Re: He-100 Part II- He P.1079 vs Me 509



bbrought wrote:
Eunometic wrote:
bbrought wrote:
Eunometic wrote:
What happens of the Coefficient of Drag of is dropped 20%-25%.

What happens of the Mach breakaway where localised supersonic flows
occur is raised by say 0.05M (33mph?)

Eunometric, you should understand though that the two improvements you
mention here are huge:

To reduce drag coefficient by 20 - 25% when you go from a biplane to a
monoplane - no problem. To reduce drag coefficient by 20 - 25% when you
already have a highly efficient airframe on the other hand is
incredibly difficult. When working with racing vehicles, you often get
excited about a 1% reduction as it could potentially mean the
difference between winning or coming last (especially in the more
"scientific" or high-tech sports).

These Coefficient of Drag improvements (about 25%) were well within the
realm of what was being discovered in the 1930s and 1940s. Have a look
at illustration 196 and 197.

http://history.nasa.gov/SP-4305/ch7.htm

Are you refering to the Buffalo work? It illustrates exactly what I
said - if you start with something bad, it is easy to make a large
reduction in drag. You are starting with a late-war fighter that
already had low drag. Improving that gets much more difficult.

Actually I wanted to emphasise the Seversky XP-41 work:
http://history.nasa.gov/SP-4305/p198.htm
The Heinkel P.1076 is to all practicable purposes in condition 1; it
was recall the 3rd or 4th iteration of the Heinkel 112, Heinkel 100
designe.

As far as drag reduction I think the freedom that surface cooling
provided to the designers could help achieve this: although WW2
fighters recovered engine cooling heat to generate thrust this still
didn't entirely compensate for drag: even in the P-51. Futhermore the
need to situate the radiator duct drives the shape of the fueselage.
An aircraft equiped with functioning surface cooling system is entirely
liberated from this constaint.

I have the following data taken from David Lediciners Computational
Flow Dynamics analysis of WW2 fighters.

"WW2 Fighter Aerodynamics" By David Ledinicer EAA 135815 (somewhere on
the internet)

The following data is given
f for equivlalent frontal area, WA wetted area, Cdw (Coeficient of drag
wetted)

Spitfire IX; f = 5.40sqft, WA= 831.2sqft , Cdw= 0.0065
P-51B; f= 4.61sqft, WA= 874.0sqft, Cdw=0.0053
P-51D; f= 4.65sqft, WA= 882.2sqft, Cdw=0.0053
Fw 190A8; f= 5.22sqft, WA= 735.0sqft, Cdw=0.0071
Fw 190D9; f= 4.77sqft, WA= 761.6sqft, Cdw=0.0063

What is amazing about this is the suprising efficiency of the Fw 190D-9
airframe, due to its low wetted area, which almost makes it as
efficient as the P-51 which has a low Cdw but higher wetted area. The
P-51's advantage were probably its laminar profile wings and their
effective retardation in compressabillity effects.

The Heinkel P.1076 compared to the Fw 190D and its Ta 152 spinoff and
indeed the allied aircaft would surely have had the following
advantages;
1 Even lower wetted area due to the absence of radiators sturctures for
engine cooling, intercooler chooling or oil cooler: all this was dealt
with by the surface cooling. In every respect the aircraft should be
considered a turboprop in characteristics becuase of this.
2 Lower Cdw due to the greater possibillities of streamlining. Surface
cooling poses less dictates on altering airframe aerodynamics to
provide a place for the radiator.
3 Better aerodynamics due to better wings (high speed profile,modest
sweep)
4 Absence of suction behined the cockpit bubble canopy.
5 Possible area ruling; slight waisting behined the engine and at the
wing juncture, slight forward sweep.

What is also startling is the relatively high equivelent flat plate
frontal area of the Spitfire IX due to its high wetted area. (The
Spitfire XIV Griffon and Spitefull would be only a little more)

What I'm saying is that the P.1076 could achieve the low wetted area of
the Fw 190D9 and the Cdw of the P-51D to achieve equivalent frontal
area of 4.03sqft. It could take advantage of new know how such as
transonic wing sections that reduce the rise in compressabillity drag.
The FW 190 and Ta 152 both had wings of NACA 23015 root and NACA 23009
tip with the Fw 190 having 2 degrees linear washout from root to 80% of
span at which point the twist ceased.

Imagine, if you will, a Fw 190D-9 with the cylindirical cowling of that
anular engine radiator deleted and neatly faired into the boss of the
propellor spiner. Thats got to reduce both wetted area and Cdw.
Likewise the P-51 with the area dedicated to the radiator scoop sides
removed and the suction drag formed by the canopy removed.


Small doesn't mean low drag though.

Actually, it very often does. Dimensional drag force is calculated as:

Agreed but it also very often does not.

In the context of the example given, the small size contributed
significantly in getting more speed from the power available. I
explained why in the rest of my disccusion.

Radial engined aircraft generally have notably higher frontal areas and
Cd; they often make up for this with the lower induced drag from their
lower weight or simply higher power to weight ratios.


Like all of the so called 'laminar profiles' it didn't maintain
laminarity

That is correct - but only at the time. Today with smooth, accurate
composite wings it works very well. All modern gliders have airfoils
designed to maximize the extent of the laminar boundary layer and these
work "as advertised".

