The Fly Baby Engines Page


Harry's Engine Page is now at www.bowersflybaby.com/tech/fenton.htm

Contents

Opinions on Engine Selection:

  • Discussion:  Fly Baby Engine Selection
  • Additional Commentaries on Engine Selection:  The engine-selection question has triggered several responses and alternate opinions:
  • Links to Sites with Engine Specifications

  • Bomar Flying Service DownloadsThis is pretty neat...Bomar has PDF copies of  the manufacturers manuals for hundreds of engines, engine accessories, and other aviation-related items.  You can find the overhaul manuals for the little Continental engines, the magnetos, carburetors, etc....all for free!
  • Technical Help:

    Questions?  Email Ron Wanttaja .

    Engine Selection

    All right.  You really like the Fly Baby, but you aren't sure what you're going to use for an engine.

    Well, what are other folks using?  Here are the engine listings for the 317 Fly Babies listed in the January 2004 FAA registration database:

    (There were about 65 aircraft for which no powerplant was listed or the engine was listed as "Amateur/Experimental")

    So:  What does the list tell us?  That most folks are going for the Continental A65 or C85 engines, which is the powerplant Pete designed the airplane for.  This is a *real* indication of the path to the best results.

    What about an auto-engine conversion?  Well, the Fly Baby is a good pick for one, with its benign handling characteristics and hell-for-stout construction.  But building your own engine is a project at LEAST as complex as building the aircraft itself.  If you go with a Continental, all of your engine-installation problems have been solved...folks know what thickness of tubing is needed for an engine mount, and what's needed to cool the engine properly.  If you look at people who have converted auto engines, you'll find the engine and the propeller-speed reduction unit (PSRU) are pretty straightforward.  But the problems come in with rigging a radiator, generating electrical power, routing exhaust, etc.  Few alternative engines are as light as the Continental, either...which means your performance is going to suffer.

    My recommendations:

    If you don't have any engine mechanical experience:

    If you don't have any engine mechanical experience (rebuilding your car engines, for example), go with the stock Continental engine, or at least an engine designed for small aircraft.

    The best pick would be an O-200 with no starter or generator (to save weight).  This will probably give you the best performance.  Alternately, go with the C85.  If cost is an issue, look into the A-65s, like Drew Fidoe mentions.

    Despite it being rated as 65 HP, the Lycoming O-145 seems a bit anemic for Fly Babies (See Harry Fenton's write-up.as to why this "65 HP engine isn't as effective as the 65 HP A-65).  The O-290 is a bit too heavy, but the O-235 is just right.  It's about the same weight as an O-200, and has been used successfully in Fly Babies.  See Rennate Reeve's airplane.

    Franklin engines are mentioned on occasion, but to quote Harry Fenton:   "The Franklin company went bankrupt 50 years ago and no parts have been made since, and aggravating this problem is that there are very few people left who know how to work on them.  Valves and bearings are in short supply, but I'm sure that substitutes could be cobbled up for experimental use.  Don't even ask about gasket sets!"

    The Walter Mikron would be a neat option, but you'll have to develop engine mounts, cowlings, cooling, etc. basically from scratch. A Continental or Lycoming installation can duplicate the configuration in a Piper or similar aircraft, where you're on your own with a Mikron.  See Harry Fenton's comments on this engine.

    Harry's positive on the Jabiru engine, although he would recommend the 120 HP version for the Fly Baby.  See his comments.

    The Rotax 912 would be a very good option, although pricey.  The Light Sport Aircraft program will probably bring the prices of these engines down a bit, and, especially, good used ones should become available.

    The Rotec Radial is a bit heavy for a single-seat Fly Baby, though if the structure is upgraded a bit, like the Hevle Tandem, it'll probably be fine.  But the Rotec is expensive, too.

    If you know engines

    If you have past engine experience, then go with an auto conversion, if you like.  I get a lot of questions about the Corvair...the Pietenpol folks have had good experiences with them, so they should be fine in Fly Babies.

    Most other engine conversions are going to require a propeller speed reduction unit (PSRU).  Slow, draggy airplanes like the Fly Baby want big, slow-turning props, and if you run engines like the Subaru, you'll need to get the prop speed down.  Personally, I'd buy a commercial conversion package that comes with a proven PSRU.

    Volkswagens are out.  They're not powerful enough.

