Bf-109 drag values

[stona]

Also please show me button head rivts in 109.. it was all flush rivet as I know.

You are correct but overall,particularly later in the war,the quality, surface finish and fit on german aircraft had fallen in standard. A fact noted by both the RLM and allied reports.
Every little gap or misaligned panel and every rough area of overspray between camouflage colours contributes to extra drag.
Cheers
Steve

 

[riacrato]

Parasitic drag is that drag caused by the aircraft and wing moving through the air. It does not produce any lift.

Induced drag is that drag caused as a byproduct of producing lift. It can be calculated from the L/D ratio of the wing cross section for a given angle of attack (given in tables) with corrections for aspect ratio, planform and wing twist. Since L/D is often around 50:1 in level flight it is a small component of drag. However when pulling G it becomes more significant.

The Me 109 wing likely had less parasitic drag since it was smaller. At very high speed, near transonic, the Spitfire wing may have had less parasitic drag since the thickness/chord ratio was less. and so less shockwave drag was created.

In terms of induced drag the Me 109 was almost certainly worse even though the wing had less parasitic drag.

This is because as the wings angle of attack is increased its lift increases rougly linearly with angle of attack however the drag tends to increase with the square of the angle of attack.

The smaller wing of the Me 109 must pull higher angles of attack to generate the same lift (though remember they have different wing sections). Because the Me 109 had slats that might have allowed about 40% extra angle of attack and roughly 40% extra lift the aircraft can certain generate a great deal of lift from its smaller wings. However to generate that high lift from small wing means more induced drag is created; this will slow the aircraft down and cause it to loose height.

The drag on a wing has two components: a parasitic and a induced component, though in charts and tables they are usually combined into one they can be seperated out in some of the equatuons which give lift and drag in terms of a polynomial.

Having sufficient power was absolutely critical for Me 109 which is probably why in late 1944 when Me 109G10, Me 109K4 and likely Me 109G14ASM were reasonably common that some P-51 pilots reported being outmanouvered at altitude.

You are right. I tend to mix up those things a lot.

 

[tomo pauk]

If total drag was high on 109, why was it so fast? Power does not explain, as the 109 did not have particular great power. It seems self contradiction so I think its incorrect. This German report shows Spitfire and 109 on same engine, so power is same. http://www.wwiiaircraftperformance.org/me109/db109g.pdf 109 is faster by about 20 kph. So drag is less obvious.

Also please show me button head rivts in 109.. it was all flush rivet as I know.

Here is my take:
The Spitfire and Bf-109s (from E untill later Gs) were pretty evenly matched in regard to Cd0 (coefficient of drag at zero speed). The Spitfire's drag (ie. drag force) was greater than the drag of those 109s because Spit's wetted area was far greater, mostly due to the wing of greater area ( G6, no gondola cannons has 590 sq ft of wetted area, Spitfire IX = 831 sq ft).
In other words, a coefficient (CdO, Cdwet etc) is NOT a same thing as the force (drag force in N, or lb). So the plane can have greater Cd0 and lower drag than the next plane we want to compare it with - simply, being a smaller plane.

 

[drgondog]

If total drag was high on 109, why was it so fast? Power does not explain, as the 109 did not have particular great power. It seems self contradiction so I think its incorrect. This German report shows Spitfire and 109 on same engine, so power is same. http://www.wwiiaircraftperformance.org/me109/db109g.pdf 109 is faster by about 20 kph. So drag is less obvious.

Also please show me button head rivts in 109.. it was all flush rivet as I know.

Tante Ju - all good questions. I will answer to best of my ability. First - I have not performed a detailed drag analysis on either the Spit or 109.

Something bothers me about the 'curves' versus 'shap breaks' displayed for Spit 5 performance. The breaks for the DB605A in Both airframes should be sharp and the same on both airframes - those are critical altitudes for the engine's stages. Further the gradually changing inflection points (presumably) are skewed to higher altitudes? For theoretically the same engine? Have you got an idea why this is so? Is the example Spit a "clipped, clapped and cropped" version of the Mk V or the less draggy elliptical planform version.

I'm also wondering why the Luftwaffe was comparing against the the 109G versus the Spit V in May 1944?

The second bothersome display is showing the critical altitude of the Mk 45 equipped (theoretically) Spit V as 6Km instead of ~ 4260km/14000 feet?

Here is the net - the CDo calcs (zero lift - all 'other' drag contributions except CDi) based on total drag is less for a Spit V than for an Me 109G per the build up approach displayed by Hoerner - so I can't comment on the value of the contrasted link to a representation of comparative drag.

Next - I didn't mean to imply that the 109G had 'button head' rivets - I was simply lumping such (as well as attach bolts for wings, gaps in sheet metal joins, dimples for flush rivets, etc into the category of parasite drag components that must be accounted for.

Last, size does matter - and hp+exhaust thrust combinations are specific areas of refined 'guestimates' when building a free body diagram/analysis of T=D

 

[tomo pauk]

At Mike Williams' site, there at many different FTHs stated for Merlin 45, ranging from 14700-21000 ft, for +9 lbs/sq in boost, all values for high speed/maximum ram.

 

[stona]

Ooops,wrong place

 

[tomo pauk]

IIRC the Messerspit was characterized as being superb climber, wile both Spitfire Hurricane were 'childishly easy to take off and land, compared with Bf-109'?

( I'm not claiming that 109 was pain to make those tasks)

 

[drgondog]

For what it is worth, climb is a function of thrust minus drag (excess thrust) divided by weight. Also typical climb speeds occurred below 200 mph - deep in the drag bucket at high CL where induced drag dominated over parasite/form drag.

 

[GregP]

Tomo Paul, Re post 23, it is zero lift, not zero speed ... probably a typo.

At zero speed ALL aircraft have zero drag. But you knew that.