Bearhawk Five Flight Testing – Tyler Williams

Source: 2023Q4 Beartracks, Tyler Williams
Some people actually know what they are doing. Me? I’m a novice. Prior to this project I had never built, rebuilt, or performed any significant repair to an airplane. Yet, here I am, 2 ½ years after receiving my Bearhawk Five kit, with a finished airplane.
Now, with my newly gained builder experience and a paltry 250 hours under my belt as a private pilot, I become a test pilot.
It has been 10 minutes since the FAA inspector shuffled his pile of papers into a folder, stepped into his car and drove away. Freedom. I preflighted N521TY twice the day before and then again with the inspector today. She was fueled up and ready.

I’m in the cockpit now, staring down runway 04. The big Lycoming O-540 is growling happily, ready and waiting for me to push that throttle full forward and give it the first taste of freedom. I go over a plan again in my head, “Accelerate. Verify airspeed alive. After the heels break ground, level off 5 ft above the runway and quickly confirm correct control authority, pull and maintain a shallow climb out to keep things cool. Watch temps. Keep climbing if all is well. Level off at 5,500 ft. FLY. Enjoy. Simulate an approach and bring the airspeed back to the onset of stall buffet and recover. Record speed and jot down an appropriate first final approach speed from there. Return to the field and set up an approach. Execute a three point landing with no flaps. Have a beer and celebrate.”
Ok, I exhale, push the throttle forward and my back gets pinned to the seat. The acceleration feels like I have let an animal off its leash. The tail is up. Wow! The handling is easy on the ground. By the time I reach full throttle she is light and ready to fly. She’s
up! I rock the wings and wag my tail, and then start climbing. 100 ft…200 ft…400 ft…600 ft…then WTF!?
My back comes off the seat under deceleration as I hear the sickening sound of an engine losing power. I drop the nose instinctively and glance at the airspeed. 75 kts. Ok, keep pressure on the nose. The throttle is still to the firewall. RPM stable but lower. Not climbing much now, but I haven’t lost all power, just some…a LOT. S*#@T, come on, really?! I glance at the adjacent runway as a bailout option and make a left turn towards it. It would be a super steep approach with a hard slip to stick in on the pavement from mid-field at this altitude. I could maybe do it, but I have consistent power and level flight now with no hiccups, just not full power. I do a quick instrument scan. Everything is in the green. Ok, left turn to downwind for runway 04. Maintaining 600ft. I try for a quick diagnosis as I fly the downwind. I leave the throttle firewalled, since it hasn’t moved and I don’t want to know what it may do if I move it. The prop responds normally but doesn’t help. I make a small mixture adjustment. Still no change. Then I hear the RPM waiver up and down briefly and then back to the same power. Is it the governor? Hell, I don’t know I need to land this plane and find out on the ground! Instrument scan…everything is still in the green. Now, how about that approach speed? So much for a simulated approach to figure out how she behaves. Oh well. I know how to land an airplane. We flew some 60 kts, no flap approaches during my Bearhawk transition training, so that should be good. Ok, 60 kts and no flaps because I haven’t tested those yet. I pull power, roll trim for 60 and notice how similar the control and trim response are to the 4-place I flew. In fact it all feels familiar to my hands, which is comforting at this moment. The landing approach is very brief since I’m only at 600ft, but in that time of intense focus I still manage to feel joy and pride when I notice how well the airplane is handling on glide. It was just as I imagined it would be, like a dream. I feel no friction in the controls, just fingertip pressure with immediate and predictable response from the plane. I’m over the threshold now, entering ground effect and rounding out. I think to myself, “Wow, she sure is docile.”

