Bearhawk Aircraft Bearhawk Tailwheels LLC Eric Newton's Builder Manuals Bearhawk Plans Bearhawk Store

Announcement

Collapse
No announcement yet.

Bearhawk Five Flight Testing Continues

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Bearhawk Five Flight Testing Continues

    I've had the good fortune of spending a little time with the latest Bearhawk today and yesterday. We've accomplished a lot, and have collected a mountain of data and footage that I've only begun to process. Expect much more! The weather has delayed us and it looks like tomorrow is not going to be ideal, but here is a basic summary of what we have done so far, picking up where Rollie left off.
    Day 1 (yesterday): First flights, airplane familiarization for me, a little landing practice, and some rudimentary airspeed calibration runs. Later in the day, we set the forward CG limit, or more accurately, we validated Bob's prediction of where the forward limit would be. We did this by ballasting the right front seat with 180 pounds of concrete, along with the 200 pounds of me in the left font seat. We burned the fuel down to a comfortable minimum, since it is stationed aft of the CG. At this stage, the prototype is equipped with a specially designed ballast system, which can hold up to 152 pounds of ballast in four removable chunks of steel, weighing 38 pounds each. We removed one ballast, and flew the airplane. Then we moved a second ballast up to the rear seat and flew it. This was where Bob expected the practical limit should be. The airplane felt good so we removed the second ballast entirely and flew it one last time. At that CG point I was still able to flare without needing to add power, which was what we were wanting to test for. The nose-heavy condition was very real though. The elevator deflection on final was about 5 inches at the counter balance. Thankfully this bird has 35 degrees nose up travel, as most new model B generation planes have. And it also has the profiled tail which makes a real difference in keeping the airflow attached at the hinge line. In rough numbers, each of my first four flights moved the CG forward 2% of MAC, or an inch and a half (rounding here). The last flight where we removed the ballast from the back seat moved the CG forward 1%, or .6 inches. After that validation, we reinstalled the steel ballast, fueled up, and took the airplane back home to Collin's house. The airplane sleeps there, but his strip is a little short to be doing experimental stuff, so we've been using the municipal airport down the road for these tests. Bob will use this information to make updates to the plans. It is not yet known whether production kits will use the ballast system, or whether that will just be a prototype tool.
    Day 2: The goal today was to find the max gross weight and the aft limit. This naturally occurs somewhat simultaneously, because there was no way for us to fly the airplane at a more forward CG while also increasing the weight. Yesterday at our forward-most test, the CG was located at the arm of the front seats. We started the day by making a trip to Tractor Supply. The problem with ballasting up an airplane of this size is it takes a lot of weight. Who knew that this kind of flight testing was such a workout? The store was out of concrete bags but they had some nice gravel and sand tubes that weighed 60 pounds each. We actually weighed each one and wrote down the true weight, which varied from 60.5 to 63 pounds. I tied down three of these in the back seat and departed Collin's for the airport, while Collin drove the rest over to the big airport. Bob wanted us to measure the gear spread at each load, so that we could make sure they did not spread beyond his 74 inch limit, center of one tire to the other. At the first flight we were around 70 inches. We added three more bags to the back seat, for a total of 360 pounds, and flew it again. The handling was slowly changing, in my opinion for the better. I think the heavier wing loading gave it a nicer rhythm in the air when I encountered the occasional bump, and it was easier to land and taxi. Next we added 60 pounds in the center of the baggage area, and 125 more pounds under the rear seat. This put the total rear seat weight at 485 pounds, and gross airplane weight at 2685. It flew fine, so we added another 60 pounds in the baggage for a total of 120, and another 60 pounds at the feet of the rear seat. Then we refueled, adding an extra 210 pounds of gas for a total airplane weight of 3019.7. That was aft of Bob's planned limit by a quarter percent MAC. With all of that on board, the takeoff roll doubled, to around 500 feet. The rate of climb, which had usually been a solid 1500 feet per minute, eroded to a paltry 1000 feet per minute at 90 knots indicated. The gear spread had reached 72 inches, leaving a significant margin for less than perfect landings. At that weight I flew some pitch stability tests. At all speeds it still had positive static pitch stability, but at speeds over around 100mph it did not have positive dynamic stability. But it was still very flyable, and did not require a high level of pilot attention or even full-time hands-on-the-stick flying. I was able to find a high spot in the overcast to repeat the stall series and found no appreciable change to the stall characteristics vs the forward loadings. This thing flies like a Bearhawk should, it just carries more, has more room, and has just absurd thrust. The engine is rated for 315 HP, and fully loaded, here are some preliminary indicated airspeeds at 2000 feet:
    19" and 1900 RPM, 6.9 GPH 110 mph IAS (leaned)
    23.2" and 2450 RPM, 14.3 GPH and 145 mph IAS (leaned)
    26.6" (WOT) and 2440 RPM, full rich mixture, 28.6 GPH, 158 mph IAS
    At the heavy weight, the landing roll without aggressive braking (it's not my airplane) was 750-1000 feet. No doubt it could be trimmed to 500-750 just by a more ambitious pilot.
    So all of that was before lunch. We decided to celebrate by eating a nice big restaurant meal, something I haven't done in 10 weeks since my home state hasn't allowed it as Missouri has.
    After lunch, we had a visit from Bearhawk builder Andrew L. and his delightful family. What we were really needing was a clear enough sky that would allow me to get up to 7500 feet for some cruise performance testing. The sky looked open enough to give it a try, so I removed much of the weight to reach a mere 2660 pounds gross, which is basically four people and no bags other than the steel ballast. I figured this would be a good middle-of-the-road testing weight, and indeed it is right in the middle of our lightest flight weight so far and our heaviest. The clouds were broken up enough to make a safe climb, so I was able to get at least three readings on four headings for 140, 150, 130, and 70 mph IAS. I have not yet had a chance to crunch these to see what they were yielding in CAS and TAS but will do that next. I started doing some glide tests to collect the best glide speed for the bootstrap spreadsheet, but after 7 runs the fuel load was getting down a little, and the clouds were spreading out more than I liked, so I descended back underneath and landed for fuel. After the short hop back home to Collin's we found a mechanical problem with the tailwheel, which spelled a possible end to the flying for this week. Thankfully Collin is as good of a mechanic as you expect him to be, and he found that we were able to fix it without any new parts. Turns out the axle bearings on the tundra tailwheel are directional, and these had been installed backwards, allowing one of the races to pop out. We removed the tailwheel and cleaned it all up, flipped the bearings, and now everything is all lubed up and ready to go for tomorrow. But the forecast is for low barely VFR ceilings again. Fine for landing practice and load testing, but no good for bootstrap glides or more cruise testing. Maybe I'll be able to make some progress with video editing.
    I have nearly all of these flights on video, and today Collin recorded around 25 minutes of talking about what it was like to build the airplane. Once I can get some of this edited down I'll post it on the Bearhawk Aircraft youtube channel. Collin also shared all of his build pictures, including some great details about some of the cool innovations that he, Bob, and Mark have employed to bring this beautiful bird off of the plans page an into the sky.

