Stephen Ingram’s Bearhawk 4-Place N789WM First Flight in Texas

Source: 2025 Q3 Beartracks
N789WM first flew on August 5th, 2025. You can read about my experience with the first flight of my newly built Bearhawk aircraft, following my transition training in North Carolina, on the Bearhawk Forums. In summary, despite careful preparation, the initial attempt was aborted due to a fouled spark plug, and the actual first flight revealed a misconfigured RPM sensor, leading to false high-RPM readings and considerable anxiety mid-flight. Minor issues like a lost fuel cap and unfastened tailwheel chains were discovered post-flight, reinforcing the importance of a thorough punch list and better planning. Ultimately, the flight was successful and educational, and shows the value of preparation, clear checklists, and learning from unexpected scenarios.
Since that first flight, there has been ongoing maintenance, discovery, and tweaking. After the first couple of hours, I was struggling to keep my cylinder temperatures within a reasonable range, and having to level off and build speed to keep the rear cylinders below 430F. I was very concerned about glazing before the rings had a chance to seat on the brand new engine. After having a friend look over my engine, and baffles, we realized a couple things: My front air dams seemed too high in his experience; and I hadn’t ever really gotten back around to sealing all the holes in the baffling. He also has a O-540, but in an RV, and he said he ended up without air dams at all. He reasoned that if my temps are high, I could remove the air dams altogether and the worst case they are too low and I have to put some back. I agreed, and drilled off the front air dams.
Next, I set about diligently and thoroughly finding every crack of light shining through the baffles and sealing it with RTV. I prefer the gray RTV, as the color blends in well with the rest of my engine. This ended up using almost an entire tube of RTV. But I felt confident that this would help address the heat issue. The main is to get that pressure differential between the upper and lower engine great enough to pull air though the cylinder fins, and it doesn’t take much, but any hole in the baffling is lost opportunity to carry away heat, and pressurizes the lower cowl.
The next flight the CHT’s were much better, and increased much more slowly. Success! But now, the next problem…my oil cooler is front mounted with a scat hose leading to a duct over the cooler to put the air through it. Lots of gaps around the fiberglass duct against the face of the oil cooler. Get another tube of RTV…
I also struggled with high CHT’s around #5, and a common solution for this, depending on how your cylinders are cast, is to build an air duct to shunt air around the backside of the cylinder. This called for breaking out the rivet gun and some scrap aluminum and within a few hours I had a decent looking duct. This greatly helped even out the CHT on #5 to something close to the other cylinders.
My project was a stalled out project with a new engine that had been sitting for a number of years. I had borescoped the internals of the engine as much as possible, and it all looked pristine. However, in the last few hours, I have had a number of seals, O-rings and gaskets start to leak. If you have had your engine for a while, the internals are probably fine, but you should expect to go through a round of fly, find the leak, replace, fly, repeat etc. Many rubber and non-metal parts of an engine wear out over the years whether they fly 1 hour or a 1000 hours. This lead me to have a number of oil leaks, an intake leak, and a fuel leak, all within the last 10 hours. Nothing catastrophic, but annoying nonetheless.
Initially, my flight controls felt very “heavy” and the adverse yaw was over the top. Thanks to the forums, and some posts I found there, I decided to go back through my tail and take it completely apart and identify any source of friction. I found quite a few places that I could have done better the first time, and most of my friction was actually in the trim tab on the left side. The hinge would bind against the paint and the clevis pin was tight in the hinge. I sanded, reamed, polished and straightened the elevators relative to each other very carefully, and this removed almost all the friction in the pitch.
For the adverse yaw, I decided to check my aileron rigging again, and raised both ailerons about 3/8 inch reflexed, as many had reported this removed a lot of the adverse yaw. I also went back through my flap rigging and made sure they were exactly equal to the wing trailing edge, and got everything as straight as possible.
The first test flight after the rigging changes was noticeably better. Most of the adverse yaw was gone, but enough to still keep you on your toes, rudder-wise in the turns that is. My autopilot no longer complained about trimming while maintaining altitude much better. I still have a very slight right roll that I am hoping a little more attention to the rigging will alleviate, but if not, I will employ the “washer trick” under the heavy wing hinge.
I am thankful that we live in the experimental side of aviation, since it allows us to experiment and to have “experimental” avionics and tools to discover and address issues quickly and confidently. Without a good engine monitor, I would not have been able to tell exactly which spark plug had fouled on my first flight. Without continuous monitoring, I would not have realized that one of my CHT problems was a leaking intake gasket. I also want to emphasize how invaluable sites like the Bearhawk Forums, Savvy Aviation, and Flysto are if you are willing to share your engine and flight data. Using Savvy, I was able to analyze engine data and dial in on the intake leak. Using Flysto, I was easily able to identify pitot-static errors, and rewatch and critique my flying. And of course the Bearhawk forums are great for tips, tricks, and the comradery surrounding this excellent airplane type.
As of the evening I am writing this, I am at 17 hours, having a wonderful time flying, looking forward to seeing other Bearhawkers out there, and just found another oil leak.

