Browsing by Author "Jones, R. I."
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Item Open Access A conceptual design methodology for low speed high altitude long endurance unmanned aerial vehicles(Cranfield University, 2000-05-03) Altman, Aaron; Jones, R. I.A conceptual design methodology was produced and subsequently coded into a Visual C++ (GUI) environment to facilitate the rapid comparison of several possible configurations to satisfy High Altitude Long Endurance (FIALE) unmanned aircraft (UAV) missions in the Low Speed (propeller driven aircraft) regime. Several comparative studies were performed to verify the applicability of traditional design methods. The traditional computational design methodologies fail in several areas such as high aspect ratio wing weight estimation and design, low Reynolds number wing design, high altitude engine performance, low Reynolds number drag estimation, unmanned aircraft design, and the conceptual design of unconventional configurations. The methodology developed for this thesis was robust enough to allow not only for consideration of these areas of inadequacy in traditional methods, but also to allow for the inclusion of advancements in the relevant technologies as they become more widely available. The following configurations were evaluated for suitability to the Low Speed HALE UAV application: conventional, canard, twin boom, multiple fuselage (conventional or canard), tandem wing, multiple fuselage tandem wing or flying wing configuration. The configurations were compared on the basis of aircraft endurance for takeoff weights ranging from 2,000 to 20,000 pounds and wing loadings ranging from 5 to 25 lbs1fe. Initial drag estimates were made using traditional parabolic drag estimation techniques. A more refined drag buildup was performed using a vortex lattice drag estimation for the lift induced drag (for all lifting components) and calculated skin friction coefficients for the parasite drag. Statistically based methods were used for other components of drag having much smaller contributions. In addition, a statistical approach was taken to the weight estimation of the major aircraft components. However, this approach made comparison of alternative configurations more difficult. Thus wing bending moments trends were evaluated and utilized in the development of weight saving values for multiple fuselage wing weight estimation. The comparative performance of each configuration is justified with direct reference to the terms in the Breguet Endurance equation. Validation was performed where possible on all modules and segments associated with the methodology, as well as for the macroscopic results. In addition, parametric studies on endurance were performed for the conventional configuration for geometric characteristics and operating conditions directly and indirectly effecting the calculated endurance and generalized results presented. Finally, a case study was performed to demonstrate this capability. A new relation was developed for aircraft empty weight prediction, a low speed airfoil figure of merit was proposed, and new constants were offered for UAV fuselage length prediction. In addition, horizontal and vertical tail volume coefficients were proposed for all of the Low Speed HALE UAV configurations considered. It was determined that the multiple fuselage configurations showed comparatively superior endurance performance across a range of takeoff weights, with several other configurations demonstrating marginal endurance improvements. Finally, a highly flexible and robust computer based conceptual design methodology was developed and validated enabling the quick comparison of a greater number of possible configurations to satisfy a given mission for Low Speed HALE UAV's and providing detailed drag and weight breakdown data.Item Open Access Experimental investigation of attachment line transition on a large swept cylinder(Cranfield University, 1997-01) Flynn, G. A.; Jones, R. I.Transition of the attachment fine boundary layer was investigated using a large swept cylinder. Results for natural transition and transition tripping with two-dimensional trip wires were simila to those obtained by Poll using a similar, but smaller, model. ]Lower displacement thickness Reynolds numbers but larger trip sizes, than for the flat-plate boundary layer, were required for transition. The investigation of transition tripping was then extended to involve three-dimensional trips. The attachment line boundary layer was less susceptible to three-dimensional trips than to two-dimensional trips but upper and lower bounds of attachment line Reynolds number for transition were identical. It was also found that the roughness Reynolds numbers for fully effective three-dimensional trips were similar for the attachment line and flat-plate boundary layers. Another common feature was the more abrupt upstream movement of the transition front with increasing Reynolds number for three-dimensional trips than for two-dimensional trips. Turbulence spreading downstream of a three-dimensional trip was also examined and, as in the flat-plate boundary layer, was found to be heavily dependent on Reynolds number (varying from 3* at low Reynolds number to a value approaching 10* as Reynolds number exceeded the value for natural transition), but was also dependent on either the trip size or the initial conditions at which the trip first introduced turbulent spots. The effects of higher levels of freestrearn turbulence were then investigated for both two-dimensional and three-dimensional trips. With a small increase in freestrea turbulence the conditions for transition with twodimensional trips were affected far more than those for three-dimensional