    The final arbiter:  your own goals

    If your goal is to have a good, reliable airplane that you can fly every weekend, go with a Continental.  If you like engines, a Fly Baby would be a good airplane to experiment with. But it *will* be a true experimental... you're likely to have a few bugs to work out.  And bugs with powerplants often result in aircraft damage.

    Other Opinions on Engine Selection

    Drew Fidoe:

    I personally think that the A-65 engine is an excellent choice for this airplane.  My airframe weighed in empty at a relatively heavy 760 lbs empty and it still performed well even when based at our local grass airstrip.

    The A-65 is less popular due to lack of starter/generator and horespoweritus, as a result the A-65 is less expensive to purchase and probably more readily available than a C series engine and parts are reasonably priced too.  Compare the acquisition cost of a good, mid-time A-65 and compare it to a Rotax or completed and flying auto conversion!

    Due to the 20 less horsepower than the C-85, I believe that prop selection is more important with the A-65, but my last A-65 had great take-off thrust with a Sensenich wood 76-CK-44 as well as a reasonable cruise.  I wish I hadn't sold my last A-65 :'(

    Harry Fenton

    {Re:  The Walter Mikron/LOM engines)

    The LOM factory is in a bit of disarray right now.  The importer out of Canada has been working to sell the engine for a number of years, but has lost some momentum over the past few years.

    In general, though, the Walter Mikron is not a bad engine, but a bit pokey for 75 hp.  It suffers the same problem as the supposed 65/75 hp Lycoming- it just doesn't have the same torque as the venerable A65.  The engine is a jewel, though, very well built, fun to look at and sounds great.  The bigger LOM engines are simply too heavy for the Fly Baby.  I have a LOM M337 in hand for a 1930's racer replica that I'm building, so I've got some first hand experience. The published weight is appealing, until you consider that it is a 24 volt dry sump engine with no prop flange.  If the 24 volt electrical system is retained, the battery will be significantly heavier than a 12 volt.  I am converting mine to 12 volt, but it is a lot of work. The engine conversion alone has added 18 months (or more) of building to my racer project.  The LOM is also a dry sump engine which requires the complexity and weight of an external oil tank, lines, cooler, etc.  The CG moment of the engine is longer due to the in-line design, also, which would wreak havoc on weight and balance issues.

    The support for the LOM engines has been contentious.  My experience has been commensurate to any project I have worked on out of Eastern Europe- fragmented, inconsistent, and wrought with politics.  My LOM engine project has tried my patience many times.  I did find a good source of support in the form of Pavel Novak from Canada.  Pavel is a Czech native and has worked on LOM engines most of his adult life.  Another ace in the hole is that my wife and her family are Czech, so I am able to rally direct support from the "olt country".

    In summary, the Mikron/Lom engines are not bad, but are kind of orphans in the industry, so be cautious.

    On another engine note, I'm fairly positive on the 120 hp, six cylinder Jabiru.  The 80 hp four is simply too small for the Fly Baby, but the six is not too bad for the claimed weight to power.  To be honest, the 120 is probably an 80-90 hp engine by the time it is fitted with a prop big enough to pull a Fly Baby.  The Jabirus make power at high rpm, like the VW, which requires small diameter props.  The small props are ok for a Sonex, but the size of the Fly Baby dictates a larger diameter prop.  A Sonex builder at my airport has had some pretty good success with the 6 cyl Jab and it sounds like a little Merlin!  Cooling is a touchy issue and cost is the biggest problem.  The six cyl will blow a 10 grand hole in your wallet.  You can buy a lot of A65 or 0200 stuff for 10 grand.

    Overall, the O200 is the best all around 100 hp powerplant when considering cost versus complexity.  $5-7K (or less) will get you a reliable O200 all day long.  The A65 can be purchased for less, but the overhaul costs will wind up the same if not more.  The only negative cost wise to the A65 is that most of the parts are 50-60 years old.  The O200 is a newer engine in current production and good quality parts are plentiful.  The A65 is a great engine, it just sometimes requires more scrounging and tinkering than an O200.

    Harry on Installing an O-235 Lycoming

    The starter for the Lycoming engine has a nose the extends forward and hits the nose bowl.  The common fix is to simply drill a hole in the nose bowl to clear the starter nose.  The hole can be left open or a domed cover fitted. All of the early Pipers that use starters have this feature, most typically just a hole in the nose bowl.

    Be aware that if your mags are not impulse coupled or set up with an ignition vibrator or SlickSTART the engine will kickback on the starter and probably break the Bendix on the starter.  The mag timing is set for 20 degrees advance of TDC, and the impulse coupling or starting vibrator will delay the spark to about TDC and prevent kickback.


