Ethan - question of Drag comparisons between 109K and P-51D

[drgondog]

Ethan - I have never seen a wind tunnel based Drag report on the Bf 109. Dr. Hoerner and others have stated that the CDtotal approaches .28-.32. Hoerner has a nice discussion of the Bf 109G in Chapter 14 of his "Fluid Dynamic Drag".

This is data without context as rigorous discussions of CD must also note that CD is plotted as a function of Reynolds number.
EDIT - I quit depending on memory - here are the corrections
At ~ 32 mph the RN=~2x10^^6 (from memory) and P-51D total CD for parasite drag is ~.0193 which includes cooling drag at Zero Lift CL/AoA. The RN=9x10^^6 at 146 mpg. At that RN the CD levels off and holds steady at 0.0155. At max speed the total CDp = .0155 (but here Compressibility multiplier is in range 1.8-2.0 .

This conversation requires a lengthy response for clarity - but Parasite Drag at top speed is dominant factor. Within the Parasite drag discussion at low angle of attack, there are four primary considerations.

First and most important is the profile drag of the lifting surfaces in level flight. The Mustang advantage dominates and a discussion of total drag force reduces to the CD of the wing multiplied by the Dynamic Pressure x Wing Area. At the same speed that the 109 is maxed out, the differences in total drag force is the ratio of wing area of Mustang (is 35% higher than 109) but the CD for the wing of the Mustang is 40-50% lower.

The next factor is profile drag of the fuselage including protuberances, gaps between control surfaces, skin gaps, radio antenna, bomb racks, carb intakes, radiator intakes, etc. The 109 was a dirty bird by comparison and these contributions in CD are not wing area determinants but individual contributions validated piece by piece in wind tunnels.

The next factor is cooling drag, which for a Mustang is astonishing, in that the Meridith Effect produces thrust at high speed but the 109 cooling drag is significant, perhaps 20-25% of the wing in magnitude in total force.

The last considerable drag force is that of friction drag. In NMF condition for the P-51D, the friction drag, particularly within the attached boundary layer, is much less than the camo Bf 109 - but this is a Wetted Area multiplication - advantage 109 with much less wetted area but offset by granularity of production camo paint surface roughness.

Hope this helps.
Bill

 

[Ethan]

Thank you for the reply. It took me some time because I'm not native English speaker or major. So, basically,P-51 does have lower total drag due to the better design.But the famous Laminar Flow Wing just did part of the job, in fact, the wings of P-51 has higher total drag than 109's.But the 109's profile drag is very horrible,I think things like the the supercharge intake and the leading edge slats produced much drag.It's not surprising for 109 was designed much earlier.The Last factor, the camo paint made the surface of 109 roughness, which surprised me, I haven't thought about this.

 

[tomo pauk]

If I may
Here is what Germans reckoned about the Mustang's wing: picture; ('w' = widerstand = drag)
From here: link

 

[pbehn]

The Last factor, the camo paint made the surface of 109 roughness, which surprised me, I haven't thought about this.

The paint used at first on mosquito night fighters was so rough it cost 25MPH in top speed.

The Aircraft - The People's Mosquito

The Mosquito NF.II was a night fighter development of the projected F.II fighter. It was fitted with early generation A.I. Mk IV radar, and painted matt black, and it first joined RAF Fighter Command in April, 1942. No. 157 Squadron, based at Castle Camps in Cambridgeshire was formed on the Mosquito NF.II, and became a major exponent of the type. The Squadron did have difficulties, not just with the temperamental early radar, but with the fact that their aircraft had been painted with a very rough matt black paint, designed to make them less visible at night. Unfortunately, the paint (coded RDM2) induced a great deal of drag on the streamlined Mosquito airframe, slowing the maximum speed by no less than 25 mph! These aircraft were soon repainted with a smooth black paint.

