Auto gasoline vs avgas

[Don]

1) I don't have a pilot license yet but I very much favor the tailwheeler design. Excuse me for what is probably a naive question, but I noticed that the Husky Aviat takeoff and landing distances seemed shorter than the Cubs. However, much of this seems to be due to the Husky having an engine using 100 octane aviation gas whereas the Cub, at least originally , used 80 octane.
Is this correct?

2) My understanding is that the FAA allows use of auto gasoline for some engines. It seems to me that the ability to use ordinary auto gasoline would be a big advantage over having to use aviation fuel, even with a reduction in power. Is my understanding correct? Also, Is this practical? Do people use
auto gasoline regularly? Are there problems with icing?

Thanks in advance for any information.

 

[StewartB]

Don,
Complicated question. First, a Husky comes stock with 180hp and a constant speed prop, as compared to a Cub with 150hp and a fixed pitch prop. 30 horsepower and an efficient prop make the difference in take-off you noted. Try a Cub with a Borer prop and the numbers get closer. Add 30 horsepower and the Cub wins, although the Husky will go faster. Different planes, different advantages. That issue doesn't have anything to do with fuel. Some guys use auto gas. Some blend auto and avgas. Some use avgas. You'll get lots of opinions as to which is better, but the arguement for auto gas is based on price, and availability, not performance. Some guys think the engine will last longer with avgas, and are willing to pay the price for that peace of mind. Some think auto gas is as good in every respect. That argument will last as long as there's gas.
SB

 

[flagold]

but I noticed that the Husky Aviat takeoff and landing distances seemed shorter than the Cubs. However, much of this seems to be due to the Husky having an engine using 100 octane aviation gas whereas the Cub, at least originally , used 80 octane.
Is this correct?

Actually, it's all due to pilot technique, Don, but I see the guys over here are practicing -- I'm confident they'll get it yet . . .

In all seriousness, I never had a problem running autofuel. It has a different burn characteristic, (burns a brownish color), but doesn't lead the plugs up, etc. As long as the plane doesn't have a fuel pump in it, I don't have a problem with it down here in the south. You do have to watch out for ethanol, etc., but the STC is basically for one type of fuel (Amoco premium unleaded) and it states not to lean the engine in there somewhere (as I recall).

Glad you like tailwheels, you're onto something there.

flagold
(the shorter takeoff and landing Husky pilot)
http://husky.taildragger.info/

 

[HydroCub]

Don,

I wouldn't ever consider owning an aircraft that required 100 LL fuel as the price will continue to rise... probably to exceed $5 within a few more years. The refining (less than 1% of fuel sold) and transporting of AvGas continues to drive up the costs. Furthermore, many low compression engines run better without the high lead content of 100 LL as it contains 4 times the lead additive the engine was designed for. My best performance has been from blending AvGas and Auto Fuel or adding some Marvel Mystery Oil to Auto Fuel when I haven't run blended fuel for some time. The spark plugs remain much cleaner as a result.

As for power, an engine will always perform best with the Octane it was designed to burn... higher octane fuel does not add power. Engines of similar displacement gain power from compression ratio increases which calls for higher octane fuel, especially at Sea Level and lower altitudes of operation.

The perfect Cub would have a light, low cost Turbine engine that puts out 200+ horsepower and is flat rated to 10k. It might not be too far away... I'm keeping my options open on a 'wide' Cub I'm working on.

 

[Marc Olson]

Which engines are considered 'low compression'? O-320?

 

[Steve Pierce]

O-320-A__ are low compression 7.00:1
O-320-B__ are High compression 8.50:1
O-320-C__are high compression engines converted to low cmpression in the field.

 

[Cubus Maximus]

Hey - as for Husky's running away - put Wip amphibs on Jim's B model back here and it runs 99 mph - that's it (maybe in a dive you can get past that) My guess is a 180 Cub on floats is going to keep up no problem.

On Wip hydraulic ski's the Husky ran 110 mph. It seems you need to have 8:50 tires or smaller on straight gear to get the speed numbers advertised.

Brad

 

[behindpropeller(s)]

auto fuel

Before running autofuel I would sugest checking your warranty. We (the shop i work in) had an 0-200 come in that had had 9 cylinders in 300 hours. We tried to get a warranty claim with continental but they said if it ever ran autofuel it was exempt. We sent the guy away, refusing just to rebuild the cylinder without a complete teardwn to find the cause.

