Aircraft Engines for the
Bearhawk by Rod Smith
[Web "master's" note: due to the size of this document, I have chosen
not to follow my convention of putting other people's writing in
italics. Hopefully this will make it easier to read the whole thing (you
Bob Barrows designed the Bearhawk for a horsepower range of 150-260.
The original prototype uses a 4-cylinder Lycoming O-360 de-rated to
170HP for use of auto gas by installing low compression pistons. The 2nd
prototype, commonly referred to as Proto II uses a 6-cylinder Lycoming
O-540 rated at 260HP. Bob recommends a maximum engine weight of 400 lbs.
At that weight you will need to install the battery in the baggage area
for weight and balance. If you go with a slightly heavier engine than
that you will have to use a lightweight wood or composite propeller. I
am going to discuss engines suitable for use in the Bearhawk. I will
confine my discussion to certified aircraft engines due to my lack of
knowledge concerning auto engine conversions. I will provide some basic
information on Lycomings, Continentals and Franklins which might be
suitable for the Bearhawk. I will provide sources for you to do further
Bob has provided information in the newsletters on building engine
mounts for four or six cylinder Lycomings. Lycomings come in a
bewildering array of models. For the uninitiated, O stands for
horizontally opposed cylinders, an I in front of the O indicates it is
fuel injected, the number after the dash is the displacement in cubic
inches. The first letter after the displacement is the model. The
letters and numbers that follow describe carburetor or injector model,
type of magnetos, sump location, size of prop bolts etc.. The weights
listed for Lycomings are dry weights with carburetor or fuel injector,
magnetos, and starter, but no alternator. It is possible to pare the
weight of any engine with use of lightweight starters and alternators,
or even further if you don't mind hand propping and go without an
The smallest Lycoming suitable for the Bearhawk would be the O-320.
They are available in 150 and 160hp versions. The 150HP engines can use
autofuel. The O-320H has a somewhat checkered history and can
consequently be bought relatively cheap. With the proper care they seem
to work out okay.
The next family of engines is the O-360s. They are rated at 180HP and
require avgas. The IO-360s come in two versions. IO-360Bs are
essentially injected O-360s and rated at 180HP. The IO-360 As and Cs are
quite a different engine. They have what are known as angle valve
cylinder heads, versus parallel valve which all the previous engines
have. Other differences are a stronger crankshaft, piston cooling
nozzles, tongue and groove connecting rods, and a tuned induction system
and are rated at 200HP. Notice how much heavier they are.
The next larger Lycoming is the 6 cylinder O and IO-540s. I'm
purposely ignoring the old O-435 and GO-480 Lycomings as they are heavy
for the HP output and would be quite hard to get parts for. The O and
IO-540s are available in parallel and angle valve configurations. For
the Bearhawk you will want to avoid the angle valve 540s as they are all
rated above 260HP and are heavier than recommended. The O-540 Bs can use
auto fuel. Notice the large variation in weight between the different
||383 New Cessna Skylane engine
For further information on Lycoming engines, go to their website at
http://www.lycoming.textron.com/. Under support, there are
many helpful articles and maintenance publications available. You can
also call them at 570-327-7278 and request the Data Pak from them. That
is where I got most of the above engine information. A complete,
detailed description of all models of Lycoming engines and a complete
guide to the nomenclature is available at
This website contains a wealth of information on both Continentals and
Lycomings, including list prices for new, factory remanufactured and
factory overhauled engines.
Only 6 cylinder Continentals are available in the correct HP range
for the Bearhawk. The model designation is similar to Lycomings.
Continental engines have mounting pads on the bottom of the engine
instead of the rear and require a bed type engine mount. You might want
to obtain a Cessna 180 engine mount to modify if installing an O-470 in
The O-300 Continental just misses the low end of the HP range at
145HP. If you have one laying around it might be a suitable engine. Can
use auto gas.
||249 dry weight, approx. 300 with accessories
The next larger size Continental is the IO-360. There are 13
turbocharged models of this engine available. For brevity I've listed
the specs for just one of them.
||327 dry weight, no accessories *Takeoff rating 210 HP @2800 rpm
||331 dry weight, no accessories
||305 dry weight, approx 370 with accessories
||301 dry weight, approx 355 with accessories
This the largest Continental engine you will want to use in the
Bearhawk. The IO-520s are too heavy and rated in the 285-300 HP range.
