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Thread: Statistical Analysis of Homebuilt Aircraft Engines

  1. #1
    rwanttaja's Avatar
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    Statistical Analysis of Homebuilt Aircraft Engines

    I did an analysis of the FAA registration database to develop some statistics on what kind of engines are installed in homebuilts. Here's an overall summary:

    About 4000 homebuilts in the registry are listed as having "AMA/EXP" engines. As part of this analysis, compared the "AMA/EXP" engine aircraft with the NTSB accident database, which almost always includes the engine type. I found about 550 of the AMA/EXP aircraft in the accident database, and from them, extrapolated the percentage of AMA/EXP aircraft that have specific aircraft engines. I used those percentages to add the appropriate number of engines to each of the main analysis engine categories.

    This aspect isn't precise... it produced slightly more aircraft with Rotorway engines than there are Rotorway helicopters registered... but I think proportionately, the numbers are pretty good.

    Ron Wanttaja

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    Here's a more detailed breakdown by specific engine types.

    The first column is the engine, the second is how many homebuilts are registered with that engine type.

    The third column is the result of my comparison of the FAA "AMA/EXP" engine registries to the NTSB accident database. About 550 of the ~4,000 "AMA/EXP" aircraft matched. The third column is how many "Hits" I got for that engine type.

    The "Calculated from AMA Set" is an estimate of the total number of AMA/EXP aircraft that are that engine type. if 55 of my "hits" are a given engine type, I assumed that 10% of the AMA/EXP engines are that type (55 out of 550). So the "Calculated" value in Column 3 would be 10% x 4000. I then add the actual number registered (Column 2) to the number calculated (Column 4) to come up with an estimated total.

    Mind you, the results in Column two are really the only reliable data. The rest is based on my projections. Note that there ARE no aircraft powered by Chevrolet liquid-cooled or KFM engines in the FAA database. These only came out when I cross-referenced the AMA/EXP engines to the NTSB accident database.

    Engine
    Registry
    In AMA Compare Set
    Calculated from AMA Set
    Total
    Aerosport
    221
    4
    29
    250
    AeroVee
    90
    6
    43
    133
    Ama/EXP
    263
    7
    0
    263
    Cam 100
    2
    2
    14
    16
    Chevrolet Liquid-Cooled
    0
    21
    153
    153
    Continental
    2900
    34
    247
    3147
    Corvair
    40
    7
    51
    91
    Cubcrafters
    30
    1
    7
    37
    Cuyuna
    42
    2
    14
    56
    ECI
    18
    6
    43
    61
    Ford
    81
    6
    43
    124
    Franklin
    106
    9
    65
    171
    GM
    5
    10
    72
    77
    Great Plains
    12
    5
    36
    48
    HAPI
    5
    7
    51
    56
    Hirth
    76
    10
    72
    148
    HKS
    67
    2
    14
    81
    Honda
    19
    5
    36
    55
    Jabiru
    547
    23
    167
    714
    Kawasaki
    18
    0
    0
    18
    KFM
    0
    18
    131
    131
    LOM
    3
    3
    21
    24
    Lycoming
    11373
    80
    583
    11956
    Mattituck
    225
    3
    21
    246
    Mazda
    17
    10
    72
    89
    McCullough
    207
    3
    21
    228
    No Entry
    115
    0
    0
    115
    None
    476
    0
    0
    476
    NSI
    0
    5
    36
    36
    Oldsmobile
    1
    0
    0
    1
    Onan
    23
    3
    21
    44
    P&W Recip
    41
    0
    0
    41
    P&W Turbine
    91
    0
    0
    91
    Revmaster
    145
    2
    14
    159
    Rotax All
    4962
    14
    226
    5188
    Rotec
    10
    2
    14
    24
    Rotorway
    187
    43
    313
    500
    Solar
    12
    5
    36
    48
    Stratus
    0
    1
    7
    7
    Subaru
    525
    32
    233
    758
    Superior
    332
    6
    43
    375
    Suzuki
    11
    3
    21
    32
    Toyota
    0
    1
    7
    7
    UL Power
    28
    8
    58
    86
    Vendeneyev
    34
    7
    51
    85
    Viking
    39
    2
    14
    53
    VW
    562
    49
    357
    919
    Walther
    67
    10
    72
    139
    Warner
    28
    0
    0
    28
    Wright
    7
    0
    0
    7
    Yamaha
    14
    5
    36
    50
    Zenoah
    29
    1
    7
    36