Tim

 

[Matt Mattson]

Brad,

You might want to point your buddy to the Husky list if he's not already on it. There's a lot to learn, not the least of which the Husky AI is an abomination. I'm assuming you've drained the water trap, so here's the real trap, to get the correct AI at high (how high is high -- I don't know) you have to open the alt air source and you'll read true airspeed. Works like a charm. The actual AI in cruise (valve closed) matches with knots on our GPS units. Doesn't seem to matter if it's an A1B or a Christen Husky . . . With some of the new manifold pressure combinations you can actually be cruising in the yellow without realizing it, so it does pay to pay attention to this glitch. Not all the guys cruise their Huskies fast like I do, and some are outright opposed to oversquare operation (even though Lycoming is not), but the AI is a problem with fast cruising if you're not aware of it. The guy that seems to have the most knowledge about this glitch is Tom D(ietrich).

On the list you'll see people refer to airspeed (valve open) or airspeed (valve closed) and this is the glitch they're referring to. (Yeah, I can here the SC peanut gallery all the way from here . . .) Have fun. MM

From the list on oversquare ops:

I threw him the following hypothetical: Since I can't maintain 9" oversquate at 7500 feet (for any listed RPMs), am I hurting anything to run at 1500 rpm, where I could maintain 23" and have full power on the prop? He said he knew of nothing it would damage to run slow, but the engine would probably really be lugged down at that low rpm. They simply haven't tested it that way.

I have an email in to a fellow named Mike Day as well, but the news that we're reading the chart correct and you can use 9" oversquare is very good news indeed, as we all just got a lot more plane performance and options with that news. -----------

Mike Day, is in fact, the second engineer that sent me the chart, again, showing all kinds of oversquare combinations which just 2 weeks ago we were told by the "experts" were illegal, immoral, innapropriate, ect., etc., etc.

I gave the following example everyone can easily try that has fuel flow:

1. Set up 2350 & 20" and lean your engine like you normally would. Note your fuel flow. Note your egt. Note your airspeed.

2. Pull back the prop to 1950 (or 2000) Note your fuel flow (it's the same) Note your egt (it has plummeted) Note your airspeed (mine increases a couple mph). Re-lean your engine to your old egt setting (the one you used for 2350/20") Note your fuel flow. You're flying the same, a couple mph faster (as in my plane), or at worst a couple mph slower on much less fuel.

Even if you don't have fuel flow you can check this example by noting your mixture control. In the above example, after you pull back the prop, note that you can lean the engine further without roughness.

Run your engine any old way you want, but remember this example if ever low on fuel -- you've been told how to stretch it.

 

[Cubus Maximus]

Thanks Matt - I'll print this out, haul it over to the shop and we'll try it.

Brad

(and I thought the Cub AI was lousy Of course the Husky is "better" than a Super Cub - I plumb forgot

 

[kase]

I unhooked my static line to my airspeed and gained around 10 mph. Made my airspeed more accurate, high and low end. Sounds like the same thing the Husky guys are doing with the alt air. I did the same thing when I was flying Dakota Cubs slotted wing Pacer and it worked the same way in that aircraft also.

 

[Matt Mattson]

(and I thought the Cub AI was lousy Of course the Husky is "better" than a Super Cub - I plumb forgot

It is! It's just for some things you have to fly it upside down to get the right reading . . . MM

PS: just because Lycoming says it's ok to run 9" oversquare doesn't mean I'd do that on a 2000 hour engine on the 3rd overhaul by No Name of Gnome (rotary engines) . . . but, even at 25"/2000, it is very quick for what it is. Not a 180, but not bad. Have fun with it.

 

[Steve Pierce]

Back to the autogas discussion. It is imperative that you break a new engine in on Avgas. The valves/seats need the lead on breakin.

 

[Guest]

The perfect Cub would have a light, low cost Turbine engine that puts out 200+ horsepower and is flat rated to 10k. It might not be too far away... I'm keeping my options open on a 'wide' Cub I'm working on.

I was wondering if anyone has pictures or info on a Cub that has a turbine engine mounted on it? I could have sworn that I saw one in a magazine in the recent past but I have dug through my supply of magazines and cant seem to find it.

Mark

 

[Jerry Burr]

Smokey

Hi Mark. That has been discussed quite a bit around here, and kind of dropped. It might be fine on water, what with back-up and all. But can you imagine taxing through the grass and hitting a small maple or alder tree. Right now it just goes thump as the tree parts hit the wing. With the prop spinning at turbo speed it would be trashed prop. I was visiting with the salesman for Bush Comp or what ever that taildragging turbine is. And he said the prop costs more than the engine. The conversation switched to Diesel power. Jerry.