 

[drgondog]

Thank you for the reply. It took me some time because I'm not native English speaker or major. So, basically,P-51 does have lower total drag due to the better design.But the famous Laminar Flow Wing just did part of the job, in fact, the wings of P-51 has higher total drag than 109's.But the 109's profile drag is very horrible,I think things like the the supercharge intake and the leading edge slats produced much drag.It's not surprising for 109 was designed much earlier.The Last factor, the camo paint made the surface of 109 roughness, which surprised me, I haven't thought about this.

Not quite, Ethan - The P-51D wing profile drag at RN=4x10^^6 is 31% of the Total Parasite drag in level flight near top speed (CD=.0155) and the surface roughness is 0.0008. These values are far below the corresponding values of the Bf 109 (CD=.030) with older airfoil design (36% of the Total Parasite Drag with combined with camo paint with surface roughness of .0035 (according to Dr Hoerner in chapter 14.)

Hoerner reported that the Bf 109E full scale drag testing at Chalais-Meudon wind tunnel in 1941 yielded a CDp Total = 0.030 NOT including Induced Drag, no Momentum Drag at the engine air intake, no tail wheel( At RN=4x10^^6).

The actual CD total for the 109 in Hoerners calculations at 380mph at 22,000 feet (RN=2x10^^7), when tail wheel, etc are added is close to 0.030, perhaps slightly more. Use the value of .030

Taking the P-51D CDp values with EVERYTHING included, bomb rack, carb intake radiatior intake, surface roughness, machine gun ports, radio mast, control surface leaks the P-51D-5 was 0.0155 at RN=2x10^^7.

At 380mph the calculated CDp including compressibility, and all other drag factors in comparison with the P-51D-5, at RN=2x10^^7 is:

Bf 109G CDp = 0.030
P-51D CDp = 0.0155

The calculated Total drag coefficient of the wing alone
Bf 109G CDp-wing= 36% of the Total Parasite Drag Coefficient = 0.0107 (from Hoerner Chapter 14.6)
P-51D CDp-wing= 31% of the Total Parasite Drag Coefficient = 0.0048 (from Fig. 9 P-51D-5 NA-8489 Performance Calculations)

To get the Drag Force for the respective wings, use the altitude of 22,000 feet (Hoerner text value) to set the following values:

Q= 1/2 *Rho * V^^2 = 184 pounds per square foot at 22,000 feet for 380mph

Bf 109G Wing Area = 172 sq ft. = S109
P-51D Wing Area = 233 sq ft. = SP51

Bf 109G Drag Force = CD * Q * S109 = 0.0075*184*172 = 237.7 pounds force opposing prop/exhaust thrust
P-51D Drag Force = CD * Q * S51 = 0.0048*184*233= 205.7 pounds " " "

Summary: P-51D Wing has 86% total drag force Less than the Bf 109G despite a P-51 Wing with 35% greater Wing Area.

This is why the Bf 109 in all its variants required much more Hp to try to match P-51 top speed. Ditto FW 190.

 

[Ethan]

Thanks for your reply, may I share your calculations with my friends?They may be interested in this too.And another question about BF109. The use of GM-1 on BF109. As I know, some of the 109T used GM-1 in field to intercept B-17s.
Also there was a plan of BF109H but ended without production.I think it's probably because GM-1 is not very affective for DB605 series. Oxygen produced by GM-1 is not controlled by intake pressure limit, and DB605 has high compression ratio and very sensitive to high intake pressure, which makes it tricky to control the amount of GM-1 injection. Besides, BF109 is not as large as Ta-152H, not much space to store N2O. That's my opinion, I want to hear some of yours.

 

[Ethan]

The paint used at first on mosquito night fighters was so rough it cost 25MPH in top speed.

The Aircraft - The People's Mosquito

The Mosquito NF.II was a night fighter development of the projected F.II fighter. It was fitted with early generation A.I. Mk IV radar, and painted matt black, and it first joined RAF Fighter Command in April, 1942. No. 157 Squadron, based at Castle Camps in Cambridgeshire was formed on the Mosquito NF.II, and became a major exponent of the type. The Squadron did have difficulties, not just with the temperamental early radar, but with the fact that their aircraft had been painted with a very rough matt black paint, designed to make them less visible at night. Unfortunately, the paint (coded RDM2) induced a great deal of drag on the streamlined Mosquito airframe, slowing the maximum speed by no less than 25 mph! These aircraft were soon repainted with a smooth black paint.