trips, for which only the transition completion conditions were affected signfficantly, resulting in a reduced extent ofthe transition region. Larger levels of turbulence appeared to have similar effects on the two trip types. Restrictions in model length and windspeed for the higher turbulence tests prevented an accurate investigation of the effects of turbulence,on the upper and lower bounds for transition tripping and on the influence of spanwise distance at higher levels of turbulence. Finally, the interaction between two trips positioned on the attachment line was examined. The effect of the second trip on the transition Reynolds number was found to a function of the streamwise separation distance between the two trips.Item Open Access A flexible, subsonic high altitude long endurance UAV conceptual design methodology(1997-05) Chang, J. M.; Jones, R. I.High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs) have been considered for use in both civil and military applications for some years. Their advantages, such as low cost, high survivability, long endurance, easy maintenance etc. relative to alternatives, make them useful to scientist and military personnel. In this thesis, a flexible conceptual design methodology for HALE UAVs has been developed. This has been implemented as a FORTRAN computer code. However, it is unlike some commercially available general aircraft design software which appears to the user as a ‘black box’. In this case, the code is broken-down into several subprograms which deal with the different aspects such as parametric study, drag, performance etc. Each of these can be either used as it stands, tailored to the user needs in a particular case or by-passed if more accurate methods or known values are available in a particular area. During production of the methodology problems were encountered in a number of areas due to the unusual operating regime and configurations of HALE UAVs. Obtaining engine data for the high altitude of interest was a problem. This was addressed through use of an existing engine modeling code to generate data. The high altitude also leads to low Reynolds numbers and along with the high aspect ratios typical of HALE UAV configurations, these place such vehicles beyond the validity limits of data sheet methods for prediction of a number of important parameters. Improved methods for the prediction of Oswald efficiency and maximum lift coefficient, in particular, are recommended to be sought. Accepting the above difficulties, an analysis of the Tier-II Plus, Global Hawk, was carried out using published data to provide some validation of the methodology and program. The results obtained provide confidence in the usefulness of the program in the analysis and investigation of HALE UAVs.Item Open Access Friction characteristics of skewed roller brakes(Cranfield University, 1998-10) Oliver-Hall, Richard.; Jones, R. I.; Strothers, P.; Harrison, A.The project sponsors design and manufacture skewed roller brake devices for use in aircraft flight control actuation systems. Design tools have previously been developed to predict the torque characteristics ofthese devices. A fundamental deficiency ofthese tools is the use ofempirical friction coefficient data gathered from a limited test sample. A need was identified to develop a friction coefficient model based on the operational parameters ofthe design, namely load, speed and lubricant viscosity. The development and validation ofthis model formed the basis ofthe technical research objective. A cost benefit analysis indicated that the sponsors could reasonably expect to gain a significant technical competitive advantage over their competitors ifthe technical research objective could be achieved. This advantage should provide opportunities for premium pricing ofthe product and enhanced opportunities to enter new markets. Additionally, the sponsors could expect lead time reductions and cost savings of £69000 from the removal ofthe need to conduct prototype tests to assess the effective friction coefficient. A friction coefficient model and skewed roller torque equation design tool have been successfully developed, satisfying the technical research objective. The friction coefficient model is defined in terms of lubrication number. The lubrication number parameter incorporates lubricant viscosity, roller speed, roller load and contact surface roughness terms, fully describing the operational parameters ofa design. Experimental evidence has validated the model using two lubricants, a hydraulic fluid, Brayco 795 and a mineral oil, Catenex 79. The tests cover a lubrication number range from 2 x 10-5 to 6 X 10-2 with a mean Hertzian stress from 0.27 to 0.61 Gpa. The success ofthis project has ensured that the sponsors will reap the cost and design lead time savings predicted in the cost benefit analysis and have the tools necessary to develop new markets and premium pricing business opportunities.Item Open Access Hydrogen aircraft concepts and ground support(Cranfield University, 2005-11) Sefain, Michael J.; Jones, R. I.As worldwide petroleum supplies diminish and prices escalate, the aviation industry will be forced to consider relying on energy resources other than kerosene for its aviation fuel needs. Additionally, there is growing environmental concern regarding greenhouse emissions particularly as aircraft cause pollution in sensitive layers of the atmosphere. These are serious implications necessitating prudence in seeking alternative fuels sooner rather than later. Liquid Hydrogen (LH2) combustion produces zero CO2 emissions, very little NOx, and water providing a solution to sustain air traffic growth whilst preventing further atmospheric pollution. Hydrogen itself is