Hybrid Force Balance

High Capacity Internal Balance for Wind Tunnel TestingThe design of the Hybrid Force Balance traces its beginnings to the late 1950’s and early 1960’s; we have a continuous history in balance design and manufacture beginning in 1954. Our Hybrid Force Balance has the advantages of both the single piece moment balance and the multi-piece force balance; balance designs are tailored to requested load capacity and geometry.

The Hybrid Force Balance directly measures two forces (one forward and one aft of the Balance Moment Center) in the normal force and side force planes and measures rolling moment and axial force. Pitching moment and yawing moment are resolved from the forces and known distances to the Balance Moment Center (BMC).

Internal Force Balance for Wind Tunnel TestingThis design has reduced deflections and higher frequency response than a moment balance while maintaining a high level of accuracy. The model or test article is attached to the outer shell’s journal (metric) section while the aft taper (non-metric) end is attached to earth / ground. This balance is reliable, with redundant multiple bridges and features a fail-safe captive outer shell.

In the early 1990’s, a dramatic increase in load capacity of the balance was obtained by incorporating a separate flexured axial element and significantly changing the flexure design of the other components. Another design evolution in the 2000’s further increased the maximum NF. For a 2.0” diameter balance, the maximum normal force increased from 3000 pounds to 7200 pounds; all of the other loads were proportionally increased.

An Evolutionary Leap Forward

High Capacity Internal Balance for Wind Tunnel TestingWind tunnel testing continues to require increased loads per unit diameter from balances. The drive to improve balance performance and increase the operating envelope for high Alpha and Beta testing requires a change in the basic balance load range. Additionally, the aircraft’s exterior lines limit the ability to accommodate large diameter balances or balances with high deflections that are required to meet these higher loads. To test at these conditions, a wind tunnel balance must be capable of providing accurate model loads data under high combined loading conditions while allowing the model to maintain its aerodynamic shape at the sting exit. The larger load capacities for the smaller diameter of the Hybrid Force Balance meet these requirements. allow it to  increased load and decreased deflection requirements have challenged us to develop our next generation of force type balance.

The size of this balance can range from 0.90” to 12.0” diameter; maximum normal force ranges from 100 lb to 100,000 lb.

The High Capacity Hybrid Force Balance increases the magnitude of the loads in all axes which allows the user to reduce overall balance inventory, while increasing capability and accuracy at the same time.

Key Benefits

  • Rigid - Accurate - Reliable
  • Flexibility in axial load range selection
  • Temperature effects reduced
  • Integral Flexure Design with improved performance
  • Cross Hatch minimizes risk of galling
  • Thick walled taper design with increase factor of safety
  • Internally mounted cable connector provides access for easy cable maintenance and replacement if needed
  • Design allows for a variety of taper interfaces to match customer existing inventory of stings
High Capacity Internal Balance for Wind Tunnel Testing
High Capacity Internal Balance for Wind Tunnel Testing

 

 

Single Piece Moment Balance

Multi Piece Force Balance

Hybrid Force Balance

Captive Design    
       
High Accuracy  
       
Limited Bi-directionality  
       
Low Deflection  
       
Low Hysterysis  
       
Redefinable Load Envelope    
       
Axial Force Load Path is Distributed    
       
Augmented Axial Capacity    

Versatility

Our unique flexure design permits a significant increase of roll moment by reducing allowable normal force

Rolling Moment vs Normal Force for Hybrid Force BalanceThe balance can be characterized over multiple load ranges, while maintaining the high accuracy performance. This would allow multiple balances covering separate load ranges to be replaced with one Hybrid Force Balance.

2.000 Balance Case Study - Possible Loads for the Same Balance

 
NF (lb) 
@ 0 PM
PM (in-lb) 
@ 0 NF
SF (lb)
@ 0 YM
YM (in-lb) 
@ 0 SF
RM (in-lb) AF (lb)
1 7,000 21,000 3,000 9,000 5,000 500
2 5,000 14,000 700 4,000 5,400 500
3 6,400 20,000 2,000 6,000 6,000 600
4 3,000 9,000 1,500 3,000 8,000 900

Summary

  • One balance can meet a wide load range while offering superior performance across the entire operating envelope.
  • Unique ability to redefine the allowable maximum component loads based on the required combination of applied loads
  • Allowable loads limits defined by either maximum Normal Force / Pitching Moment or maximum Rolling Moment conditions.
  • Lower flexure stress with nearly 3 times the maximum load
  • Significantly Lower Deflections at higher loads
  • Captive design of metric model interface
  • Ease of access for service or repairs
  • The advantages of both the single piece moment balance and the multi-piece force balance
  • Design tailored to requested load capacity and geometry
  • Increased load capacity while maintaining high level of accuracy