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Thread: Brigga and Stratton industrial engine conversion

  1. #76
    Registered User BBerson's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Thanks Dan,
    Sounds like it might be best to increase the power of a small Briggs with electric power added to the propshaft rather than attempting electric supercharging.

    We don't need 30hp continuous, but 30 seconds of 30hp for takeoff is desirable.

    Probably best to just get a 30hp Briggs, I suppose.

  2. #77
    Registered User Dan Thomas's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    There are other considerations to raising cylinder pressures in any engine. Turbos in cars now are fairly common, but so are knock sensors. When we increase cylinder pressures, we also increase the temperatures created during the first part of the burn time. Compressing a gas raises its temperature, and packing more air and fuel into a cylinder makes a bigger bang.

    Detonation is a problem in engines that run at higher compression ratios or are supercharged in some way. Aircraft engines are particularly vulnerable because of their larger cylinders and relatively low RPM. Detonation is spontaneous combustion of the air/fuel mixture, and can knock an engine to pieces in short order if it gets bad enough.

    When the sparkplug ignites the mixture, the spark sets off only a few molecules. Those then ignite molecules close by, and a chain reaction spreads the flame across the combustion chamber. This is happening as the piston passes TDC and starts downward. It's normal combustion and the flame front travels at around 100 feet per second.

    Detonation sets in when the wave of rapidly rising pressure just ahead of the flame front causes fuel molecules to break down from their complex structures into simpler structures that easily ignite at lower temperatures. The pressure wave is compressing those unburnt air and fuel molecules, raising their temperature, and the whole works can autoignite all at once in a devastating explosion. The flame front here can travel at speeds as high as 5000 feet per minute instead of the normal 100, and the pressure spike created can knock holes in pistons or break con rods and piston rings and the heat will scrub metal off the piston crown. In old cars we knew it as pinging or "spark knock" when we used a little to much throttle at low RPM ("lugging" it) or if we used cheap gas with a low octane rating.

    Detonation takes time to happen. At high RPM or in small cylinders the burn is done before autoignition can happen. In slow engines and/or large chambers, the burn has much more time to get the detonation started. Lean mixtures burn more slowly and will bring on detonations sooner. Hot intake air contributes to the cylinder temps and can start it too, so carb heat at high power settings has to be watched. We'll seldom hear detonation in an aircraft engine because of the prop and slipstream noise, and the damage is usually done before we know it.

    Cars use knock sensors now that will enrich the mixture and retard the timing to stop any detonation the computers detect. Aircraft engines have fixed timing and manual mixture controls, and we can incur detonation just be being careless. Often, just opening the throttle too quickly can create a short spell of it; remember, low RPM and high manifold pressures are conducive to it. Habitually bashing the throttle in will eventually cost you. A propeller is a heavy flywheel with a large rotational inertia, and the engine takes much longer to spool up than the one in your car.

    Now, adding a turbo to an engine raises the manifold pressures and temperatures. The old piston airliners often had turbos, or more commonly mechanically-driven superchargers, and they controlled detonation with high-octane gasolines. 115/145 octane was used in them. It was purple, but it's not the same as the purple farm gas some of you might be familiar with. I don't know if any refineries are still making it for the warbirds still flying.

    Octane rating reflects a fuel's resistance to detonation, and has absolutely nothing to do with extra energy, despite what some folks think. It's used in high-hp engines to resist detonation, not to get extra heat.

    Dan

  3. #78
    Registered User mstull's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Even though the 3,300 or so RPM most of these industrial engines turn is a perfectly reasonable prop RPM for direct drive, they don't make enough torque to turn a big enough prop to climb. Guys are using reduction drives so they can swing a big prop and make enough thrust. Unfortunately the reduction drives add even more weight to these heavy, low powered engines.
    Mark E. Stull
    mstull@wtxs.net

  4. #79
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    Re: Brigga and Stratton industrial engine conversion

    Mark, you hit the nail on the head- they are marginal for thrust.

    A better motor would be a Moto Guzzi Cali motor with a different cam and flywheel mount direct drive or gearbox. They are incredibly reliable and extremely well engineered , I rode a higher power Lemans for over 200,000 Kms and on pull down wear was minimal. I know they might be hard to get but this is probably the ultimate V twin for a aircraft. The rear main bearing is massive and would easily take the prop loads.

