Briggs vanguard conversions

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

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  1. Oct 13, 2019 #1221

    Vigilant1

    Vigilant1

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    I think I may be able to get that from my library, I've been amazed what little community libraries can now access electronically. I'll give it a shot. Of course, it will only tell us how the stock B&S engine was tested, not what a modified one (SE-33, etc) can do.
    1) I've never seen the source for the 33HP figure for the SE-33 engine, has anyone read it if was gotten by spinning a calibrated test club, or some time on a certified dyno? It might be based on comparison with flight characteristics of an SD-1 that has an engine of verified HP, or maybe just a comparison of the static RPM produced by the SE-33 spinning the same prop as another engine of known output.
    2) The info I've seen on the MiniSport pages doesn't indicate if the 33HP is for short periods or continuous. TiPi reported previously that the SD-1 requires approx 30 HP to fly at 94 kts, and the aircraft's cruise speed is 80-90 kts, so presumably the SE-33 can supply at least approx 29-30 HP continuously in the SD-1 (given the cooling airflow in this "clean" airplane and the tractor configuration). TiPi mentioned previously that he thought a fan might be needed for a pusher or a draggier plane.

    Edited to add: A page posted by the SD-1 dealer in the UK indicates that, with the SE-33 engine, the SD-1 cruises at 94 kts "@75%" The site also shows that the engine burns 1 GPH "@75%." Clearly, there's a conflict in the info that is out there.

    For what I have in mind, 29-30 HP continuous would be fine (I'd only need about 25 HP in normal climb and cruise, the 30 HP continuous is for unusual cases, but it's got to be there) and if more than that is available for a minute or so (to get off the ground and over the barn,etc), that's a nice plus. I think if somebody needs 33HP continuously to pull a draggy plane around, they might be in for some rough sledding.
     
    Last edited: Oct 13, 2019
  2. Oct 13, 2019 #1222

    blane.c

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  3. Oct 13, 2019 #1223

    blane.c

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  4. Oct 13, 2019 #1224

    blane.c

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  5. Oct 13, 2019 #1225

    blane.c

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    RONTZ COOL 7.png For inverted (heads down)? Or RONTZ COOL 8.png
     
  6. Oct 13, 2019 #1226

    blane.c

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  7. Oct 14, 2019 #1227

    karmarepair

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    Found it, https://translate.googleusercontent...700271&usg=ALkJrhiT02YjR0BOgxDxdbCGhXxfK2PT4Q

    ULI NG

    WELLER AIRCRAFT
    Roman Weller
    Beaver Street 8
    74523 Schwäbisch Hall - Beaversfeld

    Telephone: 0791-56732
    Fax: 0791-56733
    E-Mail: weller-sha@t-online.de
    Internet: www.weller-flugzeugbau.de

    https://www.weller-flugzeugbau.de/assets/pdf/Muster_Geprüft_UL_NG_Flügel_Magazin.pdf . Article in German magazine. Engine is a Vanguard 630 , 2.28 reduction drive. Welded chrome moly fuselage, empennage is wire braced, as are the wings.

    upload_2019-10-13_19-35-25.png
     
  8. Oct 14, 2019 #1228

    Vigilant1

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    So, that would be the Vanguard 627cc engine. The magazine article claims they are getting 30 HP from it, so it's being driven fairly hard. HBA member Factory Fit (Kevin Armstrong) used a heavily modified engine of this type with an Ace redrive his trike. More following this post, including some meaty comments about his setup and experiences with it.
     
  9. Oct 14, 2019 #1229

    Bille Floyd

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    Last edited: Oct 14, 2019
  10. Oct 14, 2019 #1230

    Vigilant1

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    So, how much direct drive thrust should we expect from the 810cc engine?

    Disclaimer: I’m not a propeller expert. The “method” below may or may not be valid.

    As the point of all this tinkering with the engine is to make thrust for an airplane, it’s reasonable to ask how much thrust we can expect. For the purposes here, I’ll assume we want to know how much thrust we’ll get at 2000’ MSL from an engine rated at 30 HP at SL, and driving a fixed-pitch wooden two-blade prop at 3400 RPM. I know there’s reason to believe that the engine will produce more HP than that at higher RPM, but this may be a conservative appraisal of what the engine can make on a continuous basis.