It usually costs about 5-10mph though, Mosquito has larger wetted area, the roughness of camo paint became quite significant.

 

[GregP]

Ethan,

Bf 109T's intercepting B-17s? Where? They only made 7 Bf 109T-1s and 63 Bf 109T-2 (without carrier gear). They mostly operated in Norway at first, due to their ability to take off short. That was in 1941, when there were no B-17s in Europe. Later, some of the T-2 were assigned to Helgoland. I think it was 1943. I was under the distinct impression that most were assigned to training units, with only very occasional use on operations.

Not saying you are incorrect. I'm curious, that's all.

 

[Ethan]

Ethan,

Bf 109T's intercepting B-17s? Where? They only made 7 Bf 109T-1s and 63 Bf 109T-2 (without carrier gear). They mostly operated in Norway at first, due to their ability to take off short. That was in 1941, when there were no B-17s in Europe. Later, some of the T-2 were assigned to Helgoland. I think it was 1943. I was under the distanct impression that most were assigned to training units, with only very occasional use on operations.

Not saying you are incorrect. I'm curious, that's all.

The first intercept mission against B-17 was operated by BF-109Ts.But the details of GM-1 installation, no clear evidence yet, still searching.

 

[GregP]

Any date? Or place? Or some supporting information? Where exactly did you read that?

 

[swampyankee]

The number I've usually seen for the P-51's zero-lift drag is a little greater, about 0.0167, but it's still by far the lowest value of any WWII era single-engined fighter, the Bf109 is, far and away the greatest of any of the monoplane single-engined fighters, with almost all of them between 0.020 and 0.025.

 

[drgondog]

The number I've usually seen for the P-51's zero-lift drag is a little greater, about 0.0167, but it's still by far the lowest value of any WWII era single-engined fighter, the Bf109 is, far and away the greatest of any of the monoplane single-engined fighters, with almost all of them between 0.020 and 0.025.

SwampYankee - as you know zero lift drag is not a single value. The P-51D-5 Performance Report tabulates data for 2x10^^6 or for a MAC of 6.63 ft, V=47.5 ft/sec or 32.4 mph. At RN = 20x10^^6 the velocity is 324 mph.

For consideration, taken from the Drag section of NAA Report 8449 dated 12-1-44:

The 'Zero Lift' drag is not constant with Velocity. The CDp (not including compressibility effect) for value of 0.0167 is at RN=9x10^^6 at 148 mph. The Log Plot of RN (Figure 9) from 32mph (SL), to 148 mph (SL) is a straight slope from .0193 at 2x10^^6 to .0155 at 9x10^^6.

The Plot represents CD = (CDp1 + Delta CDp1+ delta CDp2)* CD/CDinc + CDi where
CDp1 = basic minimum drag coefficient of the airframe with no gun ports, antenna, racks, roughness or gaps (i.e smooth wind tunnel model)
Delta CDp1 = drag coefficients of guns, racks, antenna, leaks and surface roughness
Delta CDp2 = drag coefficient dependent on Angle of Attack (plotted vs CL)
CD/CDinc = multiplier based on Mach number, essentially non-linear from M= 0.2 with value near zero to approximately 1.2 at 0.7M wherer the drag rise is near asymptotic. BTW the Mustang curve is far lower than say, the F4U or P-38 or P-47 or any conventional airfoil type fighter with T/c near the P-51.
CDi = Induced Drag

For comparison, the P-51H values at RN=2x10^^6 = 0.0175 (vs 0.0193) and at RN=9x10^^6 = 0.0152 (vs 0.0155). As for the points of comparison, include P-51H lower wing profile drag but higher friction drag, as the wetted surface was significantly higher than the P-51B/D (greater length, greater wing and empennage surface area).

 

[Shortround6]

Any date? Or place? Or some supporting information? Where exactly did you read that?

