Interestingly, it was acknowledged by the FAA back in the day that “some people” were running with Mogas without an approval, that those pilots had noticeably fewer accidents, in which fuel was a factor. The simple rational reason, is that pilots flying on an unapproved [at the time] fuel, were being extra vigilant so as not to get caught, and that vigilance resulted in statistically greater safety.
Peter – of course it’s fuel related. It shows an engine with far lesser tolerances can run at high power for hours in a row on bog standard fuel. How is it that an aero engine with far higher part tolerances (yet exact same compression ratio) supposedly needs such a specific fuel to keep running “at all times and altitudes” without even delivering full power?! If “vapor lock” at 19k feet is an issue, put a proper fuel pump with a return line on the engine and be done with it, cheaper than developing “specialty fuels”. “Specialty fuels” that will anyway vapor lock on the ground on tightly cowled, injected, low idle rpm engines (ask me how I know).
People like Pilot DAR have actually tested it in real life, yet somehow all that work is being dismissed on the back of zero practical evidence.
put a proper fuel pump with a return line on the engine and be done with it,
How exactly will that happen?
The option doesn’t exist. We have to use what we have.
Here is a list of some of the factors which drive fuel octane requirement.
Compression ratio
Spark timing, which is tied to combustion chamber shape
Cylinder size/bore
Squish
Number of spark plugs
Engine rpm, which is tied to geared propeller versus direct drive
Supercharged versus normally aspirated
Cylinder head/wall temperature
Most of these when changed to allow lesser octane fuel compromise the design in some other regard, and typically lowering the fuel octane requirement at a given power output means a more complex engine. If you want to make 2000 HP you need both a complex engine and high octane fuel. For GA engines of say 350 HP you can minimize the number of cylinders, run the engine at propeller speed, air cool the cylinder heads and run reasonable compression ratio with AVGAS. For smaller engines the same can be done with lower quality fuel, which is why something like an O-200 runs fine on auto fuel or the late lamented 80/87 on which those engines were designed to run.
I note that Continental picked an engine with relatively small cylinders for 91UL, 200 HP and six cylinders. The same is done with four cylinders using 100 octane fuel.
Alcohol absorbs water, which could be a good thing if (in my experience) the water didn’t come out of solution here and there, causing corrosion in storage. Little particles of corrosion then plug little holes when the engine is started, requiring disaasembly and cleaning. I’ve done a lot of it.
Hi, finally i have to give my 2 cents too…..
If you look the A350, B787, CS100, Global6000 etc… what do you realize…. all brand new aircraft with new technology engines. Then we have Tecnam P2010, Flight Design C4, Pipistrel Pathera…. with engine technology of 60 years… do you see the difference ? Why the hell do Aircraft companys build new Aircraft with such old engine technology.
Even Cessna and Piper in the meantime offer their mass products with Jet A1 engines, and also Cirrus has a test aircarft with a Diesel Engine. And this, in fact modern companys (compared to Cessna and Piper), do the opposite.
Then second wondering… would a Airline buy a Modern Aircraft with DC8 or B707 engines nowadays?
Why do GA companys and flying clubs obviously doing it? My flying club just did by modernized Aircraft, Robin DR401 with new Engine CD155. Its great to fly, easy to operate….except the french seem to have a problem with the electric part of the aircraft.
So if GA customers, like airlines, ask for modern equipment, they soon or later will get it…. if they do not buy outdated technology under pressure.
Regards
Lucas
So if GA customers, like airlines, ask for modern equipment, they soon or later will get itQuote
Perhaps, but is is more than asking for it, it’s paying for it, and it must be within the design requirements for certification.
A client sent me to SMA to buy a new diesel engine for installation into his C 182. Having agreed to pay more than $100,000 for the engine (about twice what the comparable gasoline engine would cost), after waiting two years on the promise of the engine, he gave up, and purchased a new Continental. SMA told me that we were the only potential customer, until an OEM bought hundreds, and they just would not sell one engine. Since, Cessna seems on line with that engine, but too late for us.