Can use auto fuel in the O-470-J,K,L,R,S and the IO-470-K. There is a
large variation in weight between different models. Most models of the
O,IO-470s are heavier than what Bob recommends. I've only listed those
models with a maximum weight with accessories of 425lbs.
||354 dry weight, approx 400 with accessories
||385 dry weight, approx 425 with accessories
||389 dry weight, approx 425 with accessories
||370 dry weight, approx 415 with accessories
I acquired all of the above information from Continental's website
http://www.tcmlink.com/. Look for engine spec. sheets under
products and services. You can also find operational and maintenance
information at this website.
Franklin was a Syracuse, NY engine manufacturer that went bankrupt in
the 1960s. Franklin engines were found in Stinson's and early Maules
among others. In 1975 the rights to the engine design were sold to PZL,
a Polish company. For years it was very difficult to get parts for the
engine. With the thawing of the cold war parts for the engines became
available again. Since 1993 the engines have been imported to the US by
PZL. They are an FAA certified aircraft engine. I have no personal
experience with Franklins. They seem to elicit strong opinions either
for or against them by those who have flown behind them or worked on
them. A local engine rebuilder and good friend will not allow a Franklin
in his shop. Maule Aircraft is currently working on certifying an M7
with the Franklin engine. What makes this engine attractive is its low
price new, compared to Lycomings and Continentals. One major
disadvantage is the very limited number of CS props available for this
engine. The only Franklin engine with enough HP for the Bearhawk is a 6
cylinder model with 1500 hour TBO. There is an older 165HP Franklin but
I do not have any information on it. Like the Continentals the Franklins
require a bed type engine mount.
||297 dry weight, no accessories
A Colorado distributor of this engine has a
Acquiring an Engine for your Bearhawk
Warning: Lots of personal opinions follow
Lets face it. Like most homebuilders, most of us aren't going to be
installing a brand new engine in our Bearhawks. Other options are
factory remanufactured, overhauled, or just plain used engines. I am
going to suggest that a new or just overhauled engine may not be the
best choice for your Bearhawk or any new homebuilt. A new or freshly
overhauled engine requires a break-in period. Most break-in procedures
recommend starting the engine and limiting time on the ground to the
minimum required to ensure it is operating properly and there are no oil
leaks. A takeoff at full power is followed by maintaining 70-75 percent
power until the rings seat in the cylinder walls, a process that may
take up to 25 hours. Consequences of not breaking-in the engine properly
are that it will burn oil, have abnormally high cylinder head
temperatures and not develop full power. The break-in procedure is
especially critical if chromed cylinders are used. Does this sound like
the way you want to test fly your new homebuilt?
Looking at used engines, first-run (never overhauled) engines are
more valuable and you will pay more for them. You will pay more for low
time of course. There are several strategies you can employ. You can try
to find a low time engine which will hopefully give you years of service
before an overhaul or look for a high time engine which will get you
through the flight test period and plan on overhauling it soon. When
buying a high time engine make sure you know the overhaul price for that
model of engine and calculate that into your offer.
Start looking for your engine about a year before you think you will
be ready to install it. That ought to give you enough time to find that
really great deal. It would be great to find one nearby so check around
your local airports. Trade-A-Plane is a great source for engines if you
cant find one locally. $15 gets you a year of net access plus one mailed
copy a month. You can subscribe at
http://www.trade-a-plane.com/. Just remember you are making a
huge investment. Whether buying the engine locally or over the phone, do
everything you can to ensure you are getting what you think you are.
