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The Unofficial Bearhawk FAQ



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 really should...).]

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 investigation.


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 electrical system.


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.

Model Comp. Ratio HP RPM Weight
O-320-A,E 7.00:1 150 2700 244
O-320-B,D 8.50:1 160 2700 255
O-320-H 9.00:1 160 2700 253
IO-320-B,C 8.50:1 160 2700 259


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.

Model Comp. Ratio HP RPM Weight
O-360-A 8.50:1 180 2700 269
O-360-E 9.00:1 180 2700 269
O-360-F 8.50:1 180 2700 270
IO-360-B 8.50:1 180 2700 270
IO-360-A,C 8.70:1 200 2700 293


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 models.

Model Comp. Ratio HP RPM Weight
O-540-B 7.20:1 235 2575 372
O-540-J 8.50:1 235 2400 356
O-540-L 8.50:1 235 2400 369
O-540-A 8.50:1 250 2575 356
O-540-E 8.50:1 260 2700 375
IO-540-AB 8.50:1 230 2400 383 New Cessna Skylane engine
IO-540-W 8.50:1 235 2400 400
IO-540-C 8.50:1 250 2575 375
IO-540-D 8.50:1 260 2700 381
IO-540-T 8.50:1 260 2700 412

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 http://www.prime-mover.com/Engines/Lycoming/. 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 a Bearhawk.


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.

Model Comp. Ratio HP RPM Weight
O-300-A,C,D 7.00:1 145 2700 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.

Model Comp. Ratio HP RPM Weight
IO-360-J,JB,K,KB 8.50:1 195* 2600 327 dry weight, no accessories *Takeoff rating 210 HP @2800 rpm
IO-360-C,CB,D,DB,G,GB,H,HB 8.50:1 210 2800 331 dry weight, no accessories
IO-360-ES 8.50:1 210 2800 305 dry weight, approx 370 with accessories
TSIO-360-C 7.50:1 225 2800 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.

Model Comp. Ratio HP RPM Weight
O-470-J 7.00:1 225 2550 354 dry weight, approx 400 with accessories
O-470-K,L,R,S 7.00:1 230 2600 385 dry weight, approx 425 with accessories
O-470-U 8.60:1 230 2400 389 dry weight, approx 425 with accessories
IO-470-K 7.00:1 225 2600 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.

Model Comp. Ratio HP RPM Weight
6A-350-C1R 10.5:1 220 2800 297 dry weight, no accessories

A Colorado distributor of this engine has a website.

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 airframe.

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 questions.

Shop carefully and happy hunting!

Rod Smith Bearhawk plans #246

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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 noted.

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 )
Donations Accepted


PS. Does Editorial Time Count As Building Time?

Kevin Deutscher
Bearhawk #272
Phoenix, AZ

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Rebuilding Certified Engines for Experimental Use

>If I was to rebuild a certified high time Lycoming for an experimental
>(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 good reason.

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

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How much power do you really need?

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 consider:

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 of gas.

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.

Edwards CA

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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.


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360 Horsepower Radial Engine Bearhawk?

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.

budd davisson

On December 18, 1999 Budd Davisson wrote:

Tom Kennedy wrote:
> Budd,
> I've seen some of the M-14s advertised at around $10,000!
> Does anyone know anything about the reliability of these engines and the
> availability of parts?
> Tom


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 (gesoco@together.net) 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.

budd davisson

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!

budd davisson

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.

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