Cowl Modifications for Extreme CHT Cooling

Source: 2023 Q4 Beartracks
Scott Williamson lives in the Phoenix area with his Bearhawk 4-Place. He struggled to keep the engine cool, with high ambient temperatures and high horsepower not making things easier. In the end he fabricated a fiberglass cowl exit that made a big difference in temperatures. He also enlarged the inlets and moved them up and outboard a little. The mold for the new inlets was a dog dish. Thankfully most folks won’t need to pursue such measures, but these changes fixed the high CHTs for Scott.

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.

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.

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

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!

Engine Baffles

Although it is absolutely possible to make your own baffles from scratch, using poster-board templates, many builders shortcut the process by starting out with baffle kits from Vans. Pick a set that matches the engine you are installing, with the RV-10 kit being for the 0-540. For the smaller engines, the two-seat RV kits will work best. Be sure to get the fuel injected version if you have the angle valve engine, or the carbureted version for parallel valve engines.

Keep in mind that the baffles are subjected to an extreme operating environment with lots of vibration. Be especially particular about stress risers and imperfections at the edges and holes.

Once the baffles are installed on the engine, you’ll need to trim (or extend) them to allow for a 1 inch gap between the baffles and cowling. Once the baffles are close enough to shape that you can install the cowl without making contact with the baffles, one trick to model the cowl shape onto the baffles is to mount jumbo paper clips on the baffles every inch or so. Carefully install and remove the cowl, allowing it to transfer its shape by moving the paper clips down.

All openings in the baffling, any areas that would allow air to escape, need to be sealed with High Temp RTV.

A Note on Baffling Theory
The goal of a good baffling system is to move as much air as possible through the cylinder cooling fins as efficiently as possible. This is accomplished by baffling in such a way that there are no leaks and the only way air can leave the plenum on the top side of the engine is by going either through the cylinder fins or the oil cooler. This maximizes cooling and minimizes cooling drag.

View of rear of spinner area: A nose baffle, as shown, stops circulation and leaks around the nose of the case.

When trimming the baffles enough room must be left between
the baffle and the cowling for the baffle seal.

Note the relationship of the rear baffle to the string, which stretches from the nosebowl to the firewall. Van’s baffles are too tall and using strings will establish the proper height.

Small Continental Engine Cooling, Center Hole

Source: 2015 Q3 Beartracks
Bearhawk LSA Builder Jerry Cornwell brings up an interesting question about Continental engine cooling. Some Bearhawk LSA operators have found that the engines run warm. He points out that most of the old airplanes designed around the A65 have an extra air inlet in the middle of the cowl, to direct air along the bottom of the engine and onto the oil tank. A quick survey of my Continental-powered hangar neighbors reveals the following “faces”. Jerry does seem to have a point. Perhaps LSA builders could consider something similar. Bob says he’s not done so on the prototype because he’s concerned about the additional drag.