    Phil
    Moto Guzzi

  5. #80
    Registered User BBerson's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Quote Originally Posted by mstull View Post
    Even though the 3,300 or so RPM most of these industrial engines turn is a perfectly reasonable prop RPM for direct drive, they don't make enough torque to turn a big enough prop to climb. Guys are using reduction drives so they can swing a big prop and make enough thrust. Unfortunately the reduction drives add even more weight to these heavy, low powered engines.
    Mark,
    Your comments are generally true for high drag ultralights. But a number of small airplanes have flown with direct drive industrial engines even as small as 18hp. The engines are now available in 20, 28 and 35hp now. With various methods to make them lighter they are worth looking into.

    A 900cc industrial engine should be nearly identical to the commonly used half VW on the legal eagle ultralight. I have a 670cc 24hp Honda. If it proves to be too small, I may look at the other engines that are available at that time.

  6. #81
    Registered User Dan Thomas's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Quote Originally Posted by BBerson View Post

    A 900cc industrial engine should be nearly identical to the commonly used half VW on the legal eagle ultralight. I have a 670cc 24hp Honda. If it proves to be too small, I may look at the other engines that are available at that time.
    I'd be interested to know whether the industrial engine uses the high-silica aluminum pistons that the VW probably has, or the forged steel con rods that the VW has instead of the cast aluminum rods found in so many throwaway engines, or rod bearing inserts instead of bare aluminum, and so on.

    Dan

  7. #82
    Registered User BBerson's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Dan,
    I think most of the industrial engines have forged aluminum rods. No inserts are needed.
    This is perfect for aviation in my opinion. These engines are designed for continuous output at 3600rpm. If an airplane cruises at 3200rpm, what's the problem?
    The low cost Briggs engines do not have oil pressure to the rod at all. Yet the life at 3600rpm is years. My Honda has full pressure and costs more.

    VW engines are used in many land vehicles at extreme rpm (perhaps 6000rpm). The VW or any engine at 3200 is not overstressed or overheated in most cases if the manifold pressure is normal.

  8. #83
    Registered User heavyliftpilot's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Hi, i've read up on this type of conversion...the folks at Culver Props, have what they call the 'Big Twin' and it's a 990cc generac engine (v twin). puts out 40hp, and it's lighter than the B&S. Valley Engineering - Big Twin

  9. #84
    Registered User Starman's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    According to this thread the Honda 620 cc V twin weighs only 55 lb in minimalist form, and that looks good, the 24 hp 670cc can't be too much more than that and I think it has full pressure lubrication.
    Industrial Honda GX620

  10. #85
    mz-
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    Re: Brigga and Stratton industrial engine conversion

    They're trying out B&S Vanguard V Twins in Luciole MC-30:s


    More info here:
    neet plane

  11. #86
    Registered User heavyliftpilot's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Hi, went looking for 'gaenines'....i found it, but it's gaengine.com...

  12. #87
    Registered User BBerson's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Watching that video, I could almost smell the fumes in the room.
    Sounded neat.

  13. #88
    Registered User Cy V's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Just a little reminder of what is possible with one of those B&S generator engines....



  14. #89
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    Re: Brigga and Stratton industrial engine conversion

    Now that looks pretty usable for small plane, I like it.

    I remember a very low weight for the Vangard in this setup, but forget the figure.

    The idea of a inexpensive 4 stroke is great at the right weight.
    The possibility of small composite sleek fun machine under $10K can be a reality with this cheap engine. A 100 mph aerobatic machine sounds fun to me.

    Phil

  15. #90
    Registered User Starman's Avatar
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    Re: Brigga and Stratton industrial engine conversion

    Quote Originally Posted by litespeed View Post
    Mark, you hit the nail on the head- they are marginal for thrust.

    A better motor would be a Moto Guzzi Cali motor with a different cam and flywheel mount direct drive or gearbox. They are incredibly reliable and extremely well engineered , I rode a higher power Lemans for over 200,000 Kms and on pull down wear was minimal. I know they might be hard to get but this is probably the ultimate V twin for a aircraft. The rear main bearing is massive and would easily take the prop loads.

    Phil
    Moto Guzzi
    Hi Moto Guzzi Phil, I was looking at these before and am looking at them again, however, BUT if a BMW boxer engine weighs 180lb then a Guzzi must be around the same, shouldn't it? Do you have any idea what the weight of one of those 1000cc - 1100cc units is?

    I wouldn't mind having 90hp available for takeoff but cruise would be at less than 20hp ~ as long as it's an ultralight

    I just checked and found out that the weight of the whole motorcycle is down around 400lb, but still, the engine could be half of that, but it probably isn't because transmissions are heavy, and the trans on these engines unbolts, no cutting required.

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