Float, flare, and grrrrrrease. First I smile and think to myself, “What an amazing airplane.” Then as I slow to taxi speed, I instinctively push the carb heat knob back in, and all those joyful thoughts are quickly replaced by the original “WTF?!” Nothing seems out of place. The engine is happy now and the instruments are happy. Maybe it was fuel flow, maybe something else. I taxi over to my hangar and do a runup to test everything again. She throttles up just fine and sounds great. I do a mag check, cycle the prop, test the mixture response, check the carb heat function, and then a full power static RPM check.
Everything seems ok. I disconnect the fuel line at the carb and do a quick fuel flow test. Everything checks out. I still have no idea what happened. But then again, I’m a beginner at ALL of this. Time to make phone calls. First, I glance around the panel and sit for a moment to think. Briefly, I have the thought, “I don’t remember pulling carb heat for my approach, but I remember pushing it back in while taxiing.” Weird. Must have done it without thinking. It definitely was pushed in for takeoff as I remember checking that as part of my runup checklist. Besides, the power loss was sudden and didn’t happen until I was at 600 ft. So, that couldn’t be it.”
The phone calls to various experts sparked a series of ideas and things to adjust that could diagnose/fix my sudden power loss/RPM drop issue. None of these uncovered the issue. I check adjustments, follow all recommendations and do another full power runup, as advised. All I can do so far is trust the people that actually know what they are talking about. As I reach full throttle I notice the carb heat knob creep out maybe ½”. Now THAT catches my eye! Suddenly things start to make sense and I start to get happier as I realize my engine is fine after all. Something is amiss with my carb heat box. Could it be opening itself when hit with enough air pressure? It is a brand new design after all and I’m the first one to fly with it. Time for another test flight. And this is what phase 1 is all about.
I crawl back in the cockpit, fire up the beast and make a new plan to depart the crosswind runway. In the event I need to abort on climb out, I can turn and land into the wind on the adjacent runway. I line up and firewall the throttle. I see 2700 RPM and she’s off! Climbing out, I glance at the airspeed and as I pass through 80 kts, the carb heat knob shoots out and the engine chokes again. AH HA! I push it back in and full power returns. I have an answer…well half of it anyway! Man that feels good. After a spin around the pattern I come back to land. The carb heat is being blown open after about 80 kts. It’s a strange design issue, but it should be an easy fix. Replacing the standard push/pull cable with a detented one will keep it locked in any position. But why such a drastic change in RPM? Seems like it was really choking the engine rather than causing a small RMP drop. It turns out the carb heat shroud that I installed was not allowing adequate airflow. It wrapped too far around the exhaust and needed further trimming. The education continues.
The following weekend, I fuel her up and set off into the sky to test the new cable and modified shroud. This time on climb out, the carb heat stays put and the engine runs beautifully. I continue my climb to gain some decent altitude and think about the initial series of flight maneuvers I finally get to do. Then I glance down at my engine monitor. My oil temp is at red-line and climbing! Come-on, now what?! I abort the flying tasks yet again and quickly return for a landing. Back on the ground, I pull the cowling off, check the baffling, check the oil cooler, disconnect the oil cooler lines and ensure oil is actually flowing and on and on. Everything seems good. Time for phone calls again. After a series of ideas that were all checked off, I hear, “It could be a bad Vernatherm.” I say, “Oh the Vernatherm. Yeah I’ll check that.” I did not say to my friend what I was really thinking…”What the heck is a Vernatherm?” The education continues. I learn what it is, how it works, and how to remove and inspect it for correct function. Sure enough…bad vernatherm. I install a new one and wait for the weekend to arrive with great anticipation.

What will the engine monitor say this time? Will I get to fly for more than 5 minutes before I’m forced to land and troubleshoot something else? Will I get to enjoy a nice flight? Maybe I’ll get some altitude for the first time and do some maneuvers? And I did.. Finally, I flew my new Bearhawk Five and landed when I wanted to. The carb heat stayed put and didn’t choke the engine when applied, the oil temps were perfect. The engine was truly happy, and so was I. Since the first couple weeks of troubleshooting I have been enjoying a wonderful airplane. I continue to learn and refine things each time I fly. This 40 hour test period is a valuable time. I’ve sorted out a heavy wing and have her flying hands off at cruise now. I’ve fiddled with the gas caps and finally dialed in how to use them with little to no cussing. I tightened up the trim tabs as others have done, to remove the play and vibration in them. I added some turbulator strips to the horizontal stabilizer struts. She feels super smooth now. The airplane continues to get better, and more refined with each test and tweak, and so does my technique, knowledge and experience. The flight testing is fun. Maneuvers are fun. Stalls of every kind are very fun…way better than circling the field for hours and “flying off the time.” I’m working on my short field techniques, learning what the airplane likes and figuring out how to get the most out of it. To say I’m enjoying it is an understatement. Being a pilot again feels amazing. The 2.5 years spent building now seems like the blink of an eye. I’m back in the cockpit now, doing what I love.
The numbers I have at this point are not really news-worthy. It performs as advertised for an unmodified, kit-built Bearhawk Five and I couldn’t be happier about this. The takeaway for me so far is that the learning thankfully never stops. The test period has not been mindless circling to burn off time. It has been an education. I have more textbook testing procedures to perform during this phase 1, and then lots to work on after that. To really take this plane where it was intended to go, I’ll be testing and learning far beyond the 40 hours around my airport. This is not a $100 hamburger machine after all. It is a tool for exploration. For now, I’m still a novice, but each new step out of my comfort zone and each step closer to the edge of the envelope adds to the bucket of knowledge, experience and stories to tell. And that is what it’s all about.

