Simplified Proof Loading By William E. Brown, EAA 10669 Capt., USAF APO 9247, New York, N.Y.

INTRODUCTION

BROWN-JODEL D-9FG WING

The following sequence illustrates the steps which were taken to static test the modified folding wing of my Jodel D-9. In light of the several in-flight structural failures which have taken place in the past, the information should be of interest to anyone building an original or modifying a proven design. No originality is claimed, the methods having been lifted from a number of sources and simplified where possible to suit the test undertaken. Details of the test have not been described and emphasis has been placed on the analytical procedure so that it may be applied to other aircraft. The test described was undertaken as a part of an engineering special-problems course I am taking at the University of Missouri. I am indebted to Richard N. Pugh, my instructor, for the interest taken in the project and

Airfoil NACA 23012 Spa.

Chord 39H"

Stations -vw-l

2.

W-2

W-3

W-4 W-5 W-6 FIG. I —WING LAYOUT

W-7

3.

Gross Weight

Drag Effects

felt to be justified, since it is small compared to the lift.

interest was in verifying strength of the wing-folding modification. If the test were applied to a two-spar wing, 4.

it would be necessary to compute the load division between the spars (see Ref. 2 or Ref. 4). In this case, the entire wing would have to be tested and the weights hung over the spars by straps or some

Center of Pressure Effects

The twisting moments on the wing were ignored. This is valid for the airfoil in question (NACA 23012) which has little center of pressure movement, but would not be valid for all airfoils, especially some of the older ones.

other means. 5. LOADING ASSUMPTIONS

Angle of Attack Effects

The wing was tilted 12 deg. for the test to simulate the wing at the angle of attack giving the maximum lift coefficient.

The entire validity of any test rests on the assumptions made. Only if these are carefully verified, can the test represent the conditions it was meant to represent. With this in mind, the loading assumptions used in the test are described. Remember, they may or may not be

6.

Effects of Wing Weight

The wing weight itself is not involved in creating a

beam load on the spar. Wing weight was subtracted from the gross weight to obtain the net weight carried by the wing. Wing weight was estimated using a weight

valid for another type of test and should be carefully examined before they are applied to another airplane. The assumptions made were:

of 1.35 Ibs. per sq. ft. for cantilever wings (Ref. 2). This proved to be very close to the actual wing weight

Load Factor

A load factor of 4.4 G was chosen as suitable to demonstrate basic airworthiness of the wing (CAR utility category). The wing was designed for 9 G.

when the wing components were weighed later. Gross wt. = GW = 575 Ibs.

Wetted Wing Area/Semi-span = A = 47.84 ft.2

TABLE 1 — LOAD SUMMARY W-]

AREA BETWEEN STATIONS

W-2

576

W-3

6 19

W-4

6.19

W-5

9.08

W-6

6 19

W-7

5.73

W-8

483

Tip

387

(FT/')

FRACTION OF C,. REMAINING AFTER

TOTAL WETTED WING ARF>,

47.84 ft .'

1 0

1.0

EFFECTIVE WETTED AREA BETWEEN STATIONS

5.76

6 19

NET WING LOADING LBS /FT '

521

1 0

1.0

1.0

1.0

046

0.38

6.19

908

6.19

573

222

1 47

LOSSES

SPAR LOAD LBS/G

BAGS NEEDED PER G

16

NOVEMBER 1965

TOTAL EFFECTIVE

= WETTED WING AREA 42.83 ft.'

521

521

30.0

32.2

322

2-l5Lb

2-16 Lb

2-16 Lb

521

473

3 16 Lb

Tip 12-28-64

Airfoil drag effects were ignored in the test. This was

Only the spar box itself was tested (see Fig. 2). Primary

Stations

W-8

Maximum design-gross weight of 575 Ibs. was used for all calculations.

the assistance given in carrying out the test. The Jodel has a single-spar cantilever wing (see Fig 1).

1.

Chord 47'/