    The airplane has exceeded my expectations, and I'm honored to have a chance to get some time in it.

    So having said all of that, I have a few more days with the airplane. There are 11.3 hours on the meter, and all of Bob's safety tests are complete. What flying would you like to see, what data would you like to have, and what questions do you have for Collin or Bob?

    Attached Files

  • #2
    Sounds like fun! Thanks for sharing the info!

    This is the airplane I wish existed when I started my build. That 12” of extra cabin length would ensure I could fit my family of 5 in the plane as the kids grow.

    Is the cabin any taller in the rear area? What’s the hight (floor to ceiling) at the rear seat and the height at the rear bulkhead?

    No doubt you guys have your methods of testing worked out but using the methods and documenting the testing using the EAA manual would have provided standardized data that would have been very interesting to review.
    Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

    Comment


    • #3
      Nice write up.

      Comment


      • #4
        You got a lot done in a couple days! Nice work, and great to hear that you were able to remove half the ballast.
        Rollie VanDorn
        Zanesville, OH
        Patrol Quick Build

        Comment


        • #5
          Originally posted by whee
          Sounds like fun! Thanks for sharing the info!

          This is the airplane I wish existed when I started my build. That 12” of extra cabin length would ensure I could fit my family of 5 in the plane as the kids grow.

          Is the cabin any taller in the rear area? What’s the hight (floor to ceiling) at the rear seat and the height at the rear bulkhead?

          No doubt you guys have your methods of testing worked out but using the methods and documenting the testing using the EAA manual would have provided standardized data that would have been very interesting to review.
          Jon, this one does not have a headliner, so I measured from the floor to the top horizontal tube, parallel to the aft bulkhead, and got 34 inches. In the middle it is a couple inches taller because of the space made by the stringers. This will vary depending on how the ceiling is finished out. Measuring from the floor to the ceiling, with the tape measure tangent to the front of the bottom of the rear seat, I get 44 inches. I will say that in this installation the rear seat is positioned to give the back seaters very ample legroom. If I were building one, I would want to consider some sort of track system that would allow repositioning of the seat, and lots of cargo tiedown flexibility. It seems like the bigger the cabin and cargo area get, the more tricky it is to tie one little thing down in the middle. Imagine the possibilities of being able to hook in tiedown rings, quickly remove or install one or two back seats, and position them at 1" increments!

