FEA­TURES Tech Log

Ad­vice for in­hibit­ing and stor­ing an air­craft that re­mains in­ac­tive dur­ing the win­ter months

Pilot - - CONTENTS - Words Bob Grim­stead

How to pre­pare your air­craft for win­ter in or­der to get the best out of it, come the new fly­ing sea­son

We all know that the best way to keep your air­craft’s en­gine healthy is to fly at least one hour ev­ery week, en­sur­ing the oil tem­per­a­ture rises above 70°C (185°F) for sev­eral min­utes to boil off the dis­solved wa­ter and acids. But this is not al­ways prac­ti­cal, es­pe­cially over win­ter be­cause of weather, the con­di­tion of your air­field, and other com­mit­ments, in­clud­ing fi­nan­cial ones.

I now prop­erly in­hibit and store my aero­planes for the win­ter (I’m lucky that I can fly in sun­nier climes) and it’s also a great op­por­tu­nity to tackle those nig­gling things which re­quire ground­ing for a few days, such as weld­ing or paint­ing. I must be do­ing some­thing right be­cause, when I had my Champ’s 1940s en­gine re­built a few years ago, the en­gi­neers found no cor­ro­sion what­so­ever and very lit­tle in­ter­nal wear de­spite its be­ing near the nom­i­nal 1,800-hour life.

First, let me of­fer some ad­vice I learned the hard way: if you can’t fly your air­craft weekly, don’t sim­ply run the en­gine on the ground or− worse still− pull the pro­pel­ler around a few times ev­ery week or so. The mov­ing parts within the en­gine (pre­dom­i­nantly the pis­ton rings and camshaft) will scrape off what­ever thin oil film is left on the sta­tion­ary parts (mainly the cylin­der walls and cam fol­low­ers) and the in­take and ex­haust valves will open and close, let­ting in whole litres of cold, moist air to cor­rode (rust) those sur­faces you have just wiped clean of oil!

You can per­form sim­ple main­te­nance tasks in­clud­ing: drain­ing and re­fill­ing the en­gine oil and chang­ing the fil­ter; check­ing and fill­ing the fuel tank(s); check­ing and in­flat­ing tyres; check­ing, charg­ing and chang­ing the bat­tery; and gen­eral clean­ing and lu­bri­ca­tion of the air­frame and con­trols where noth­ing needs to be un­done or dis­con­nected. If you are un­cer­tain about any of these tasks, ask your en­gi­neer to su­per­vise the first time. And don’t for­get to make ap­pro­pri­ate log­book en­tries.

It takes a day to pre­pare an aero­plane for win­ter, and an­other to ready it for flight again in spring. I usu­ally split the work over sev­eral days be­cause it’s more ef­fi­cient. I work in se­quence, ac­cord­ing to the value of the air­craft’s com­po­nents, start­ing with the en­gine, fol­lowed by the pro­pel­ler, avion­ics, bat­tery, wheels and tyres, and the in­te­rior.

First, wash off the bugs and stains

First, I wash it all over, us­ing a mild sol­vent to get the squashed bugs off the lead­ing edges and petrol (fuel) to re­move oil smears and stains. This gets rid of any salt de­posited by our is­land-na­tion’s al­ways damp air, neu­tralises cor­ro­sive in­dus­trial pol­lu­tants, and en­ables a thor­ough check of the whole air­frame, par­tic­u­larly for ar­eas that might need a lick of paint or re-lu­bri­cat­ing be­fore win­ter proper sets in and lower tem­per­a­tures ren­der paint­ing im­prac­ti­cal. At this stage I lu­bri­cate all mov­ing parts.

Re­move all dust and dirt from your trans­paren­cies, es­pe­cially if you are go­ing to cover them, as un­clean per­spex can cloud if the cover shifts. I put an old, soft, flan­nel sheet be­tween cover and plex­i­glas as ad­di­tional pro­tec­tion.

