Feasibility study for a two chemical spray system for the WHO/OMS onchocerciasis control Program in West Africa

)' ffofi'ln, / t , I .t -a a -7. t t FEHSiBit-iTv STUDi FOR A TWO CHEMICHU SPxAr SySTEM FOR THE wnOzOMS ONCHOCERCIASIS CONTROU PROGRAMPIE IN WEST AFRICA Ai, M.J. Bazalgette BSc. MSc. t*Consuitfipf August - October tvgr Aerial Operatioris Unit, Odienne, Cote o'Ivoire t {& 's ,$I "Il+'..*l: n, -#[ 'i. ti * a .s / tl ; * + Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page i Page 8 Figure 1 Figure 2 INDEX Introd uction The Current Spray System Objectives of a Two Cnemical Spray System Different Tan k Desig ns The Pump, Turbrne Flowmeters, Valve and Nozzle Assemblies Manuai Valves Recirculation ano Contamination Avoidance Further Factors in Tank Design |r.p Positioning Filler Points Dump Doors Modifying the Existrng Tanks Conclusion The Current Spray System A Possible Two Chemical Spray System J* t -1- Introd uction The onchocerciasrs controt Programme employs Hughes 5oo D ancj E helicopters to spray larvicicjes into rivers throughout the programme area, to prevent the breeding of the vector of onchocerciasis, theblackfly simulium damnosum. six ciifferent chemicais are usecj indifferent rivers at different times for reasons of resistance and variations in river discharge. The spray system as currently fitteci can only hoid one chemrcai at a time because it has a singie tank. This situatron can grve rrse to the need for iong ferry fiishts ciuring a circuit to cnange cnemicars, covering the same ground several times. For exampie a mai n r-i ver may be treatecj wrtn one cnentrcai , then the ireircopter must fty to a fuei clepot, offioao tne chemrcai , reroaci with another arrd retrace its steps to treat rhe trroutartes. Foirowrng tnis rt may weii have to ioao rne ftrsr cnemtcat agat n oeiore conunurng. it rs therefore ciear tnat fi lgnt ttme couto oe saveo ano the prrots worxioaci recjucecj if a means couto oe rouno ro carry rwo chemrcals at the same time. Trre Cur-r-ent Spray Sysrem (iy9O - lJyZ) Tne system rn use at present was oevelopeo oy E verg reen Helrcopters Inc. I n cor)J u ltcltor) i"i rcronat r ano is xnown as tne Mooei y5OO0. specrfrcaly ror rne uCP wrth Srmpiex ano it conststs of an externat oely tan K assernoty attacneo ur) oerrlearn the heiicopter, and associatecj eiectronics for controiiing anci monrtorrng the spray operatrons, mounred rnside the heitcoprer. Tne exrernai tank is macie of fr bregiass ar)q can oe qurckiy and strnpty removeci from the aircraft for mat nrenance. It comprises a.30O irtre ranK witn a sump assembiy ancj emergency dump door, an erectrrc rnotor- anci centrifugai pump wrtir a fitter, two spray booms liar-ge ano smal i.) with their owrl flow metering turbrnes and nozzies. ar)ct a system for- recrrcurating rne cnemlcat DacK tnto the rann from ir)e boom. (see fiS. 1) \Tan K o o o o a ,] Dump Door Figure 1 The Current Spray System Recirculation Valve / ,, Recirculdtion Lipe \' t t.,t Motor P p Filter Sh ut-off Val ve Sump Low Poi nt Drai n Vent Si tht Gauge Flow I'teters Frlr Large Boom Drain/Offload Valve Smali Boom zles -2- The pilot's control box is mounted on the left hand cockpit upright in front of the pilot's left knee. With this he can preset the drop quantity and select which nozzles it will be sprayed through. .The combination of the drop quantity and number of nozzles selected determines the length of time a drop will take. Thus the pilot canjudge his drop to reach from bank to bank of rivers of varying w i dths. Once the two factors above are set all the pilot does to make the drop is to press the drop trigger on the cyclic stick. To suspend the drop (for example if the far bank is reached while still spraying) the pilot flicks forward the shut-off switch (also on the cyclic), and flicks it aft when positioned to continue. The purpose of having two booms is to allow large drops to be made at high flowrates through the large boom, while small drops are made through the small boom. What actually happens when the pilot presses the drop trigger is that the selected nozzle valves open and the pump operates. Chemical is pumped through the flow turbine which meters the quantity sprayed and when the selected quantity is reached the nozzle valves close and the pump stops automatically. The metering system is very accurate and when a tankload of 150 litres is sprayed the meter will record this within one or two litres. As it stands the system is effective, reliable and simple to operate, as well as being aerodynamic and allowing a cruising speed of 1'lO knots. It would therefore be sensible to use the existing system as a starting point for any further development. Objectives of a Two Chemical Spray System. 1. The tank should be divided into two compartments. 