Used six cylinder Lycomings are more available and no more expensive
than four cylinder Lycomings. The Continentals also may be easier to
find used as they are not used extensively in kitplanes. According to
Bob Barrows, one of the advantages of the 6 cylinder Lycoming is that it
runs much smoother at low power settings (1800rpm, 18" manifold
pressure) than the 4 cylinder. As far as how much HP to install in the
Bearhawk within Bob's recommended range, that is going to have to be a
strictly personal decision for each builder. I think lots of HP is
great, but so is low weight. The extra HP will not buy you much in extra
speed but it will significantly increase climb rate and shorten takeoff
distance. I can testify that the Bearhawk with 170HP installed is no
slouch in the takeoff and climb department, thanks to a lightweight
Two suggestions: if you plan on flying on floats, go with one of the
bigger engines, if you want say 235HP, try to find one of the lightest
235HP engine models available. You can see from the above tables that
there can be big weight variations in the same engine family. The
ability to burn auto fuel may be an important factor for you. Personally
I'm a big fan of 6 cylinder Lycomings. Probably comes from spending over
500 hours behind an O-540 over some of the roughest country in North
America. In that time it never skipped a beat and never required more
than oil changes, spark plug cleaning and an occasional adjustment to
the magneto timing. They are a very smooth running engine. On the other
hand a good friend flies a Stinson with an O-470 Continental and he has
had just as good luck with it and wouldn't think of parting with it. If
you don't have any experience with a particular engine model you are
interested in I would suggest talking to as many pilots as you can who
fly behind one. Try to get a flight with one of them. Ask lots of
Shop carefully and happy hunting!
Rod Smith Bearhawk plans #246
Back to FAQ's
Lycoming Vs. Continental?
On January 18, 2000 Kevin Deutscher wrote:
Both Lycoming and Continental engines are beautiful works of art and
excellent choices for an aircraft power plant. ( That should light up
the e-mail )
I spent a number of years, a number of years ago employed by a major
west coast rebuilder ( still in business and doing well ). My function
was cylinders, cylinders and more cylinders, and some assembly.
Although I will not take the resident expert position at the moment
and will make further comments at a later date the following can be
Budd; your engines last a long time because you fly them often and
maintain them. Your replacement engines are quality and old worn out
parts are replaced. You are a shining example, keep up the good work.
Continentals: Cylinders crack, barrels crack, sparkplug holes crack,
exhaust port at valve guides crack. Cranks crack and counterweights come
apart. Light cases crack. Starters can be a nightmare.
Lycomings: Eat up exhaust valves, piston pin plugs come apart, valve
lifters are horrid, camshafts are the luck of the draw, rocker arm
support bosses crack thru fall off, cases leak like a British car.
Pushrods bend. Oh and then there are the light flange cranks and light
cylinders. Klinkers can turn off all the fire in the cylinders quick.
I have seen both makes of engines go to TBO spotless, and others not
make it half way with a Top Overhaul to help.......Why........ the
OPERATOR and MAINTENANCE. (oops! I did not mean to yell so loud )
My Bearhawk will have 6 cylinders. ( All New Cylinders)
Continental 520 470 ( O or IO ), or IO 360
Lycoming 540 ( O or IO )
PS. Does Editorial Time Count As Building Time?
Back to FAQ's
Certified Engines for Experimental Use
>If I was to rebuild a certified high time Lycoming for an
>(I'm specifically thinking of an O-540) and wanted to do a real
>good/reliable job of it about how much *less* would it be than if it
>were being rebuilt for a certified plane (ignoring labor or the cost
>of having the rebuild signed off by an A&P)?
>Or IOW are there *non-certified* parts out there for rebuilding
>engines that are less expensive (by enough margin to make it feasible)
>than certified parts?
My thoughts on rebuilding your own engine are unless you have someone
who is well-versed to help you through it locally, I'd go ahead and send
my core to Bob Barrows and let him do it. That's assuming that you're at
least located on the continent of North America.
Yellow tagged parts are normally okay if you know the source VERY
well. One man's junk is another man's treasure, one man's junk MAY BE
another man's yellow tag. You can't "eyeball" a critical engine part.