abundant and can be produced from renewable sources meaning worldwide availability and sustainability permitting sustainable growth of aviation at high rates (typically 4-5% per year). Despite these major advantages, there are compromises to be made. The low density fuel means ingenuity must be exercised to design an aircraft configuration which will accommodate a fuel volume more than four times that which would normally be required. Practical unconventional aircraft conceptual designs providing solutions to this problem are presented including estimates of performance, mass, and relative cost- and energy-effectiveness. To provide a means to produce, store and transport the fuel safely and efficiently, ground support operations have been systematically checked and the required airport infrastructure defined. Technical issues such as safety, airworthiness certification, environmental issues and system synergies are also discussed, and an outline plan is presented providing the R&D necessary to introduce LH2-fuelled civil aircraft into service. This Thesis proves that LH2 has sufficient long term promise to justify more substantial R&D offering possible improvement in performance and engine reliability. The overall cost for a LH2 aircraft are within reasonable values, and the requirement for new equipment to maintain and support LH2-fuelled aircraft is not extensive. Importantly LH2 is at least as safe.Item Open Access The introduction of laminar flow to the design and optimisation of transport aircraft(Cranfield University, 1997-03) Wilson, R. A. L.; Jones, R. I.A methodology has been developed to model the direct consequences of laminar flow technology on wing, empennage and nacelle surfaces. In particular two concepts were considered, namely Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC). The methodology was introduced into an existing numerical design synthesis for commercial transport aircraft, which was linked to a non-linear constrained optimisation code. This permitted the impact of laminar flow technology on the optimum aircraft configuration and Direct Operating Costs (DOC) to be assessed. Cont/d.Item Open Access Investigation of improvements in aircraft braking design(Cranfield University, 2004-10) Bailey, David A.; Jones, R. I.This work investigates and provides a methodology that enables better prediction of brake performance. Aircraft brake performance depends on the tribological properties of the friction couple used in the brake design. The behaviour of this couple combines both surface and bulk characteristics of the material. The increase in aircraft performance requirements has led to the development of new brake designs and new friction materials. The development of brakes for large commercial aircraft has stabilised to that of a carbon-carbon composite multi-disk brake design. The results of this investigation established a relationship between mean mass loading and the mean friction radius of the brake. This relationship provides a statistically good description of the results and will provide the brake performance engineer with a useful tool. In addition, the variance within the results of the 100 Normals aircraft qualification programme was also studied. In this case the relationship is not particularly good at describing the results. A case study has been included to promote further understanding of the developed methodology and to illustrate some of the trade-offs required when designing a carbon brake. The design of a multi-disk brake is a complex engineering task that requires many specialist engineering disciplines such as structural analysis and dynamic analysis etc. The wider context of aircraft braking is even broader and requires not only mechanical engineering skills but also electronic and software engineering. This research addresses all aspects of system integration and provides a framework of understanding on the interaction and dependencies of the various components.Item Open Access Novel ice protection system suitable for UAV composite wings(2005-02) Bhakta, Besant; Jones, R. I.The existence o f an atmospheric icing th re a t to a irc ra ft operating in moist, low altitudes at temperatures below freezing is well known. The objective o f this study was to develop an a irc ra ft ice protection system suitable fo r a UAV composite wing. Conventional wing leading edge ice protection systems were examined and found to either, necessitate significant electrical power, or were costly with respect to system mass. A low cost and low power technology capable o f protecting the UAV wing leading edge was identified. I t was proposed th a t a commercial magnetostrictive actuator fitte d to and in direct contact with the non-airflow wing surface would provide mechanical impulses to break the ice-wing surface bond. Assuming the accreted ice was o f a form expected o f te s t points in the FAR/ JAR Appendix C flight-icing envelope. Computational simulations demonstrated th a t pairs o f magnetostrictive actuators acting in unison a t a 0.3m span spacing, and deployed along the upper and lower wing leading edge surfaces a t around the 7% chord coordinate, would successfully break the ice-surface bond. I t was estimated th a t fo r a medium endurance UAV o f Predator B class, the proposed system power requirements is 500W at a 45kg total system mass. The proposed system would be more competitive than conventional systems if the use o f consumer grade electronics and control systems, harnessing etc. were permitted, together with the removal o f system redundancy and fail-safe provision requirements necessary fo r manned aircraft. Further work would require the demonstration o f a physical de-icing installation in the icing wind tunnel.