    Methodology: The table contains estimates for several propeller lengths and design speeds. In each case I used Jan Carlsson’s propeller design program to give the expected efficiency of the propeller at its design speed. I was not able to make the program give me reliable projections for a propellers at airspeeds other than the design speed, so I estimated “off design speed” propeller efficiency using a graph from Raymer’s Aircraft Design: A Conceptual Approach (Ed 1, Fig 13.10). That lookup table, made from the published graph, is in the spreadsheet attached.

    In general, relative to its design airspeed, a propeller loses efficiency fairly slowly at airspeeds below its design speed, but loses efficiency rapidly at airspeeds above the design speed (at airspeeds above its design speed the propeller blades are at low AoAs). For example, if a particular prop has a design speed of 100 MPH, it might be 75% efficient at that airspeed. At 30 MPH below its design speed, 70 MPH, its efficiency is reduced to 0.82 of its 100 MPH design efficiency, so its new efficiency is 0.75 x 0.82 = 62%. Now, if we go the same 30 MPH above its design speed, to 130 MPH, the prop is just 50% as efficient as it was at its design speed (so, 0.75 x 0.50 = 37% propeller efficiency).

    After finding/estimating the efficiency for the prop at various airspeeds, I found the thrust by applying the following equation:
    Thrust (in lbs) = Engine power (HP) x propeller efficiency x 375 (a constant) / airspeed (MPH)
    The tyrannical term in that equation is the divsion by the airspeed at the end. Because of that, thrust declines with increasing airspeed even for propellers designed for higher speeds.

    I’ve attached an excel spreadsheet in case you’d like to sort things differently (don’t blame me if it falls apart!) or catch my spreadsheet errors. The PDF version may be useful if you just want to look at the numbers. The process I used has a lot of manual steps, which means it is both slow and prone to error.

    Observations from the estimates:
    - Though these 42-28" props are short compared to "regular" GA aircraft props, because of the modest HP we are using, they have very reasonable propeller disk loadings (lower than a C-152, etc). Even at modest climb speeds, at these RPMs there appears to be little gain from going with long propellers. If these numbers are right, it looks like most people choosing these engines and running direct drive to climb and cruise a small sportplane at 60-120 MPH will probably choose a 44"to 46" propeller.
    - As noted above, prop efficiency (and, especially, thrust) numbers fall off relatively rapidly above a propeller's design speed, but the efficiency (and esp the thrust) hold up somewhat better at airspeeds below the propeller's design speed. For folks looking to balance a desire for higher cruise speed and good climb rate, this would argue for choosing a propeller optimized for speeds closer to the cruise speed than the climb speed. OTOH, from a safety standpoint, acceptable climb rate almost always trumps cruise speed. So, more compromises . . .

    If anyone has prop design/thrust information for this engine (or other small engines) in direct drive that we could use for comparison, that would be great. I believe MiniSport uses a Helix 48” composite prop on their SE-33 engine, but I’m not sure of the pitch or of the thrust they are getting in flight. M. Colomban reportedly went through quite a development effort to design the Arplast propeller used on the MC-30, but I’m not sure of the specs on it, performance, etc. The data here is “open loop”--based on Jan’s propeller calculator and some extrapolation for off-design speeds. It would be great to get some real world numbers.

    Notes:
    – The prop planform is the “Jan Carlsson Standard”
    – The prop pitch optimization I chose in Jan’s program is “standard”, so, it is coarser than a pure climb prop but finer than a pure cruise prop .
    – The tables show the blade width at 75% span because the propeller blades designed by Jan’s program get quite narrow (and thin) at longer prop lengths and these relatively small HP levels. Some people may choose to give up a little bit of efficiency to get a propeller that is more robust.
    - The estimates are for a 30HP (at sea level) engine taken to 2000’ MSL (so, producing 27.9HP) at 3400 RPM. The propellers are wooden, 2 blade and (obviously) fixed pitch.
    - Jan’s calculator does not provide thrust values below 40 MPH, and traditional methods don’t do well at those low speeds. So, for takeoff roll, etc we’ll have to use other means to get thrust estimates. Even a completely stalled blade produces thrust (though inefficiently).
    - For many small airplanes, rate of climb is very sensitive to the available thrust. Even a few pounds difference in thrust levels can significantly change the climb rate. My data has some obvious glitches (e.g. I can't explain why the props designed for 70 MPH are shown as being more efficient at 60 MPH than the props designed for 60 MPH. The method I used probably also overstates the 60 MPH capabilities of the higher-pitched props at 42" diameter--surely all of the 42" diameter props have efficiencies of less than 35% at 60 MPH). The estimates here (and elsewhere) may be useful for planning, but getting real numbers in flight will be critical.
     