Aluminum parts such as pistons, cases, etc. need to be inspected with
Zyglo (dye), ferrous parts like the rods, crankshaft, and camshaft need
to be inspected with magnaflux. Parts also need to be checked to ensure
they are within dimensional tolerances, so you'll need a good set of
ten-thousands micrometers, a granite surface block, a few dial
indicators, depth gauges, v-blocks, etc. Unless you have an inspection
shop laying around (or have ready access to one, along with someone who
knows how to use all that stuff), I'd say you're better off buying parts
from a good outfit who has done all of that. Even then, I'd verify
everything I stuck into my engine even IF I purchased from a reputable
shop. "Monday" parts do exist. Even the best mechanics and techs can
have a bad day in the shop and miss a step.
Twenty years ago I did a complete rebuild on an O540, and even earned
my A&P ticket doing it. The thing held oil pressure, had great
compression, and purred like a kitten. Would I do it again unsupervised?
No way, even though the FAA say's I have a card in my wallet with a "P"
on it. My "A" is a lot stronger than my "P", and I tend to think the
engine is sort of a critical flight component. That's not to say I
wouldn't rebuild my own engine today, but ONLY if I had someone locally
with gobs of CURRENT experience. I may be coming off as a bit extreme,
or overly cautious. Perhaps I am. Of course, your engine is
"experimental", but when it comes to keeping the prop turning, that's
one "experiment" you want to succeed. Since my last rebuild in 1980
there have been some ADs on the O-540 that I probably don't know about.
Sure, some ADs seem frivolous, but by and large they exist for a very
To sum it up. If you want to do your own OH, that's fine. Go for it,
but do so as long as you have a good mentor who can help you through it.
For your parts, know the source, and take all necessary precautions
before putting something in your engine. There are bad new parts out
there, and bad yellow tagged parts as well. The part doesn't know
whether it's going into a certified engine or not. Each part is an
individual, and has to stand on its own merit, regardless of what others
say its integrity is. As mechanics, we have the ultimate responsibility
to make sure that every part that goes in is one that we would be
comfortable flying behind 500 hours from now.
Planter "Preaching to the Choir" Bob
Back to FAQ's
How much power do you
Float-By Shooter wrote:
> I have yet to decide what level of power I will be happy with.
> Obviously more is better,
On April 2, 1998 Russ Erb wrote in response:
I disagree--more is not always better. Here's what you need to
More power will get you a shorter takeoff, faster rate of climb, and
a faster cruise/top speed. While the difference in takeoff and rate of
climb will be noticeable (those of you who NEED STOL take note), adding
power just to get more speed in usually a losing proposition. While your
thrust will go up with an increase in power, remember drag goes up with
the SQUARE of the airspeed. The end result is that it takes a lot of
extra power to get a little bit more airspeed.
What's worse is the whole fuel economy issue. I found when I did a
similar study on another airplane a few years ago, that the fuel
consumption increases faster than the speed does. Hence, assuming you
would fly at, say, 75% power of whatever engine you had, as your engine
size increased, your range would DECREASE! Doesn't do a lot of good to
have a 180 knot Bearhawk that has to land every hour because you're out
As I've said before, design is mission driven. Decide what you're
going to do with the airplane, and get the minimum size engine that will
acceptably accomplish that mission. If you'll always fly off of paved
runways with less than a full load and aren't in a super hurry, then a
150 HP may be okay for you. If you're one of our guys in Alaska who plan
to throw a dead moose in the back and then take off of some short lake,
then you'll probably want the 260 HP engine and just suck up the loss of
fuel economy and range.
Personally, right now I'm planning on using a 220 HP Franklin because
I expect to one day fly off of 660 ft and 970 ft grass strips in my back
yard. I need the STOL performance. On the other hand, pulling the
throttle back from 75% to 55% drops fuel flow down from about 13 gal/hr
to 9 gal/hr (I think) with a loss of about 10 knots true airspeed. I can
probably live with that.
