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

Discussion in 'Firewall Forward / Props / Fuel system' started by TiPi, Oct 4, 2019.

1. Oct 4, 2019

TiPi

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2. Oct 4, 2019

Hot Wings

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3 Observations:

Well organized and clear log!

You may not need the check valve in the engine/sump line - even being a 2 cylinder. I'd test without first and be ready to add if needed.

The stock case vent area can be used as a secondary oil drain into the head sump - and may turn out to be rather significant oil path in the running engine. If there is standing oil there (unlikely with a a nose gear plane) simply lifting the tail during oil change should drain that small amount of oil well enough to not need a second drain plug?

3. Oct 4, 2019

Vigilant1

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Thanks for starting this companion thread, TiPi.
The overview of other available engines was useful, and did a concise job of showing the alternatives. One other aspect I found interesting is the relative cost of the various choices. I don't know if this holds worldwide, but at least for US buyers the retail price of the 810cc is a bargain.

Engine..............................Displacement...... Retail price (USD)...........$/cc B&S Commercial 810 (49T).........810cc..................$999...................... 1.2
B&S Vanguard 810 (49V)............810cc.................$1150...................... 1.4 B&S 38 series Horizontal...........627cc..................$1400...................... 2.3
B&S 54 series (Vanguard, horiz)...896cc..................$1700......................1.9 B&S 61 series (Vanguard, horiz)...993cc..................$2200......................2.2
Honda GX690.........................688cc..................$1200......................1.7 Kawasaki 72 (horiz).................725cc..................$2000...................... 2.8
Kohler 725............................725cc..................$2000.......................2.8 It's a rare day when the aviation part we need has the best weight-per-performance AND carries the lowest price. Obviously, by "regular" aviation standards, all these engines are inexpensive, and when we think of the costs inherent in building/operating a plane, a difference of a few hundred dollars is hardly worth mentioning. Still,$300-\$1000 saved on the initial engine purchase can go a long way toward acquiring the needed custom bits (to turn the engine, get the lubrication right, change the pushrods, get the propeller mounted, etc).

To revisit an earlier point on your build: I got the impression from your comment here that, if you were starting this project today, you might begin with the Vanguard (model 49V) rather than the Commercial series (Model 49T) in order to get the plated exhaust valves and automobile-style pistons. Have I got that about right?

Thanks again.

4. Oct 5, 2019

Vigilant1

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Oil mist in the case: will there be enough to keep the cam lobes happy?
I'm familiar with "dippers" and "spoons" fitted to conrods and crankshafts of horizontal shaft engines to dip into the oil pan and sling oil around the crankcase, assuring there's plenty of oil mist for lubricating everything. Vertical shaft engines often use paddles to accomplish the same thing. If oil is removed to a remote sump, will there be sufficient mist to keep everything lubed? In a "heads down" install, the spillage from the bearings will drain to the heads, so rockers will be happy, and it will surely wet the bores and dance around in the piston skirts keeping the small rod ends slippery. But will there be enough of the slippery stuff bouncing around to keep the cam lobes and lifters (aka "followers") lubricated?
I'd have similar concerns about "heads up", but with the sump right under the crank throws, I'd think there will be more splashing and windage to whip up some mist.

If deliberate cam lobe/lifter lube is needed, maybe a drip bar could be hung over it, tapped into the passage in the case leading from the cam end bearing to the flywheel-end crankshaft bearing (the same channel tapped in the SE-33 for the external oil feed to the heads).

Last edited: Oct 5, 2019
5. Oct 5, 2019

TiPi

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As this is a pressure lube system with a circulation of 12 lpm, there will be close to 50% of that oil flung around by the rotating crankshaft (off the mains and the crank journal). Everything will be drenched in oil except what is in the heads. The cam lobes wil get enough oil in upside-down and right side up installations. Both camshaft bearings are on the pressure lube supply, so no problem there.

The best option is the Vanguard series, just a lot of stuff that is not needed. A possibility is the short-block engine plus the missing items (cylinder heads, starter motor, coils, carburetor, alternator and some small bits). Costwise not much difference to a full engine but lighter and smaller, especially if the flywheel is not needed.

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6. Oct 5, 2019

TiPi

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The V-twin has significant pulsing in the crankcase (approx 0.6lt per rev), that will cause a lot of flow reversal in the drain line and affect the flow back to the tank.

7. Oct 5, 2019

Basil

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If you are driving off the PTO end then how are you going to mount the engine since all the built in mounting holes are on the PTO end?

8. Oct 5, 2019

TiPi

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Hi Basil, you have to ask the difficult question
Plan at the moment is a sort-of bed mount, using 2 mounting holes on the PTO end and 2 at the flywheel end. Those are holding the tin sheet under the flywheel, 4 x 1/4" bolt holes all up.

9. Oct 5, 2019

Hot Wings

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Yes, lots of pulsing with a 2 cyl system (1/2 VWs are even worse) but that can be used to advantage depending on the volume of the scavenge line and the arrangement of the air/oil separator.

Another option to consider: Rather than the pressure from the blowby being the only motivator of oil transfer, using vacuum on the tank can work just as well and has some real benefits, both functional and environmental.

If you do use a check valve consider a Tesla valve. They work very well, with no moving parts.

10. Oct 5, 2019

pictsidhe

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I'm not sure that a check valve is necessary either. A simple sharp edged nozzle projecting into the dry sump will have a significant one way effect. With that nozzle well above the oil level and directing flow circumferentially, you should be fine. If not, add a valve. A tesla valve with a mix of oil and gas will want to fill it's pockets with oil while the gas blows down the centre, which will probably reduce it's effectiveness.