New Bearhawk Carb Heat Box Development

Source: 2023Q1 Beartracks, Mark Goldberg and Dave Lenart
Since we have been selling kits, builders needing a carb heat box have had few options. A carb heat box from Aircraft Spruce for the 540 installations, and a couple of choices for carb heat boxes for four cylinder engine installations. ALL of the available carb heat boxes have to be modified for use on our kits. They all have the air inlet on the SIDE for the heated air. This does not work with the cowlings as designed by Bob. The air inlet needs to be on the back/aft part.
About six months ago I spoke with the manufacturer of the larger carb heat boxes for the 540 installations. I requested that he make some for us that do not need to be modified, that they have the air inlet on the back which is what we all have to do to make them work. He turned me down and said he wasn’t interested. Then, about a week later, he called me back and said he would make me a batch of ten. But only if I paid up front for the ten and at full retail price that Spruce charges. So at that point I went from just disappointed that he didn’t want to help to slightly pissed off that he offered to do it but with unreasonable terms. I should add that these units are not well
designed and rugged. After a few hundred hours of use/vibration – they almost always need the bearings for the flapper shaft replaced. So I explained what had happened to Bob, and he proposed designing a new carb heat box himself. Bob’s design is made of 5052 aluminum in .050 (not steel like the others). It is one pound lighter than the four cylinder carb heat box mostly used, and I suspect maybe 1.5 lbs lighter than the old box for the 540 installations. And knowing how Bob designs things – this one will be rugged and long lasting.
It took a few tries for the kit factory workers to get a prototype to meet Bob’s approval. But that has now been achieved. This new one was sent to Dave Lenart to trial fit it on a Patrol he is finishing up. This was all very timely as Dave was just starting the cowling. As Dave describes below, we all decided that having two boxes would be better than one that would work on both engine sizes. The Lycoming 360 carb heat boxes will have a smaller filter than the one for 540’s. Both will be washable K&N flat panel air filters. Better than expensive Bracket filters that have to be thrown away. We expect to have both sizes of the carb heat boxes available in mid to late April. Pricing will be in the $500 range. Dave Lenart says: Bob sent me his new aluminum air box to try fitting on a Patrol build with an O360 under construction. The air box is a very nice piece, all welded aluminum construction, smooth operating flapper door and set up with a K&N filter. The carb heat connector is on the rear of the unit as needed and angled up at a 45 degree angle which puts the carb heat connection in a good place for the Bearhawks. There is no exit air hole on the bottom of the airbox which is not needed and robs horsepower. The large air box is about 4 1/4″ taller at its highest point than the heat box sold at spruce for an O360 that uses a bracket Bracket BA 5110 filter. This build is using the Hartzell Trailblazer constant speed prop and the 14 inch nose bowl which is a couple inches deeper than other nose bowls. In this application with the larger filter housing, the top of the filter extends into the engine cowl bottom by about 3 inches which requires building a small angled box to fill the gap and serve as a ramp into the air filter. If you are using a cross over exhaust this filter will be about an half inch away from the cross over tube. This is one reason why it will be better to have a shorter version of the same air box for the O360, using a 6-inch tall filter instead of the 9-inch. I made a few suggestions that will be incorporated into the production boxes but this is a nice alternative to what’s currently on the market. Much better construction and no modifications needed.

Engine Cooling Follow-Up

In the last issue I wrote about cooling, especially based on the shape of the lower cowl. I decided to install a fixed lip at the cowl outlet, and in the process also enlarge the opening by an inch and a half. I had not wanted to make the opening any larger over concerns about how thin the connection area was between the two lower cowl halves, but the new lip served as a doubler so I enlarged the opening. Here are the before and after:






I had hoped to download the EMS recorded data so that I could be more quantitative, but unfortunately it was lost in the fire. Generally, I can say it was a vast improvement. Before, a takeoff with a warm engine would have the CHTs over 400 in the first 1500-2000 feet, climbing at 90 knots. With the new cowl lip, Mike and I were able to climb with our Oshkosh load at 70 knots and the temps started to reach 400 climbing through 6000 feet. At a less steep and more normal climb angle, temps were never a concern, which was the intended design goal. While at Oskhosh, I took photos of several other airplanes for comparison. There is a lot of variety. Bobby Stokes enlarged the intake openings, added the Carbon Cub style louvers, and lower cowl flaps (O-540):


Mark Scott uses more typical louvers with his O-540:





Bill Anton had the largest lower cowl opening of the Oshkosh samples, though I believe he also has the most horsepower and thus BTUs to shed. I also appreciate how he riveted the lip on the top (behind the yellow) of the lower cowl.

The installation is visually appealing. None of this analysis is conclusive enough to say “do it this way,” but hopefully seeing some of the variety will help narrow down the norms of lower cowl configurations.

Bearhawk Patrol Glider Tug “Lucy” Update

Source: 2021 Q3 Beartracks, Alan Aurthur
Link to previous articles:
Australian Bearhawk Patrol Glider Tug Called “Lucy”
Australian Bearhawk Patrol Glider Tug Called “Lucy”

