Aerodynamic estimation techniques for aerostats and airships

Abstract

A semi-empirical steady-state model o f a finned axisymmetric body i s developed and used t o compute h u l l -f i n mutual i n t e r f e r e n c e factors and cross f l o w drag c o e f f i c i e n t s from wind tunnel data on f i v e aerostats and a i r s h i p s . The r e s u l t s a r e i n general agreement w i t h expectations from theory and provide a basis f o r p r e d i c t i n g aerodynamic c o e f f i c i e n t s . The model i s extended t o unsteady motion by considering t h e l o c a l f l o w on f i n i t e h u l l segments and t h e f i n s . This dynamic model i s a p p l i c a b l e t o n o n -l i n e a r simulations and t h e computation o f r o t a t i o n a l s t a b i l i t y d e r i v at i v e s f o r which equations a r e d e r i v e d . For one zerostat, r o t a t i o n a l s t a b i l i t y d e r i v a t i v e s c a l c u l a t e d from s t a t i c wind tunnel data a r e compared w i t h experimental r e s u l t s from a w h i r l ing-arm tow tank. I n t r o d u c t i o n The m o t i v a t i o n f o r t h i s research came from t h e need t o a c c u r a t e l y represent an a e r o s t a t ' s , o r a i r s h i p ' s , aerodynamic forces and moments i n flight-dynamic analyses, such as s t a b i l i t y c a lc u l a t i o n s and non-linear s i m u l a t i o n . This paper presents a c r o s s -f l o w a n a l y t i c a l model f o r f i n n e d axisymmetric bodies, which are t r a d i t i o n a l l y LTA-vehicle c o n f i g u r a t i o n s . The model permits a n a l y s i s o f s t a t i c wind tunnel data t o o b t a i n e m p i r i c a l f a c t o r s t o account f o r mutual h u l l -f i n i n t e r f e r e n c e , and provides a means o f computing forces and moments when t h e v e h i c l e i s i n dynamic motion. This a n a l y s i s draws much on t h e work o f e a r l i e r researchers; t h e r e p r e s e n t a t i o n o f t h e ' 3 equations f o r an a r b i t r a r y body undergoing general motions i n i n v i s c i d f l u i d show t h e way i n which these e f f e c t s i n t e g r a t e t o g i v e forces and moments. This provided t h e basis f o r t h e present r e p r e s e n t a t i o n o f t h e h u l l ' s unsteadyf o r c e d i s t r i b u t i o n , as described l a t e r . --

Dynamics/Control of a Radio Telescope Receiver Supported by a Tethered Aerostat

“…18 Most of these quantitiescan be estimatedwith good con dence using the methods discussed by Jones and DeLaurier. 6 The cross ow drag coef cient was more dif cult to estimate accurately, but we found relatively little change in our results with changes in this parameter.…”

Effect of diamond shaped strut with cylindrical pitch rod in subsonic wind tunnel testing

“…D I would take out any interference effects due to supports and can be estimated in future by subtracting the model-on wind-on condition from the model off-wind on condition. This is a shortcut (not perfect) to avoid lengthy procedures involving measurements with an inverted model [21].…”

Harnessing marine current energy with tethered submerged systems: Experimental tests and numerical model analysis of an innovative concept

“…A complete and relatively accurate methodology for developing an aerodynamic model of airships may be found in reference [4], [5]. A particular treatment has to be dedicated to the determination of the aerodynamic characteristics of the bodies of revolution which may represent, in our case, both the buoyant body and the payload carrying body.…”