Briggs vanguard conversions

Discussion in 'Firewall Forward / Props / Fuel system' started by Hephaestus, May 12, 2019.

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  1. Nov 9, 2019 #1301

    Vigilant1

    Vigilant1

    Vigilant1

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    Physically: Colorado. But you can drop him a note using this forum's "Conversation" function (it's a personal message). He has been monitoring this thread and is working on a B&S conversion of his own. He's a bit busy now--he bought the rights to some classic Fauvel designs (AV-36, etc) and he's busy bringing the (not in great shape) plans into the 21st century, and make some modifications where needed.
     
  2. Nov 9, 2019 #1302

    TiPi

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    I'm not a fan of closed-loop EFI for an application where power and fuel economy are the 2nd & 3rd priority after reliability:
    - you will give away ~10% power if running lambda 1 at WOT
    - you will give away ~10% fuel economy if running lambda 1 at cruise power

    To run an aircraft engine at various power settings, mixture ratios and altitudes requires either an EFI system with air mass meter and multiple maps for each combination. The other option is to use a wide-band sensor and manually fine-tune a simple map based on MAP and TPS.

    I have the manual for the B&S EFI system, it is very detailed (150 pages) as this system is going into a repair industry that has very limited exposure to EFI at this point. Similar to the automotive industry in the early 80s.

    Couple of points to the B&S EFI system on a V-twin:
    - intake track still needs to be separated as much as possible to prevent uneven air mass flow between the cylinders
    - I would not use the B&S ECM
    - too many critical outputs (ignition driver, fuel injector driver)
    - too many single-point inputs causing engine stoppage or unknown engine output-response:
    upload_2019-11-9_14-37-4.png
    upload_2019-11-9_14-37-53.png
    upload_2019-11-9_14-40-43.png
    upload_2019-11-9_14-41-42.png
    Crank Position Sensor
    upload_2019-11-9_14-43-46.png
    upload_2019-11-9_14-44-26.png upload_2019-11-9_14-45-16.png
    There is no information on the consequences for a faulty/missing air temp sensor or engine temp sensor signal. Generally, the impacts are only small as long as the O2 sensor (closed-loop) is OK and only affect start and warm-up.
     
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  3. Nov 9, 2019 #1303

    blane.c

    blane.c

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    (1) I would like to know about the stock B&S EFI if disregarding the computer portion are the rest of the components adequate? Like the plenum, butterfly's, injectors, and the various sensors. Or would the plenum need to be resized and also the injectors or if some of the sensors are not robust enough? Basically can the components other than the brain be utilized for an aviation engine or is the whole thing scrap? This considering that most are discussing 20% - 30% power increase from stock to an aviation powerplant.

    (2)Can the computer portion be reprogrammed or does it need to be ripped out and replaced?

    So does it make more sense to modify a stock system to work or build a whole system from scratch? Or is it Frankensteinish some parts are ok but more than just the brain is "Abbie Normal"?
     
  4. Nov 9, 2019 #1304

    Vigilant1

    Vigilant1

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    blane.c,
    Unsolicited input:. If you are still aiming for multi engines (as I am), it would seem you are in a slightly different situation than most. If you lose an engine but can safely fly on the power provided by the remaining noisy one(s) using the HP provided by stock EFI, then using that OEM system could be an attractive option. Given the (lower) consequences of one engine failure, maybe you can accept some unanswered questions on failure modes (?). You'd get the advantages of factory EFI (no carb ice, possibly better fuel efficiency, no fiddling around with mixture controls) at a rock bottom price. Just be sure the stock HP is enough, that you don't need to burn 100LL, and that all engines don't have a single point of failure (e.g. electric system/voltage spike, etc).
    I'll probably go with a carb, especially since it seems I'd need to have access to 30 HP. Rarely, but it has to be there.
    Sorry, not an answer to your question.
     
