1) Title of the invention
Ground effect tests on an aircraft model using towing tank facility

2) Field of invention
It is a quantitative experimental aerodynamic technique to study the effect of ground proximity on an aircraft model. It is an innovative technique to measure the ground effect using towing tank facility, with the sink rate simulation.

3) Use of invention
This simple technique can be used to study the effect of ground proximity on an aircraft model, without the requirement of complicated add-ons like moving belt, boundary layer suctions etc. Apart from this, the facility can be thought of for carrying out normal wind tunnel testing on larger / full-scale UAV models without boundary & wall corrections.

4) Prior art
Customary ground effect testing in wind tunnels are based on fixed attitude of the model with varying the pedestal height, or, keep the ground line fixed and vary the model height at various alphas. To alleviate the surface boundary layer effect, these techniques need moving belt or suction ahead of ground board plane etc.

5) Draw backs of prior art
The normal testing quite cumbersome and involved, especially in matching of moving belt speed with tunnel speed. Apart from this controlling of flapping effect of the belt is too tricky. The suction methodology to control the boundary layer is not effective for larger spans, with longer test sections. Also, for medium sized wind tunnels simulating the sink rate is very cumbersome.

6) Comparison between prior art and present invention
The present technique of measuring effect of ground on an aircraft model simulates the realistic conditions without the need of moving belt. Apart from this the sink rate is also simulated more realistically, which is not possible in conventional testing facilities. Above all since there are no boundary & wall interference corrections the values are more accurate.

7) Aim of the invention
The main objective of this invention is to find out a novel and better way of testing the aircraft models to study the effect of ground during takeoff and landing conditions.

8) Summary of the present invention
The existing towing tank facility at NSTL, Vizag which is generally used for testing of ship models was explored to carry out the ground effect test simulation including sink rate. Separate super structure was constructed to mount the sink rate mechanism and string to hold the model. Provision was made to bring the model as close as 50mm (model scale) to maximum value of 2 meters (model scale) from the surface. All the touch down conditions including cross flow conditions were simulated and the results were analyzed for dynamic effect of ground effect tests. The results depicted that the lift is marginally increased with corresponding nose down movement due to good proximity. Elevon effectiveness also improved with good proximity while the impacts of lateral & directional characteristics are negligible.

9) Brief description of drawings
Fig-1 shows the ground effect test set up that has to be kept inside the wind tunnel test section for ground effect study (conventional method)
Fig-2 shows the schematic diagram of test set up included for the present invention.
Fig-3 shows the pictorial view of ground effect test support systems at NSTL.
Fig-4 shows the pictorial view of model closer to the water bed.
Table 1 shows the summary of ground effect test result

10) Statement of invention
Study of effects of ground proximity on the basic characteristics of an aircraft is mandatory in design and development of aircraft, especially to analyze the impact of ground proximity on lift and pitching moment in order to arrive at the optimum deployment of control surfaces. Till date wind tunnels with moving belt techniques were being used to meet these requirements.

11) Detailed description of invention

The towing tank facility at NSTL was identified to explore the possibility of carrying out load measurements on the model in proximity of the ground. The towing tank facility at NSTL is being used for testing of scaled ship model, which has a carriage which moves on rails separated by a distance of 8 meters, for a length of 500 meters. The depth of the water tank is 8 meters. The usual test speed is 3 m/s while maximum speed is 20 m/s. The carriage is equipped with all the instrumentation required for data acquisition for ship testing.

A separate structure was fabricated to meet the model along with the sink rate mechanism and the six component balance. The portable data acquisition system was positioned in carriage, including the control for different height from the water level. The minimum height from the water level tried was zero mm (model scale) and the maximum height was 2000 mm. The angle of incidence was varied from 0 to 16 degrees covering the entire requirement of takeoff and landing.

The sink rate was also varied between 0.7 m/s to 1 m/s maximum, single point test was carried out for all the designated angle of attack and the dynamic data was captured during sink rate simulation. The data acquired was processed and the differential loads are tabulated for various heights. Typical results at zero height are depicted in table - 1.

Claims

1. This novel technique can be used to study the effect of ground proximity on any aircraft, without the requirement of complicated add-ons like moving belt, boundary layer suctions etc.

2. The testing techniques can be carried out for normal wind tunnel testing on larger or full-scale UAV models without boundary & wall corrections