mtv wrote:Also, a friend got field approvals to remove the fuel pumps on a number of Avcon converted 170 and 172s. He did so by replacing the fuel line between the fuel selector and the gascolator with a larger diameter line. The original line was too small to reliably flow max fuel for an O-360 in all attitudes. Pretty simple way to get rid of two pumps and some weight.

MTV

If you could share a name or more details- private message if you like, that would be great!

IMO, the old line was big enough, the agitation the pumps added to the system was the culprit in the very brief Peterson test. The hot fuel on a hot day, running through two pumps, it caused the easily vaporized components to flash. Get rid of the pumps, the fuel isn't disturbed, and it stays a liquid. That said, if going to a bigger line makes everyone happy, that is a small price to pay, I'll stand in line in order to get rid of two pumps that only add weight and likely decrease safety. (if you want to understand the problem better, do some reading on fuel distillation curves).

And, an observation for those concerned about running mogas in a 8.5 to 1 compression O-360. The engines run fine when in a Cherokee (STC available), and now, put them in a Cessna, and somehow it will damage the engine?

A fellow named Fred Dyen taught at the University of AK, Fairbanks aviation maintenance program many years ago. He got field approvals on at least a few Avcon conversions, and offered to get one for my 170.

Fred is teaching at a community college in the Midwest now. I’ll see if I can remember where. I believe all he was doing was removing pumps and replacing the fuel lines from the selector forward with larger diameter line.

Probably a lot harder to get approved nowadays

MTV

Thanks for the lead. I've chatted with Fred, he is at Blue Ridge Community College in Virginia, still teaching aviation. He thinks he can probably track down a copy of the field approval. I'll follow up here on the forum for those that might be interested.

I would be interested in this too.

From a maintenance standpoint a low-compression engine will run better on mogas than 100LL. A lot of the energy in 100LL just goes out the exhaust pipe in engines that were designed to run on 80/87, and mogas won't foul the plugs or valves nearly as much as 100LL. The downside to mogas is stability, and to a lesser extent vapor pressure issues. If an engine was originally intended to run 80/87 I wouldn't think twice about STC'ing it for mogas. Higher compression engines, and injected engines, the warm fuzzy's not there.
- The anecdote about blended gas and/or lead substitutes for the Franklin 150/165 being the notable exception.

I would like a copy of that field approval as well if you don't mind sending me one. I'm doing the avcon conversion on my '56 172 soon.

An update on the fuel pump removal and autogas effort.

Fred Dyen shared a proposed Field Approval for a N170WM and an Avcon STC, both supporting fuel pump removal. I ordered the FAA CD on N170WM, to check and see if a 337 had been accepted. It is a neat airplane with a lot of mods, but nothing on fuel pump removal. The Avcon STC supports fuel pump removal on later model 172's with fixed pitch. I suspect the STC was going off of Penn Yan and Air Plains success with no fuel pumps.
Discussion with Todd Peterson has confirmed STC available when system is gravity.

So, still in data collection mode before trying for the approval. If anyone has-

A tail number for any 17_ with O-360/constant speed AND the fuel pumps REMOVED would be helpful. Will talk to the owner or order CD so the basis for the change can be known.

Access to a 175 with the big engine, the O-470 conversion? How was the extra fuel demand accommodated? If the system remained gravity, a duplicate fuel system would of course provide an O-360 adequate fuel flows so that could be part of the justification.

I am also very interested in the 337, field approval document, or whatever else.

I am told that the Avcon conversion for a C172D includes instructions for going to gravity feed. The 172E doesn't have that option in the STC.

I just went to the FAA[dt]gov site. When I attempted to locate 'N170WM' I got a page which said that N-number is neither registered or reserved. Could be wrecked, exported, or slowly sinking into it's tiedown some place.

PapernScissors wrote: When I attempted to locate 'N170WM' I got a page which said that N-number is neither registered or reserved. Could be wrecked, exported, or slowly sinking into it's tiedown some place.

Not sure why. I've ordered a few CD's before, and N170WM was the first one I've requested that didn't pop up right away. The menu still gives an option to direct a manual search, which I did, and surprise a week or two later the cd showed up in the mail. Then you pay your $10 since it was found. I think 170WM is very much still around, the registration folder has recent business.

Fred54 wrote:Thanks for the lead. I've chatted with Fred, he is at Blue Ridge Community College in Virginia, still teaching aviation. He thinks he can probably track down a copy of the field approval. I'll follow up here on the forum for those that might be interested.

