Briggs & Stratton Vanguard 23hp build

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bl_dg

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OK, starting a thread for my engine conversion. I just purchased a Vanguard 23hp engine. (386447 series) The goal is to minimize weight and maximize -reliable- horsepower. This will be a direct drive installation, so I do not forsee pushing the engine much past 4,000 rpm. Looking for incremental improvements. No billet spark plugs!

I will be mounting the prop on the flywheel end, because.. that's what Briggs (Europe) did on the ULTRA UAV. Since I won't need the PTO end, I was able to save some money by getting a 'generator' model with the internal spline PTO. I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall, rather than using a bed-mount engine installation.

But first is getting some base line info on the engine. So unless I can find someone with a dyno, I will be building some Eiffel clubs.

See attached photos of the engine.
 

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  • 386447 - PTO end.jpg
    386447 - PTO end.jpg
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Vigilant1

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Bl_dg,
I'm looking forward to reading more thanks for starting the thread.

Admin question: Do you want to take comments/questions here? That can get messy, but everyone is gonna have questions.
The alternative is to start your "just my own comments" thread in the "Build Log" subforum (no one else can post on it there), then leave this here retitled as your Q&A thread.

Mark
 

Tiger Tim

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I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall
Alright, that’s just clever. Are there any internal differences between covers that may affect oil distribution inside the case?
 

TiPi

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OK, starting a thread for my engine conversion. I just purchased a Vanguard 23hp engine. (386447 series) The goal is to minimize weight and maximize -reliable- horsepower. This will be a direct drive installation, so I do not forsee pushing the engine much past 4,000 rpm. Looking for incremental improvements. No billet spark plugs!

I will be mounting the prop on the flywheel end, because.. that's what Briggs (Europe) did on the ULTRA UAV. Since I won't need the PTO end, I was able to save some money by getting a 'generator' model with the internal spline PTO. I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall, rather than using a bed-mount engine installation.

But first is getting some base line info on the engine. So unless I can find someone with a dyno, I will be building some Eiffel clubs.

See attached photos of the engine.
Thanks for starting the new thread👍
bl_dg, sorry to tell you that the sump from the vertical engine is very unlikely to fit on the case of the horizontal engine. The vertical engine has the oil reservoir in the sump, so the sump has a deeper space. The crankshaft and camshaft are most likley too short for the deep sump.

Camshaft, oil pump, cover (sump) gasket and many more parts have different P/N between vertical & horizontal.
1663581199058.png 1663581323765.png
 

Vigilant1

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(Edited to add strikethroghs. I misread your first post, apologies).

To jump ahead a bit:
- With the prop on the PTO end, what's your plan for the flywheel and the stuff that is on the OEM flywheel (alternator, ignition, starter ring gear)?

- Will it be heads up or heads down? From the oil pan discussion, I'm guessing it'll be heads up.

I like your approach of measuring the HP of the stock engine first, and in a reliable way. That seems a very good start.

Thanks again for sharing your efforts here.

Mark
 
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cluttonfred

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I'll be following this with interest as I would love to see the steps involved to gauge how hard a project it would be for a non-engine guy like myself as well as the final time, effort, cost, weight, and power. It would also be great to see how much of an impact an Ace redrive ($800 delivered to the USA) would have on the real-world pulling or pushing power of the engine.
 

Vigilant1

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It would also be great to see how much of an impact an Ace redrive ($800 delivered to the USA) would have on the real-world pulling or pushing power of the engine.
That's a tough bit of information to measure if we care about thrust at climb and cruise airspeeds. We'd need two very similar planes, one with direct drive and one with a PSRU.
Lots of folks measure static thrust, but that is not indicative of the situation at typical flight speeds.
 
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cluttonfred

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That's a tough bit of information to measure if we care about thrust at climb and cruise airspeeds. We'd need two very similar planes, one with direct drive and one with a PSRU.
Lots of folks measure static thrust, but that is hardly indicative of the situation at typical flight speeds.

