Usable single-seater on 24 hp?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Feb 5, 2020.

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  1. Feb 13, 2020 #101

    blane.c

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    1835cc is about 115ci and 2180cc about 133ci, Cont. A-65 170ci (O-170) When you go liquid cooled and propeller reduction the dynamics change but people seem to overdo it and expect to much with not enough displacement. It isn't a straight hp swap and I don't know what the curve or factor is but empirically it could be figured out with as much data as is available. I mean think about it put an engine in place of a 3600rpm 60hp that has to do 6000rpm to push 60hp and it obviously hasn't the same torque, and yes that does matter. You can use a smaller displacement engine but maybe to compensate to some degree for torque it has to put out 70hp (just throwing out a number) to be equal in reality, it isn't the same.
     
  2. Feb 13, 2020 #102

    Vigilant1

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    How is it an indictment of the VW engine? Of course things change with density altitude, etc, but the 2180cc VW engine in front of my Sonex allows 2 folks to fly with better than 450 fpm ROC.
    Unless something is very wrong, it is hard to see how adding 15hp to the nose of a VP-2 (1835cc =60hp , 2180cc =75 hp) only improved ROC by 50 fpm.
     
    Last edited: Feb 13, 2020
  3. Feb 13, 2020 #103

    blane.c

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    because it was only about 18ci
     
  4. Feb 13, 2020 #104

    Vigilant1

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    It's a bit more than 20 CI. HP -->thrust is what allows climb, the 75 hp is a legit max power for a 2180cc VW engine. If that plane was getting 400 fpm with an 1835cc engine, there's no explaining why it would only get 450 with a 2180. The engines weigh virtually the same.
     
    Last edited: Feb 13, 2020
  5. Feb 13, 2020 #105

    Himat

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    The Micro-IMP did fly on 25hp.;)

    What astonish me is that you are talking about designing for 100 to 150kg pilots! Ok, I have grown heavier by the years, but I am still less than 90kg. Not tall, but at 180cm not short either.
     
  6. Feb 13, 2020 #106

    TiPi

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    slight correction: the SD-1 can be built with an empty weight of 120kg with the 33hp V-twin (meeting the German 120kg class). Fuel is 28lt eg 20kg so enough useful load for 100kg pilot & incidentals.
     
  7. Feb 13, 2020 #107

    cluttonfred

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    On the VWs, I would say that those engines were not as well-developed as they could have been since those were the early days of VW-powered aircraft in the USA. Specifically, the prototype VP-2 was using a 60" diameter prop (60 x 30 with the small engines and 60 x 32 with the bigger ones), which suggests to me they were running at lower RPMs than is now typical for aircraft VWs.

    Himat, it's not 150 kg pilots but 150 kg useful load (including fuel), but regardless it's seems better do design for how people are rather than how they should be. In the USA, the average adult male is 5' 9" (175 cm) tall and weighs about 200 lb (91 kg). Obviously, there is quite a range above and below that, so to include the majority of adults you need to accommodate larger and smaller weights and sizes. For men, even if you exclude the heaviest 10%, you still need to go up to 256 lb (116 kg or so), so about 120 kg ready to fly. Add in fuel and the rest and you are quickly approaching 150 kg.

    TiPi, I was trying to find numbers for similar engines and the SD-1 130 kg empty weight was taken from this magazine flight test review: https://www.pilotweb.aero/features/flight-tests/flight-test-spacek-sd-1-minisport-1-5350149
     
  8. Feb 14, 2020 #108

    TFF

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    A-65 turning 2500 rpm is about 136 ft lb of torque. A VW making 65 at 3600 is about 95 ft lb of torque. That’s a pretty good difference. I think it’s worth working backwards from the prop and what performance one wants. Pick the performance, pick the prop that should give it, then figure out engine with/without drive that can deliver. The other way around always ends up short with associated disappointment.
     
  9. Feb 14, 2020 #109

    poormansairforce

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    If the prop rpm is equal with a PSRU then its its exactly the same torque at the prop.
     
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  10. Feb 14, 2020 #110

    lr27

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    Himat: There was a time I could do 6 chinups but weighed 82 kilos. That was a long time ago.

    TFF: I think it's unnecessarily restrictive to pick the prop first. You might pick something that would be best for an A-65, but if you picked an engine and redrive with a choice of ratios, you might want more reduction and a larger prop for a slow plane or less reduction and a smaller prop for something light and fast. Unfortunately, we don't have infinite choices. If we had CVT redrives, THEN you could pick the prop first.

    PMAF: Minus any losses in the redrive.
     
  11. Feb 14, 2020 #111

    blane.c

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    I think it is like the jet engines that need to spool up to make power, there is a time lag. Same with smaller displacement and redrive, same hp when it gets there.
     
  12. Feb 14, 2020 #112

    lr27

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    If the smaller displacement engine has the same horsepower, than it should spin up the same prop almost as fast as a larger displacement, direct drive engine. The only difference would be the slight loss in the redrive. (I'm neglecting the mass of the moving parts in the engine, because I think the small engine would have an advantage.)
     
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  13. Feb 14, 2020 #113

    TiPi

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    no worries, this one has the larger fuel tank (35lt vs 28) and fitted with the rescue system (9kg). If you want to fly on 24hp, minimum weight is required eg no luxuries. There are a few SD-1 units flying with the 630cm3 B&S, roughly 24hp. Suitable for "UL pilots" only. One plane has racked up over 1,000h now. I'm pretty much the average bloke in weight, just a bit shorter :(
     
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  14. Feb 14, 2020 #114

    Vigilant1

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    Yep, the SD-1 looks to be a great fit for the desired specs in the original post. As a kit- built plane, it can't be finished as inexpensively as a from-plans design, but the kit prices seem reasonable and it does save a lot of scrounging.
     
  15. Feb 14, 2020 #115

    mullacharjak

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    2674as.jpg Mini straton D7/D8 would easily fly with the V twin engine.A conventional landing gear may be added.But the wing needs to be simplified like a kolb Ultrastar maybe.
     
    Last edited: Feb 14, 2020
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  16. Feb 14, 2020 #116

    blane.c

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    I liked the sound of geared engines, 2800rpm max engine 1260rpm propeller. It is the sound I object with smaller geared engines, it clouds my objectivity. I would expound but sensitivity issues regarding others … .
     
  17. Feb 14, 2020 #117

    Victor Bravo

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    SPEAKING of the Kolb series....

    Matthew I know tis wasn't nearly what you had originally imagined, but what if you put the V-twin on a Kolb 103 Firefly? It would likely not meet Part 103 any more, of course, the V-twin is heavier than the 2-strokes, but you said Part 103 wasn't a deal-breaker..

    BUT, they are shown to be able to fly reasonably well on low power, they're the "cleanest" of the ultralight airplanes.

    You'd have incredibly good folding wings and tail, Kolb's signature "secret sauce". It works really well.

    With a little attention paid to the aileron hinge system (use something other than Kolb's piano hinges), you would have a very good flying airplane that could store in the smallest space possible for a conventional configuration.

    (edit) Oratex and Tuffy bike wheels and a wood prop might get you back to 254 pounds.
     
    Last edited: Feb 14, 2020
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