Thirty-four months have gone by, and Lucy has completed just over 200 hours and 150 glider tows.
Climbing to 22000 feet, the real limiting factor is the pilot. Not only do you need a good supply of oxygen, the -38C outside air temperature means you need a good heater or very warm clothing. The other limiting factor is at 22000 ft the elevator control had reached full aft; this could be improved by some ballast in the baggage compartment or a passenger.
A few cross-country flights experimenting with prop pitch and cruising RPM revealed a few limitations with the Mazda engine. Firstly, that the mixture cannot be leaned or the EGTs rises rapidly up to over 1000C if you don’t watch it.
The fuel consumption has settled at between 11.8 and 13.2 gallons per hour and with the right pitch setting around 100kts cruise speed with around 50% throttle. The positive is that although it can burn expensive aviation gasoline it is much happier with 98 octane Mogas.
Very steep climbs are possible coupled with high climb rates and very high fuel flows. The downside is that with fuel levels below about 7.9 gallons per side the forward fuel outlet will unport and the injection pumps will suck air followed by a rapid increase in the EGTs and then rough running. The problem is not easily overcome. The header tank with the submerged pumps has about five minutes of fuel so with low fuel levels steep climb outs need to be limited to less than that. However, five minutes on full power equals a more than 5000ft climb.
Where the turbo charged Mazda engine really shines is in glider towing to more than the normal 2000 ft above ground level. Climbs with a glider on tow average 600 ft/min at sea level, this obviously reduces with altitude however at 10000 ft this is still around 350 ft/min. The average climb rate to 10000 ft was 440 ft/min.
The next step will be to see how high we can tow to; the guess is that around 15000 ft will be the practical limit. 15000 ft on a still winter’s day should produce a glider flight time of over two hours.
The real success is the Bearhawk Patrol airframe, we have had absolutely no problems and no failures in any of the kit components, our only problems have been with our custom engine installation and with a bit of luck it has now settled down. Time will tell.

Russ Erb’s Engine Cooling Experience

Source: 2021 Q2 Beartracks, Russ Erb
Three Sigma was originally built with a cowl flap that had sufficient exit area according to experience and rules of thumb. However, engine cooling was marginal and power settings were limited to about 65% power continuous. While the cowl flap exit area was sufficiently large, the airflow areas through the cowl were suspected to be significantly less, being blocked by the exhaust pipes, mufflers, heat muffs, and a large amount of SCAT tubing. The cooling air, having flown over the cylinders, was having a hard time getting to the cowl flap exit. Because cooling was so marginal, the cowl flap was always in the full open position.
The easy way to open up more cooling exit area was to cut holes in the sides of the cowling such that the cooling air could flow around the cylinders and out the side of the cowling without having to pass around the exhaust pipes and SCAT tubing. The first modification was to add louvers from Avery Tools (no longer in business). This showed some improvement, but not as much as desired. A more aggressive set of louvers were built up from sheet aluminum to fit in the same mounting. It was hoped that the more aggressive louvers would produce a low pressure area to help draw the cooling air out.
Cooling was better with these new louvers, but the cowl flaps remained fully open unless the outside air temperature was very cold, such as about 40F or below.
My cooling problems may be somewhat unique to Three Sigma. At Oshkosh 2013 I spoke to another Bearhawk builder who also had a Lycoming O-540. Looking up his cooling exit showed a similar sea of SCAT tubing like on Three Sigma. However, he reported having no troubles with engine cooling. There was one difference in the cowling, though. Three Sigma was built with the MC-3B Pitts nose bowl called out in the plans and Beartracks. The other Bearhawk was built with the nose bowl provided by R&B Aircraft. The R&B Aircraft nose bowl lower edge is about one to two inches lower than the MC-3B nose bowl, which means the lower skin of the cowling is that much lower below the exhaust pipes, which means that the area for airflow in this area is doubled, allowing for better cooling.
An unexpected result happened after the 2018 condition inspection. A portion of the lower cowl behind the carburetor was found to have cracked and fully separated. The cowl was repaired with a doubler that reduced the open area around the carburetor, which was assumed to be an auxiliary cooling air exit path. However, for reasons not fully understood, this change resulted in noticeably better engine cooling. Why this happened I can’t explain.
With this change, the cowl flap can be closed after a few minutes at cruise power for outside air temperatures below 60F and maybe even 70F. While closing the cowl flaps theoretically reduces drag and increases cruise airspeed, in practice the difference is unmeasurable. However, it does keep the engine from over-cooling itself.

Engine Cooling – Lips, Louvers and Flaps

Source: 2021 Q2 Beartracks, Jared Yates
Engine cooling is on the short list of things that builders have ongoing problems with. It doesn’t have to be this way, but I’m not really one to talk. Last week on a hot summer afternoon, we flew our Bearhawk 20 miles north for a photo mission and ice cream run. We shut down long enough to eat ice cream and visit for a few minutes, then started up to fly home. This is the worst case scenario for cooling, since the cowl temperatures rise after shutdown. While enroute, the engine is making lots of heat, but there is airflow to remove that heat. Once the plane is not in the realm of flying speed, the residual heat in the engine parts gets transferred to the air inside the cowl, and everything except the engine gets warmer. After departure and reaching 2000’ AGL, our highest CHTs were up to 425 and climbing.
The challenge with this scenario is that reducing engine output is one way to reduce the temps, but that also reduces the airspeed, which reduces the cooling airflow. I know from experience and education that cooling improvements are incremental. One silver bullet seldom solves the problem, but if I’m going to fly to Oshkosh this year, I need to start incrementing.
Cooling effectiveness feels like black magic, but as I wrote about in the 2015 Q3 issue of Beartracks, it is fairly easy to measure and quantify with a home-made manometer, followed by noting CHTs in flight after making a change. If one wants to burn the fuel and go to the trouble, it is possible to set up the manometer, fly to get a baseline, make a mitigating modification that is supposed to help lower temps, and then fly to see if the pressure differential changed.
As I prepare to start this process, I’ve been collecting data about what those mitigations are. First, we have to ensure a good seal between the baffles and the top cowl, or do like Rob Caldwell did and install a plenum:

