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XyZspineZyX
08-08-2003, 04:54 PM
I wanted to start a new post because it is apparent that while some of us are amateur aviation historians or pilots, others know very little about the technical development of aircraft. I am using the question about radial versus inline engines as an example but the reference I mention below covers much more including airfoil shapes, wing loadings, and flaps. This is a great reference and it is online at:

http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm

It is out of print so you have to use the on-line version.

An example of content on the effect of streamlining on drag. These results indicate that use of a cowling on a radial engine configuration (compared to a streamlined point nose) did not increase drag a great deal (only from .0166 to .0186). The illustrations did not post and the layout is much better (and understandable) in the original document:

"Drag cleanup investigations are still performed even today. A modern twin-engine general aviation aircraft is the most recent example of such an investigation. The procedure followed in a wartime drag cleanup study consisted of the following steps: First, the aircraft was examined in detail, those features suspected of causing unnecessary drag were identified, and necessary changes to eliminate the suspected unnecessary drag were planned. The airplane was then put in a faired and sealed condition in which all protrusions were either removed or carefully faired, all openings were closed, and all external leaks were sealed. The airplane was then returned to its service condition, item by item, and the drag was evaluated for each step. The procedure is illustrated by the results contained in figure 5.5 taken from reference 42, which shows the sources of drag for the Seversky XP-41 aircraft. The XP-41 airplane was very similar in appearance to the Seversky XP-35 shown in figure 4.14. Figure 5.5 shows that the aircraft drag was evaluated for 18 different conditions, which are indicated by sketches on the left-hand side of the figure and described on the right-hand side of the figure. The drag coefficient of the clean airplane was 0.0166, as....



--------------------------------------------------------------------------------

Condition number
Description
CD (CL = 0.15)
[Delta] CD
[Delta] CD, percent a

1
Completely faired condition, long nose fairing
0.0166
-
-

2
Completely faired condition, bluntnose fairing
0.0169
-
-

3
Original cowling added, no airflow through cowling
0.0186
0.0020
12.0

4
Landing-gear seals and fairing removed
0.0188
0.0002
1.2

5
Oil cooler installed
0.0205
0.0017
10.2

6
Canopy fairing removed
0.0203
-0.0002
-1.2

7
Carburetor air scoop added
0.0209
0.0006
3.6

8
Sanded walkway added
0.0216
0.0007
4.2

9
Ejector chute added
0.0219
0.0003
1.8

10
Exhaust stacks added
0.0225
0.0006
3.6

11
Intercooler added
0.0236
0.0011
6.6

12
Cowling exit opened
0.0247
0.0011
6.6

13
Accessory exit opened
0.0252
0.0005
3.0

14
Cowling fairing and seals removed
0.0261
0.0009
5.4

15
Cockpit ventilator opened
0.0262
0.0001
0.6

16
Cowling venturi installed
0.0264
0.0002
1.2

17
Blast tubes added
0.0267
0.0003
1.8

18
Antenna installed
0.0275
0.0008
4.8


Total 0.0109



a Percentages based on completely faired condition with long nose fairing.






Figure 5.5 - Experimental study of drag sources on Seversky XP-41. [from ref. 42]

XyZspineZyX
08-08-2003, 04:54 PM
I wanted to start a new post because it is apparent that while some of us are amateur aviation historians or pilots, others know very little about the technical development of aircraft. I am using the question about radial versus inline engines as an example but the reference I mention below covers much more including airfoil shapes, wing loadings, and flaps. This is a great reference and it is online at:

http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm

It is out of print so you have to use the on-line version.

An example of content on the effect of streamlining on drag. These results indicate that use of a cowling on a radial engine configuration (compared to a streamlined point nose) did not increase drag a great deal (only from .0166 to .0186). The illustrations did not post and the layout is much better (and understandable) in the original document:

"Drag cleanup investigations are still performed even today. A modern twin-engine general aviation aircraft is the most recent example of such an investigation. The procedure followed in a wartime drag cleanup study consisted of the following steps: First, the aircraft was examined in detail, those features suspected of causing unnecessary drag were identified, and necessary changes to eliminate the suspected unnecessary drag were planned. The airplane was then put in a faired and sealed condition in which all protrusions were either removed or carefully faired, all openings were closed, and all external leaks were sealed. The airplane was then returned to its service condition, item by item, and the drag was evaluated for each step. The procedure is illustrated by the results contained in figure 5.5 taken from reference 42, which shows the sources of drag for the Seversky XP-41 aircraft. The XP-41 airplane was very similar in appearance to the Seversky XP-35 shown in figure 4.14. Figure 5.5 shows that the aircraft drag was evaluated for 18 different conditions, which are indicated by sketches on the left-hand side of the figure and described on the right-hand side of the figure. The drag coefficient of the clean airplane was 0.0166, as....



--------------------------------------------------------------------------------

Condition number
Description
CD (CL = 0.15)
[Delta] CD
[Delta] CD, percent a

1
Completely faired condition, long nose fairing
0.0166
-
-

2
Completely faired condition, bluntnose fairing
0.0169
-
-

3
Original cowling added, no airflow through cowling
0.0186
0.0020
12.0

4
Landing-gear seals and fairing removed
0.0188
0.0002
1.2

5
Oil cooler installed
0.0205
0.0017
10.2

6
Canopy fairing removed
0.0203
-0.0002
-1.2

7
Carburetor air scoop added
0.0209
0.0006
3.6

8
Sanded walkway added
0.0216
0.0007
4.2

9
Ejector chute added
0.0219
0.0003
1.8

10
Exhaust stacks added
0.0225
0.0006
3.6

11
Intercooler added
0.0236
0.0011
6.6

12
Cowling exit opened
0.0247
0.0011
6.6

13
Accessory exit opened
0.0252
0.0005
3.0

14
Cowling fairing and seals removed
0.0261
0.0009
5.4

15
Cockpit ventilator opened
0.0262
0.0001
0.6

16
Cowling venturi installed
0.0264
0.0002
1.2

17
Blast tubes added
0.0267
0.0003
1.8

18
Antenna installed
0.0275
0.0008
4.8


Total 0.0109



a Percentages based on completely faired condition with long nose fairing.






Figure 5.5 - Experimental study of drag sources on Seversky XP-41. [from ref. 42]

XyZspineZyX
08-08-2003, 09:22 PM
I know it is lame to bump your own post but the above really is an interesting reference and it is free.

And it is a change from talking about the patch.

XyZspineZyX
08-08-2003, 09:45 PM
Interesting- book marked it - maybe most of the ppl here already have this, but I didn't, so ...

thanks /i/smilies/16x16_smiley-happy.gif And a little bump to save you from lameness /i/smilies/16x16_smiley-wink.gif

Cheers,
Cold_gambler

XyZspineZyX
08-09-2003, 12:17 AM
Thanks for the link/info.