Vampire vs Me 262

[kool kitty89]

But back on topic, according to The Incomplete Guide to Airfoil Usage the Me 262 used

NACA 00011-0.825-35 at the root NACA 00009-1.1-40 at tip.

The -35 and -40 are position of max thickness as % chord, the middle figure pertains to radius (and sharpness) of the LE of the wing. 9they are German modifications to the orginal naming system) explained here: Aerospaceweb.org | Ask Us - German Modifications to NACA Airfoils

But why use the 5-series naming system when a 0011 and 00011 airfoil should be the same. (both are symmetrical with no chamber -thus CL should be zero at an AoA of 0- and max thickness of 11% of chord, and by default would have max thickness at 30% chord. Why use a more complex naming system when there should be no difference.

Also shouldn't such an airfoil have a relatively low CLmax, particularly with the low thickness ratio? (it's similar in design to a laminar flow airfoil)

[Soren]

The LE radius doesn't matter much when slats are fitted. The problem without slats is sudden and sharp stalls and low AoA's.

[kool kitty89]

OK but why the 5-series? ie 00011, instead of 0011, the figures Delcyros posted were for the 00xx 4-series airfoils.

And I'm pretty sure the overall shape (planform, aifoil section, area, span) are identical now that I've looked into it more. The difference was the internal structure was strenghthened with increased internal fuel capacity, this necessitated a new tail assembly. With the round tips it had a span of 40.0ft, area is unknown but probably ~270 ft^2. (not much of a change due to the small size of the tips clipped on the FB.5's 38' span with 262 ft^2)

From de Havilland Vampire and Sea Vampire (1946 - 1969) military aircraft - Vic Flintham

F Mark I The Mark I first flew (TG274) on 20 April 1945 with a square cut tail fin after modifications to the prototype to establish the best fin and rudder configuration. The first aircraft went to 247 Sqn from March 1946 and as production progressed improvements were introduced on the line. From the 40th aircraft the Goblin 2 of 3,100lb thrust was introduced together with auxiliary underwing fuel tanks and from the 51st machine the type had a pressurized cockpit and bubble canopy.
Service Fighter 3, 20, 54, 72, 130, 247, 501, 600, 605, 608, 613 Anti-aircraft co-operation 595, 631 Training 1689 Flt; 202, 203, 208 AFS; CFS; 19 FTS; 102, 103 FRS; 226 OCU; RAFC Communications FCCS; 12 GCF; Acklington APS Other AFDS; CFE; ETPS; NGTE; WEE

and

F Mark 3 The short range of the early aircraft was addressed in the Mark 3 which was built to specification F.3/47 and carried more fuel in wing tanks resulting in extended range (730 to 1,145 miles). The tanks caused stability problems which were cured by lowering the tailplane, extending its chord and changing the shape of the fin and rudder. The prototype was TG275 which flew on 4 November 1945 and the type joined 54 Sqn in April 1948.
Service Fighter 5, 20, 32, 54, 72, 73, 247, 502, 601, 604, 605, 608, 614 Training CFS Communications 25, 602, 603; Chivenor, Odiham, Thorney Island SFs; Other AMSDU; 1, 4, 5 CAACU; CFE; 1 OFU; TEU Khartoum; TFU

[Soren]

Probably because of the different angle of the trailing edge on the outer wing.

[kool kitty89]

What would be the difference between a 0011 and 00011 airfoil then. (the entire wing uses the 5-series 000xx according to the figures) Both have 0 chamber (and 0 chord chamber location), the same max thickness at the same location. THe only difference is that the 5-digit one specifies a CL of 0.

And it should be noted that the entire wing outboard of the nacelles is of the same airfoil section. NACA 00009-1.1-40 (just interesting)


Also if you assume the Vampire Mk.I and F.3 had an area of 270 ft^2 with 40.0 ft span (estimated from the 2' higher span than the 262 ft^2 clipped wing, possibly more area)

AR is calculated to be 5.93 a bit better than you previously stated. And the wing loading of the Mk.I would be more than 25% lower than the 262 in same configuration. (full load clean configuration) at 10480 lbs gross weight (assuming the 270 ft figure) it would be 42.5 lb/ft^2 (~208 kg/m^2) compared to 6,400 kg Me 262 at 60.3 lb/ft^2 (294 kg/m^2); ~41% higher for the Me 262.


And for thrust/weight the 2,700-2,770 lbf engine would be very similr to the Me 262, with a small edge to the 262 with 004B-3/4 engines of 890 kp thrust. (8.73 kN). Nominal thrust on the Vampire with the Goblin I would be ~2,600-2,700 lbf. The losses from the Vampire's short, albeit angled, intakes should be minimal an exhaust losses should be nonexistant, total thrust loss probably only 2-3%. Reasonable considdering the XP-80 with its long and angled intakes and very long exhaust cut it's 2,700 lbf H-1B Goblin engine by nearly 10% down to ~2,460 lbf, not quite as bad on the Later XP-80A and dirivatives after they got the bountary layer bleeds. Similar losses were encountered on the He 178 with its long exhaust. A long ehaust having much more of an effect than the intake, cutting the 500 kp max HeS-3b down to ~450 kp. (one of the major reasons for external engin mounts of the early low thrust engines, putting no penalty on thrust, also the reason for the Vampire's design facilitating the minimal exhaust pipe length)

Though the Goblin II powered Vampire Mk.I (41 production model onward) wasn't built until the war ended it's pretty valid to compare to a 004D/E powered 262. The 004D had a nominal thrust of 930 kp (near 9,000 rpm iirc) by delcyros' figures, the 1,050 kp figure is at 10,000 rpm which was overrev. The 004E put out 1,000 kp nomimal dry thrust (1,200 kp AB iirc). The Goblin II put out 3,000-3,100 lbf (1,362-1,407 kp; 13.4-13.8 kN). Comparing the 2x 1,000 kp and 3,100 lbf (~3,000 nominal) the thrust/weight is very close.

[kool kitty89]

I wonder why they clipped the top of the Vampire's tail from the Spider crab (first/#1) prototype to the change in later prototypes and the Mk.I. (I know the changes in CoG among other changes resulted in the new tail on the F.3, but that's different, the F.3 had the same wing though)

The prototype's tail is clearly seen here with full triangular fins, they appear to be the same as the Mk.I's save the I had them clipped at the top. The F.3 also had a much lower tailplane, right aganst the booms, almost in the jetwash.

The taller tail should have offered better stability and spin characteristics. (the short fin was blanked in a sharp high AoA stall as Delcyros mentioned, creating a dangerous situation that could be hard to recover from)

The F 3's "guitar pick" fins (similar to the DH.88's fin) improved a lot of these characteristics though. (the much later T.11 trainer also got a new tail)

The #1 prototype and the MkI are clearly seen here: Vampire




Mk.I


F.3 vampire:



And here's some info on variants and differences: [1.0] Vampire Variants