ICING,PT2.
To further explain the pics; The `Cheyenne` also happened to be doing similar trials to us,but we were not permitted to get close to it or meet the crew.You can see the rig and steamspray droplets ,but even on a sunny day,it still ices the blades.Other times and temperature will give a continuous cloud stream ,so one is in IMC,but we had a `volunteer` on an extra `long-lead`,outside the rotor disc to warn if we were drifting,also spray painted lines,like on ski-slopes,otherwise hover/radalt hold,and use the Doppler...!! luntil the aerials iced up..
All the aircraft rotor blades actually had the same blade section,NACA0012,root to tip,and varying twist,but constant chord.However, the Wasp(and Scout) are more `rigid` spanwise,compared to the `paddlewheels` on the WX,S-King and later Gazelle,and so flex more over their length during rotation.There are videos taken by cameras mounted on rotorheads showing blades bending and flexing,and this is why,when we started going into `natural icing(IMC) in the cruise,fixed collective,there would be a rise in `tq`,ng ptit,some increase in vibration ,and then a fall in tq,etc as ice was shed, then it would start again the process.
We only flew in IMC IN `stratiform clouds` as there is usually a fairly constant droplet size,and fairly constant temperature as well,all measured in the a/c instrumentation.Also ,for safety ,Ontario around Ottawa is fairly flat,and we only flew with a minimum cloud base of 2000ft agl.Of course not all days are the same ,but if it wasn`t clear,then we`d do more `rig` work,or fly in snow.Also,excursions into IMC were for short periods,ie 5 mins,pop out check for shedding, try for 10 mins,and so on,until one had a good feel for what was happening,then maybe climb 1-2000ft,different temp/droplet size,more power,stir/rinse repeat as required.Then you get the unexpected,TQ starts going up,vibrations increase,not shedding,start turning and descending to get out of it ,go back and have a coffee...or three..Well,how do you know when to quit....? Whadddya do if the `donk(s)` quit? Autorotate..? Yes,but you`ve got ice on the blades as welll?
Before we went to Canada we had to set-up the autorotation RPM by doing full autos back at minimum RRPM,range and transient setting on the collective ,and hence blade angles,then join up the power and set those collective setting noting how much` torque` you were using...now compare that `change in blade angle` TQ differential,in increments up to max TQ ,to check it is a consistent `Delta `TQ.You now have a figure for what is`hopefully` a realistic TQ rise,and shedding.You now go and adjust the collective,to give about another 20 RRPM increase ,`,to be sure,to be sure`,and that is one reason for wearing parachutes as well...I think for the WX,we used about 5-600 ftlbs,as a maximum`D TQ`.....However,prudence usually dictated that we chickened-out if the TQ was rising fast,or the w/droplet size/temp changed rapidly..
I`ll continue 2morrow ,if you want more tales from Cold Winters..
TGIFin Ottawa as interesting 50 yrs ago,Capital city,lots of Company HQs=lots of secretaries= 7-1 ratio f-m...!!
Note for `Crab`,please do not use my name if you go punting around in icing in that WX...!!!!