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Technical Chat Tips and Advice, including flying the Luscombe

Moderator: HTB

 #6366  by Nige
 Tue Jul 05, 2011 1:37 pm
With fuel/maintaince [some landing fees!] costs so high, I'm now looking at using Mogas in Brug, which has been converted some time ago for it's use, as possibilty.. Ho hum... :?

 #8013  by howell
 Sat May 25, 2013 7:14 am
Hi All
With ever rising fuel costs and for us based in South Devon the availability of Avgas it has increasingly become a problem.
While Plymouth Airport was open it was a 10 minute flight to collect fuel, sadly that is no longer possible as the airport has closed.
Last weekend I picked up avgas at Bodmin @ £2.10 litre plus £9 for a landing, the £88 invoice made my eyes water, who said the Cornish were tight!
My good friend John Kempton and I have found a local garage selling forecourt unleaded fuel @ 1.51 litre which we have tested and found ethanol free.
This represents a massive saving on Avgas prices and the purchase is very convenient.
But try as we may it seems very difficult to find out the chemical compound of garage forecourt fuel.
We may well continue to operate on ethanol free unleaded and throw in the occasional can of avgas when the purse allows.
Any and all feedback welcome.
Chris Howell G-SAGE.
 #8017  by Mike Cross
 Wed May 29, 2013 11:11 am
Over here in Savannah GA the boating community doesn't like using fuel with ethanol and retailers are offering ethanol-free "Marine" fuel at a premium price.

Some years ago a friend died in an EFATO. The AAIB postulated the cause as vapor lock resulting from Mogas use. Safety is all about managing risk. This should include what colour your wings are, where you park, and being prepared not to fly if it gets too warm. In my view Mogas use increases the level of risk but not necessarily to an unacceptable level dependent on the individual aircraft characteristics and subject to good awareness and decision making on the part of the pilot. The Luscombe fuel arrangement is relatively benign compared to that on his Cornell.

AAIB bulletin here.
 #8018  by howell
 Wed May 29, 2013 6:43 pm
We have found our local Texaco garage sell Texaco Supreme @ 1.41 litre, we have tested this fuel and it is ethanol free.
Chris Howell. G-SAGE.
 #8019  by Robert Lees
 Wed May 29, 2013 6:59 pm

Well done for testing for ethanol. What are occasionally described as "aromatics", these additives can have implications upon not only the vapour pressure (to which Mike's reply above refers) but also to the condition of hoses, gaskets, etc, and in particular rubber items.

Many Luscombes fitted with A65 to C90 range engines have Stromberg carburettors, with often unknown and undocumented neoprene needles which can swell up and affect fuel flow, if using fuels containing aromatics.

(Low wing aircraft with the same engines as stated above [but now including the 0-200] have mechanical fuel pumps with rubber diaphrams which can suffer the same issue...but of couse the Luscombe, like my aircraft, is gravity fed, so this info is just for info!)

My advice to all is to check for aromatics (e.g. ethanol) in any purchased fuel, as Chris has done, but also to ensure your carb, fuel lines and tanks are not affected by its use.

These old engines of course will run fine on the fuel itself...most of them were designed to run on 73 octane!

 #8021  by Tom
 Sun Jun 02, 2013 8:39 pm
Hi Chris
Since starting the thread, we modified the fuel system with the guidance from Pete and our inspector, replacing all rubber component’s with new ethanol proof type. This include rubber hoses, gascolator seal and replacing needle valve for stainless type. This needs bedding in with valve grinding paste to form a good seat and so preventing the carb dripping as many do.

All rubber components used where left in a sample of petrol for 2/3 weeks to ensure there was no breakdown of the material.

We always consider temperature and altitude and refuel accordingly, we have now done over 500hrs mostly on petrol with no problems, apart from one time I foolishly left a can of fuel in the car on a hot day, inflight the engine ran roughly, vapour locking I assume, but picked up as soon as I changed tank to the cooler fuel!