For your en­gine, first change the oil. Old oil (af­ter more than a few days or fly­ing hours’ use) ab­sorbs wa­ter, acids and other cor­ro­sive chem­i­cals which cause in­ter­nal en­gine dam­age if left for very long. Get that oil good and hot with a min­i­mum half-hour flight (ground-run­ning is not suf­fi­cient), then quickly drain it all out into a suit­able con­tainer. Volk­swa­gens, Ro­taxes and four-cylin­der Con­ti­nen­tals hold less than five litres, so a cut-open five-litre plas­tic oil jug (or metal can) makes an ideal re­cep­ta­cle. A Ly­coming might need some­thing larger. On a tail-wheeler if the sump plug is in the cen­tre of its lower crank­case (as with a Ly­coming or Volk­swa­gen) rather than at the rear you will have to lift the tail and get the sump hor­i­zon­tal to drain it. Leave it overnight to get ev­ery last drop out. The Maule’s and Fourniers’ tails stay raised, but I don’t bother with the Champ (more on that later).

By the way, if you have a bay­o­net-style quick-drain fit­ting on your sump, don’t let it ‘ping’ shut un­der its in­ter­nal spring pres­sure. The cen­tral brass rod is merely peened over at its end, and re­peated snap­ping shut grad­u­ally un-peens this ‘shop head’. The sur­pris­ingly com­mon re­sult is that, dur­ing your first flight af­ter an oil change, pre­sum­ably when the quick-drain bar­rel warms and ex­pands just enough, that spring drives out the cen­tral shaft, fol­lowed by all your oil.

Re­move your oil fil­ter or screen and check it for de­bris. Tiny black car­bon gran­ules are no cause for con­cern, but any metal flakes, par­tic­u­larly if they are mag­netic, are very bad news. These gen­er­ally come from the camshaft and fol­low­ers and mean a com­plete, costly en­gine over­haul. If it’s al­right, clean the screen in petrol and re-fit it (with fresh cop­per washer/s), or re­place the spin-on fil­ter with a shiny new one, and wire-lock them. Re-fit the sump plug with a new washer or gen­tly close the quick-drain, and place a large drip tray un­der your en­gine be­fore re-fill­ing with oil as, in­evitably, some will spill out.

My aero­planes have the three most com­mon types of en­gines: a Ly­coming O-360 in the Maule, a Con­ti­nen­tal C85 in the Champ, and Volk­swa­gen-de­rived Rec­ti­mos in the Fourniers. The pri­or­i­ties are slightly dif­fer­ent for each man­u­fac­turer, so I’ll cover each sep­a­rately (I don’t have any main­te­nance ex­pe­ri­ence of ra­dial en­gines).

Ly­comings are dif­fi­cult to pro­tect...

Ly­comings are the most dif­fi­cult to pro­tect be­cause their camshafts run along the top of the en­gine and any lu­bri­cant quickly drains away down into the crank­case, leav­ing the case-hard­ened cam lobes and cam-fol­low­ers (‘valve-lifters’ in Amer­i­can par­lance) to at­tract con­den­sa­tion. This causes minute rust spots which then be­come tiny cor­ro­sion pits and break through the thin layer of case-hard­en­ing. Next time you start your en­gine the bare cam lobes scrape across the dry cam-fol­low­ers un­til the en­gine has run long enough and the oil has be­come thin enough to lu­bri­cate them by splash-feed. This bare metal-to-metal scuff­ing causes very rapid wear, lead­ing to spalling and flak­ing away of the hard­ened sur­face; the cam lobes wear down so en­gine power and air­craft per­for­mance quickly de­te­ri­o­rate. This is usu­ally the first symp­tom un­til metal flakes show up in the screen or fil­ter.

Ly­coming sug­gests a spe­cial (costly) in­hibit­ing oil, but I’ll share the re­sults of my avi­a­tion lu­bri­cants re­search with you. In the eight­ies, Shell de­vel­oped a semisyn­thetic multi­grade oil with ad­di­tives es­pe­cially de­vised to min­imise wear on un­der-utilised en­gines and, in 1993, an ex­tra ad­di­tive made the oil more ‘sticky’ when cold, so it doesn’t eas­ily run off bare metal sur­faces, thus act­ing as a cor­ro­sion

in­hibitor. This oil is Aeroshell 15W50− equiv­a­lent in vis­cos­ity to both W80 and W100 oils− and, yes, at £7 or so per litre it is around ten per cent more ex­pen­sive than ‘or­di­nary’ mono­grade avi­a­tion lu­bri­cants, but noth­ing like as costly as an en­gine over­haul. Ex­cept when break­ing them in, I use this oil all year around in both my cer­ti­fied aero en­gines and I hear that Ly­coming man­dates its use if run­ning on UL91 fuel.