    Last edited: Nov 9, 2019
  5. Nov 9, 2019 #1305

    blane.c

    blane.c

    blane.c

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    It will make more sense when I see some modified engines power curves, I "assume" modified that the power curve will be steeper before peak torque than stock at around 3050RPM and flatten out after that to 3600RPM +or-. If this prove to be true then for 33hp to 35hp at 3600RPM there will be around 30hp to 31hp at 3050RPM and 20hp + or - at 2300RPM. Dialing in a fixed propeller that is efficient between 2300RPM and 3050RPM seems more likely than a propeller that is efficient up to 3600RPM. The aviation engines that I am familiar with that have maximum except take-off (METO) power ratings have that rating at about .54 of the cubic inch displacement. 49.43ci x .54 = 26.69hp so call it 27hp that is likely about the maximum sustainable and any power above that is take-off power only. Nobody runs there engine at METO either, climb is generally about .83 of that so 27 x .83 = 22.41 or 22hp and high cruise is generally .75 of METO so 27 x .75 = 20.25 or 20hp. So 35hp is about 30% more than the .54 x 49.43ci which is fine for take-off power and 75% of that is around 27hp which is roughly equivalent to METO it is just not normal to cruise at that high of a power setting in comparison to the ci displacement. Proper cooling will be critical. The biggest challenge however is a propeller that is efficient for such a wide RPM range I think. Therefore propeller efficiency and the RPM range it can be efficient is going to dictate the actual amount of power each individual is going to obtain or try to. To expect a fixed pitch prop to work from 2300RPM or less up to 3600RPM or more is just not logical. So considering taking advantage of the modifications that are being discussed and hoping the torque curve is somewhat predictable then you can make or buy a propeller to work in the powerband best suited to your needs, more range then steeper pitch and less top end horsepower or finer pitch and more top end horsepower but less range. To get it all would take a constant speed propeller which is to heavy for most applications and likely the engine as well. Using a flexible pitch propeller is an option worth looking into and may broaden the useable power range of these engines, my concern is that if such a propeller were used it would need to be at flat pitch at maximum horsepower and RPM because if it is designed for less power and RPM it may twist beyond design limit. I don't know if that would prove true but it concerns me. An RPM cutout may work if trying to get a broader powerband and still have efficiency at cruise using a flexible propeller but is another thing to malfunction. Anyway if the power curve is predictable and we do the modifications to the engine and the propeller is carved for cruising at less than 75% METO power so at around 2200RPM and it is a normal propeller we might be lucky enough to see rated horsepower but at a much lower RPM than the stock engine likely around 2700RPM - 2800RPM because of the increase in torque. Of course until some results are in of the testing with clubs we can only conjecture.

    I believe that the use of the term METO power is appropriate in regards these engine in light of the idea that we are increasing the power or the potential for power beyond stock which is at or about 0.54 of the cubic inch displacement (what a coincidence) and analogous to a boosted engine typically 20% to 30% more power than stock.
     
  6. Nov 9, 2019 #1306

    BBerson

    BBerson

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    Don't need constant speed. A simple in-flight cockpit " twistable" prop like IVO designed is enough for a small speed range.
     
  7. Nov 9, 2019 #1307

    Vigilant1

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    For a direct drive installation on these industrial engines, the weight of the adjustable IVO would be a concern. I think a Prince P-tip prop might have some promise, and they reportedly give a few inches of pitch change on response to loading. Simple, nothing to go wrong, but certainly not as much adjustment as an IVO.
    The stock power curve for these engines looks a lot like the power curve for aero VW engines--a fairly straight line up to 3600 RPM. The B&S are designed to be run at that speed (unlike a Lycoming or Cont), and so is a VW. They can mow all day at that RPM.

    It seems to me that, for a multi engine installation, the challenge is this: For the (rare but critical) single engine climb scenario, you may need each engine to be able to make full rated power at low speed (?60-70mph? for best climb angle?). Full power means 3600 RPM or so. A prop with pitch fine enough to let the engine get to 3600 RPM at 65 mph may be too flat to develop much thrust at a more reasonable cruising speed (e.g. 100 mph). That's what the graphs say.
    A very light 2 position prop would be nice.
     
    Last edited: Nov 9, 2019
  8. Nov 9, 2019 #1308

    BBerson

    BBerson

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    I didn't mean actual IVO, but fixed blades like IVO, but twistable. (like IVO but home made and smaller) It's sort of like the "rigid rotor" helicopter blades that are not really rigid. They are " bearingless" and simple.

    My Grob (Hoffmann) prop is two position (actually three with feather). It only takes about 1/16" between low and high pitch for a 500 rpm change.
     
  9. Nov 9, 2019 #1309

    Vigilant1

    Vigilant1

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    Maybe that would work. The IVO composite blades mount (solidly) into metal collars. I don't know if that setup provides the self-damping properties that makes solid wood/composite wrapped wood core props so attractive from a resonance standpoint. Maybe we they do.

    Another subject:. Any thoughts on what, if any, mods would be required to run these engines at higher RPM (say, 4500 rpm) but moderate MP so they still are only putting out approx stock HP? The marine engines are designed for high RPMs, do they use lighter pistons or anything exotic? The cylinder pressures would be low, but all the inertial loadings would be higher than at 3600 RPM.
    I'd think a twin with fixed-pitch props in normal cruise might see high RPMs but with props significantly underpitched, so moderate load. Basically, both engines turning fast but "loafing" since the props are flat and the aero loads are shared between them.
     