2. Any increase in werght must be kept to the aosoiute mintmum, because the helicopter is often operating at the maxrmum weight possible. Therefore the weight of any extra egutpment directly reduces the quantity of fuel or chemical that can be carried. 3. At any state of loading, for example with one tank empty and one tank fuli, the aircraft must oe loadecj withrn its centre of gravity and balance limits. 4. Contamination of each chemi.cal by mixing with the other shoulci be kept to a minimum, especially iwhen changing from a hard chemicar to soft one or when precipitation'of a solid would occur on mixing. 5. It must still be possible to recircuiate the chemicals through the spray boom and back into the tank. 6. The system should be simple and as little changed as possible from the present one. 7. The modifications should cost as little as possible. 8. The electronics must be modified "i,n order to recdrd the. sprayedquantity of each cherhical separately\ \. ' \..r a -?- Different Tank Designs The Present Tank This tank holds 3OO litres but the helicopter is seldom able to take off with this much weight. The most common load is .l50 litres or 200 litres when a pilot flies with no observer. The Size of Compartments in a Two Chamber Tank The ratio of compartments, when divided, could be set in unequal parts, but splitting the existing tank evenly would give t5O litres in each compartment. In view of the fact that 15O litres is the quantity most commonly carried, it is unlikely that more than 15O litres of one chemical would be needed while two were being carrieci. When spraying only one chemical, both compartments could be filled with it. In terms of simplicity of design, dividing the tank into two equal compartments would be the best option. Assuming that the compartments are to be of equal size, there are several ways in which they could be divided: a. Laterally This ciesign would make the area of the partitron as smali as possibie but it would cause balance problems il'one compartment was fuii and the other empty. The piiot's freedom of control in pitcn woulcj be reduced and this can be very dangerous. A further p.roblem woulo be created if the tank was based on the present one, in that the sump and pump are at the front of the unit and the pipework necessary to feed the pump from the rear tank woulo be complicated. b. Longitudinally This form of division would also create a weight imbalance but since the tank is longer than it is wide, the rolling moments created by having one tank empty and the other full would be less than th'e pitching moments described in a. above. Also having the 5ircraft unbalanced to one side is l'tsss dangerous \han\having it Jnbhlarlced fore and aft. -4- The effect of having one sicje full and the other empty wouid be similar to having one pilot and one rear seat passenger on the same side. Preliminary enquiries have indicated that this would be the best tank configuration. c. Internal Division i,r ii) This would be a means of using i) a fixed inner tank or ii) a frexible bladder as used in many aircraft fuei celi appltcations. The advantage would be that whatever the contents in each tank the centre of gravity woulcj be in the same place. The ciisacivantage in i) is that it would be very complicated to build and even more so to repair, and in ii) that no bladders available were designed to contain chemicals of the nature used and corrosion wouicj take place resulting in short bladcjer life. These systems are therefore to oe avoidecj unless made necessary by centre of gravity consicjerations. The Pump, Turbrne Fiowmeters, yai ve and i.rozzie Assemoiies At present t.he srngie rank feeos via a surnp otrectty trtrougrr a t.5 rrrch bore prpe (wtth snut-off val ve) ro a centrtlugat pump or-lven by a 28 volt, l05 aflrp eiectr-rc tnotor. Tne c;hemtcai ts pumpeo rr)r-ougr] tne irowmeter-rur-oitre to tne spray boom wnere vai ves open as selecteo to spray tllrough tile aplJroprrate rrozzies. Hrr rhrs equipment ts heavy anci altrrough trre loeat sotutton to avoto contarnination wouiq De to nave two comprereiy separate sysrems, tn reairty trtis rs out ot tne ouestton. A nreans must riter-efore be found to use onty one purnp ano everythrng erse downstream. Thrs couio be achrevecj oy ustng some krno of serection vai ve flrecnanrsm, to feed chemrcai fr-om errirer- tan compartmerlt \or Dotn rn rhe case of one chernrcar Detng useo/ tnto tne pump. ideaiiy tnis wouici be by means of a servo-con#oiieo trrree-y ay vai ve, sucn that the piiot neeci oniy turn a swrtch rn iire cockpt ro cnange chemicai. On discussron with one of the Oesigners of the tanr< it was iearrreo rhat a suitabie three-way vat ve does not extst tr) tne stze requtreo. At this pornt it sirould be noted that even when the new selection rs macie, some.