Cowl Air Pressure Testing

Source: 2015 Q3 Beartracks, Jared Yates
Readers may recall Bob Triplett’s reference to measuring air pressure differential under the cowl by connecting tubes to a mechanical airspeed indicator. There is a great article on this topic by Jimmy Tubbs from ECI. This article is so useful because it brings quantitative measurement to a topic that is often relegated to intuition and guessing. Bob spoke about wanting to test his pressure differential to narrow down the cause of a high CHT. In my case, I’m interested in diagnosing a high oil temperature. Bob Barrows suggested that I measure the pressure differential on the front and back of the oil cooler, to see if it is getting adequate airflow. I already have reason to believe that it is getting good oil flow.
The concept is that for air to flow, there must be a pressure differential. For example, Lycoming has provided that a top/bottom pressure differential of 6.5 inches of water should be considered a minimum to adequately cool the O-360 in cruise. What does water have to do with any of this? It’s just a measure of pressure. A certain volume of water will have a certain weight, and when water settled in the bottom of a U-shaped loop of tubing is subjected to air pressure, it will move up or down. Our altimeter settings are delivered in “inches of mercury,” but any liquid can be used to measure air pressure. We aren’t talking about cubic inches of liquid; we can cancel out the width and diameter dimensions, because they are the same on both ends of the loop. The more dense the liquid, the smaller the movement of the liquid, and thus instrument– so that’s one reason why mercury has been a popular choice for barometers.
When it comes to measuring pressure in a bouncing airplane, mercury is sub-optimal for several reasons, so maybe that’s why Lycoming provides the number in the more convenient “inches of water” unit. Airspeed indicators are similar to barometers, except that instead of measuring pressure relative to a standard (that’s what an altimeter does), they measure pressure relative to two sources. Usually those two sources are pitot and static, but it will gladly measure whatever one connects to it. This means that an airspeed indicator can also measure pressure differentials in the cowl. Folks who have been building airplanes for a while probably have airspeed indicators sitting around, but I didn’t. I posted a question to the Matronics Aeroelectric list to see if anyone had a suggestion for a device that could measure low air pressure, and I learned that I could actually solve this problem on my own, by building a manometer. Contrary to the name, this isn’t a device that measures machismo- that’s a stud finder. Rather, it’s just the name for an instrument that uses a column of liquid to measure pressure.
To make the manometer, I purchased a 20 foot roll of clear vinyl tubing from the hardware store, with a 3/8 OD and 1/4 ID. I used some very thin scrap aluminum tubing to create some piccolo tubes. This tubing is available at hobby shops, and occasionally at big box home stores, but leftover brake lines might work well too. This task only requires two piccolo tubes, but I had plenty of stock and got a little carried away making extras. I smashed one end in a vice, and drilled several unorganized 1/16” holes. The goal is to create a static air source at the desired measurement site, and the piccolo tubes help negate possible errors created by moving air over the end of just a plain, squarely cut tube end. This is related to why we put static ports on both sides of the fuselage.
I sourced a piece of non-PMA cardboard (homebuilding has its advantages) and marked graduations in 1/2” increments, with small 1/4” lines. In retrospect, it would have been better if I had numbered the whole inches instead of the halves, but it still worked fine. I used small wire ties to attach a loop of the tubing to the cardboard, and added some small aluminum splicing tubes at the top. In theory, one could run a single tube all the way from the top of the engine, into the cabin, around the loop, and back out to the underside of the engine. I didn’t want to do it this way because it would complicate adding water, and because I wanted to test several differentials on a single flight. This required running a four labeled lines back to the cockpit, which I could connect to the manometer one pair at a time. To get the lines through the firewall, I disconnected the duct from the heat muff to the cabin heat box, opened the cabin heat valve, and ran the lines through there.
I did the flight testing by myself, but it would also work to have someone else to help with the readings. As always, the first priority is to maintain control of the airplane, and not get distracted with science experiments.
Between the top of the engine and the bottom, I found a difference of 4” in climb, and 7” in cruise. On the ground with 1700 RPM, the difference was 3/4”, and in flight at idle and 70 knots the difference was 2”. These meas-urements and my CHT indications agree that I have plenty of airflow for cylinder cooling.
I disconnected those lines and connected lines from the front and back of the oil cooler. In climb, cruise, and descent I read 4, 6, and 3.5 inches. To put those numbers into more familiar units, 5 inches of water equates to 98 knots on an airspeed indicator, or .18 psi. These are very low pressures.
Next I measured the difference between the top of the engine and the front face of the oil cooler. This would show how much of a loss I had just in getting the air from the high pressure area to the cooler. In climb, cruise, and descent, this showed a steady 2” in all phases. In climb, that’s half of my pressure differential, and 1/3 in cruise. Next quarter I’ll have de-tails on the corrective action. Until then, I’ve included a photo of the old installation in case you’d like to make any guesses. This method would be great for sizing cowl inlets and outlets, and deciding if remedies like cowl flaps or louvers are required for a particular installation.