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    Last edited: Oct 14, 2019
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  11. Oct 14, 2019 #1231

    BBerson

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    I think Jan used his own engine hp estimates rather than customer or manufacturer hp "claims".
    Using optimistic hp numbers for prop design will only end up with the engine not getting up to that required rpm.
     
  12. Oct 14, 2019 #1232

    Vigilant1

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    Id like to find hard numbers for the 810cc engine in airplane trim. Do you think 30 HP at sea level std day is optimistic?
     
  13. Oct 14, 2019 #1233

    BBerson

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    I always think claims above the manufacturer number is optimistic. I just don't think these engines can produce much more (or any more) than rated power at the rated rpm with simple minor tuning. And they will produce significantly less in climb where you need the power. So why even be concerned with exceeding the rated hp? It could only happen in full power max cruise. Is that the planned purpose?

    For direct drive you can try exceeding the rated rpm for more power. But then the prop size is smaller so less efficient, so might not gain much beyond extra noise.
     
    Last edited: Oct 14, 2019
  14. Oct 14, 2019 #1234

    Vigilant1

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    I can't dispute your reasoning. The approved testing procedures for gross HP are pretty liberal (no air filter, etc). There does seem to be room for improved induction, CR, timing, and for possibly higher RPMs, but as far as I've read, the estimated increased output is a matter of conjecture. This is aside from any heat/CHT issues.
     
  15. Oct 14, 2019 #1235

    karmarepair

    karmarepair

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    Actual dyno data for a Vanguard 627 conversion. upload_2019-10-14_14-6-18.png

    I don't know why you'd go to the trouble of creating this data then exaggerate it. Based on this, I have NO trouble believing that the 810s can make the 33 hp continuous at 3600 RPM claimed by the Czech promotor of the SE-33 engine package for the SD-1.
     
  16. Oct 14, 2019 #1236

    Vigilant1

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    Forgive my skepticism, but commercial dyno numbers can be very "optimistic." I'm not questioning anyone's honesty, but dyno inflation is a thing (the highest reading dyno gets more business. Tinkerers/racers like good numbers). And, it would be useful to know how the engine was prepped, how much money was spent, and how it held up in a actual use. A wooden "club dyno" is hard to cheat and easy to make.
    I'm not disputing that 33hp at 3600 RPM is possible for the 810cc. But, on this issue I'm from (near) Missouri.
     
    Last edited: Oct 14, 2019
  17. Oct 14, 2019 #1237

    BBerson

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    Using optimistic numbers at every turn and calculation and spreadsheet is how Peter made an overweight and underpowered Raptor.
    The real world is cruel and all design tolerances usually add up badly. Designers should use pessimistic data (or first hand self witnessed numbers).

    I discard post 1235 because I don't know what KM is.
     
  18. Oct 14, 2019 #1238

    TiPi

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    The 33hp is max, not continuous. From the German POH:
    Max take-off power: 33hp @ 3,600rpm
    Max continuous power: 30hp @ 3,300rpm
    Fuel burn @ 75%power: 5.9 lt/h
    Fuel burn @ max power: 7.1 lt/h
    Fuel burn @ 55% power: 4.6 lt/h
     
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  19. Oct 15, 2019 #1239

    blane.c

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    No. I believe (yes we all know what Orion thinks about that) that it is entirely possible to get hp at or slightly more than 3,600RPM that exceeds 30hp with modifications, TIPI's hope for 35hp is entirely likely … @ … straight and level @ sea level, wide open throttle (WOT) and full rich. Like BBerson says as soon as you point the nose skyward the RPM will fall off and naturally the hp with it. What we end up with as actual take-off hp is speculative, it would be helpful to get better pilot reports from the SD-1's. Sometimes when you take-off you break ground and level off as close to the ground as practical to gain an airspeed you can hold in climb before pitching up, technique is going to be important with low hp engines. Low angle climbs may be beneficial in rate of climb and cooler running engines, time will tell.

    Again pilot reports would be helpful. Especially if they included meaningful propeller information.
     
  20. Oct 15, 2019 #1240

    Vigilant1

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    If we want 3600 RPM and full power in climb, it's easy enough to make that happen (by picking a prop with a pitch fine enough to allow the engine to get to 3600 RPM and full power at typical climb airspeed. ) Obviously, that means at higher airspeeds the blades will be at low effective AoAs and there won't be much load on the engine and, despite the RPM, the engine will be loading and burn will be low--along with the thrust.
     
    Last edited: Oct 15, 2019

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