Back to FAQ's
Is it even
possible to have Too Much Power?
On December 20, 1999 Budd Davisson wrote:
Re: thirsty engines
Like so many others, I've often wondered how much effect cubic inches
has on an airplane when it's in level cruise. I found out when I had the
opportunity to do a back to back evaluation of the Pitts S2A with the
IO-360 and the S2B with the IO-540. Identical airframes with the only
difference being the B has a pressure cowl and the A doesn't. I was
always curious why there was such a huge difference between the two. The
B cruises at 175 mph and the A at 135 mph and the rates of climb are
1800 and 2600 fpm respectively.
The B had a Shadin fuel totalizer so I could tell exactly wht it was
burning. I decided (possibly erroneously) that if I brought the power on
the B back to where it was burning the same amount of fuel as the A in
the same situation, about 10 gph, it should be putting out about the
same horsepower. When I did that, the cruise came down to 160-165, still
30 mph faster than the A.
Then I brought the power back to give me the same indicated cruise
I'd get out of an A in the same situation. I was showing 14-15 inches of
manifold pressure, the engine was barely running and I was burning over
a gallon less than the A!
I'm not certain what I proved by that little game, but it convinced
me that big props and lots of cubic inches have an effect that we don't,
or can't, always take into account.
If you don't want to burn the gas in a big engine, bring the go lever
back. But, if you want the performance, it's there. At higher altitudes,
those extra cubes make all the difference.
Out here (Arizona) I don't think I'd want an 0-360 powered 'Hawk.
Density altitude is a very real fact of life and it's not unusual to be
looking at DA's of 8-10,000 feet on takeoff. Flown right, an 0-360 'Hawk
would do just fine, but I'm your basic chicken and like a lot of margin.
On Bob's note about the second prototype he said the highest power
setting he used was 21 square (137 mph). Does anyone know what that
equates to in %, horsepower and fuel burn? I'd guess it at around 55%
and maybe 11 gallons.
Few of us flies much more than 100 hours a year, if that. So, if
there's a 3 gallon/hour difference, that's 300 gallons/year or about
$600. I can think of about a dozen times, while I was staring at the
trees at the end of a runway, when I would have been happy to put $1000
cash in your hand, if you could just give me another 60 horses.
In the end, I guess I just like big motors. With the 'Hawk, it's
pretty hard to go wrong. With any motor it performs really well. I'll
bet with a 160 and kept light it would be a great flatlands airplane.
Back to FAQ's
360 Horsepower Radial
The Bearhawk is intended for use with engines ranging
from at least 150 horsepower, up to a maximum of 260. Concerning the
maximum, the general opinion has been that 260 ponies in the light
Bearhawk airframe ought to be more than enough power for just about
anybody. A bigger engine would just be excessive, expensive, and
probably too heavy. Or so the reasoning went. Recently, a 'new' member
of the e-mail list posted that this might not be so. This new member
just so happens to be Mr. Budd Davisson, whose article in the August
1995 issue of sport aviation convinced many of the list members to build
the Bearhawk in the first place....
On December 18, 1999 Budd Davisson wrote:
Re: radial engines
I've already done a design studyof the hawk mounting an M-14P
Vendenyev Russian radial of 360 hp. The weight is only about 400 pounds
and the engines are available new with American plugs, fittings,
electrical for $18,500. I also did some other structural stuff as I
wanted to use the airplane as a serious bush bird. I've got drawings of
the airplane finished, but don't now how to send them out. I could
probably drag them into photoshop and make them into a jpeg.
If anyone is interested, I'll drag them out and send them along. It's
an airplane with distinct Mulligan/Mullicoupe overtones and I think it
is unbelievably beautiful. Plus, the power to weight ratio is better
than my Pitts by quite a bit. Yeehah!
BTW; don't even think about 220 Continentals or 680 Lycomings as they
are big and heavy. The M-14P is only an inch wider than a Lycoming and
about the same weight as a big 0-540.
