Gravity feed for Lycoming

Dooley · Post by **Dooley** » Sat Jan 15, 2005 3:41 am

I want to take the fuel pumps, electric and mechanical off of my Avcon converted C170A. Save weight and unneeded complexity. I think a fellow in Alaska has done this and I can't see why not. What do you think Dooley

Roesbery · Post by **Roesbery** » Sat Jan 15, 2005 6:08 pm

It will work without them, but The STC calls for those goodies to be there.

Post by **GAHorn** » Wed Feb 23, 2005 6:14 pm

I don't know about taking those off. If the STC called for them, there's probably a fuel-flow reason for them.
I do know about Sanger, TX tho'.

Just east of you about 10 miles is a ranch strip on top of a Mesa that I built for a former employer. If the Highway Dept wanted to build a highway there, they'd have gone around that mesa, but that's where the owner wanted it. Two years of bulldozing and blasting, and road-building, and paving out in the middle of nowhere.
The Air Force doesn't have a security fence as good as the one we put up. (We used two drilling rigs to drill 10" holes 6 feet deep, 6-feet apart, to set 8" creosoted poles 18-feet long into that rock, to make a 10' high fench over 13,000' long. We then fenced it with buffalo-proof grid-wire fencing.
We constructed 350' turn-arounds and aprons, and paved it to handle up to B-727-100 he intended to buy for flights all the way to China. (With a fuel stop or two, of course. He intended to build a World Trade Center in Bejing for the Chinese gov't.) It was all an expensive pipe-dream. The largest thing I ever landed on it was a Hawker. Most of the time all I did was land the K-Air or the C-206 on it. That was all back in the early/mid 80's.
Just for fun, I landed my 170 on it about 5 years ago. Nearly wrecked the airplane avoiding scrub-brush on the runway. It's now got mesquite trees growing up thru the ashpalt due to disuse. What a waste. D-bar Ranch, Robt. Lee, TX

HA · Post by HA » Wed Feb 23, 2005 10:57 pm

why take the fuel pumps off? you'll save, oh let's see, about 4 lbs of pumps. you'll find out that the FAA probably required all those pumps due to fuel flow needs under certain conditions, like takeoff or climb power, to meet the certification standards (FAR 33 for engines, IIRC). You'll kill something like 500lbs of trees trying to make your point with the local federales, and then to make your plane airworthy again you'll put the pumps back on.

seems simpler to just wear tennis shoes instead of boots if you want to save 4 lbs

Dave Clark · Post by **Dave Clark** » Thu Feb 24, 2005 12:47 am

Compexity???? Pretty tough to pull and push the switch huh?

The pumps are both usually pretty long lived. Why risk it for very little gain?

zero.one.victor · Post by **zero.one.victor** » Thu Feb 24, 2005 4:36 am

While fuel pump(s) may be necessary ( physically or legally) even in gravity-feed systems, I can see Dooley's point about complexity. As you probably know, the ragwing 170 was certificated with a fuel pump. This is due (I believe) to the fact that if the siphon action in the fuel lines(s) is broken, under certain circumstances it can not be started again by gravity feed alone. This is because the fuel lines turn forward out of the tanks and go down the forward door post, instead of the aft door post like the A & B. So if the siphon breaks and the fuel level is lower than the high point in the line (top of the forward door post),as when the airplane is in a nose-high attitude, the fuel pump is required to re-start the siphon action-- gravity won't do it. I figured all this out when I had totally drained the tanks, and I had to darn near fill the tanks up to the top before I had any flow thru the lines.
Stock, the fuel system is plumbed with a couple t's and a check-valved bypass line, so if the fuel pump was to fail the fuel could still flow via gravity feed. I believe simpler is better. I would like to convert to an electric fuel pump with an internal bypass, mounted on the firewall. The fuel line would come out of the gascolator, to the fuel pump, and on to the carb. I have copies of several field-approved 337's for electric pump installations- the trouble is, every one of those installations duplicated the extra lines,t's, and checkvalve as per the original mechanical pump installation. All un- necesary!
I don't get it-- why bother to convert to an electric pump & still run all this extra, unnecesary stuff? To me, the whole point is to simplify things-- the lines & fittings you don't have, can't leak. I would probably have a hard time getting an electric pump installation approved without at least some other previously-approved 337's for documentation, and I don't figure the change is worth the trouble if I still have to run all the extra stuff. So I haven't pursued the issue.