          Regarding the test plan, so far Bob has been calling the shots. He's not comfortable enough with his ankle to travel out here and do it himself, so I've been the proxy on his behalf. As of yesterday we have finished his checklist, opening the door for the next stage. I don't have a copy of the latest EAA manual and don't think I can get one before the end of the week, but let me know if there's anything in particular you'd like to see. We've got plenty more hours to fly just to get it out of Phase 1, and even once it is out and about, testing will continue indefinitely as someone else puts it to work in more backcountry-like flying.

          Comment


          • #6
            If the increased CG range is proportional to the increased gross weight. Bob and Mark have a winner. Thanks for taking the time to update the latest info. I still thing the regular 4 place fits my needs. But if I was looking to start a new kit, I would go for the big one.

            Comment


            • #7
              Great write up, thank you for spending the time to fill us in. Regarding the forward limit and the ballast system, are we to assume that you started this forward testing with all 4 ballast compartments full and ended with 2 of them occupied when at the tested forward limit? As you stated, this was done with 180# in the right seat. Bottom line, what is it looking like will be required to fly this thing solo? 75 pounds in baggage area? 100?
              Mike

              Comment


              • jaredyates
                jaredyates commented
                Editing a comment
                Keep in mind that Bob is likely to tweak the firewall and engine location in the final version of the plans. But in this particular airframe, two of the four ballasts is ok with a single front seat pilot of 200 pounds, down to a fuel load of 40 gallons. To carry less fuel, it would probably make sense to keep in three of the four ballasts.

            • #8
              Thanks for the great information Jared. Even though this is not a plane I need at this stage in my life, I find it very exciting. I can just imagine it on floats, getting a couple hunters home with 5-600#s of Moose meat. Please keep the information coming.

              Comment


              • #9
                Originally posted by jaredyates View Post

                Jon, this one does not have a headliner, so I measured from the floor to the top horizontal tube, parallel to the aft bulkhead, and got 34 inches. In the middle it is a couple inches taller because of the space made by the stringers. This will vary depending on how the ceiling is finished out. Measuring from the floor to the ceiling, with the tape measure tangent to the front of the bottom of the rear seat, I get 44 inches. I will say that in this installation the rear seat is positioned to give the back seaters very ample legroom. If I were building one, I would want to consider some sort of track system that would allow repositioning of the seat, and lots of cargo tiedown flexibility. It seems like the bigger the cabin and cargo area get, the more tricky it is to tie one little thing down in the middle. Imagine the possibilities of being able to hook in tiedown rings, quickly remove or install one or two back seats, and position them at 1" increments!

                Regarding the test plan, so far Bob has been calling the shots. He's not comfortable enough with his ankle to travel out here and do it himself, so I've been the proxy on his behalf. As of yesterday we have finished his checklist, opening the door for the next stage. I don't have a copy of the latest EAA manual and don't think I can get one before the end of the week, but let me know if there's anything in particular you'd like to see. We've got plenty more hours to fly just to get it out of Phase 1, and even once it is out and about, testing will continue indefinitely as someone else puts it to work in more backcountry-like flying.
                Thanks Jared! That’s exactly what I was looking for.

                I have a seat track system in my plane that is just as you describe and it is awesome.

                My manual must be at the hangar. If I can find it I’ll send you a pic of a couple tasks I’d be interested in seeing the data on.
                Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

                Comment


                • #10
                  Here are the processed results from yesterday's cruise testing. First, on the climb from 1000 MSL to 7500 MSL, it was indicating 30gph, 90mph, and took 7 minutes. Reaching 7500, the highest CHT was 327, and the oil temp was 210. This was at a weight of 2660 pounds. All speeds are mph.

                  At 7500 feet, I made at least three runs in each direction at each speed. I'm hoping to make a video that explains the methods but will have to see how things are going.

                  The first condition was wide open throttle showing 22.3 inches, 2400 rpm, mixture leaned to 12.3 GPH. The instrument calculated engine output to be 56%, IAS was 141, calculated CAS was 132.5, and the calculated TAS was 151.1. If I owned the airplane and were going somewhere, this would be my "going places" power setting.

                  For the second run, the prop and throttle stayed the same, but I went to full rich on the mixture. This increased the fuel flow to 17 gph, with the instrument calculating 71% HP. IAS was 151, CAS was 142.5, TAS was 162.5. While there are cases where the extra 10 knots would be nice, the increased fuel flow to get it is likely a concern for most applications, but there are always cases with strong headwinds, trying to get there before dark, etc where it might be nice to have this option.