One way to study this seal is to watch the wear pattern where the rubber strips rub the aluminum. Another is to use a flashlight to check for leak areas. I feel like in my case I have this worked out pretty well, so on to the next step.
Perhaps the two biggest variables are the inlet and outlet areas. The inlet areas are fairly fixed unless we start designing our own nose bowl openings, but we see lots of variation in the outlet size. This photo shows Ray Strickland’s O-540 powered Bearhawk:

He has a large area, along with a pronounced lip to help reduce pressure. In my case, I’m not running such a large opening, though I feel like the maximum size of the opening has been limited by the way I’ve tied in the fiberglass airbox fairing. If I move the trailing edge of the cowl forward, it will diminish the amount of aluminum left to hold the lower cowl together, but maybe this is what I’ll need to do.
That brings us to the next mitigator, which is the lip. The lip is most commonly composite or aluminum. Starting with a soft 5052 or similar aluminum, the lip can be made with a shrinker and stretcher. That type of lip will also add strength to the lower cowl, just as flanging a rib adds stiffness. It has been proposed that the upward flex of an un-lipped cowl in this area might actually lead to an automatically-reduced opening size, which would be most unfortunate. What is the optimum length of the lip and angle? I can’t tell you, but it sure would be interesting to have some data. For now the best I can do is study the sample of available planes, and hope that the Type-Certificated crowd is flying behind an R&D department that considered all of the possibilities. Intuition and observation seem to point to around 2 inches of material at an angle of around 30 degrees.
All of the above mysteries about cowl lips are moot with the next option, which are adjustable cowl flaps. In some ways, we could think of the lip itself as a cowl flap, but that it’s always open. When enabling the option to adjust the opening, the design considerations change. Builders have executed a variety of different designs. Jonathan Battson made two openings, roughly 5×8 inches, but says he’d rather have them 30% bigger:

He used a piano hinge at the leading edge and made the flaps out of .025 aluminum. When open, they are deflected around 4 inches at the trailing edge. Jonathan uses an adjustment knob to manually operate the flaps and finds that he can reduce CHTs by 30 degrees, though he finds that he usually sets them either fully open or fully closed. One of his primary concerns was being able to keep the engine warmer during long descents. And since engine cooling makes drag, it makes sense to only produce the cooling and drag when the engine needs it. This is a big advantage of adjustable cowl flaps. Here’s a video of Battson’s cowl flaps.
Jon Wheeler used a similar concept, but used input from Jonathan to increase the size to 8.25 inches long, 6.5 inches wide, and 4.5 inches of deflection. Jon used electric linear actuators (Actuonix P16-100-64-12-S) instead of a manual cable. Jon also moved the flaps further up on the cowl, closer to the area where builders have also used louvers.


Speaking of louvers, those are a common option, especially on airplanes with the bigger engines. Lots of folks use salvage Piper parts (PN# 87405-802 (left), PN#87405-803 (right)) with the intent being to further reduce the air pressure below the engine. Jon Wheeler’s implementation of cowl flaps certainly approaches the function of the louvers and how they exploit the relative low pressure area there. Builder Bobby Stokes was having trouble with cooling, so he did some tuft testing and manometer testing. In his louver installation, the cooling and differential pressure were both worse. His louvers are much higher up on the cowl than many others, and there has been some discussion on the forum about which direction the louvers should face. Bobby did find that the fixed cowl flap or deflector at the bottom made the largest difference. He made a version that was adjustable, but didn’t find that the adjustment was necessary and has since gone back to a fixed flap.

Another common mitigation is to round the angle that the exiting airflow experiences at the corner between the firewall and the tunnel. I added a fairing here a few years ago, made from .020 2024-T3, bent on a slip roller. The idea is that this radius fairing helps reduce airflow separation right at the point that shows up in silver on the picture of Ray’s airplane above.
Next quarter I’ll have more news, either a tale of what didn’t work, or more hopefully, what did.

Patrol Builder Update from Joe Mason

Source: 2021 Q1 Beartracks
Joe Mason and his dad Mike are building a Patrol from a Quick-Build kit in Twin Falls, Idaho. They are installing an Aero Sport Power O-375 with 200 horsepower, and a Hartzell Trailblazer prop. Joe says, “We are hoping that this engine/prop combo will be a good one. At our home base we see some pretty high DA during the summer and that’s what drove us to try that larger engine.” They started on the kit in September 2018 and were painting in February 2021. The panel is built around a Dynon Skyview system and so far the paint quality looks outstanding.