Actually I believe it still doesn't work very well, it works reasonably
well. They are still vulnerable to dirt, insects etc but at least they
are not vulnerable to surface roughness, bad paint, aluminium dimpling
etc. Attemps at using this technology comercialy have failed or relied
on secretions of lubriants from the leading edge to clear detritus of.

The modern airfoils are generally designed to be much more robust than
their predecessors. Of course, most glider pilots will at the very
least wipe their leading edges before a flying session (at least this
was the case for all the clubs where I have flown over the years). For
what its worth - my PhD was in 3D inverse aerodynamic design - I spent
a lot of time on this problem then as well as practical experience on
actual designs since. This technology is used in one way or another on
virtually every modern subsonic design out there where performance is
important. In case you were curious, the other field in which I have
worked over the years is flight dynamics and flying qualities of
fighter aircraft.

By 3D inverse aerodynamic design you mean that you begin with the
pressure distributions you want and then develop the airfoil or
fueselage from that in a similar way that Eastman Jacobs inverted
Theodersons conformal mapping methods (theordresens methods could to
within 10% estimate drag and lift of any arbitray airfoil) to derive
the first laminar profiles from a desirable pressure gradients?




As a side topic what would a supercritical airfoil, perhaps with modest
sweep have done for a Spitefull?

That is difficult to say, not knowing what the limiting factors in its
design were.

What software is out there suitable for CFD? Are there modules for
MATLAB etc?





Doriner Do 335 also initialy had handling problems; these were dealt
with by increasing the wings breadth at the roots to give a mild
Handley Page Victor crescent wing like appearence. The thiner section
then stalled earlier than the tips. Also mildly 'area ruled' the
aircraft.

I am curious as to how you believe this aircraft was "mildly area
ruled". I don't see any pinching of the fuselage around the wing to
compensate for the wing area.

"Pinching" or "waisting" isn't necessary to area rule an aircraft.
Since when have you seen a pinched waist since the F-102? The 'bubble'
of the b707 flight deck/upper deck is carefully profiled and positioned
to 'area rule' the aircraft.

Generally when a new aircraft is expected to fly in or through the
transonic regime, it is possible to implement area ruling in more
subtle ways than the traditional pinching if taking it into account
right from the beginning. That being said, there is a retired Mirage F1
standing just outside my office which has a very obvious contraction of
the fuselage underneath the wing. I am sure there are more examples of
this besides the F-102. In the case of your Do 335, you would have had
to pinch the fuselage as there was nothing else in the design helping
with "area ruling".


However it isn't strictly 'area ruling' since true area ruling must
conform to the cross sectional area of a Sears-Haack body. All that it
does is to ensure changes in cross sectional area are less radical.

Even if not a perfect application of the area rule it still reduces or
delays incipient wave drag.

However, in the Dornier example there is no evidence of any attempt to
area rule the aircraft.

Area ruling was often accidental that came out of trial and error in
the wind tunnel from wing-fueselage integration etc. Practical
empirical methods preceded a sound theoretical understanding. The flat
sides of the P-51 proably helped here. They don't 'coke bottle in' but
at least they don't bulge out either.


In fact, the deepest part of the fuselage
is where the wing is located, so there would be a very sharp increase
in cross-sectional area at this point.

Yes, but root sweep reduced the suddenness of cross sectional area
change, inner sweep on the wing roots as on the Do 335 also does this.
I'm not refering to the perfect application of the area rule as pers
Sears Haack. Dornier actually realised that they could do a lot better
aerodynamically than the Do 335 and proposed the P.247 aricraft that
they expected to fly much faster than Do 335 but on only one engine:
http://www.luft46.com/dornier/dop247.html

The small amount of LE sweep on the Do 335 would have done little to
make up for the increased cross-sectional area of the fuselage at the
same location.

We're in the realm of a opinion here since we don't have a CFD model
however I am willing to admit that it may have been something ranging
from a little more than nothing to a few mph.


It was a lot better than most aircraft of the era the rather fast P51H
had its canopy placed in a rather unfavourable position for instance.

I agree that the Mustang was not good either. If anything, the long
thin fuselage of the Do 335 would have helped a little, but I still see
very little in its layout to suggest any form of area ruling
(accidental or otherwise).

Practical experience shows that the pusher configuration, if
implemented thoughtfully, has more advantages than disadvantages
aerodynamically. Propeller efficiency losses of 2-3% are
counterballanced by greater reductions in drag due to less turbulence
and the 'boundary layer' suction of the pusher propeller helping to
maintain laminar flow over the fueselage. Ofcourse this must be done
with a good clean fueselage to begin with but as those using pusher
configurations are already concerned with aerodynamic efficiency this
is already acounted for. It's not without reason that Burt Ruttans
aircraft are so often pushers. (incidently he is credited with
producing the first truely laminar flow wing)

Burt Rutan's designs are often pushers because he likes the canard
layout. This layout usually leads to a pusher configuration since the
CG and mass distribution requirements makes it a better choice. I have
yet to see conclusive evidence that either pusher or tractor
configuration is fundamentally better than the other. Each has its
proponents, but I am not convinced either way.

There are a significant amount of attempts to produce ultrafast
aircraft using a pusher configuration so many people have at least
thought it worth attempting.

.

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