    Ron Wanttaja
    Last edited by rwanttaja; 10-31-2016 at 12:54 AM.

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    I'm trying to wrap my head around the data, and I think I might be over-thinking it.

    Is this simply "what kind of engines are in homebuilts" and nothing more? Or with the inclusion of NTSB data is there some other data we can tease out?

    Btw, if NTSB data is used, there could be more aircraft with a special type of engine installed than registered. One would only have to, through misfortune, make the NTSB records twice with the same aircraft.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

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    Quote Originally Posted by Frank Giger View Post
    I'm trying to wrap my head around the data, and I think I might be over-thinking it.

    Is this simply "what kind of engines are in homebuilts" and nothing more? Or with the inclusion of NTSB data is there some other data we can tease out?
    Yes, this is basically trying to answer a question in another forum about how many auto-conversions are installed in homebuilts. It should be easy enough to extract from the FAA registration database. But about 4000 homebuilts have an entry that just says, "Amateur-Built/Experimental Engine."

    While the FAA database includes a lot of VW and Subaru engines (and a smaller number of Corvairs), it really lists few of the V6/V8 sorts of conversions that seem to get all the press. As you can see above, the January 2016 FAA database shows *no* aircraft powered by Chevrolet engines (other than Corvairs). Yet they can be found in the NTSB database, so the assumption is many of the liquid-cooled Chevy engines are actually listed with the generic AMA/EXP tag.

    But...how many of the 4000 are of each type? Are they all auto conversions? Or are folks registering their Continentals and Lycomings as AMA/EXP for their own reasons (such as their not coming up on an AD search....).

    So I took those 4000 and compared them to my NTSB accident database. The NTSB almost always lists the engine. So, for about 550 of those 4000, I found accident reports (I did have to be careful it wasn't another plane with the same N-Number). I worked out how many of the 550 were Lycomings, Continentals, etc. As you'll see above, while the FAA database shows no Chevy-powered homebuilts, there were 21 just in that 550-aircraft sample. So, obviously, the number of auto-engine homebuilts were being under-reported, and my analysis was an attempt to extract the true fleet sized.

    Quote Originally Posted by Frank Giger View Post
    Btw, if NTSB data is used, there could be more aircraft with a special type of engine installed than registered. One would only have to, through misfortune, make the NTSB records twice with the same aircraft.
    Oh, yes, found several of those. Some planes had more than one accident, with a different engine each time.

    Ron Wanttaja
    Last edited by rwanttaja; 10-31-2016 at 01:46 PM.

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    Here's a quick data point. My engine is a Superior XP-360. I just looked up my info on the FAA site. They have it listed as AMA/EXPR.

    I also looked up the Rotorway I owned. It shows as "unknown."
    Someday I'll come up with something profound to put here.

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    Quote Originally Posted by Frank Giger View Post
    Btw, if NTSB data is used, there could be more aircraft with a special type of engine installed than registered. One would only have to, through misfortune, make the NTSB records twice with the same aircraft.
    The other aspect of this is *how* airplanes end up in the NTSB database. If Engine AAA has low reliability, it'll have a disproportionate number of accidents. This may distort my prediction of total aircraft with that engine, producing a larger number of predicted planes with the AAA engine. I see my table's calculated number as more of a max.

    The best message, I think, is from the pie chart. Other than VWs and Subarus, the percent of the Homebuilt Fleet operating auto engines is really quite low. Even with a process that might be biased towards them.