The Incremental Improvement of Engine Temperatures

Source: 2020 Q4 Beartracks, Karl Clifford
My son, Jeffrey, purchased a four-place Bearhawk Quick Build Kit #82 in 2009. The Kit had originally been purchased in 2007 from AviPro Aircraft, (now Bearhawk Aircraft) by someone else, who had not even uncrated the kit. I have been Jeff’s helper in building the plane over the last ten years. The airworthiness certificate was finally issued on July 2, 2020. N976JC flies great. The engine is a new Lycoming YO-540-A4D5 rated at 250HP. Propeller is a constant speed two-bladed Hartzell carbon fiber. It has a Vetterman exhaust, a JPI EDM-900 engine monitor, and a Garmin G-5 electronic flight instrument. Empty weight came in at 1480 pounds. Very simple.
The only meaningful changes from the original design are a large skylight, a 2 inch extension of the fiberglass nose bowl to accommodate the very long neck on the Hartzell prop hub, and rigging the flaps so they can go negative about 4 degrees to achieve a slightly faster cruise speed.


We have flown it about 50 hours. The performance is unbelievable. While we have not fully mastered its STOL capabilities, we have gotten takeoffs and landings down to around 300 feet, with room for improvement I believe.
Jeff and I are both fairly tall guys, and with the seat all the way back we could not reach the flap handle without loosening our shoulder harness and leaning way forward and down. Not something we wanted to be doing when flying low and slow. So we made a short T-shaped grab handle that swings back from the flap handle that allows us to easily get the first notch of flaps without leaning way down. We can then easily reach the flap handle itself for subsequent notches. We also modified all flap notches so that the top button does not have to be pushed to pull flaps. The top button is pushed only to lower flaps. We like both of these changes.
The only real “problem” we encountered was high CHTs. We went thought a number of changes to the baffling before we finally arrived at what seems to work best. I would like to briefly describe what we ended up with so that subsequent builders might benefit from our experience. I suspect a fair portion of our problem was due to trying to break-in a new engine in the hot summer temperatures of West Texas. While we were flying mostly in the early morning hours, the OATs were still in the 80s and low 90s mostly.
During the engine installation we had very carefully installed the Van’s baffling kit for the 0-540 per Van’s instructions. It is a quality kit, well worth the money. We had very tight baffling.
Initially the CHT on takeoff for #2 cylinder (left front) and #5 (right rear) would go way over 400º F on takeoff with only a very short climb out. The CHTs on the other cylinders were also high, but not like #2 and #5. We would be pulling back the throttle to about 50% power very soon after takeoff to keep CHTs down. Of course, the Bearhawk still climbs out nicely even at only 50% power. We understand that the very rich fuel flow with full throttle helps cool the cylinders, hence the reason for normally taking off and climbing out with full throttle. But that was just not working for us.
The first thing we did was to increase the size of the opening at the bottom rear of the engine cowling to hopefully increase airflow over the engine. That helped a lot. Mark Goldberg had told me back during the building process to make that opening “plenty big”. Wish I had really taken that to heart. Make it PLENTY BIG. But that was not enough to totally solve the problem.

The next thing we did was to round out the bottom edge of the firewall with a rolled piece of aluminum sheet. The photo to the left shows the enlarged opening and the rolled sheet exit. I had read that the Van’s RV builders do this a lot. I was surprised how much this helped. Funny how moving air does not like sharp corners. But that was still not enough to solve the problem. I would mention that I later saw a similar rounded edge on the bottom of the firewall of a recent model Husky. So I guess the experts also think this helps.
Next we fabricated and added little inter-cylinder baffles on both sides of the barrels of the middle cylinders. These inter-cylinder baffles did not come with the Van’s baffle kit. A lot of air flow was being lost through these openings between the cylinders. Closing these openings helped. At this point the CHTs on all cylinders except for #2 and #5 were down in an acceptable range.
Next we looked at the #2 cylinder (left front) more closely, We theorized that the upward moving prop on the left side was pushing air up and back over the top of the #2 cylinder, mostly missing it. There is a lot of extra room inside the cowling above the #2 cylinder. Using aluminum sheet we added a simple “ceiling” in the tunnel running from the opening in the nose bowl back to just above the #2 cylinder. The ceiling begins just above the top of the opening in the nose bowl and extends straight back with a downward lip at its rear to force air down toward the #2 cylinder. This largely solved the CHT problem for the #2 cylinder. Our theory that the CHT problem with the #2 cylinder was being caused by the upward moving prop pushing air up and back over the top of the #2 cylinder seems to have been correct. That theory seems to be further supported by the fact there was not a similar problem with the #1 cylinder (right front). The downward moving prop on the right side pushes the air down and back directly into the #1 cylinder, not over it. So the right side seems to function fine without a ceiling in the tunnel. I would mention that a part of the problem with the high CHT on #2 cylinder is that it has the hottest EGT at all throttle and rpm settings. Nothing we can do about that. We did check for an intake manifold air leak, with none found. This hottest EGT is just due to the way the air/fuel mixture is distributed in the intake manifold among the cylinders. It does make the need for adequate air cooling for the #2 cylinder that much more important.

