RAVIN Aircraft Manufacturers. Wing Design Specifications

 Wing Design Specifications

A standard NACA 64-series profile was used with a bit of "voodoo" brought into the shape by Francois Jordaan.  The standard handshake overlap main spar design is used to join the two spars in the fuselage.

Wing Design Data

This report presents the results of a static loading test of the wings of aircraft with serial number 500-0509A which was performed at the SA RAVIN facility on Plot 13A, Airport road, Cynthiavale, close to the Wonderboom Air Port, Pretoria. The test was witnessed by the SACAA certification engineer Mr Phillip Ferreira on Wednesday 16^th October 2005.

1. Test Procedure

The spanwise lift distribution on the wings was calculated in a spreadsheet program, using the Schrenk approximation. The resulting wing bending moments were calculated for a number of loading cases. The most critical case (highest bending moment) was found to be with 50% fuel in the tanks (230 kg) and with the aircraft loaded to its maximum take-off mass of 1620 kg. The resulting shear force and bending moment distribution was used as the test load and this distribution was used to calculate the whiffletree geometry (see Appendix A).

To demonstrate the test load (limit load at n=4.4 + 20%) the wings were mounted in a specially constructed steel whiffletree frame via the main spar bolts, rear spar bolts and forward spar attachment brackets that are used to attach the wings to the fuselage. Appendix B gives a general view of the wing mounted in the whiffletree frame.

The aerodynamic load distribution was simulated by applying input loads at 8 points on each wing. The 8 load introduction cradles were interconnected by spreader beams in such a way that the total load applied to each wing by a hydraulic actuator is distributed between the 8 load introduction points in the correct proportions. The load applied to the right hand wing was measured by means of a load cell. Since the two identical hydraulic actuators applying loads to the right hand and left hand wings are connected to the hydraulic power supply in parallel, it is assumed that the loads applied to the two wings will be identical for practical purposes.

The test load is calculated as follows:

A calibrated electronic load cell was used to measure the applied loads. Appendix C presents the load cell calibration certificate. The load cell readout was recorded as representing the zero load condition with the spreader beams and loading cradles only suspended from the hydraulic cylinders. A load of approximately 50% of the test load was applied to the wings via the hydraulic actuators, and then relaxed to the “zero” condition. The zero deflection positions at each wing tip leading edge was then marked. The maximum load was then applied to the wings and the deflections marked. The load was then removed and the residual zero-load deflections noted.

2. Test Observations

The following load cell readings and deflections were noted:

The deflection of 50 mm at the tip of the R/H wing is due to settling in the rig due to the pre-load. The actual deflection of the wing at the test load is therefore 135 mm.

The maximum load actually applied was 129% of the aircraft limit load, and was maintained for at least twenty seconds without any signs of failure or yield.

The aileron mounted to the R/H wing moved freely at the maximum test load, indicating no tendency to bind up under load.

3. Discussion of Test Observations

The purpose of the 50% pre-load is to allow the wing to “settle” in the test rig. Some residual deflections are expected after this load is removed.

After “settling”, there was no measurable residual wing deflection after the test. This indicates that at limit load + 20% the wing was acting within its elastic stress limits.

No residual deflections were measured after removal of the 129% load, indicating no permanent deformation in the wing structure.

The test observations are typical of what may have been expected.

4. Conclusion

From the foregoing considerations it is concluded that:

a.         The wings of the Ravin 500 aircraft, serial number 500-0509A have been  demonstrated to be structurally adequate to carry their intended load at the aircraft limit load factor.

b.         The main spar sets were built as a batch, using the same batch of Carbon Fibre material and resins. It was agreed between SA Ravin and the SACAA (Messrs P Ferreira and A Swanepoel) that the results of this static load test shall apply to the three wings built as a batch, without the need to test the other two wings. The results of this static load test therefore apply wings with the following serial numbers:

·           500-0509A,

·           500-0510 and

·           500-0511

These wings are therefore considered structurally safe to be used throughout the Ravin 500 aircraft’s operating envelope.

Winglets

Most of the Ravin 500’s are fitted with Winglets.  This is a vast improvement on the wingtips.  The aircraft is much more stable,

has an increase in speed of approximately 5 to7 knots,  more stability at higher altitudes, more docile on landing and improved aesthetics.

Wingload and fluttertests

  See Test Reports below.