Oil costs next to nothing.
Even in my IO540 I put in about £70 in oil and that is using pricey Shell 15W/50. Straight oil can be bulk bought at half that price.
And even with the £20 Camguard bottle thrown in, a 50hr oil change costs me only £90 in oil (actually less since on Ed Kollin's advice here I am switching to 50% 15W/50 and 50% W80) which is about £2/hour which is below insignificant.
I suppose a 50hr check done by a company (as is necessary if you are a school) is not insignificant, at a few hundred quid (I used to pay £600 for ~5 man-hours work, on the TB20, before starting to do them myself in 2005) but does the use of 91UL actually replace a 50hr check with a 100hr check? There is other stuff to do besides an oil change.
" Straight oil can be bulk bought at half that price."
Where?
"does the use of 91UL actually replace a 50hr check with a 100hr check?"
Not sure to be honest but I could ask my maintenance organisation and but I pretty sure you don't have to change the oil and the spark plugs have a longer life on UL91.
I would also stick my neck out and say its a fact the the Rotax engine longevity is significantly increased when it is run on unleaded. I've heard of schools selling there rotax units at TBO to the microlight boys who then run then for another two thousand hours or so.
For me, the biggest issue with leaded fuel is cleaning the spark plugs two or three times between replacement. It's a big pain in the neck that I'd prefer not to do. I'd probably pay a little extra for unleaded if it were available in my market, unless I was flying so much that the additional cost started to hurt. Both my engines were run on unleaded auto fuel for years, now unavailable locally except for fuel with STC ineligible alcohol content.
I change the oil on my Continental 4-cyl every 25 hrs (no filter), and did it last Saturday. The 100W oil cost the US equivalent of £15. Labor was about 30 minutes because I checked the screen, as I do every 50 hrs. The oil screen sealing ring was £1.
On my Lycoming its 50 hr intervals, £30 for 100W Plus, and £13 for a filter. Labor is again about 30 minutes. I've thought about adding Cam Guard and may do it in the future. Not necessary on the Continental.
All of the above is owner performed maintenance for N-registry Part 91 operated aircraft.
I've asked the Total UK manager to read this thread and respond. I know him/have taken him flying in the past.
My 912S must have its servicing intervals halved if using AVGAS. The problem results in . . .
"fouled piston rings, deposits on spark plugs, deposits in the combustion chamber and exhaust port and can sometimes cause sticking valves. The lead can also accumulate in the slipper clutch and sprag clutch, which can prevent them from functioning correctly, as well as gumming up the wastegate on 914 series engines"
See page 5 at this link for some images:
I am keen on UL91, but not at a premium over AVGAS. But i am also keen on avoiding filling up my a/c with jerrycans for safety reasons . . .
My 912S must have its servicing intervals halved if using AVGAS. The problem results in . . .
"fouled piston rings, deposits on spark plugs, deposits in the combustion chamber and exhaust port and can sometimes cause sticking valves. The lead can also accumulate in the slipper clutch and sprag clutch, which can prevent them from functioning correctly, as well as gumming up the wastegate on 914 series engines"
I have to wonder about Rotax Marketing, selling an engine which is so apparently badly affected by 100LL, when actually 100LL is by far the most common GA fuel sold around Europe, after Jet-A1 of course.
The vast majority of GA-accessible (by that I mean under €500 to land, or GA not banned outright 
) airports that sell any fuel other than Jet-A1, sell only 100LL.
I realise there are many GA airfields that do sell Mogas, and many that sell 91UL too, but taking the European picture as a whole, I would not buy a Rotax aircraft for European touring.
"I have to wonder about Rotax Marketing, selling an engine which is so apparently badly affected by 100LL, when actually 100LL is by far the most common GA fuel sold around Europe, after Jet-A1 of course."
Well for me the attraction of a Rotax 912S is that it is a multi-fuel engine (including MOGAS), has a very good reliability record, costs £12k and has been the engine of choice for a Europa.
I'm given to understand that the days of 100LL are numbered, with only a few (actually 1?) refinery in the world making it. Talk to the MAF guys and they'll tell you that getting hold of AVGAS is getting very difficult in many parts of the world. And in time, that problem is going to come here too.
So an unleaded alternative, especially in the light of the environmental lobby, is going to become essential.
However, I do still question the strategy (if that's what it is) of pricing UL91 higher than AVGAS . . .