    Harry on the Corvair

    I've been planning to make a post about engines that I looked at during Sun n Fun, but I've been so busy, I haven't had the time.  It's a nice, rainy Memorial day weekend, so now I have the time!

    Bill Wynne has put together a nice conversion of the Corvair and his knowledge, parts support, manuals and web page are really good.  Bill and his team are enthusiastic and well spoken about what they sell, which I feel is very important.  No over zealous wild performance claims, but a general, positive confidence about his products.  The Corvair has generally been around for a while, so I like the fact that there is a calendar history to the engine and some design and operational perspective to draw from.  Parts supply seems to be no problem and the cost of the conversion seems reasonable for the horsepower of the engine.

    I really like the look of his conversions.  They are very clean, simple and, well, look more like aircraft engines than clumsy auto engine conversions.  There was a Zenith 601 on the flight line with the cowling off all week and it really looked good!  There is some extra plumbing and wiring with the Corvair, but nothing complex.

    The prop used for the Zenith appeared to be a pretty decent club, not the toothpick typically used with VW and Jabiru engines.  Therein lies the Achilles heel of most alternative engines- they may be able to produce a theoretical horsepower appropriate to the Fly Baby, but can't produce enough torque to swing the size of prop required for the Fly Baby.  I think that Wynne claims higher numbers, but my eyeball estimate is that the Corvair would probably provide the effective thrust of an 80/85 hp engine by the time a prop big enough to haul around a Fly Baby is installed.  Keep in mind that most Fly Babys are using 69"-72" diameter props and the Corvairs seem to run about 59"-66" props.  Yes, part of the diameter issue is related to the difference in rpm- a low 2150-2450 rpm for the Continental and a high 2650-3000 for the Corvair.  The loss of propulsive disc area is a consideration.

    However, I really like the potential of the Corvair and Wynne's support and packaging looks reasonable.  I haven't flown behind one, yet, but I have seen a Pietenpol at Brodhead, WI flying with a Corvair.  The Piet performed well and the engine sounded good- kind of up-pitch like a giant chainsaw engine, but not as high rpm.

    I think that the Corvair is a good alternative, but success will be determined by the airframe choice.  Frontal area and airframe thrust requirements are the key components.  Low drag airframes yield better results on low thrust/hp.  Additionally, high drag airframes may work well due to low weight and airfoil characteristics.  The Piet is a slower, more docile airplane than the Fly Baby and is more tolerant to varying degrees of engine thrust.  The KRs are light with small frontal area at the cowling and work well with the Corvair.  The Zenith is also a good choice in that it is clean, with a fairly thick, high lift airfoil.  The Fly Baby is a relatively big, heavy, draggy airplane compared to the Piets, KRs and Zenair.  But the Corvair falls into a reasonable set of compromises and would probably work out ok for the Fly Baby.

    I have to admit- I'd like to build one!  The package sure is interesting and just looks like a fun engine.  I have a an antique Salvay-Stark Skyhopper homebuilt in the corner of the hangar that would be a perfect subject for such an experiment.  Hmmmm......

    Harry


    Harry Fenton on Hard-Starting Lycomings

    Originally, one of the folks on the Fly Baby mailing list mentioned his wife's Lycoming O-235-powered Fly Baby was hard to start (hand-propping) and asked about adding a second impulse mag.  Harry didn't have the exact engine model to start with, so discussed the issue generically.  Eventually, he did discover the model, and provided more detail:

    > Renate is very small and she can now move the plane on her own- Now all we
    > have to do is find a way for her to swing the prop on her own. She cant start it
    > I always have to swing the prop- We are looking in to fitting a 2nd impulse
    > coupling on the O235 to make starting easier

    [Harry's first response:]

    Adding the second impulse mag is simply, but will cost money- big surprise.

    All Lycoming engines fitted with a single impulse are approved via the Type Certificate to be fitted with a second impulse magneto.  Here's how it works:

    Back to the O-235- which model do you have?  The O-235-L2C is a notorious hard starter and needs some changes to the lag angle and priming system to get it to start right.   Interestingly, if this engine is used in a Cessna 152 with a 24 volt direct drive starter, it requires mags with 5 degree lag angles.  This seems contrary in that the mags will fire about 15 degrees before TDC, allowing for the potential for kickback.  The problem is that the high speed starter spins the engine so fast that the coupling does not release at the correct point dynamically.  For example, a 20 degree lag angle mag will unlatch at about 10 degrees after TDC when used with a 24 volt, fast turning starter.  The 5 degree mag will unlatch at about 20 degrees when being spun fast.