    Ron Wanttaja

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    The statistical analyst of my past cringes at the sussing of engine reliability by type and incident/accident from the rather dubious databases available - though I know you've done it in the past.

    I'm actually not that surprised at what you dug out when I got to thinking about it.

    I've come to put homebuilts into two categories in my head - Light and Heavy.

    "Light" as in either within LSA criteria or very close to it. At those weights and wing areas, Rotax and VW are more than enough to do the job pretty well. My little Nieuport, for example, or a Pietenpol for another, are as much "flying machine" as airplane in the common way of thinking of it.

    That they make up just a third of what's out there also fits.

    "Heavy" as in "going places." RV's, KR2's, all the way up to twin engine JAG's, put little VW's out of the mix. What one needs is a robust engine that is preferably air-cooled, and no matter how much we try to come up with a good alternative, the Lycombings and Continentals fit the bill the best. Once one factors in all the modifications and possible complexities of converting a large automotive engine for aircraft use, we tend to default to the safest and surest route for power plants.

    I'm not saying the Corvair folks haven't dialed in that conversion - they have - but it's the exception, and it's a pretty tight community with the Corvair College being one of the coolest things going, but it's the exception rather than the rule.

    We all like to trump up our calls to innovation, but in the end 99% of us go with what has something of a proven track record.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

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    Quote Originally Posted by Frank Giger View Post
    The statistical analyst of my past cringes at the sussing of engine reliability by type and incident/accident from the rather dubious databases available - though I know you've done it in the past.
    I hears ya, bro. The data is crippled, no question, but it's the only information we've got to work on. This is why I spend a lot of time explaining my process, so folks understand how much assumptions and side-calculations are involved.

    I try...despite the flaws in the data...because either people ask outright questions, or make outrageous claims. "There are 1500 examples of this engine flying, of COURSE it's reliable!" somebody might say...but if the FAA database shows only three, and even my loosest approximations reveal only a dozen or so more, what does that mean?

    I'm actually kind of surprised at how few inroads the Chevy-Ford-GM etc. liquid-cooled engines have made, in homebuilt aviation. What's more, there's some about of roil. I looked in my 2007 aircraft registration database and found five examples of one given engine type. There were six examples using the same engine in my 2015 database... all but one were different aircraft.

    Quote Originally Posted by Frank Giger View Post
    I've come to put homebuilts into two categories in my head - Light and Heavy.

    "Light" as in either within LSA criteria or very close to it. At those weights and wing areas, Rotax and VW are more than enough to do the job pretty well. My little Nieuport, for example, or a Pietenpol for another, are as much "flying machine" as airplane in the common way of thinking of it.

    That they make up just a third of what's out there also fits.
    I think it's probably more, once you factor in all the Continental A65s through O-200s, and the Lyc O-235.

    My next analysis project, I guess. Retiring in a couple of months. Fortunately, I apparently already have a hobby.....

    Ron Wanttaja

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    Quote Originally Posted by rwanttaja View Post
    My next analysis project, I guess. Retiring in a couple of months. Fortunately, I apparently already have a hobby.....
    Congratulations on retirement Ron! If you get bored there is always airplane building......

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    Quote Originally Posted by martymayes View Post
    Congratulations on retirement Ron! If you get bored there is always airplane building......
    Currently contemplating the "Fly Baby Grande". Lengthened cockpit, widened fuselage, deeper instrument panel (current panel is too shallow to install most conventional electronics). A few other mods that have occurred to me, over the years.

    The thought is to build the fuselage, then transfer the engine, wings, tail, and gear from my current Fly Baby. Actually, transferring most of the engine...leaving behind the generator, so I don't have to install a transponder or ADS-B. I figure I can thus build a new airplane for less than ADS-B would cost.

    Other than that, I'll probably be writing quite a bit.

    Ron Wanttaja

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