I pay £4.65 a litre for oil (total non multigrade). The maintenance company that service the aircraft I use charge £5.50 (aeroshell 15-50)
If I used an aircraft from pleasure/touring I would actively seek out a rotax powered machine. The type of airfields I find that I am visiting more and more don't stock Avgas.
But then I am predominately a VFR flyer who never flies of the creases of my map.
The vast majority ( ... ) sell only 100LL.
Hm. Rather sharp at the edge, that phrase. What are your sources, apart from personal experience? Kindly prepare to rephrase, than take a look at (for just one example)
http://www.dulv.de/app/so.asp?o=/obj/BA18FF1E-7EEF-4B96-A1C4-C39A6A174DEA/outline/Dmogas_120412.pdf
And another point, if you'll excuse me: arriving anywhere and expecting anything required to be available for the money is a rich man's luxury. Humble people can get a long way with a little inventivity, accepting a bit of discomfort (1 or 2 km walk to a fuel station?), some good luck at times, and, above all, good friends. The smaller/less expensive the craft, the more likely one is to get help from locals. I have no fear of landing, without any prior consultation, at a small totally unknown field, but with an obvious buzz of microlight flying, and get my 40 or 50 litres of mogas in one way or another. Low-cost flying is borne by camaraderie, it needs to. And I've never had it fail on me, in my very limited career. Which of course does not reduce the importance of flight planning - but one CAN generally rely on help if things go wrong. Needless to say, the same helpful attitude is offered to strangers popping up.
All of this changing nothing to our concensus that UL91 is doomed if more expensive than 100LL. I reckon somebody at Total will realise, sooner or later. Again, that company is not a charity, not by a long way.
What are your sources, apart from personal experience?
None - only my personal experience, some snippets of which are here. And I write up only trips which are somehow different from the previous ones...
I fully accept that I don't operate in the microlight/homebuilt/farm-strip community (some of which can live out of car petrol transported in jerrycans) but if we discuss the topic of 91UL or 100LL marketing, one has to look at the wider GA scene.
I am not saying this is happening here on EuroGA, but there is a commonly expressed sentiment on some pilot forums which is basically "I am allright Jack" and it appears particularly in the 100LL type discussions.
Unfortunately "we" are all in this together. If the bigger airports (which tend to be the ones I fly to - even Le Touquet which I went to today - damn cold it was too ) kills off 100LL then GA will be forced to shrink to farm strips, and what will happen in the long term?
At least in the UK, farm strips operate mostly discreetly (they have to, due to usually no planning permission) so they are relatively closed to newcomers, have a very low public profile (very little public pleasure flying; in fact in most countries zero legal public pleasure flying, etc) and in the fullness of time they will collapse into their own black hole.
With GA as it currently stands, and with so much fuel burnt by engines which need 100LL, there is only one way forward if you want to remove lead and that is "100UL".
This is being played out much more strongly in the USA, where a large % of avgas burnt has to be 100 octane (lots of 10:1 and higher CR engines, and lots of turbocharged engines etc).
If TOTAL want to make a lot of money, they should make 100UL. How to make 100UL is no secret; there are multiple approaches. None of them is perfect, but anything lesser (like 91UL) is just going to fragment the market and fragment the GA community. That is why I am not ashamed to say I am glad the "91UL marketing experiment" appears to be a failure - even though my engine is (or probably is about now) certified for 91UL so I have no axe in the debate.
Fortunately most GA airfield managers know which side their bread it buttered...
I do agree we are all in this togther.
But I don't agree with grass strips collasping if anything I feel they will go from strength to strenth.
I started out in 89 and first worked at an instructor in 93. At that time there wasn't anywhere the number of grass strips there is today.
I also never visited them. I used to call up East Midlands Airport off the cuff - any chance of an ILS/SRA/NDB and not once did I get refused. Also not once did I ever get a fee.
Until last year we used EMA as part of our QXC it was 38 quid to land. It then went up in price to 138 quid all in. We no longer go there and use Hucknall or Nottingham instead (free or 12 quid) I simply can't justify these sort of charges.
If I ever flew to mum and pop who live in Castle Donington (2 miles from EMA) then I would route into Nottingham* and get a taxi. I would only divert into EMA due weather.
*shame the tight fisted previous operator was too tight to pay the NDB charges I have a dodgy 27 approach plate still kicking about in my flight bag. And I've flown it quite a few times in VFR.
