B&S 49-series (810cm3/49ci) for aircraft use - TiPi's Q&A thread

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karmarepair

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karmarepair

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it looks like a small in-line fuel pump (motorbike EFI), needs 2-3bar pressure and resistant to oil and temperature (still gets hot), also needs a built-in check valve. Plumbed from the sump to the pump outlet port through the pump cover.
View attachment 89729
Common US pump like that http://walbrofuelpumps.com/walbro-gsl395-fuel-pump.html May be bigger than needed. Lots of these applications put the pump IN the tank.
It looks like Jan mounted this right over where the PTO used to be.
 

karmarepair

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If you know someone who can weld aluminum, a small dry-sump tank shouldn't be too hard to fabricate.
For 2 litres, you should be able to scrounge an offcut of large diameter tube as a starting point.
True. From Carrol Smith's "Prepare To Win":IMG_20191024_084000993_BURST001.jpg
 

JohnB

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Zero experience with dry sumps, at least I don't remember any in the last 60 yrs of wrenching.
I'm guessing that the return hose I.D. size will have to be fiddled with as we are using blowby to make it happen, too large will let the gas pass without moving the oil much and too small will be restrictive ...... or am I creating an issue where there is none?

JohnB
 

TiPi

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Zero experience with dry sumps, at least I don't remember any in the last 60 yrs of wrenching.
I'm guessing that the return hose I.D. size will have to be fiddled with as we are using blowby to make it happen, too large will let the gas pass without moving the oil much and too small will be restrictive ...... or am I creating an issue where there is none?

JohnB
Quite right John, I'm looking at 8-10mm at the moment. The 912 uses a 12mm (1/2") hose for all oil lines (suction & return). Next 5 year rubber replacement is coming up so will have to source all of those hoses again. The oil line on the Briggs is 8mm (to the oil cooler), so oil suction line will also be 10mm to start.
 

karmarepair

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it looks like a small in-line fuel pump (motorbike EFI), needs 2-3bar pressure and resistant to oil and temperature (still gets hot), also needs a built-in check valve. Plumbed from the sump to the pump outlet port through the pump cover.
View attachment 89729
This rather nice gear pump I found on e-bay is also rather heavy.

New message from: gkwholesale
~5.75 lbs.

Your previous message

What does your pump weigh?

Electric Scavenge Gear Pump 12 volt Turbo Oil Evacuation New 12v BEST DEAL


Price: $87.99
 

Vigilant1

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We only need a few ounces, right? Enough to fill the pump chambers and the pickup tube? Wouldn't a manual stroke pump (like a fuel primer for a carb) do the trick? Cheap.,light, and reliable.
 

TiPi

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Better option would be a manual priming pump from an old-fashioned mechanical diesel (stil need check valves in the line as well).
 

Hot Wings

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What's the fascination with electric everything? It's heavy!
Why the fascination with a priming pump?
Just keep the top of the oil level in the tank at, or slightly above, the oil pump. It then stays primed*. The only leakage is going to be around the oil pump drive shaft and that will all flow between the cylinders so there will be no hazard from hydraulic lock. Of course this presumes a Rotax style dry-sump rather than simple gravity drain.

* presuming a sealed system that can't draw air, and you don't turn the prop backwards - just like the Rotax system
 

litespeed

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I agree with as simple as possible, also tends to be cheaper and lighter.

It just needs a few ounces and be heat proof to low degree, check valves in the right places can ensure it only feels cold oil on startup. For reliability it should only have flow on startup then be isolated.

A simple plunger/syringe could do it. The bulb could if done well.

Its not the price that offends with having a electric pump but the weight and failure potential. Unless we get heavy most will be like a fuel pump and not really suited. That begs the question, can it be done with all the advantages sought from electric and be light and safe enough?

How much weight are you prepared to compromise?
 

pictsidhe

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I'm going to fix the briggs pump so that it will self prime. Lightest and most reliable, but not the easiest. It will need a plate with accurate ports put in the bottom of the pump cavity.
 

Hephaestus

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What's the fascination with electric everything? It's heavy!

Just how long do you expect that will last? Subjected to hot oil - that's not going to survive very long. And it would have to be outside thr primary oil loop as it likely wouldn't hold together at operating pressure.

I'd plan to do some serious testing before i hopped into an aircraft with that setup.
 

Hot Wings

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Just realized we have commandeered TIPI's Q+A thread.
Unless it is directly related to his project we probably should be using the other B+S threads?
 

pictsidhe

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Just how long do you expect that will last? Subjected to hot oil - that's not going to survive very long. And it would have to be outside thr primary oil loop as it likely wouldn't hold together at operating pressure.

I'd plan to do some serious testing before i hopped into an aircraft with that setup.
Well, if I used one from a major car manufacturer, it should outlast the engine. It goes in the suction side. I'd be far more dubious about a lot of the electric solutions proposed.
 

TiPi

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I'm going to fix the briggs pump so that it will self prime. Lightest and most reliable, but not the easiest. It will need a plate with accurate ports put in the bottom of the pump cavity.
Just be careful, these ports have been cut for a reason.
One possibility to assist with priming is the fact that the V-twin has a pumping action in the crankcase of approx 200cm3 per revolution. If the oil/air discharge line contains a check valve (as I have planned), there will be a slight vacuum at every turn when pulling the engine through. This will assist greatly with pulling oil from a tank that is a bit below the pump inlet. It will only work in a dry-sump system with a vented tank and a sealed crankcase. It would involve some trial and error to work out how many turns the engine needs to prime the pump when dry (a clear suction hose will show quickly what it takes).
I would not use any rubber pump that is not designed for 120deg C oil!
 

pictsidhe

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The ports are cast, not cut. The reason being that it is cheapest and fine for an immersed pump. I'd put money on horizontal engines having much tighter ports.
 

DRFlyer

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I'm fairly interested in using this engine on an HM293, actually saw one on Pouguide.org with a redrive so I guess it's been used before. Looking to drop some weight and complexity, do you think this engine could be modified in a way where it could be hand-propped? It looked like the starter was overly beefy, and it would be nice to just forego a starter battery and heavy cables.
 

Vigilant1

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Looking to drop some weight and complexity, do you think this engine could be modified in a way where it could be hand-propped? It looked like the starter was overly beefy, and it would be nice to just forego a starter battery and heavy cables.
Are you using a PSRU? You wouldn't be able to hand prop through that. In direct drive, the question would be whether you could spin it fast enough to generate a spark using the magnetrons. I haven't seen a hand-propped Briggs.
 

TiPi

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Hand-propping a Briggs would require a few mods:
  • Remove the decompression mechanism in the camshaft
  • Have a heavy prop
  • Depending on carburetor location, add a fuel primer
  • Ideally, have an ignition coil with retard for starting (25deg BTDC is difficult to overcome consistently)

At the point of the magnet passing the coil, the engine speed would need to be >250rpm

Not impossible but I wouldn't trade the risks involved for the weight gained. Adapting a lightweight highspeed starter motor and Li-Fe battery are the safer option. You also need to look at the mass of the airframe and what hand-propping would do to that (balance)?
 
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