BE-33 Running AutoGas?

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DJTorrente
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BE-33 Running AutoGas?

Postby DJTorrente » Wed May 16, 2012 10:20 am

I just read that the BE-33 with an IO-470 can be STC'd to run auto fuel. Does/did/would Jeb (or Jack or Dave) run auto fuel?
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Jeb
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Re: BE-33 Running AutoGas?

Postby Jeb » Thu May 17, 2012 9:18 am

DJ:

Good catch, and good question. The answer is, "It depends." <g>

First off, most LSAs run just fine on what I'll call mogas (premium unleaded automotive fuel, with no more than 10% ethanol). In fact, Rotax recommends mogas for its engines. When running 100LL in a Rotax, maintenance frequency recommendations are shortened, thanks to the higher lead content. Many other "traditional" aircraft engines, basically relatively low-powered Lycomings and Continentals, run just fine on mogas, also. In many instances, the issue isn't how the engine runs, but how the mogas might affect other components in the fuel system, namely bladders, gaskets and o-rings. So, when you ask if Dave or I have ever flown something powered by mogas, the answer is "yes," but it was a Rotax or low-powered Lyc/Con.

As for the IO-470 and BE33s generally, here's the deal...

There are many flavors of IO-470s. Early Debs -- and even earlier Bonanzas -- came from the factory with the IO-470-K, rated at 225hp at 2600 rpm. This is a low-compression engine, at 7:1. Thanks to its low compression ratio, detonation and pre-ignition aren't huge issues. So, the nominal 93 octane in mogas works just fine in them. But it's the only engine in the Debonair series eligible for the mogas STC (and one of the few injected engines). The other IO-470s (e.g., the IO-470-N at 260hp and other engines which might be installed aftermarket) aren't eligible for mogas STCs, thanks to their higher compression ratios. Please note also when we talk about running mogas in anything other than something powered by a Rotax/Jabiru/etc., we're also talking ethanol-free mogas of 93 (pump) octane or greater (octane rating methods differ for mogas and avgas). The STCs for such engines require the fuel to be ethanol-free.

Moving up the compression ladder in the IO-470/520 series, none of those engines can legally run mogas, thanks to the lack of detonation/pre-ignition protection. The IO-520-BA in my Deb, at 285hp and an 8.5:1 compression ratio, never will be eligible for a mogas STC without significantly derating it. I don't even want to think about the bladders/gaskets/o-rings. So mogas isn't an option for me and my airplane, but it is for earlier, lower-powered Bos and Debs.

(There are two factory flavors of Debs: the straight 33, plus the A/B/C33 models came with the IO-470-K. The C33A I have came with the IO-520-BA. The "A" suffix appended by Beech to the 33 series means it has the IO-520 from the factory. Many non-A-suffix models have been upgraded by STC to 260/285/300hp engines).

All of that having been said, the detonation/pre-ignition protections are needed most at high power settings, like takeoff or going around at full-power and low altitude (non-turbocharged). When cruising, they're much less necessary. The point here is some people flying certificated, non-LSA aircraft have occasionally pointed out that filling one tank with 100LL (for takeoff) and the other with mogas (for cruising at low power) is a solution. Of course, to do so legally, they must have a mogas STC. I have not and will not do that; can't speak for Dave, but I doubt he would, either.

HTH. More than you wanted to know, I'm sure.

Jeb

Dave Higdon
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Re: BE-33 Running AutoGas?

Postby Dave Higdon » Thu May 17, 2012 10:51 am

DJ...seconding all of Jeb's post...yeah, our old Cherokee 140 had the auto-fuel STC and ran fine on it, whether in 100 percent saturation of mixed with 100LL...cleaner plugs, cooler...probably cost us a knot or two...but...our old Comanche was originally a 91 Octane engine and was not eligible for the STC...and even is the engine had been, the fuel bladders and some other components in the fuel system were not compatible with mogas...as for Rotax....no reason not to use it and, as Jeb noted, the engine likes mogas better...

Dave

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champguy
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Re: BE-33 Running AutoGas?

Postby champguy » Thu May 17, 2012 10:18 pm

The other issue with mogas is that it goes stale if left sitting in a vented tank. I wouldn't hesitate to use it if I got caught somewhere on a cross country, but I wouldn't let the sun go down without burning it up on the way to top up with avgas.
An exageration perhaps, but seriously I would not put the plane in the hanger to sit for a while with mogas in the tank and fuel lines.
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DJTorrente
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Re: BE-33 Running AutoGas?

Postby DJTorrente » Fri May 18, 2012 10:21 am

Are the concerns over rings, bladder, fuel lines, etc., solely a function of the ethanol? I know its getting much harder to find ethanol-free fuel, but where it can be found, that might be a solution.

I'd love to see the PA-32-260 STC'd for mogas. Based on the similarities between the low compression O-360 and its bigger brother the 0-540, I'd like to think it is feasible and just that nobody has been convinced of the market case to certify it. The EAA STC is available for low-compression Cherokees (-140, -150, -151) and also for the O-540, but only in its 235 HP configuration (compressing 7.2:1). The 250 and 260 HP versions of the O-540 run at 8.5:1, but its not like they are wringing 300+HP out of them like some other models.

Thanks for the answers!
"Good Rock... Welcome to Oshkosh"
AirVenture 2019: July 22-28 http://www.airventure.org

Like they say in baseball, there's always next year.

-DJTorrente

Jeb
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Re: BE-33 Running AutoGas?

Postby Jeb » Fri May 18, 2012 10:41 am

DJ:

Yes, it's my understanding the concerns about swelled/deteriorated gaskets/o-rings involves the ethanol, although the mogas itself may also be responsible in some instances. It depends....

<g>

I doubt you'll ever see anything with a compression ratio higher than 7.5:1 or so approved for mogas.

Looking at the different engine models from Lyc/Con, it's always been of interest to me how they go about increasing hp. The O-360 Lyc, for example, puts out 180hp nominal. Add fuel injection to the same engine and it puts out 200hp. Change a couple of things on a 150hp O-320 and it puts out 160. Same is true for Continental: Take an O-470 putting out 230hp, inject it, and you're looking at 260hp. It's not all that simple, I know, but those are the basic configuration changes...

HTH...

Jeb

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jackhodgson
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Re: BE-33 Running AutoGas?

Postby jackhodgson » Mon May 21, 2012 9:18 am

Eventually all the "high performance" aircraft will be converted to turbines, then they can all just burn used fry-oil.

#onlyhalfjoking

// Jack


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