Ly­comings have a wet sump, mean­ing the oil stays in the bot­tom of the crank­case when not be­ing pumped around the en­gine. To cover the camshaft and fol­low­ers com­pletely in oil for win­ter, I sim­ply fill the crank­case to its brim− or specif­i­cally the breather, which is right on top at the back of the en­gine. That’s why I put the Maule hor­i­zon­tal. It takes about 24 litres of oil, two boxes of a dozen quart bot­tles. Fill­ing the sump is easy: put a clean con­tainer un­der the breather out­let (I use the first emp­tied quart bot­tle) and then pour in all the oth­ers through the filler un­til oil drib­bles out of your breather. Then close up the breather out­let− a small cork works although you can buy spe­cial bungs− and re­place the dip­stick/filler cap. Your crank­case is now a sealed con­tainer; the hy­gro­scopic oil can­not ab­sorb mois­ture and your en­gine in­ter­nals are weath­er­proof.

Car­ing for a Con­ti­nen­tal

Con­ti­nen­tal camshafts are at the bot­tom of the crank­case, so as long as you have some oil in there the cams and fol­low­ers should be pretty well cov­ered. But they have dry sumps, mean­ing the oil is held in a sep­a­rate, usu­ally rugby-ball-shaped ves­sel, so my Con­ti­nen­tal process is a lit­tle dif­fer­ent. Af­ter adding the four or five quarts of fresh Aeroshell 15W50 and re­plac­ing the filler cap, I start the en­gine and al­low it to run for about forty sec­onds, so the new oil will be pumped and sloshed all around the in­ter­nals with­out ac­tu­ally warm­ing up or thin­ning very much or be­ing scav­enged back into the oil tank. Then I stop the en­gine and also seal the breather to keep out mois­ture and con­den­sa­tion.

VWS are dif­fer­ent

Volk­swa­gens are dif­fer­ent again. Their camshafts are at the bot­tom of the crank­case, but they have wet sumps. So although it might seem pos­si­ble to fill them right up like a Ly­coming, the front crank­shaft oil seal is a scroll which only keeps the oil in­side when the en­gine is ac­tu­ally turn­ing, so if you pour in much more than four litres the over­fill trick­les out overnight. There­fore, as with the Champ, I start the Fournier’s en­gine, let it run for thirty sec­onds (they’re smaller en­gines) then stop it, hop­ing the fresh oil has been lib­er­ally flung around the in­ter­nals. Bung up the breather and your crank­case is sealed. In­ci­den­tally, don’t use Aeroshell 15W50 in a VW en­gine dur­ing the fly­ing sea­son; mo­tor oils are the only ap­pro­pri­ate lu­bri­cant for a VW, and only those with an ex­act per­cent­age of a par­tic­u­lar ad­di­tive called ZDDP, vi­tal for your Volk­swa­gen. I use Comma or Hal­fords’ ‘Clas­sic’ 20/50 multi­grade or Cas­trol ‘GTX for older ve­hi­cles’.

Now you need to seal up the cylin­ders against ex­ter­nal air, which means bung­ing up your ex­hausts and car­bu­ret­tor in­take. An aerosol can cap works well as an ex­haust bung so long as there isn’t a tiny hole in it (or block that up). For the Fourniers’ per­fo­rated si­lencers, the

ad­he­sives on all the duct or PVC tapes I have tried seem to be sol­u­ble in oil, so I sim­ply ac­cept the leak­age. I use tightly folded cloths to cover the in­takes. Some­times I in­sert a bag of sil­ica gel des­ic­cant.