On December 18, 1999 Budd Davisson wrote:
Tom Kennedy wrote:
> I've seen some of the M-14s advertised at around $10,000!
> Does anyone know anything about the reliability of these engines and
> availability of parts?
The M-14 radial is a world all unto itself and it's a wonderful
world. I love the engine. It has a few operating characteristics that
are different than American radials, but every single one of those has
been addressed and taken care of by the Kimballs (KJKimball@aol.com)in
Zellwood Florida who sell the Model 12 Pitts Kits, etc. They also make a
slick cowling for the engine that could be modified for the 'Hawk...I
think. They also have Russian/SAE fitting kits made up to make plumbing
easier, as well as a completely self-contained starter panel that mounts
on the firewall. Very neat stuff.
The engine is unbelievably well built in typical Russian manner.
Crude where it can afford to be crude, well done where it needs to be.
It is 620 cubic inches and supercharged (not turbo) more for fuel
distribution than anything else, but it does let it pull about 31-33
inches on takeoff. And yes, it does turn the "wrong" way. It uses a
pneumatic starter so there's an airtank on board and the smart money
carries something like a bail-out bottle orsmall scuba tank on board as
a back up. A tank like that is good for 25 or more starts.
There a quite a number of NOS engines floating around for $14-$16,000
but they all have Russian ignition harness and plugs. Yak West in
Vermont (firstname.lastname@example.org) is having brand new ones made with US
plugs and ignition, B & C alternator, etc. They go for $18,500 and are,
without a doubt, the cheapest, best horsepower for the buck you can lay
your hands on.
There are rebuilt engines on the market for as low as $8000, but I
have no experience with them so I can't comment. If they were rebuilt by
the Russians or Rumanians, they are probably as good as new, but I don't
know that for sure.
My idea was to build the airplane as a modern antique, right down to
a dished out, triangular instrument panel, round the bottom of the
doors, wood trim on theinterior, etc. It would really be a hoot! And it
would be a serious performer.
Anyway, that's my input on the engines. If anyone cares, I did an
article on them a couple years back for Sport Aviation, but lots has
changed since then. All for the better.
On December 19, 1999 Budd Davisson wrote:
Russ Erb wrote:
> I assume you thought about how you would beef up the structure, since
> you would be going above the 260 HP design limit. Comments?
Not as many beef-ups as you'd assume because the weight isn't
changing. The primary beef ups I did involved a few minor changes in the
side truss to relocate the rear gear attach point because of the much
taller gear which requires a sub-truss inside the fuselage. That doesn't
even have to be done, if the beefing is restricted to the present attach
but it would involve some fairly heavy metal. I didn't do a finite
element analysis of the wing, but because of the possible speeds, I
might consider going up a little on the bottom sheets but that would be
all. Bob's work is really quite good, even with this horsepower.
This airplane would be working in the same speed ranges he used for
his calculations so not much needs changing.
With this power, two people and half fuel, the power to weight ratio
is the same as a single-hole, big engine Pitts but the wing loading
would be the same as a normal, light Bearhawk.
FYI, at gross weights a 172 is wing loaded at 15 pounds while the
'Hawk at gross is 13.3. That's where the airplane is getting much of its
performance because that's a HUGE difference. Now think about using the
Vendenyev. At 1900 pounds, the wing loading would be 10.6 with a power
loading of 5.3. The airplane would literally leap off the ground.
Besides the light wing loading and astronomical power loading, that big
prop would be "blowing" the inner wing panels, including the flaps, so
takeoff would be mind boggling.
If I keep writing this stuff, I'm going to talk myself into building
the airplane. Someone get me under control! Please!
Interesting, eh? After reading the above, you should now be in the
proper state of mind (lying in a puddle of your own drool) to view the
concept drawing that Budd was kind enough to provide to the list.
Lastly, it should go without saying that modifying your aircraft in
this manner exceeds the designer's recommendations and should NOT be
done unless you fully understand the ramifications of what you are
doing. To the best of my knowledge, nobody has actually tried this.
Back to FAQ's