                  Pulling the throttle off of the stop and getting out of the economizer (does FI have an economizer?) I set the throttle to yield 130 indicated. This ended up being 17.4 inches, 2400, and leaned to 12.8 gph. A little mixture adjustment goes a long way in this setup, and from the look of things I probably could have leaned it a little more. But the intended focus for this run was less on the engine output and more on the airspeed indicator. At 130 IAS, we got 122.1 CAS, and 142.6 TAS.

                  I made a few runs at 70 to check the instrument error there. And I tried one at 60 but at that high altitude and weight, the indicated stall speed was just above 60. But it looks like it is indicating about 2-3 knots higher than CAS at those low speeds. The pitot tube, like the rudder trim, requires that we pick one speed to be the most accurate. Speeds above and below the ideal will have errors, so if we set it to be perfect in cruise, it will be worse in the Vso range etc. This is a plain tube pitot which is bendable but if we bend it, all of the above CAS is moot and we'll have to start over.

                  Comment


                  • #11
                    I'm curious, with the same exact wing as the B model, how is the C.G. envelope larger? The chord is the same, is the center of pressure somehow that much further back on the wing with a larger fuselage? Am I missing something else?
                    Last edited by zkelley2; 05-21-2020, 04:00 PM.

                    Comment


                    • #12
                      Longer arm between the wing and tail.

                      Comment


                      • zkelley2
                        zkelley2 commented
                        Editing a comment
                        Does that move the center of pressure aft? There is no issue of tail up(nose down) authority in the 4 place, even at wildly aft CG. Like a lot further aft then 22.5

                      • Bcone1381
                        Bcone1381 commented
                        Editing a comment
                        No it does not move the Cp aft.

                        The longer arm gives the aircraft more pitch up authority at slow speeds during the flare. Which is what we run out of at the forward end of the CG envelop during the landing flare. I think theoretically that the AFT Cg limit will be about the same point on the Riblett Airfoil as the Model B and the Patrol. So maybe the range will be a smidgeon larger with the longer fuselage.

                        (Maybe I should have let Rod answer.)

                    • #13
                      Here are my guesses... Bob wanted the forward limit to be based on flare authority, which is of course tail related. He knew about where to expect this, and the aft cg to be, but wanted all of these numbers to be verified. He also wanted to observe the spread of the main wheels, since all of those parts are different from the 4-place. I don't have a set of model B plans, but you have me curious, where does he put the aft limit?

                      Comment


                      • Archer39J
                        Archer39J commented
                        Editing a comment
                        Aft CG limit is 22.5" on the model B.

                      • jaredyates
                        jaredyates commented
                        Editing a comment
                        Bob will be the one to specify the aft limit and I don't want to speak for him, but let's say that lines up pretty close to what we were flying with the five.

                    • #14
                      Longer arms give not just pitch authority, but pitch damping. It effects both static and dynamic pitch stability. Same is true in yaw. Longer versions of the same airplane just fly better. There are not a lot of short and long versions of GA aircraft. I flew 5 different aircraft types with 2 or 3 different fuselage lengths. The long ones always felt more solid, especially in turbulence.

                      Hopefully that also will expand the CG range because of the longer moment arm.

                      Comment


                      • svyolo
                        svyolo commented
                        Editing a comment
                        All modern commercial aircraft that I can think of came in at least 2 different lengths. I think the champion is the A320. They had 4. 318/319/320/321. 737's have 3.

                      • AKKen07
                        AKKen07 commented
                        Editing a comment
                        Random marginally relevant comment here:
                        For what its worth the shorter 737s are more fun... :P.
                        Some people just love the long Cadillac stability of the long ones though.
                        Beech just added a bunch more fins to the 1900 to make it fly right... I wonder what a 4 place would look like with 1/2 dozen fins on the tail...
                        I liked the shorter -7 CRJs better than the -9s as well for the same reason. But I like short flights and sportier handling over long cruises and hands-off stability.
                        Last edited by AKKen07; 05-27-2020, 08:57 AM. Reason: Added more useless chatter

                    • #15
                      I'm assuming the landing gear legs are longer to maintain a similar deck angle to the 4-place?

                      Comment


                      • Collin Campbell
                        Collin Campbell commented
                        Editing a comment
                        The gear legs are longer due to the wider distance (for added strength) between the attach points on the fuselage. (16 1/2" vs. 13 1/2" on the 4-place) But the distance from the axle to the fuselage remains the same...(26") The gear leg tubes on the 5 are .083, and the axles are beefed up to .188"

                        Of course, the deck angle will be determined by the tire size...

                      • whee
                        whee commented
                        Editing a comment
                        Thanks for the info Collin. I was hoping the gear legs were longer and would fit the BH.
                    Working...
                    X