How many GA customers are willing to pay the high cost for new engine development and certification, when the old tried and true is easily available? What to do when the prevailing design requirements for certification are simply contradictory to new technology? A sticking point has always been that the engine must be able to continue to run with no outside source of electrical power. That has always been a show stopper for electronic ignition development for certified aircraft.
To be a certified design, a GA aircraft must have a certified engine (and propeller), so as long as GA aircraft purchasers choose the relatively economical tried and true 70 year old engine designs, that’s what they’ll get. I attended many ASTM aviation fuel meetings back in the ’80’s. At each biannual meeting, the US Environmental Protection Agency (EPA) representative would stand up and tell the audience that the EPA would ban all leaded gasoline – meaning 100LL within ten years. The threatened bad would be extended only if it was obvious that meaningful development of a lead free replacement signaled the need to grant an extension to such a ban. And where are they with that today? We still have 100LL. Knowing that if you take the lead out of 100LL, you pretty well have 80/87, which was discontinued about 25 years ago, even though it is the specified fuel for 60% of GA aircraft.
So the world would be just right, if all the “big” GA engines which required high octane went diesel or turbine, and burned Jet fuel, and production of 100LL just returned to 80/87 for the rest of the aircraft. Consider the ubiquitous C 150/152, Cessna only changed to the 152 to stop using the O-200, which did not agree with 100LL, to the Lycoming 235 which would. If 80/87 remained common, so would the O-200 and the 150.
The GA market wishes for far more than it can (will) afford. A car manufacturer will invest in engine development for the sale of a million cars, but the plane manufacturer has much greater certification costs, more restrictive requirements, and a market 1/1000 that size to amortize costs. There is no business model there….
We have discussed it here many times that there is simply no real market for SEPs any more (see the last few years’ GAMA reports). Where there is no market, there is no investment and innovation.
On the other hand, Lucas has a point here: it’s obviously not that there is no investment in the SEP sector of GA. There is lots of it on the airframe side. For the Pantera, P2010, C4, M10, etc. hundreds of millions are being invested (IMHO: drained, from a purely investor’s perspective; they will never have a return on these).
So the question is: why in airframes yes, in engines no?
I do not agree with Pilot DAR, i do not ask to change all old engines to new ones (i will not change the engine of my 2007 Panda, but sure, the new one will have improvements in fuel consumption), i.e. C150. But i’m wondering why new Airframes are developed with old engine technology. The diesel technology is here, Continental is working on the CD300 , CD230, CD155 and CD135 are already certified, so no reason to build in 60 years old technology. The additional weight of the diesel engines can be compensated by the 30-40% less consumption.
A sticking point has always been that the engine must be able to continue to run with no outside source of electrical power. That has always been a show stopper for electronic ignition development for certified aircraft.
I would have two questions on this.
How did Thielerts ever get certified, when a total electrical failure shuts down both engines on a DA42? I know it’s unlikely to happen, but it’s been (very famously) done.
What is complicated about a little alternator which powers just the ECU+ignition? The mfg cost of such a device is of the order of $100.
no real market for SEPs any more
Certainly even the mightly Cirrus is in decline compared to their great days, but SEPs remain the only healthy area in certified piston GA. There is more innovation in uncertified piston GA but due to operating limitations (not an issue for ~99% of flying within the USA, of course) this scene will always be limited to somewhere well below 100% of the activity.
The problem is that new airframe sales are low, and customers are happy with the present market leaders.
@Pilotdar .. Sma is at present not interested in the aftermaket, thus the “go away” price. They told me this explicitely. The price has nothing to do with what they need or with the certification. If that were to be the case they would go for a far more aggressive sales strategy.
One day it will all come together.. I am hopeful we will see it this decade.
I would gladly upgrade my 270hp tio-540 for a 300+ hp diesel, wether continental or sma or ..,?
Going from 155-160kts @17gph running Avgas
To 180-200kts @10-12gph jet a(x) @FL100
Sounds sweet to me
