring "Louis IV" closest to the camera and the three others
stacked down below and behind it, you'll see three versions of the
Mustang in that one photo: Louis IV is a D Mustang without the dorsal
fin, the next one is a D with the dorsal fin. Next is another D
without the dorsal fin and finally a B which of course had the turtle
deck. All are carrying drop tanks which did not help stability.

But back in those days fighters were fighters. You worked and flew
with what you had. Most of the Me 109 pilots actually liked flying it
(some didn't) and could take advantage of the characteristics that
made it a good fighter.

Corky Scott