Fill up the cylin­ders

Next, I re­move the top spark­ing plug from each cylin­der and fill it with fresh en­gine oil. As an ap­prox­i­mate guide to how much is needed, a Ly­coming O-360 dis­places 5.9 litres, so one cylin­der takes a max­i­mum of quart and a half, as do the iden­ti­cal cylin­ders of a flat-six O-540. O-320s take one and a third quarts and O-235s just un­der a quart apiece. All the four-cylin­der Con­ti­nen­tals dis­place around 200 cu in or 3.27 litres, so their cylin­ders need about three-quar­ters of a quart. The six-cylin­der O-300s and C145s again utilise iden­ti­cal cylin­ders. A 1700 VW cylin­der holds just un­der half a quart, while a 1200 cylin­der holds one third. And if you don’t know what en­gine your aero­plane has, shame on you!

Of course, at any time one of your four cylin­ders will have an open ex­haust valve while an­other will have an open in­take valve, so quite a lot of oil will seep out of the com­bus­tion cham­bers – thus the drip tray. But in the process your valve seats, faces and stems should be­come wet­ted with nice, cold, and com­par­a­tively thick and sticky 15W50, pro­tect­ing them as well as you pos­si­bly can. There’s an al­ter­na­tive for Volk­swa­gens: pop off the rocker box cov­ers and undo the two nuts (or bolts) hold­ing down the rocker shaft each side. This en­sures that all four valves on each cylin­der bank are closed.

Now you can re-fit your spark­ing plugs to the oil-filled cylin­ders. You could use des­ic­cant plugs packed with sil­ica gel in the part-full ones but I don’t bother. Just re-fit all the spark­ing plugs to make each cylin­der a sealed con­tainer and so min­imise cor­ro­sion. Ex­pe­ri­ence tells me that any mi­nor valve face and seat cor­ro­sion (a par­tic­u­lar prob­lem with Volk­swa­gens) wears off as they ro­tate against each other in the first few fly­ing hours any­way. And re­plac­ing valves, seats or even a whole cylin­der on any en­gine costs a tiny frac­tion of a full over­haul, so the crank­case and its in­ter­nals are the im­por­tant com­po­nents to pro­tect. What­ever you do, if you fill the cylin­ders with oil, be sure to plac­ard the en­gine ‘Do not turn’.

Don’t use WD40!

Fi­nally, spray the whole ex­te­rior of each en­gine with a pro­pri­etary rust-in­hibit­ing fluid. I use Bal­lis­tol, sim­ply be­cause a gun­smith friend rec­om­mended it, but there are prob­a­bly other, bet­ter sprays. Don’t use WD40 be­cause, as its name im­plies, it is only a wa­ter-dis­per­sant last­ing forty days, and not a proper cor­ro­sion in­hib­iter.

Now for the pro­pel­ler. If it’s alu­minium, I wash it with wa­ter and then petrol, and coat it all over with a thin layer of grease to pre­vent cor­ro­sion (which shows up as tiny, dusty, white spots). A con­stant-speed pro­pel­ler should have a few pumps of the ap­pro­pri­ate grease squirted into its hub to re­place any in­side that might have ab­sorbed mois­ture.

Spe­cial care for wooden pro­pel­lers

Wooden pro­pel­lers have dif­fer­ent is­sues. Again, wash off all the nasty, po­ten­tially acidic bugs, grass and other flora. Polish the brass lead­ing edges if you have them. Wood ex­pands in the win­ter, so un­less yours is se­cured with Bell­man wash­ers it’s im­por­tant at the very least to cut the wire-lock­ing and un­wind each bolt a full turn to pre­vent the front crush-plate from cut­ting into the wood fi­bres. This of course means that you will have to get your in­spec­tor in­volved in the re-torquing and wire-lock­ing process next spring. Be­cause of this, I reckon it’s just as easy to re­move the whole thing, and I take it home to store in my nice dry garage, sort of repli­cat­ing sum­mer at­mo­spheric con­di­tions so the wood doesn’t ex­pand too much, even­tu­ally crack­ing the paint and caus­ing other prob­lems. Be­cause wood has a mois­ture con­tent and this will mi­grate

over time, it is im­por­tant to store your pro­pel­ler on its back (driven) face rather than in the ori­en­ta­tion it has on your aero­plane, and never with one blade up and the other down.