  10. Nov 9, 2019 #1310

    TiPi

    TiPi

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    Fixed-pitch propellers work along the propeller power absorption rules: an aircraft engine will generally work from max rpm (below redline at WOT) to 90% rpm (75% power) or 86% (65% power). That means for an engine with max power at 3,600 rpm, the normal operation rpm range is from 3,100 (65% power), 3,240 rpm (75% power) to WOT (whatever static rpm and 3,600 rpm straight and level). Any rpm below that is of no use for a normal aircraft in flight (except descending and landing). The propeller dia & pitch need to be worked out to give the best compromise performance at those rpms and the flight speeds of the aircraft (biased to climb or cruise).
    upload_2019-11-10_9-21-21.png
     
  11. Nov 9, 2019 #1311

    BBerson

    BBerson

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    Reduce the pitch and set the power with the throttle. Not much point in running a prop at a high inefficient rpm at reduced throttle. Generally you want wide open throttle at max rpm, I think.
     
  12. Nov 10, 2019 at 12:16 AM #1312

    Vigilant1

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    The problem/challenge may be unique to the multi-engine situation. If we need to be able to climb with one engine inop, it calls for max power (or a large % of max power) at best climb angle airspeed on the remaining engine. And it will be pulling an airplane with one stopped prop, so draggy. That drives us to a fairly fine pitch prop. But, for the 99% of the time that both engines are running they can both pull the airframe through the air (reduced load on each engine) and higher cruise speeds are theoretically possible--except that the prop runs out of pitch. If we can turn the prop faster, the effective AoA of the blades inceases and they again start pulling. It's not as efficient as a variable pitch prop (because of increased engine pumping losses and some reduced prop efficiency at higher RPM), but it should be effective (if not efficient). At least in theory. But if the engine can't mechanically take 4500 RPM (at low MP) for hours at a time, then it's not gonna work.
     
  13. Nov 10, 2019 at 12:25 AM #1313

    BBerson

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    Nothing unique about twins. The fixed pitch is a compromise for both twins and singles.
    The adjustable prop gets about 30% more power for climb. Molt Taylor has an article about this (1981 Sport Aviation). Many of his experiments were with controllable props.
     
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  14. Nov 10, 2019 at 1:14 AM #1314

    Neal Scherm

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  15. Nov 11, 2019 at 9:49 PM #1315

    blane.c

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    Exactly. Which is what concerns me. Cruise for a fixed propeller that gets what it can at 3600RPM is going to be at or near .54 x the ci displacement = hp at 3100RPM which is essentially cruising at full rated power. Getting rid of heat is going to be essential at that kind of load. The engine is not likely to see good fuel economy either it is likely going to need to run a bit on the rich side for cooling the combustion chamber. It is may be the animal we live with but a prop that would be efficient over a wider RPM range would be helpful.
     
  16. Nov 12, 2019 at 2:57 AM #1316

    Vigilant1

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    I think we have to be careful in comparing these little engines to "real" airplane engines. There's certainly a lot of knowledge that crosses over well, but there's some that we should take a hard look at. I'd suggest that "cruise RPM" may be one of the differences.

    A Lycoming O-360: Stroke =4.375". At the manufacturer's RPM used for HP specs (2700 RPM for most models), the engine has a peak piston speed of 51.6 FPS and an average piston speed of 32.8 FPS

    B&S 49 series engine: Stroke = 2.89". Piston speed at 3600 RPM: Peak--45.39 FPS. Average--28.9 FPS. At 3600 RPM, the B&S has the same piston speeds as an O-360 turning at 2375 RPM. That seems like very moderate territory to me. The short stroke of these engines may help explain why they can live a long time in hard use at relatively high RPMs (by airplane standards).

    This comparison doesn't address the heat issue, but may be a clue to what is reasonable from a mechanical/stress perspective. Average and peak piston speeds don't tell us everything, but are a good quick guide to the reciprocating/cyclic stresses that the main and wrist bearings, conrods, crankshaft, valve train components, etc will be under.
     
    Last edited: Nov 13, 2019 at 3:01 AM
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  17. Nov 12, 2019 at 3:01 PM #1317

    pictsidhe

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    Forget rpm, piston speed is far more important for the engine. At 3600RPM, an indusrtial twin is smack in the happy zone for both life and decent fuel efficiency. .
     
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  18. Nov 12, 2019 at 3:10 PM #1318

    blane.c

    blane.c

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    Well just speculating anyway. Are there any numbers available from people flying the SD1 with the 810cc engine? That would be good information.
     
  19. Nov 12, 2019 at 3:21 PM #1319

    Vigilant1

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    The German SD1 POH has some specs (30 HP continuous at 3300 RPM, fuel flows, allowable CHT, etc). Some of that is in this thread, '(I'd include a link but I'm on my phone.). Search this thread for "German".
     
  20. Nov 12, 2019 at 4:03 PM #1320

    BBerson

    BBerson

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    I think it's more about finding the happy zone for the prop rpm. (direct drive)
     
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