 

[Don]

auto gas vs avgas

Thanks very much for the info. I realize that I was somewhat unclear on my initial post. To clarify, my (probably mistaken) understanding is that:
a) All other things being equal (weight, prop, wings,etc) the greater horsepower of a 180 hp Lycoming O-320 will allow a shorter takeoff than what's obtained with the the 150 hp Lycoming O-320
b) The 180 hp Lycoming is high compression and hence requires high octane (100 ) although my impression from poster flagold is that
there is a STC that lets the 180 hp Lycoming use premium unleaded autogas (91 octane)???
c) The 150 hp Lycoming can be STC'd to use regular 87 octane autogas. My understanding from Petersens ( http://www.autofuelstc.com/pa/petersenaviation.html and http://www.fsv2000.at/woche/2001_10/petersen_stc_text_engl.pdf
is that several precautions are needed:

(1) Use gas from major chains and Follow instructions in STC; e.g.,
(2) Test to ensure that alcohol has not been added as an additive
(3) Take greater precautions against vapor lock , especially in spring (winter blend fuel vs hot temperatures). Use gravity feed fuel system instead of fuel pump. Test fuel with Hodges Volatility Test
(4) Icing can set in sooner with autogas so be prepared to use carb heat
(5) Use 100 LL in first 25 hours after engine overhaul
(6) Replace composite floats with metal floats

d) When I opined that use of auto gas is a big advantage I was thinking of being free from having to use an airport. It seems to me
that the great thing about the tailwheeler is being able to set down anywhere -- of having your own airstrip if you have a few acres in the country. My understanding is that a Cub with a 150 Lycoming and autogas STC can be refueled in the middle of nowhere from a pickup whereas a 180 hp Husky will have to fly to an airport to get 100 LL. Or is it that a Husky or 180 hp SuperCub can also be STC'd to use auto gas and can refueled from the back of a pickup -- but require the use of premium (91 octane ) auto gas??

Or does none of this matter -- is the continental US so crowded that every location has a public airport within a short (40 mile ) distance?

I know that this is probably a stupid question but do people ever extend their range by carrying a 5 gallon can of gasoline in the baggage compartment?? --or is that too dangerous? What about having a cache of gasoline at say , an isolated hunting cabin?

 

[irishfield]

The perfect Cub would have a light, low cost Turbine engine that puts out 200+ horsepower and is flat rated to 10k. It might not be too far away... I'm keeping my options open on a 'wide' Cub I'm working on.

I was wondering if anyone has pictures or info on a Cub that has a turbine engine mounted on it? I could have sworn that I saw one in a magazine in the recent past but I have dug through my supply of magazines and cant seem to find it.

Mark

I posted a picture from Sun n Fun of the Smith Aircraft cub on CLAMAR Amphibs sporting an ATP turbine awhile back to the archives here.

Props not turning any faster on a turbine (thanks to the gear box) than it is on your Lycoming!
SORRY JERRY, I see what you mean after I read it again. Yes the turbine "free wheels" the prop at a higher speed when idling by changing the prop pitch to remove the thrust. Under power no different, but I see what you mean about meandering through the weeds with the turbine spinning away at speed and the prop pitched out!
Cheers,
Wayne

 

[Guest]

You could fuel your plane from a tank in the back of your pickup if you are out in the field. Go to Tractor Supply or equivelent. Buy a 55 to 110 gal tank and a 12 volt pump. Put on a good filter and get 24 ft of hose and you have your portable fueling system. Fill your tank with 91 oct auto gas and start fueling your high compression 160 or 180 lyc. If you need more range buy a belly tank or bigger wing tanks.

 

[Lew]

Husky vs. Cub

I fly a 90hp PA-11, a 180hp CC PA-18, a 180hp AV-1A, and a 180hp AV-1B for work. We use auto fuel in all. Just follow the STC guidelines. While I think it is a Ford/Chevy thing, to me they will both do roughly 80% the same missions. But when I need to haul a load or get into a real tight spot I reach for a Cub. For just plain pleasure of the hands on experience the Cubs are a pleasure, the Huskies are very stick heavy-painfully at times. If I am going on a long trip or if I need the altitudes in the high-teens in the rockies for whatever reason, I use a Husky. The Cub is a 65 year old design that continues to evolve into a more impressive machine. The Husky is about 30 and is in my opinion somewhat limited on custom built evolution. I can go on on the differences at length, but the short of it is the Cub continues daily to win the "one-airplane-only" debate for me.