    But, here's the catch:  if the engine is being turn slowly, such as during hand propping, the 5 degree magneto is sure to result in kickback and possibly broken knuckles.  This was a huge problem initially with the Rutan Long Eze design.  The O-235 was the preferred engine and for performance and weight savings most builders left off the starter.  But, the stock 5 degree mag kicked back during hand propping.  Adding to the problem was the fact that the Eze was typically fitted with a short, lightweight prop that offered no inertia to pull the crankshaft over TDC.

    I'm going to guess that you either have an O-235-L2C or an O-235-C series.  Both engines, while similar in designation, are significantly different. The -L2C, due to compression ratio, is approved to run only 100 octane whereas the -C series is approved to run on 80 octane and can run on mogas.

    Within the -L2C series there are quite a number of variations of magneto, ignition harness routing, primer installation, and carburetor types.  The -L2C was used in Piper, Cessna, and Beech airframes and each had their own idea on configuration and cost reduction.  Compounding the problem is the fact that Lycoming really struggled to improve hard starting issues and lead fouling problems during the initial years of production and implemented a dozen or so "fixes".  As a result, the configuration differed even within the subsets of variation.

    The priming system varied on the O-235-L2C depending upon the airframe in which is was installed.  Some were set up to prime only one cylinder and others were set up to prime four.  There are also a couple of versions where one airframer spec'd out an accelerator pump carb and one did not.

    Ultimately, the best set up for the -L2C engine (or any engine) is two impulse mags, four point primer, and carb with an accelerator pump.  If a starter is used, a geared starter to reduce starter rpm is best.  If the starter spins too fast, the coupling disengages and the engine becomes hard to start.  In many cases, high torque starters are kind of self defeating thanks to the impulse coupling disengagement speed.

    Considering kickback and hard starting, there could be several causes. First, as previously described, the lag angle of the impulse coupling should be close to the number of degrees of engine advance, e.g., if the engine advance is 25 degrees, the lag of the coupling should be 25 degrees.

    When starting, the non-impulse mag should be grounded as it can potentially generate a spark hot enough to start the engine.  The non-impulse mag is timed to fire at engine advance, so first spark delivered wins the starting game.

    Ensure that the p-leads, or the ignition switch wires, are not reversed. This condition happens all of the time and usually after an engine has been removed and reinstalled at overhaul.  The left magneto is usually the impulse coupled magneto and the right non-impulsed and, if the p-leads get reversed, the right becomes hot during start and the left is grounded.  The net result will be kickback and hard starting.

    Another potential problem may be that your engine is an O-235-C1 or C1B.  In their original configuration, both magnetos on these engine models are non-impulsed and will be tough to start by hand propping.

    Harry

    > Thank you for this input--We will check on what O235 we have- and YES our motor
    > kicks back like a Mule Will all the expense and effort be worth while to fit the extra
    >  impulse coupling ?i.e. Will it start better or would we be better off fitting a starter
    > alternator bat. etc ?

    [Harry's Response:]

    I would not put a starter on the engine unless it is for convenience.  With the correct magnetos, the engine should start well, even with one impulse. However, the Slick K4525-40 kit would be a good start.  This is a complete ignition kit with two Slick impulse mags, harness, shielded plugs and the extra gasket, spacers and studs required.  The only additional part to purchase would be the Lycoming 61665 drive gear.  Unfortunately, this gear is expensive and runs anywhere from $250 used to nearly $500 new.  The kit will run about $1100, maybe less, via the usual US discount sources.  Ouch!

    Your best bet would be to be sure that the engine is being started on the impulse mag only when being hand swung.  Also, it would be worthwhile to have the impulse mag inspected to make sure that it is top form.  That will have to be the subject of another e-mail!

    Anyway, if you give me the engine model and mage models, I can help you further.

    Harry

    (A Day or So Later)

    >According to the log books its a 0-235-CIB

    It looks like your engine is an O-235-C1B as removed from a Piper Colt .  As delivered from the factory, this engine was configured with two, non-impulse mags.  The left mag was originally a retard breaker magneto which used two sets of points, one for starting, one for running.  The start set of points acted as a switch for a device called a starting vibrator.  The vibrator is powered by the aircraft electrical system and energized by a special ignition switch.