Next we looked more closely at the #5 cylinder (right rear). The location on the engine case of the #5 cylinder is staggered forward somewhat and the rear baffle behind it is set back several inches from the cylinder so as to be in line with the rear baffle for the left side of the engine. We theorized that the air was to some extent flowing over the top of the #5 cylinder and missing it, and that something was needed to force all the air down toward the cylinder. So we added a new “false” rear baffle located just behind the #5 cylinder that curves upward and forward to catch and force all the air down toward the cylinder. That new false rear baffle extends up all the way to the top of the engine cowling and has a gap seal at its top. We did leave a fairly small opening at the far right side of the false baffle to allow some air to flow on back to the 4” scat tube opening in the right rear baffle that leads to the oil cooler located behind the right rear baffle. This false rear baffle solved the CHT problem for the #5 cylinder. We had some initial concerns that it might create problems for the oil cooler. But we’ve noticed no increase in oil temps. The oil cooler continues to work great, with oil temps rarely going over 200º F.

We managed to get all of these changes made before OATs cooled off too much in the fall. With 90º F OAT we can now takeoff and climb out without any CHT going over 380º F if we don’t extend the climb out too long. Even with a more extended climb out all CHTs stay well under 400º F. At cruise all CHTs are down below 375º F and the spread among all cylinders is only about 20º F. On a cooler day CHTs are much lower. In cruise we can now lean the hottest EGT to over 1300º F. Before these changes we could not lean at all. Some of the improvement is undoubtedly due to the break-in of the new engine, so we cannot give total credit to the baffling additions.
It would have been much easier, and made for a much cleaner installation, if we had made these baffling additions during the original construction process, rather than adding them piecemeal as we ended up doing. So, I’d recommend to anyone currently building that he or she consider incorporating these additions to the baffling initially. Feel free to contact me if you have any questions or comments. Karl Clifford, Lubbock, Texas.
806-470-1480 4636c@att.net

Bearhawk Patrol Glider Tug Called “Lucy” Follow Up, Altitude Record

Source: 2020 Q3 Beartracks, Alan Arthur, Doug Harrington and Avon Furphy

Eighteen months have gone by down in Australia and Lucy has completed almost 100 hours and 85 glider tows.

Initially the Mazda 13B rotary engine was naturally aspirated and although the performance with around 180 – 200 HP was more than satisfactory for normal flying the performance towing a 600kg (1322 pounds) glider on a 40 degree Celsius day was not spectacular.
Early on we had a problem when the engine started to consume excessive amounts of oil, there were no leaks and the exhaust was not wet and oily, what was happening was that the engine runs so hot that the oil leaking into the combustion chamber was being burnt as additional fuel. At the same time the air fuel ratio indicator was showing an erratic mixture that could not be corrected by adjustments to the fuel map. Hindsight is a wonderful thing and now we know what causes erratic mixtures.
The engine had to be removed and the rotor oil seals replaced, on a Mazda rotary that means a complete strip down. The opportunity was taken while the engine was out to fit a standard Mazda turbo charger. That sounds simple but was anything but. The engine bay configuration and the engine mount necessitated a quite radical custom installation.

Starting with the fabrication of an exhaust manifold that placed the turbo charger behind the engine in a spot that was previously occupied by dual batteries and a few other accessories.
The batteries had to be moved to the rear fuselage to compensate for the anticipated additional weight forward of the C of G.
The exhaust system and mufflers had to be completely reworked.


The turbocharger needed to be restricted to a boost pressure of no more than 6 psi, the standard turbo engine had low compression rotors; ours had high compression rotors and the advice was that this combination of high compression rotors and high boost pressure would cause seal and pinging problems. The waste gate controller was modified so that it was producing a maximum of 5.6 psi.
The next area for rework was the intake manifold and throttle body. Space was a limiting factor, so the standard manifold was cut and welded to keep the intake system as low as possible and oriented in the easiest direction for the plumbing connections.


Space constraints dictated that an intercooler could not be fitted and was probably not necessary with the low boost pressure.

First engine runs proved to be very positive, boost pressure was spot on and manifold pressure was up to 42” at static rpm. Fuel flows had gone up considerably from around 35 liters per hour to 50 l/hr (9.2 gph to 13 gph).
One of our original problems before the turbo was having to run the ground adjustable prop in the full fine position to achieve acceptable RPM in climb. After the turbocharger was fitted, we had to increase the pitch to limit the RPM.
Glider towing times before the turbocharger were in the order to 9 minutes to 2000ft chock to chock towing a 600kg glider; after the turbo the times are in the order of 6 minutes. Lucy’s tow times now closely match the times that are produced by a Piper Pawnee. Our estimate is that Lucy is producing around 240HP
Thirty hours have been completed with the turbo with no problems of any kind. One of the most common problems with auto engines in aircraft is cooling and particularly during taxi and ground operations; our dual radiators and double sized oil cooler have proved to be up to the additional heat produced by the turbo.
Where to next? With the turbo charger the obvious question is how high will it go? When the ideal day came round, a clear blue sky and almost zero wind at any altitude it was time to borrow an oxygen system from the gliding club and see how high Lucy could climb.
A couple of practice climbs to 12500 ft and 15000 ft on previous days sorted out the radiator expansion tank problems and then a full throttle climb to 22000ft answered that question. Lucy’s operation ceiling is around 22000ft where the climb rate fell to around 100 ft/min. The Mazda rotary engine performed faultlessly and even picked up RPM as she climbed, no doubt due to reduced prop drag at higher altitudes. The real limiting factor is the pilot, not only do you need a good supply of oxygen the -38C outside air temperature means you need a good heater or very warm clothing.