I was actually thinking of the same engine on the same plane and then just compare real-world performance with and without the redrive.
 

Vigilant1

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It would also be great to see how much of an impact an Ace redrive ($800 delivered to the USA) would have on the real-world pulling or pushing power of the engine.
FWIW, a while back I used Jan's program to compare expected thrust at 50mph airspeed from a 23 HP engine at 3600 rpm using direct drive and using a PSRU. More here: "Micromaster"-- Centerline twin using small industrial engines

NB! The props are optimized for 50mph, so there would be differences as we get farther away from the design point of the props. But, at higher speeds we know that the thrust advantage of a larger prop diminishes.

Direct drive: 46"dia, 14.7" pitch. Expected thrust: 95lbs (approx).

PSRU: 1 : 1.5 ratio, 65" prop dia, 24.5" prop pitch. Expected thrust: 106 lbs (approx).

The difference in thrust is equivalent to about 2.6 HP of engine output at this airspeed.

If we spent $2500 to buy our engine and get it modified, that's $109/HP. The additional 2.6 effective HP from the $800 PSRU cost us $308 each. It also increased our weight.

Direct measurements would be great if we can get them. The PSRU will probably prove especially worthwhile at very low airspeeds or if we want to modify the engine for higher RPM. PSRU is good for trikes and ultralights. The SD-1s and Lucioles are doing fine with the simplicity of direct drive.
If one does want to fly around at 50 MPH using over about 20hp from a 627cc engine, one will need to figure out how to cool it. Hint: Don't throw away that stock blower fan.
 
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TFF

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With a prop reduction you could also put something like a 46x 44 on combo with the same 1.5 ratio. Thats not how our thought process is geared. ( yea pretty bad).
That’s not going on a CLT, Cub like trainer, but it would sure make something like a BD5 happy, if it made weight. There is always the perfect prop for an airplane. We don’t ever seem to look at it that way. We start with the engine and ask what if. What compromises do we have to have to get as close as we can? Engine weight, gearboxes, simplicity, fuel, vibration, combustion cycles. Fixed pitch, you are always trying to get away with what you can. You don’t want to put a capable combo 46x44 on an SD-1 and pull the wings off at 200.
The airframe needs a certain prop. The engine is the connection. If you can’t find something to work, even if it’s unreasonable like a turbine, the airframe was unreasonable from the start.
 

Lucky Dog

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This thread is actually useful. So many v-twin conversion threads are populated by specious claims or engineering axioms from1935. What kind of airplane are you planning to bolt this engine to? Tipi is the source here for direct drive. He's done the homework. Your Briggs is the lightest industrial V twin that will pull or push a small airplane into the sky, but it will take modification in the neighborhood of about $500 to $1000 to get the thrust you'll need. Most of the flying 23 hp 627cc model 38 Vanguards are modified to put out 30 to 35 hp at 4300 to 4500 rpm with maximum torque at 4000 rpm. Of course that requires a reduction drive to maximize torque at a more optimal propeller rpm (2400 is the target for most reduction drives). The target RPM for small direct-drive engines is 3500, with a cruise RPM somewhere around 3000 to 3200. In this case, increasing the bore and lengthening the stroke of the model 38 engine are the best ways to increase torque and thus produce more thrust. The cost for each strategy is about the same, but the direct drive, while benefitting from its simplicity and potentially lighter weight, will not achieve the thrust of the redrive unit. Reduction drives allow the engine's and propeller's performance to be optimized separately. The faster turning direct-drive propeller's pitch and diameter are confined by tip drag losses which narrow the climb-and-cruise performance window for low-power engines. Both strategies work, however, if the aircraft is a good fit.
 
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bl_dg

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Wow!
tumblr_inline_mr52w596NJ1qz4rgp540.gif

OK - so...

The parts manuals on the Briggs site say that both vert and horz engine use the same gasket, so hopefully, vert pan will fit. I'll figure out the oil pump when I get to that stage.