Eric

blueldr · Post by **blueldr** » Thu Feb 24, 2005 6:21 pm

I've always heard that the fuel lines in the C-170 (Ragwing) were 5/16" tubing and that was the reason for the fuel pump on the engine. The A and B models use 3/8" tube. I've heard of C-170s working fine without the pump, but ran into problems when a knowledgeable IA ran the annual. Considering what kind of pump is used, they're a real rip off.

mvivion · Post by **mvivion** » Fri Feb 25, 2005 5:04 am

A local IA, Fred Dyen, got a number of Avcon converted 170 B's field approved for removal of the pumps. The key was replacement of one small section of fuel line with a slightly larger line. As I recall, the section of line wasn't long at all, maybe a foot or two. In any case, it was this constriction in size of the line which dictated the pumps in the first place.

Fred offered to do my airplane, and I opted not to, just cause I can't see a down side to having fuel pumps, other than weight, and as noted here, it doesn't save that much.

Fred is in the lower 48 now, and I don't know if you'd ever convince the FAA to field approve this mod again now.

Mike

blueldr · Post by **blueldr** » Sat Feb 26, 2005 5:31 am

Mike,

The fuel line constriction is interesting. I've only worked on B models, but I don't ever remember seeing anything other than 3/8" tubing from the fuel tank all the way to the gascolator, and then a #6 hose to the carburetor. The finger screen at the tank outlet is made from a #6 flare x 1/4"male NPT nipple, and is probably has as small a hole as any place in the line.

Dave Clark · Post by **Dave Clark** » Sat Feb 26, 2005 2:32 pm

BL is correct. I've been told the fuel pump (electric) was added in lieu of changing all fuel system lines from 3/8" to 1/2". I believe there is some regulation on how much fuel must flow for a given amount of horsepower, (probably a considerable amount more that it could possibly use). Now the point is why would anyone believe he's smarter than the collective minds of the engineers that came up with the STC in the first place? To me it's a little like saying "I think I'll remove one of my mags, I really don't need the complexity of two".

And please no-one take this personnaly, because no offense is intended and I know my wording might seem harsh.

zero.one.victor · Post by **zero.one.victor** » Sat Feb 26, 2005 3:03 pm

Dave, I've got a brother who's an engineer, & I can outsmart him any day of the week!
Fuel pump(s) on an engine mod are maybe one thing, but if you tell me that Cessna installed a (single) fuel pump on the ragwing due to their superior engineering I'd have to disagree. It seems like an afterthought--instead of going back & routing and/or sizing the lines properly, we'll just add this fuel pump to meet flow requirements (or whatever)--especially when you consider that the factory put in the bypass/checkvalve arrangement so the engine wouldn't quit in case of pump failure. I believe the fuel pressure gauge is to indicate the drop in fuel pressure if the pump should fail.
BTW, Harry Dellicker told me that the reason he didn't add the ragwing onto his O-360 STC was that the lines are too small to get the required flowage, even with pump(s) added. Required flowage being something like full-power gph plus 25% (?) safety factor, per FAA requirements.

Eric

mvivion · Post by **mvivion** » Sun Feb 27, 2005 5:15 am

I honestly don't know how long the fuel line was that Fred replaced to keep the FAA happy. I also noted that I'd not be so sure you could get the same thing field approved now.

You'd have to talk to Fred about it, or someone that has his field approval done. I don't have it, but as noted, he offered to do it to my airplane.

It was a smaller line somewhere according to him that required the pumps.

That's all I know, which ain't much.

Mike

Post by **GAHorn** » Mon Feb 28, 2005 6:00 pm

My memory has been known to play tricks on me, but I seem to recall that certification requirements of gravity fuel systems is 150% excess capacity.

zero.one.victor · Post by **zero.one.victor** » Thu Mar 10, 2005 6:03 pm

I seem to recall the 150% figure also. And that was 150% of full-power fuel flow.
I looked up an article by Oregon member Paul Rostykus in the Q3/2000 170 News, about converting his B model to a 220 horse PZL-Franklin. He doesn't mention adding a fuel pump to the system, but he does mention that "replacing the tubular fuel line with the flexible hose from the fuel selector to the gascolator was a pain." Didn't explain why the replacement, but it might be that this is the same short section of fuel line that Mike mentioned 6 posts back.
BTW, Paul has this airplane listed for sale on Trade A Plane online for $48K, in case anyone's interested. Seeing his ad was what prompted me to look up his article about the conversion.

Eric