What next, more glider towing and cross-country flights experimenting with prop pitch and cruising RPM with an aim to reach an economical cruise consumption.

Winter 2020 Builder Update from Rob Caldwell

Source: 2020 Q1 Beartracks, Rob Caldwell
21 Month Build Update


It’s March of 2020 and I wanted to share an update on the build status of my Bearhawk 4 Place (N6408C). I’m pretty sure I could be further along than I am if it weren’t for all the “distractions” I elected to pursue. I call them distractions, but really, I made some choices to do a few things differently.
I took delivery of my kit on June 1, 2018 and spend an average of 3 hours a day building. I built a rotisserie for the fuselage and that has been a tremendous help. If you’ve seen my YouTube videos you know I’m working in a long narrow (cramped) 2 car tandem garage that is
attached to my home. Super convenient for maximum building time. And I really don’t mind the tight quarters at all.
What I did differently:
• Lowered the two middle stand offs and stringers at the top of the cabin. This flattens the sky light and removes the Bearhawk “hump”
• Raised both door thresholds by 3”. I will be installing gullwing doors
• Modified the upper and lower door pieces that came with the kit to create the gullwing door frame
• Tilted the instrument panel 30 degrees forward for easier visibility. (Confirmed that this would not increase glare from the flat screen Dynon EFIS / PFD & AviDyne WAAS navigator)
• Also, hinged the instrument panel so it tilts back during the build. The panel cannot hinge after the control cables are installed.
• Using the SolidWorks CAD program (free for EAA members), I designed a control cable offset block mounted to the panel that will allow the controls to continue to operate at the intended 90 degree angle to Station B
• Fabricated a control cable mount for the parking brake, alt air & and cabin heat controls
• Cast in place a carbon fiber plenum for the top of the IO-540 engine
• Custom built all of the engine cowling pieces and doors. Installed Piper style cowl door latches.
• Modified the nose bowl with a ram air inlet for the forward-facing fuel controller
• Fabricated fiberglass conical airbox to include the alternate air door
• Recessed two flush mount Baja landing lights into the nose bowl
• Fabricated a housing on gull wing doors for spring loaded center case two-point latch (bell crank style)
• Made carbon fiber rear bulkhead panels, cargo door panels, wing root panels, etc.
Everyone says I am making great progress. But, I know my perfectionism and desire to constantly re-do everything is slowing me down. So, I have to keep reminding myself of something I heard from an RV-10 builder, “perfection is the enemy of progress”. That is so true!
You won’t build yours as I did mine. And I know many of you will whisper behind my back, “He built it TOO heavy!”. And that’s ok, you don’t have to whisper, I know it. But my mission isn’t as a utilitarian back country hauler. As Mike Silvernagle says, it’s a “business traveler”; the best description for my intended purpose.
My business takes me all over the east coast of the U.S. and I look forward to the days of avoiding TSA and flying myself to business meetings in an airplane that will be equipped for improved comfort. Speaking of weight, if I can keep my empty weight under 1,550lbs, I’ll be happy. I’m trying to use lightweight materials where I can, but I will also have leather seats and a fully carpeted interior, and an IFR instrument panel that includes a WAAS navigator that weighs 13lbs.
The engine I have installed is a new Lycoming IO-540 Thunderbolt that Mark Goldberg helped me purchase directly from Lycoming. I decided that if I was shopping for an experimental engine, I wanted it directly from the manufacturer. It feels like a safer decision to
purchase an engine with a recently cast engine case, improved manufacturing tooling and assembly tolerances. Plus, the Thunderbolt division will only go so far in producing an engine with a maximum compression ratio of 9:1. They let you decide if you want electronic ignition (on you to install), or mags. It does come equipped with the experimental Airflow Performance fuel injection system.
Reflecting back over the almost 2 years, much of my time was spent studying the manuals and plans, acquiring the appropriate tools, and learning to perfect certain processes. For example, I was intimidated about fabric covering and the painting process. But thankfully Stewart Systems has excellent YouTube training videos for all of it. As a result, I think I did a decent job covering and painting the fuselage. In fact, covering and painting have been my most enjoyable building tasks. I chose Stewart Systems because their products are all water based which was a safety consideration over solvent based systems, especially in the closed quarters attached to my home that I am working in.
Based on my experience so far, I plan to build another Bearhawk in the future. Probably a Patrol. I know I can do a better job next time and I enjoy the challenge and rewards of building my own aircraft. With any luck, the 4 Place will be flying before the end of 2020!