I'm VERY interested. Thanks

Fred54 wrote:An update on the fuel pump removal and autogas effort.

Fred Dyen shared a proposed Field Approval for a N170WM and an Avcon STC, both supporting fuel pump removal. I ordered the FAA CD on N170WM, to check and see if a 337 had been accepted. It is a neat airplane with a lot of mods, but nothing on fuel pump removal. The Avcon STC supports fuel pump removal on later model 172's with fixed pitch. I suspect the STC was going off of Penn Yan and Air Plains success with no fuel pumps.
Discussion with Todd Peterson has confirmed STC available when system is gravity.

So, still in data collection mode before trying for the approval. If anyone has-

A tail number for any 17_ with O-360/constant speed AND the fuel pumps REMOVED would be helpful. Will talk to the owner or order CD so the basis for the change can be known.

Access to a 175 with the big engine, the O-470 conversion? How was the extra fuel demand accommodated? If the system remained gravity, a duplicate fuel system would of course provide an O-360 adequate fuel flows so that could be part of the justification.

The one 175 with an O-470 that I flew had both manual and electric pumps.

MTV

I have spoke to Fred twice in the past two or so months, he said he was going to send me his field approval for removing the pumps, haven’t seen it come through yet. I hate to keep bugging him, I’ll give it a few more weeks and poke again....

Why do you want to eliminate the fuel pump? Mine has two, the engine driven one and the electric one. I only use the electric one on take offs and landings. Because it was standard equipment in the stock P172D which had a 175 hp Continental, the owners manual provides for using it whenever changing tanks at higher altitudes, but I pretty much forget to do that--usually "remember" when I see the fuel pressure light go on momentarily on my fuel flow gauge. But the point is that while gravity feed works fine on lower powered engines, force feeding with a fuel pump is more necessary when the power goes up.

Cary

So that must be why the 180 hp Cardinal had a fuel pump. It cost my patrol company a little skin work on the stabilator, however. On a fuel starvation forced landing I maneuvered to line up with an 80 the long, half mile, way and no mesquite. So meybe try the fuel pump, I think. Engine caught long enough to mess up the long way. 45 degrees left followed by 90 degrees right (from 100'AGL) got me about 500,' angled across the remainder of the same field. I landed short of the barbed wire fence, zoomed over cutting a gash in the stabilater on a steel pole, and relanded short of the mesquite.

Without default energy management turns, the two steep banked turns would not have been possible. 100' is a lot of vertical space available. With practice it is usable and prevents stall. Don't wait until you need it to practice.

Yes, stopping sooner for fuel works as well.

Cary wrote:Why do you want to eliminate the fuel pump? Mine has two, the engine driven one and the electric one. I only use the electric one on take offs and landings. Because it was standard equipment in the stock P172D which had a 175 hp Continental, the owners manual provides for using it whenever changing tanks at higher altitudes, but I pretty much forget to do that--usually "remember" when I see the fuel pressure light go on momentarily on my fuel flow gauge. But the point is that while gravity feed works fine on lower powered engines, force feeding with a fuel pump is more necessary when the power goes up.

Cary

I have the avcon 180hp conversion on my 175 and have no fuel pumps. The stock gravity system supplies in excess of 25gph to the carb right down to the last drop. The O-360 at sea level and 2700rpm is burning somewhere in the ballpark of 16gph. Removing the pumps also allows you to use the MoGas STC, athough some would argue the STC is not required since Lycoming published S.I. 1070A. For me just getting rid of the complexity of the extra components, electrical and plumbing is worth removing them. Less fittings to leak, less electrical load, no need for fuel pressure gauge, less cost and less maintenance. The only reason an electrical pump is even installed is in the event of the mechanical pump failing, the only reason the mechanical pump is there is because the O-360A1A/A1D engines used in the conversions came out of Mooney's which were low wing and needed the pump. Legend has it the guys developing the STC's were initially required to use the pumps because they were already on the engines. It wasn't until a little later they came out with the paperwork to remove them, but that document only covers 172's and omitted mention of any 175 S/N's.

The P172D like the 180hp conversions with a CSP, can require that extra (albiet small) amount of flow. The aircraft with the pumps removed increased the size of the fuel line from the selector valve fwd, meeting the minimum 150% flow requirement without pumps.

Newbizor wrote:….. Removing the pumps also allows you to use the MoGas STC, athough some would argue the STC is not required since Lycoming published S.I. 1070A. For me just getting rid of the complexity of the extra components, electrical and plumbing is worth removing them. Less fittings to leak, less electrical load, no need for fuel pressure gauge, less cost and less maintenance......