-4 litr-es of chenricai useci prevrously will remain in the pump, th: hoses ancj the spray boom, however thrs wrli be discusseo i ater. I (( I -5- Pump t Pumpt tanK I Tank Z Tan k 'l Tank 2 i) one three-way vatve rr) two two-way vaives The alternarive woulo be two two-way val ves in the conrrgurarron shown above. Agatn it would be ideai if these vaives couid be servo-powerecj but no such val ves exist in the stze necessary ancj abie to run on 28 voits DC. For exampie a similar vaive for tire Turbo Thrush to worK rn a I inch pipe haci to be made speciaity, cost $.3oooper unit ano was iarge ancj extremely heavy. It can tnererore be assumeci thar a t.5 tncn vai ve would be larger, neavterano even more expensive. Electrlc val ves also consume current even when not actuai ly moving, placrng an extra strar n on the generator wnrcn rs ai reaci y werKrng aL rrs limit when the spray purTlp ts rur)ntng. compresseci ar r powereci val ves are another opuon but tnere rs no compressecj at r avai rable from the turbine engtne of tne t-lugnes (power is iost if ar r rs biecj trom the compressor). Hgar n sucn var ves are aiso bulky. Manuai valves In view of tne above factors it would seem far more sensrore to abancion tire icjea of automatic valves and move to a manuai system. In the programme area it is not hard to frnd a clearing where a priot can land, exit the heircopter, ciose one val ve, open anotner and continue. Hltirougn tlils rs more work than movirr g a swrtcir rt rs considerably less than ferryrng to a depot, offloadrng and reloading. A suitable vaive would be the shut-off valve already useo between tire tank and the pump. it is a gate valve with a manual tap on the ' outside anci has a i.5 inch bore. Thrs valve would nave aii the . advantages of being light, cheap, available and proven. Tnere is,, r also ver-y little scope for it to malfunction. operatlng on one \ chemical woulci sirnply be a matter of leaving both vaives open. It would be very useful ir sensors could be fitted to the valves todetect if they were open or closed; this could give an auciible warning if the piiot opened both valves at once when drrferent chemicals were in each compartment and also inform tire applrcation controller when the tank selection is changed. t t \ \ I7 / L. -6- Recirculation anci Contamination Hvoidance It has alreaciy been stateci that recircuiation must stili be aitowed to take place withrn a two-chemicai system. The recrrcuiation vaive is currentiy fitted to the ieft hand end of the spray boom, at the opposite encj to the iniet from the pump. it is a self contained, remote controi electrtc baii valve and is small and light. For this reason it would seem suitabie to use two such vai ves mounted stcie by side in a similar piace to the current one, each one feeding a recircuiation itne ln one tank chamber. It has aiso been statecj that a contamination probiem wiil arise if .3-4 iitres of one chemtcai wili be left in the PumP, the hoses anci the spray boom aiter changing to a different one. The possioiiity shouicj be investigated of using selective recrrculation to save thts chemical using the procedure outlinecj beiow: (refer to ftgure 2) i. The ptlot closes seiector vai ve I and opens selecror vaive 2 z. ie seiects r-eclrcuratton val ve I to open wnen the pump ls operateo for recircuiatton. s. Tire pump ts run to r-ectr-curate tne exacr voi urne ol crlemlcai Tound ilt tne pumP, nOSeS ano Spray Doom;- rhis voiume is rneasureci by the rrowmeter wrllcrl ls extrernely accurale, xe':trculatlorl vai ve j tnerl closes ano tne PL,lmP SIOPS' 4. Now tite rernat rllr)g auar)Lliy citamoer I ano cricfilr'-cl : nas Ine spray rlozzles. rras beerr returneo to tanK tnrough rne system to r-eacrl cT cnerntcat I oeen pumpeci ;J 2 To oilure arly rraces oT cnerl)lcal i remat nln9, t herr open s ari cr i I r c sy srem ls recl rcu lateo ior- recrrcuratron val ve a snor r rrme. o, To cr)ange Da.cK to cllernlcal l. lrlts wrloie proceour-e is repeareo, tnis tlme ctostrlg val ve Z, re-oper)lng val ve l. erc. 7. efter Ilitrng oorr) cnarr oers wrtit orte cnemtcai ar)o trlen sprayln9. a srntriar DrOCeour-e COutU Oe uSeO Io pUmp.tne remat nlng quarltlly lnto one slngle tarl K Lrlamoer. rt snouio oe noreo rr)ar some or citemtcat i wtti be refr tn Lrle sfilarl t bOOm aS nO reclr Cutalton vat ve tS fttteCj to it, nowever tl)ls lS i ar ready tite case wnen cnanging cnenucars wrth tite cur-r'er)t systerll arlo rs cotrsiciereo accepraDle. Tire above proceuur-e wtit requtre cttanges to ti'le software and rt SngutCi Oe pOsstDle Io IIaKe parIS Z-5 napperl autotllatlCaliy airer- the piiot has rnaoe rtts seiecjttort wlth the martuai valves. tanK / o tanK I 1 ?