Eliminating fuel pumps

[GAHorn]

The ragwing has the same size lines/fittings as later aircraft. The problem is not the size lines.

The problem is the ragwing fuel system brings fuel from the tank...forward to the front doorpost, then down to the gascolator and engine.

During takeoff and climb...this is an UPHILL climb for the gravity fuel system to get from the tank to the engine.

Later designs of the A and B models bring the fuel down the rear doorpost, ...resolving the issue.

[corefile]

I thought of this thread as I was waiting to take off yesterday. It was a bit warm and I was taking off after a half-hour fuel stop. The fuel pressure normally indicates a solid 6 psi, but idling in the runup area I saw it occasionally dropping into the 3 psi range, then back up to 5. A few vapor bubbles, maybe. I put on the electric pump for takeoff as usual, and the pressure went back up to 6, and it stayed there after takeoff after I shut the pump off.

Marvel-Schebler calls for a minimum of 1.5 psi inlet pressure, I think, so I was still well above that, but considering how sketchy the Avcon design is, why would you mess around with your fuel supply for such a minor return? The AC fuel pump is $350 new outright, the electric pump is less than $100, and both will last a full TBO run.

Just sayin'.

Why is the Avcon conversion sketchy? Is there a better 180 conversion then the Avcon?

[minton]

I thought of this thread as I was waiting to take off yesterday. It was a bit warm and I was taking off after a half-hour fuel stop. The fuel pressure normally indicates a solid 6 psi, but idling in the runup area I saw it occasionally dropping into the 3 psi range, then back up to 5. A few vapor bubbles, maybe. I put on the electric pump for takeoff as usual, and the pressure went back up to 6, and it stayed there after takeoff after I shut the pump off.

Marvel-Schebler calls for a minimum of 1.5 psi inlet pressure, I think, so I was still well above that, but considering how sketchy the Avcon design is, why would you mess around with your fuel supply for such a minor return? The AC fuel pump is $350 new outright, the electric pump is less than $100, and both will last a full TBO run.

Just sayin'.

Why is the Avcon conversion sketchy? Is there a better 180 conversion then the Avcon?

Since I have worked as an A&P I've been surprised as to how many ways a mouse trap can be engineered. In this case all 3 versions that I know of require fuel pumps. As I've mentioned in earlier posts I believe it's because of other than fuel line sizing and more to do with fuel tank outlet positioning and all of the undersized fittings within the system that could impact the "Head pressure" at the carb. inlet. Just say'in.

[DaveF]

I used the word "sketchy" because the Avcon documentation is sparse and support is nonexistent. The AFM supplement only claims the converted airplane will perform no worse than stock. That's laughably true but completely unhelpful, so the Avcon owner has to be his own test pilot to find the real Vx, Vy, ROC, and takeoff numbers. That makes me wonder how much engineering was done in support of the STC, so even though I know the engine/prop installation worked great in Mooneys and Pipers, what are the limits in the 170? I just wouldn't mess with my fuel system design for what in my opinion is minimal return.

Avcon has essentially not existed for many years. They have lost their production certificate, so they can't supply parts. They quit answering the phone a long time ago. Del-Air and Stoots Aviation are the current sources for Lycoming engine conversions. Both are very good, as far as I know.

[c170b53]

John somehow I can't help thinking, most will remember you by the phase " Just saying"
Just sayin back at ya!

[GAHorn]

I would wager that a 170B with the IO-360 conversion (as well as the O-360 LYcs) would be very similar in performance to the data provided for a T-41 (which was a 172 with the same engine.)

[interstellardust]

170s got fuel pumps?

[Bruce Fenstermacher]

Yes Bill, the '48 had and requires a fuel pump from the factory. Conversions to O-360 and IO-360 require a fuel pump. Stock 170A and B models do not.

[ghostflyer]

A tail dragger is faster in the air as a same model with a nose wheel . It can be up to 4 knots faster. We had a 180hp cessna 172 ( 5 years old ) in the shop on a regular occasion and then we didn't see him for some time ,and while away the owner had it converted to a tail dragger. I had done about 15 hours flying it with the nose wheel and got to know it very well. The owner didn't bring it in to the shop for about 18 months. Then suddenly he reappeared and the nose wheel had gone and a tail wheel had appeared. The job was very well done and all the paper work was ok. The main gear had moved forward and sprouted leaf springs for the undercarriage as per a cessna 180 model. The look ?? Well it was unconventional with the swept tail . It was exciting to fly it ,but not the way of exciting that you would expect . On a 3 point landing the rudder was so sensitive and twitchy . You become the ground loop king . It was better to wheel it on for a landing and hold the tail up as long as possible . Sorry. I got side tracked , this is supposed to be about eleminating fuel pumps ,which is a crazy thing to do . You have got to keep the go juice moving under all conditions .

[48RagwingPilot]

FWIW, the Seattle FSDO recently approved my 337 to remove the fuel pump, check valve, fuel pressure gauge and associated plumbing from my '48 C170. New fuel lines were installed with routing down the aft door posts to the fuel selector valve ala the A and B models. I drafted the 337 and flight manual supplement myself (with a few edits from the FSDO) and did the work under the close supervision of my A&P/IA. Not an easy project, but I now have a new and much simpler fuel delivery system.

[GAHorn]

FWIW, the Seattle FSDO recently approved my 337 to remove the fuel pump, check valve, fuel pressure gauge and associated plumbing from my '48 C170. New fuel lines were installed with routing down the aft door posts to the fuel selector valve ala the A and B models. I drafted the 337 and flight manual supplement myself (with a few edits from the FSDO) and did the work under the close supervision of my A&P/IA. Not an easy project, but I now have a new and much simpler fuel delivery system.

Excellent move! (But I'm surprised they didn't also require A/B tanks, caps, and vents.)

[3958v]

George I am sure there is no way to get an A or B tank in a Ragwing as the 12.5 gallon tank about needs a shoe horn to install as is. Bill K

[48RagwingPilot]

The question of tankage, vents and caps never came up. The FAA accepted that the only reason for the fuel pump was that the lines turned forward out of the tanks rather than aft.