11. Oct 11, 2019 at 10:09 PM

Vigilant1

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Tipi,
Looking back at your post on the carb/induction system:
-- It appears that you are going to try to make the stock Nikki carb work, though the throat size and the venturi size may be prove marginal, and the carb lacks mixture control (you have a work-around). What are your thoughts on the stock Vanguard EFI system or going with another aftermarket carb that is the right size, has mixture control, etc?
-- Carb heat: Are you planning for any?
-- Induction runner heat: This might not be an important factor for you due to the short distance between the carb (presumably below the engine) and the intake ports on the head. The Lucioles often have the carb below and long runners to the head, and many of them use bleed exhaust in a small pipe to warm the runner.

Some homebuilders have fitted a hot oil box to the body of their carb to heat it. This accomplishes 3 things:
1) Prevents carb ice by keeping the carb warm enough so that ice can't attach to it.
2) Slightly warms the induction air to keep the fuel from condensing in the runners. It's less noticeable (and has less of an impact on performance) than dedicated "carb heat," but is enough to keep the fuel from forming droplets in the runners, playing havoc with the mixture, etc.
3) Cools the oil (quite a bit, 20 deg F in one example, link below). This could prove handy for us if the stock B&S oil cooler fins prove a little too tight to flow enough cooling air at our available plenum pressures. If we can cool with "free" heat from the cold intake, it leaves more airflow available for the heads (or, we make the intake smaller and reduce drag).
"Pops" has such a setup on his VW, and likes it. Discussion and photos here: https://www.homebuiltairplanes.com/forums/threads/hot-oil-box-oil-cooler.24527/

12. Oct 11, 2019 at 11:56 PM

TiPi

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I definitively will have some sort of carb heating, just not sure yet how that will look. The heads have a long intak port in the head and will add quite a bit of heat where it is not needed. One option I'm looking at is lining that to reduce the temperature increase.
My preference at this stage is to use the warmed air from the oil cooler as intake air, controlled with a flap that will switch to cold air at full throttle and gradually add more warm air with closing the throttle (full hot a low throttle settings).
As a first pass, I'll be using the original carburetor and just improve the areas that impinge on air flow. Measuring the MAP pressure, you can asses the pressure drop through the carby and evaluate if a bigger one will add any flow. I also have the flow bench to measure my improvements and can simulate a larger carburetor and see if the flow rate of the whole system improves.

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13. Oct 12, 2019 at 12:46 AM

Vigilant1

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I'm not very familiar with the way the ports are set up in the head, but is it possible that the long intake runner serves to cool the head a little bit? It isn't a cross flow head, and having the cool induction charge take away some heat would be consistent with the intended use of the engine (not ultimate power per cc, but long life under punishing conditions).

14. Oct 12, 2019 at 1:26 AM

TiPi

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I think it is simply for design reasons, getting the intake port connection to the side of the head where they fit the manifold rather than a more complicated manifold setup. The EX port is very short but a 90deg intersection of 2 x 25mm holes (sharp edges). The IN port also has shar edged where it intersects the valve area and the port is angled 30deg from the flange face (30deg kink).
So there is quite some room for improvement without too much work.
I would call this a cross-flow head, IN and EX are not on the same side but not exactly opposite either but more than 90deg apart

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15. Oct 12, 2019 at 3:25 AM

Vigilant1

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Thanks, the photos make it clear that you are right about that.
Some of the B&S ads from a few years ago made a big point of those "cooling arches" on the head. I have trouble seeing that they are anything special, I wouldn't be surprised if they are really there for other reasons (to make it easier to pull the part from the mold, to give a robot a good place to grip, etc).

16. Oct 12, 2019 at 3:56 AM

pictsidhe

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The ports are pretty ugly for flow, but Briggs compensated by making them big. Peak torque is close to where we need it, so increasing flow won't help much. It may even decrease power if it takes the peak above our chosen rpm.
Ideally, smaller ports with similar flow would be used. That would require filling in the ports of the smaller versions and drastically reshaping them. A lot of work, and the gain won't be huge.

17. Oct 12, 2019 at 5:10 AM

mm4440

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Do you think the B&S has enough finning on their cylinder head?

18. Oct 12, 2019 at 5:14 AM

TiPi

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I think so. They are staying cool in their intended application under some pretty adverse conditions and the SE33 has no problems with about 200deg C in climb on hot days. Took them a few goes to get the airflow right.
16hp/head for the SE33, 45-50hp for the Lycosaurus

19. Oct 12, 2019 at 5:30 PM

karmarepair

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What is your plan for a hub to drive the prop? Have you seen the Universal Hovercraft hubs, which use Taperlock couplings to grab a straight shaft?
http://hovercraft.com/content/index.php?main_page=product_standard_info&cPath=189_388&products_id=49 Hub
Companion Taperlock bushing http://hovercraft.com/content/index.php?main_page=product_standard_info&cPath=189_59&products_id=69

Next question: You've been clear the flywheel needs to lose a LOT of weight to keep it from fighting the torsional inertia of the prop - what is your plan for putting it on a diet?

20. Oct 13, 2019 at 1:11 AM

TiPi

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I have something similar in mind, based around SKF or Fenner keyless shaft locking devices. The nominal torque from the tuned 49 will be around 66Nm, application factor is 3-5 (plus a safety margin of 2) means the min transmittable torque on a 28mm shaft needs to be 400Nm.
This is from Tsubaki:

I can't identify the manufacturer of the Hovercraft hub, would like to see some engineering data first.

I will just about lose my flywheel completely, only a 6mm alu disc with the alu ring gear and the ignition magnet (and counter weight). I have changed the desing since this pic was taken, now making an alu hub with the disc mounted on a flange face towards the engine (spacers for the ring gear no longer required). Alternator will be moved to the PTO side.