Look­ing af­ter the electrics

If you wish, you could also re­move the ra­dios for dry stor­age at home. The bat­tery is next. ‘Wet’ lead/acid bat­ter­ies are much more tol­er­ant of long pe­ri­ods of in­ac­tiv­ity than gel cell ones− a cou­ple of hun­dred quid for an an­nual re­place­ment Gill ‘dry’ bat­tery taught me that! All bat­ter­ies de­te­ri­o­rate more rapidly when left un­charged, so I dis­con­nect and fully charge them. Some­times I leave one on a trickle-charge through­out the win­ter, be­ing care­ful to en­sure it stands on its own in the open, on a non-com­bustible sur­face (e.g. the con­crete hangar floor, well away

from the aero­planes) just in case a spark should ig­nite the hy­dro­gen gas given off dur­ing charg­ing.

Then wheels and tyres. Pump up the tyres to a slight over­pres­sure to al­low for win­ter os­mo­sis, then put blocks un­der the axles or brake cal­lipers to sup­port the air­craft’s weight in case one or more of the tyres should de­flate. Not only might this cause wingtip dam­age, but pro­longed rest­ing on a flat tyre will ruin it− and a 600 by six tyre and tube can cost £200. If there is any chance of flood­ing, put the wheels into wide flex­i­ble plas­tic an­i­mal feed­ing buck­ets. This also helps foil rats and mice, who will nib­ble your rib-stitch­ing and wiring− plus their urine is a deadly cor­ro­sive to steel and alu­minium (and it stinks!) That’s an­other rea­son to raise your tail-wheel− putting it on an old ca­ble drum again foils those ro­dents.

Leave only a drop of fuel in the tanks

Siphon or drain any re­main­ing on­board fuel out of the tank(s), leav­ing a lit­tle to keep the bot­tom of each tank and fuel gauge sender cov­ered to pro­tect them from cor­ro­sion. Then dis­pose of this fuel, be­cause av­gas in an open con­tainer (with its manda­tory vents, a fuel tank counts as an open con­tainer) has only a three­month life, whereas in a sealed jerry can it has a twelve-month life. Mo­gas only has a one-month ‘shelf life’.

If your hangar is damp you might care to re­move your up­hol­stery, or even the com­plete seats to avoid mildew. I just put the cush­ions with the ra­dios in my study. I do spray the wings and tail with mould in­hibitor, although I am still un­de­cided on its ef­fec­tive­ness.

Fi­nally I fit the tai­lored cover. If this doesn’t en­velop the fuel fillers, seal them, and the tank vents and pitot tube, with duct tape, and tape up any un­cov­ered cock­pit vents. Cowl­ing in­take bungs cut from foam are a good idea, although their main pur­pose is to dis­cour­age birds from nest­ing in the spring when you re­move that cover.

That’s it. Come back in spring.

Bob’s Champ, fully winterised and tied down for the du­ra­tion...

Be­fore you lay it up for the win­ter, first wash it!

bag and Bob rec­om­mends us­ing both a dessi­cant cap that close-fit­ting bung (in this case an aerosol mois­ture fits per­fectly) to pro­tect the ex­haust from

Dessi­cant bags also go in the air fil­ter in­take — do not for­get they are there!

One thing that’s eas­ily missed: don’t for­get to plug the breather tube out­let

Air in­take bungs in place

Damp find­ing its way into a wooden pro­pel­ler will cause the hub to swell and may af­fect bal­ance: Bob avoids both prob­lems by re­mov­ing his aero­planes’ props and stor­ing them in dry con­di­tions

Nest and cor­ro­sion from ro­dent urine re­vealed as a Cub wing is stripped — good rea­son to keep the mice out!

Dis­con­nect and charge the bat­tery, leav­ing it like this to avoid resid­ual cur­rent drain­ing it dur­ing the win­ter

Re­mov­ing the ra­dios is one fur­ther easy but op­tional pre­cau­tion

The sub­stan­tial part of Bob’s UK fleet, tucked up safely for win­ter

Mouse-proof­ing the Fournier ‘s sin­gle main­wheel — Bob’s way of keep­ing out the lit­tle devils

Wheel blocked — to avoid dam­age should the tyre de­flate — and chocked, so the air­craft can­not move

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