Good post, and good reasoning.
Simpler is usually better.

Newbizor wrote:

Cary wrote:Why do you want to eliminate the fuel pump? Mine has two, the engine driven one and the electric one. I only use the electric one on take offs and landings. Because it was standard equipment in the stock P172D which had a 175 hp Continental, the owners manual provides for using it whenever changing tanks at higher altitudes, but I pretty much forget to do that--usually "remember" when I see the fuel pressure light go on momentarily on my fuel flow gauge. But the point is that while gravity feed works fine on lower powered engines, force feeding with a fuel pump is more necessary when the power goes up.

Cary

I have the avcon 180hp conversion on my 175 and have no fuel pumps. The stock gravity system supplies in excess of 25gph to the carb right down to the last drop. The O-360 at sea level and 2700rpm is burning somewhere in the ballpark of 16gph. Removing the pumps also allows you to use the MoGas STC, athough some would argue the STC is not required since Lycoming published S.I. 1070A. For me just getting rid of the complexity of the extra components, electrical and plumbing is worth removing them. Less fittings to leak, less electrical load, no need for fuel pressure gauge, less cost and less maintenance. The only reason an electrical pump is even installed is in the event of the mechanical pump failing, the only reason the mechanical pump is there is because the O-360A1A/A1D engines used in the conversions came out of Mooney's which were low wing and needed the pump. Legend has it the guys developing the STC's were initially required to use the pumps because they were already on the engines. It wasn't until a little later they came out with the paperwork to remove them, but that document only covers 172's and omitted mention of any 175 S/N's.

The P172D like the 180hp conversions with a CSP, can require that extra (albiet small) amount of flow. The aircraft with the pumps removed increased the size of the fuel line from the selector valve fwd, meeting the minimum 150% flow requirement without pumps.

I can't dispute any of what you say, other than that the P172D came with an electric fuel pump from Cessna--don't know if it had an engine driven pump. The owners manual calls for using it for take offs, landings, and when changing tanks above 5000' MSL. The original switch is on the panel. My original conversion was from a wrecked Mooney, although its current engine was built from scratch after the original conversion engine threw a rod, which required that I land in a field. It has an engine driven fuel pump which normally puts out about 2 1/2 psi, whereas the electric pump puts out around 4 psi. So far, the only extra "maintenance" my fuel system has ever required in the almost 16 years I've had the airplane was not maintenance at all, but converting the glass gascolator bowl to an aluminum Steve's Gascolator. Both fuel pumps have continued to work just fine, although I am taking a chance to say that, I suppose.

Cary

Cary wrote:... So far, the only extra "maintenance" my fuel system has ever required in the almost 16 years I've had the airplane was not maintenance at all, but converting the glass gascolator bowl to an aluminum Steve's Gascolator. Both fuel pumps have continued to work just fine, although I am taking a chance to say that, I suppose.

Cary

I wish my mechanical fuel pump behaved as nicely as yours. It quit at about 2500 hours TTE and 500 hrs SMOH. The diaphragm developed multiple cracks that spewed 100LL all over the engine compartment. Not fun.

I'm also interested in reducing unnecessary complexity in my fuel system. Two fuel pumps at least doubles the probability of a potentially catastrophic failure.

PapernScissors wrote:

Cary wrote:... So far, the only extra "maintenance" my fuel system has ever required in the almost 16 years I've had the airplane was not maintenance at all, but converting the glass gascolator bowl to an aluminum Steve's Gascolator. Both fuel pumps have continued to work just fine, although I am taking a chance to say that, I suppose.

Cary

I wish my mechanical fuel pump behaved as nicely as yours. It quit at about 2500 hours TTE and 500 hrs SMOH. The diaphragm developed multiple cracks that spewed 100LL all over the engine compartment. Not fun.

I'm also interested in reducing unnecessary complexity in my fuel system. Two fuel pumps at least doubles the probability of a potentially catastrophic failure.

That's the same argument against twins--double the chance of an engine failure. Or perhaps the argument for a glider--no chance for an engine failure. But you're right--simplicity is probably best, but not totally achievable as long as we must rely on an engine with umpty-ump pieces and parts that can fail.

Cary

Cary wrote:
That's the same argument against twins--double the chance of an engine failure. Or perhaps the argument for a glider--no chance for an engine failure.

Cary

There ARE positives from unneeded complexity forward of the firewall: Real world practice of EP and Engine Out scenarios we might not otherwise see.