Greg, Helgoland is an Island in the corner of the North Sea about 45 miles north of Wilhelmshaven and about 50 miles south of the Danish border. (about 40 miles west of the coast of the German "neck").
It is certainly in a geographic location to intercept allied bombers going to/from Germany if they use the overwater North sea routes.
In fact the British bombed the everloving SH** out of it in the closing month of the war.

Not to mention what they did in 1947 (largest non-nuclear explosion in history).

Edit:

Radinger &Schick's book Messerschmitt Bf 109 A-E says about 12 (or less?) 109T s were sent to Heligoland after April of 1943 so the timing looks good also.
Wither they ever attacked a formation or just (even?) attacked stragglers/damaged aircraft is certainly subject to question.

 

[Ethan]

Greg, Helgoland is an Island in the corner of the North Sea about 45 miles north of Wilhelmshaven and about 50 miles south of the Danish border. (about 40 miles west of the coast of the German "neck").
It is certainly in a geographic location to intercept allied bombers going to/from Germany if they use the overwater North sea routes.
In fact the British bombed the everloving SH** out of it in the closing month of the war.

Not to mention what they did in 1947 (largest non-nuclear explosion in history).

Edit:

Radinger &Schick's book Messerschmitt Bf 109 A-E says about 12 (or less?) 109T s were sent to Heligoland after April of 1943 so the timing looks good also.
Wither they ever attacked a formation or just (even?) attacked stragglers/damaged aircraft is certainly subject to question.

1941.9.8 JG77's 109Ts from Stavanger intercepted B-17s.That's what I got

 

[Ethan]

Any date? Or place? Or some supporting information? Where exactly did you read that?

1941.9.8 JG77's BF109Ts from Stavanger shot down three B-17s belongs to RAF, numbers are AN525,AN533 and AN535.

 

[swampyankee]

Overall, I tend to put pretty large error bands on these values, even wind tunnel results of actual aircraft being tested.
The point I was failing to make is that both the P-51 and Bf109 are outliers, with the Mustang having much lower zero-lift drag that its contemporaries in WWII and the Bf109 much greater.

 

[drgondog]

I agree your points swampyankee.

That said, NAA conducted a series of propellerless dive tests on a P-51B up to 0.75M to compare the results with the NACA wind tunnel tests for Total Zero Lift Drag as well as CL versus CD for lift related pressure drag.

Offhand I don't know if any other fighters were tested in that manner.

 

[Deleted member 68059]

Hi Ethan,
109T was supposed to be an aircraft carrier fighter, so in terms of B17 intercepts not really the major force. (Interestingly the 109S was being developed for Laminar Flow wings....)

GM-1 was used on all frontline Luftwaffe single engine aircraft, introduction dates vary and usage was not total in every squadron, so I do not see GM1 being a 109T specific question.

I can recommend you post the source for your comments about GM-1 on the DB605 - as the information you posted does not match the original material I have. It was used with great sucess on the DB605 - in fact the greatest difficulty was just the handling of it on the ground, and making the special tanks for it in the airframe.

Regards

Calum

 

[Deleted member 68059]

Hi Bill,
I can tell you that if you were to say the 109 has a drag of 0.03, it would not be an inaccurate statement; if you understand my meaning.

As has been said, these numbers are however fraught with difficulty unless you have a corresponding report from the same wind-tunnel. (However I`d be shocked if another competent tunnel got it more than 20% out.) This particular one was done in France at Chailais Meudon.

 

[swampyankee]

I've done analysis of wind tunnel data (somewhere in Sikorsky's archives is an internal report of which I was a co-author....) and the differences, even for something as straightforward as measuring a 2-D airfoil, between tunnels is significant. Both the P-51 and Bf109 are far enough away from the zero-lift drag coefficients of their contemporaries to be outliers; most ww2 single-engine fighters were between about 0.020 and 0.025.

Just looking at its performance relative to the larger, heavier P-40 indicates that the Bf109 is not efficient: the Messerschmidt's performance is not as much better as the P-40 as it should be.