- Figure 2 A Possiole Two Chemicai Spray System Motor Recrrcuiation Vai ves Pump Fiiter Selector Val ves Two Sumps Dump Doors Vent Sigirr Gauges F tow Meters Frii-2 F ilr-1 Booms and Nozzles -7- Further Factors in Tank Design In the development of the current tank many problems were encountered with the design of the sump. It was difficult to achieve sufficient flow from the tank into the pump such that the pump could run at full speecj without sucking air (cavitation). If a two chamber tank system is built the design of the sumps will be crucial and it is unlikely that the total volume after dividing in two will be as great as the current volume of the single tank due to internal modificattons. At present there is a small tube running from the top of the pump housing back irrto the sump; this allows air that collects in the top of the pump to be sucked back through it and expelled. If there are now two tank chambers feecjing the pump there must be one tube to each sump from the pump housing. The piiot would have to open or close a vaive in each tube as he changes the main selectron vaives to avoid these tubes being a source of contamination. It should also be noted that having two sumps side by side would increase the frontal area of the spray tank. This would cause cirag and a smali reduction in maximum speed. Pump Positioning The mocjifrcatrons to tne tank and the instai iatton or a Y-ptece and vai ves between the sumps ancj tne pump would mean movlng the pump further forward. dtsptactng tne centre of gravrty. if ritts displacement were too gr-eat to remai n within timits, some otirer piece of equipment, for exampie the matn ai rcraft battery, couio oe sntfteo aft to comper-rsare. ! i I"iotor Pump 4 r-prece Val ves Val ve Sump Increaseci Drstance Doubie Sump i) current system ri) two chemical system Filier Pornts The fiiler pornts for both tanks should be on the right hand sicie of the aircratt (the samg sicjei as the fulel frller: point). This will simpiify the ioading dpgra\on. ' '..i -8- Dump Doors In the current system a dump door is fitted on the undersicie of the tank besicje the sump. This is a self-containeci unit with its own soienoici to open it. It is operated in an emergency by pressing a guardecj button on the coliective. This allows the chemical to be released rapidly if the aircraft is about to make an emergency lancjrng. With the tank divided longitudinaiiy, two dump doors of the same type could be positionecj on either side of the sump, one for each chamber. They woulcj both operate together when the dump switch was presseci. The extra weight and cjrag of a seconcj door woulci be acceptab i e. Modifyrng the Exrsting Tanks nlthough aii these modifications are based on the exisrrng srngle tank, anci perhaps an olcj tank couid be usecj 1'or a prototype, the final product would invoive sucir funoamenrai r-eburiding (cutttng ln halr ancj instaiiing a partition; fittrng rwo sumps, etc.) that compieteiy new tanKS wouici have to be built. Thrs rs because fir:regrass tilar has oeen cut ano r-epar reci ts never as strong as the ortgtnar mouideo itern and tt ls atso mucit heavrer-. Therefore new tatlKs woulc nave Io oe constructeo'once a cjetariecj oestgn iras Deeri cjecroeo or) ano rirrs wrir be expenstve t tire curr errt tanxs cost $300,000 for tweive units/, Hncrirar-y par-rs sucn as rne ourTlp, coulo arl ce trartsier-reo trom oro filotor. Ttowrneter-s ar)o sor-a.y uoorns TATI KS. ce lri uor)cluslcn tt ts rrte oplrllorl cri tite autitor tnar a rwo cnefilrcat spray slr'stetn rs feasibre ri a oecrease rn tne cnerllcat carry tng capactty can accepreo. Tnrs wrri aiso be accompanred i-ly a srrgi'tt oecr ease maximurn speeri irr strat ght ano rever firghr. To rnrntrnlse tr)e tncrease tn welgnt oI equtprnent tt wili oo ,rrUar,rr,, not to cjemand too high a degree of automation, particuiarly with regarci ro the srluL-off val ves for each tanK cornpartrnent. ustng rnar)uat gale vai ves nere wiii save a gr-ear clear of exrr-a *.'gn( ano cost. The cost of modifications will be refiecteci in an increaseci cosr to tne programme for each flisht hour; it must be carefuily consroeree whether tiris expertse wiii be recovereci through a recjucecj fiight hour requirernent. Consrueration may also be given at this stage to tire posstorlity of shrftirrg to a more powerful version of the hughes 5oo. Hitirougir this wouicj cost rnor-e agai n, it wouid oe abie to car-ry more and be more suiteo to the temperature conci rtrorrs errcountered wirrle worKtng for theprogramrne. . ( ( If the number of helicopters used and the riumber of flight ir6urs availauie is to clecrease in the future, it will be important to make maximum use of the resources avaiiable. Using a two chemicai sysrem, perhaps in conjunction with more powerfui helicopters, may be rite best way to achieve this.