Really pleased with the results and well worth the effort and cost

 #8022  by howell
 Sun Jun 02, 2013 8:47 pm
Many Thanks Tom.
I was surprised that The LAA do not hold records for aircraft cleared for Mogas
Chris G-SAGE.


 #8220  by Rob
 Fri Nov 15, 2013 9:25 pm
Pete, tried to look for the seal for the gascolator (I have the Original glas type one) I am away from the plane right now so cannot look. Looked on the LAS site for Vitol but cannot find anything.



BTW I have the Petersen STC and a stainless steel needle.
Pete Bush wrote:Hi Tom,
I have heard a rumour that the LAA are not giving out any more Mogas exemptions at the moment as they are worried about future ethenol content.
If you did want to convert your Luscombe for Mogas use and assuming you have a Stromberg carb, probably the most important part to replace is the float needle valve as the originals have a neoprene tip that can swell in mogas and cause engine failure. Aircraft Spruce/LAS do a stainless needle and seat kit (Pt No 07-14222).
This needle is a relatively straight forward job but the seat can be more difficult, the carb float level has to be set up pretty precisely and obviously a new gasket (07-0220) fitted on completion. The disadvantage with a steel needle is that they don't seal as well as the neoprene item and can let fuel through, this is not a problem when the engine is running or if you are in the habit of turning your fuel off after flight but if you have old and leaky fuel taps then you may have a leaky carb.
You then have to consider every rubber item that the fuel contacts in your aircraft including Gascolator seal, tank caps, rubber hoses ect. Mogas tends to attack the standard aviation AN grade hoses and O rings so a mogas proof alternative has to be fitted. Viton is a relatively new kind of rubber that is mogas and avgas proof, LAS do a Viton seal replacement for the ACS type gascolator, I also replaced the O ring primer seals on G-BROO with Viton items.

The LAA used to do a check list for mogas use that your inspector signs off, I suggest you contact your inspector and/or the LAA before starting work. There is plenty to read on the LAA forum regarding fuel.

Realy good to see your Luscombe in the air again, you have both done a fantastic job.

Pete (G-BROO)
 #8222  by Pete Bush
 Sat Nov 16, 2013 2:14 pm

Viton seal part number is 10536-1, not sure if it will fit the old glass type gascolators though.

 #8223  by howell
 Sat Nov 16, 2013 7:44 pm
Running on a lot of mogas this summer, just drained it all out and filled up with avgas.
Back tracking this week and the engine stopped, maybe carb ice.
Now struggling with rough running on the right hand mag which feeds the lower cylinders, recent all new spark plugs, slick mags only done 100 hours, new leads.
Going to start with replacing four of the spark plugs that feed from the right hand mag to try and start indentifying the problem.
Mogas has a much shorter shelve life even though been using ethanol free, thinking that any long non flying weeks maybe better off with avgas in the fuel tank.
Any feedback welcome.
Chris Howell.
 #8230  by howell
 Mon Nov 18, 2013 9:23 pm
No success so far on the rough running changed all the spark plugs no change still popping on the right hand mag.
Need to check the HT leads, the tester is nearly £100 ouch.
 #8231  by Pete Bush
 Mon Nov 18, 2013 10:59 pm
Hi Chris,

Have you checked the mag timing? A high power ground run with a blip of over 2000 RPM may have an effect, make sure your are well chocked and tail wheel tied down.

 #8232  by howell
 Tue Nov 19, 2013 7:15 am
Dear Pete
Not checked the mag timing yet, need some help on that one hoping to get a friend over!!
Could you explain the blip over 2000 rpm
I normally get up to 2000 rpm on a static full power run up not much over!
 #8233  by Pete Bush
 Tue Nov 19, 2013 10:23 am
All I mean Chris is give it a short period on high revs during a ground run, sometimes clearers the odd miss. Don’t forget to tie it down!! I would get the mag timing looked at first though.

 #8234  by howell
 Tue Nov 19, 2013 2:27 pm
Thanks Pete, will have another go tomorrow and I have a good friend close by who will check the mags for me.

I will update with progress, thanks for your support.