Engine will be direct drive, heads up. Looking at something like a Davis DA-11.

For now, the focus is on the dyno question. And budget. And time. What is the least-cost method of doing dyno testing? The Eiffel clubs are within my abilities - just need a planer and a jointer. ($!)
 

Vigilant1

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Your Briggs is the lightest industrial V twin that will pull or push a small airplane into the sky, but it will take modification in the neighborhood of about $500 to $1000 to get the thrust you'll need. Most of the flying 23 hp 627cc model 38 Vanguards are modified to put out 30 to 35 hp at 4300 to 4500 rpm with maximum torque at 4000 rpm.
And, it is worth keeping the end goal in sight when choosing a starting point. If we want 30hp or more, the required modifications, cost, and RPMs may be lower if we start with the 810cc engine as our base engine. The steps to turning it to the horizontal shaft orientation are well known and not hard, the engine will be under less stress and the heads under less heat load. As a bonus, the 810s are about the same or cheaper to buy. Weight of the 810cc ready to fly (Spacek) is 77 lbs, a modified 627cc engine (Spacek) is lighter.

There's nothing wrong with the Vanguard 627cc engines. Like every engine, it'll have natural limits. They can be stretched with money and effort, but they'll still be there.
 
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Vigilant1

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What is the least-cost method of doing dyno testing? The Eiffel clubs are within my abilities - just need a planer and a jointer. ($!)
That's the best way to go, IMO. Accurate and not subject to "helpful', optimistic dyno calibration. You likely know the details, but they are in the attachment here.
Maybe look around for a MakerSpace, Vo-tec school, or a woodworkers club near you to fabricate the clubs? It seems a shame to buy a jointer for this alone (unless you secretly want one anyway!). At the small widths involved, you can probably get by using a jointer, no need for a planer (again, unless you want one anyway.)
Mark
 
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llemon

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I read Fred Weick's propeller book recently and he makes this interesting point about gearing;
propeller gearing weick aircraft propeller design pg 200.png
The formula for Cs is;
propeller gearing weick aircraft propeller design pg 177.png

23hp engine @3000 rpm;
23 hp Cs.png
The speed where it goes over 1.3 is ~94mph
 

Vigilant1

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I read Fred Weick's propeller book recently and he makes this interesting point about gearing;
View attachment 130010
The formula for Cs is;
View attachment 130011

23hp engine @3000 rpm;
View attachment 130012
The speed where it goes over 1.3 is ~94mphF
Thanks for that.

FWIW, at 3600 RPM (and sea level) C2 crossover point is approx 101 mph.

Of course, the magnitude of the direct drive vs PSRU difference at the airspeed of interest has primary practical significance, rather than the particular crossover point.

It's probably worth mentioning the mechanical losses from the belt drive (shown in belt and bearing heating). It's not a lot, but it ain't zero, either. Gates Corp says the loss is from 2-5%, and if it is at the high end of that we're losing about 1hp to PSRU friction.
 
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rv7charlie

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NB! The props are optimized for 50mph, so there would be differences as we get farther away from the design point of the props. But, at higher speeds we know that the thrust advantage of a larger prop diminishes.

Direct drive: 46"dia, 14.7" pitch. Expected thrust: 95lbs (approx).

PSRU: 1 : 1.5 ratio, 65" prop dia, 24.5" prop pitch. Expected thrust: 106 lbs (approx).

The difference in thrust is equivalent to about 2.6 HP of engine output at this airspeed.
What's the thrust difference at say, 30 mph? What's the difference at 100 mph?

Everything's a compromise. If an extra 8 lbs (for a redrive) pushes you out of pt103 and that's important, then it's an unacceptable compromise. If the weight can be tolerated and it cuts the takeoff run by 30-40% and doesn't reduce cruise or top speed, then the compromise would look pretty good to me, unless I was flying something with UL performance from a long paved runway and had no interest in off-airport operations.
 
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