    However, the starting vibrator system often proved to be troublesome and it was not unusual to convert from the retard breaker system to an impulse magneto.

    Sooo, more detective work on your end is required.  It is relatively easy to determine if an impulse mag is installed.  When the prop is pulled through, there should be an audible click or snap as the impulse coupling unlatches. If you turn the prop through and hear no snap, then you probably have non-impulse mags.  To visually confirm the type of mags, check where the two mags mount to the accessory case.  An impulse mag will have a 1" spacer between the mag and the accessory case.  The spacer will be absent on non-impulse mags.

    If you have one impulse mag installed, we can probably sort out the starting problem- the mag may need maintenance or the switch wiring is wrong.  If non-impulse, direct drive, retard breaker mags are installed, the solution is not so easy.  You will either need to rig up a starting booster or install an impulse mag.

    Harry


    Differences Between A-Series Continental Engines

    Compression Ratios, Horsepower and RPM:

    Engine
    Power
     @ RPM
    Compression Ratio
    A-50
    50 HP
    1,900 RPM
    5.4 : 1
    A-65
    65 HP
    2,300 RPM
    6.3 : 1
    A-75
    75 HP
    2,600 RPM
    6.3 : 1
    A-80
    80 HP
    2,700 RPM
    7.55 : 1

    Modifications made to A-65 for power upgrade:

    References:
    1. Engines for Homebuilt Aircraft & Ultralights, by Joe Christy
    2. Continental A-65/A-75 manual
    3. Fresno Airparts advert (Trade-A-Plane)
    Courtesy of Drew Fidoe

    Continental C-Series Dash Numbers

    From the Continental A&C Series Parts Interchangeability Catalog.

    C85 and C90 engines are designated as C85-8, C85-12, C90-8F, C90-8FJ, etc. These various "dash" numbers and letters indicate the following:

    -8:     No provision for starter and generator
    -12:   Provision for starter and generator
    -14:   Provision for starter and generator, and "Lord" engine  mounts (late Cessna l40 only)
    F:      Flange crankshaft
    J:      Fuel injector
    Example:    C90-12FJ indicates a 90 horsepower engine with starter and generator, flange crankshaft, and fuel injector.

    C85 and C90 -8 and -12 engines have different accessory sections, different rotation of tachometer drive, and the magnetos are NOT interchangeable. You cannot convert a -8 engine to a -12 engine in the field, or vice versa.

    The C145-2 engine is the "common" 145 horsepower Continental engine.  The C145-2H engine has provisions for a hydraulic propeller control. (See the Catalog for difference in front main bearings).


    Continental A-Series Dash Numbers

    Engine Series
    Dash
    No.
    Ignition
    Exhaust 
    Direction
    Oil Sump 
    Type
    Starter
    A50
    -1
    Single
    Up
    Dry
     
     
    -2
    Dual
    Up
    Dry
    Yes
     
    -3
    Dual
    Up
    Dry
     
     
    -4
    Single
    Down
    Wet
     
     
    -5
    Dual
    Down
    Wet
     
     
    -6
    Dual
    Down
    Wet
    Yes
     
    -7
    Single
    Down
    Wet
     
     
    -8
    Dual
    Down
    Wet
     
     
    -9
    Dual
    Down
    Wet
    Yes
    A65
    -1
    Single
    Up
    Wet
     
     
    -3
    Dual
    Up
    Wet
     
     
    -6
    Dual
    Up
    Wet
    Yes
     
    -7
    Single
    Down
    Wet
     
     
    -8
    Dual
    Down
    Wet
     
     
    -9
    Dual
    Down
    Wet
    Yes
    A75
    -3
    Dual
    Up
    Wet
     
     
    -6
    Dual
    Up
    Wet
    Yes
     
    -8
    Dual
    Down
    Wet
     
     
    -9
    Dual
    Down
    Wet
    Yes
    A80
    -3
    Dual
    Up
    Wet
     
     
    -6
    Dual
    Up
    Wet
    Yes
     
    -8
    Dual
    Down
    Wet
     
     
    -9
    Dual
    Down
    Wet
    Yes

    Letters after the Dash Number indicate other characteristics, such as "F" for a flanged crankshaft, "J" for fuel injection, and "H" for being set up to take a variable-pitch propeller.  If an engine has been modified, it also gets "C" as a suffix.
     
     


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