Building the Bearhawk

[@MDLuthier]

Very competent video editing, given three very different presentation styles and supporting graphics. Anyone that has done a video project of this nature knows how much work was required, and the talent and skill needed to produce a video package of this nature. Lessons learned? Bearhawks are pretty cool and Chapter 524's presentation team and video editor(s) are top notch.

[@Sideways71]

Wow! What a HUGE project!

[@MDLuthier]

Carlo's scratch-built project is moving pretty quickly... since receiving his plans in Sep 2023, one wing is skinned and the other is getting close to closing out, so under a year to get the toughest part of the airplane built from plans. And that is with a significant number of mods and improvements, including wet wing, capacitance fuel level, CNC milled inspection ports (no rim inside the wing, so no knuckle-busting nutplates), and the usual optimized weldments, etc.

[@EllipsisAircraft]

7:40 the issue I have always objected to, is the numbers on their website for stall speeds would require lift coefficients greater than 3, after factoring in even a small tail down-load; OR reducing the aircraft weight to its listed empty weight, plus 150-200lbs if using a believable CLmax of 1.7-1.9 for a typical partial span flap, rag and tube aircraft. I'm not knocking the design or designer. It clearly works well for countless people. But it raises alarm bells to publish nonsensical data that was clearly read off an uncalibrated airspeed indicator/pitot by someone who should know better. Or worse; derived from make believe. I highly doubt these aircraft can actually achieve, in no wind conditions, on a 59 degree day, at 0MSL, the claimed 32mph, 35mph, 36, and 38mph stall speeds they list for various models online. The dynamic pressure at 35mph is so laughably low, even ultralights have a hard time operating there. E.g. Patrol is as of today published 2,000gross weight (that by definition is the weight performance numbers are derived for). And 180ft^2 wing. 2k/180 = 11.111...lb/sqft. (22/15)x 36mph stall = 52.8ft/s Rho is 0.002377 0.5*rho(V^2) is 3.3135 lbs/ft of dynamic pressure. (Q) 11.111.../q = CLmax of 3.353. Not even with a Helio Courier could you ever achieve that CLmax! (And it came close, with full span deployable slats, and 70% span flaps. It achieved a phenomenal CL~3.0 in practice)... Run numbers backwards and use CLmax of 1.8 (Same as Super cub, Vans RV-8. Not Husky, which has better, gnarly slotted flaps). And you find a stall speed of 49mph. This is at aft-cg of course, as fwd Ch means a larger tail download that would raise stall speed to 50mph even. A far cry from 36! (Which would correspond to a gross weight of 1,073lbs. Which is exactly -77lbs BELOW its listed empty weight).😂 Even if You plug in a Clmax of 2. Same story, you cant even bring fuel with your own bodyweight and achieve those stall speeds. Use a giant (unbelievable favorable) CLmax of 2.5. Then it gives you a low fuel, solo weight that might be useful for STOL competitions. (341lbs, including pilot, oil, and fuel, 36mph stall with CLmax of 2.5). This "accusation" is evidenced by the fact people aren't using these in STOL drags. Yet many other known STOL or bush designs are showing up in droves. Including carbon cubs, Zeniths, as well as C180s. But not many bearhawks showing up, let alone winning those events. If these vitally important performance numbers are this egregiously fudged. I wonder what other, much harder to verify numbers are pencil whipped?

[@MDLuthier]

52% span x1/3 chord plain flap on the patrol - they are barn doors compared with the PA-18's ~35% x 1/4c. Not a rag wing airplane - flush-riveted, stressed skin, single strut with fabric control surfaces (as in most high performance aircraft through the middle of WW2). Fabric control surfaces are more structurally efficient in design speed range and the aerodynamics are virtually the same as heavier stress-skin construction. Flush riveted Riblett wing matters a lot at cruise and less at the low end, but helps a bit on controlling separation. Some builders have gone with VGs and given up a few mph on the top end, but I suspect the consensus is that VGs add predictability in less-than-ideal conditions, versus trimming the Vso number in a meaningful way. Most manufacturers quote Vso (velocity - stall in landing config for the casual reader) at something other than max gross. A 1000 lb Patrol (Bob's O-320 fixed pitch prototype) with 185 lb pilot and 2.5 gallons usable left (thus about 1200 lb at landing) will stall at 36.5 mph CAS per the flight test data. A more realistic 195 hp CS on a Patrol with a decent panel will tip the scales closer to 1200 lbs empty weight, and with 312 lbs of fuel, 400 lbs of meat, and 85 lbs of baggage, Vso is now 47.2 mph CAS at 2000 lb (max gross on wheels/skis). Could I find another 5 mph by adding slotted, double slotted, or other higher lift config? Yup. For 99.9% of missions flown, would I be happy with the weight gain, the airspeed loss, and the additional mechanical complexity, maintenance, and added failure modes? Not so much. I'm concerned with - and I suspect most folks looking at the 'hawks versus other options - is speed range. For my config (195 hp/two-bladed CS prop), I'll see Vso around 45 mph for most missions and max cruise of 150 or more if I can pay the gas bill. If I throttle back to 135, I'll see about 7.5 gallon/hr burn and about 6.5 hrs duration with reserves for just under 900 miles zero-wind range. In a nutshell, that is the value proposition, versus slogging along 40 mph slower with a max range of 500 miles, but enjoying the fantasy that I too can win a STOL competition. If STOL drag is your jam, get an airplane optimized for the job (land slow/cruise slow), then mod the shit out of it. For the rest of us that are content to get into and out of 800 foot farm and ranch strips, but still cruise at 172/182 speeds, the Bearhawks are fit to mission. After flying helos for 30 years in the military and civil world, landing super short has little novelty, but dropping in on friends in Florida or NE Ohio with farm strips after a doable day of flying without breaking the bank can be fun... Bearhawks in STOL Drag? Might see them. 13,000+ PA-18 and clones out there and something like 200 or less flown in competition. With a couple hundred 'hawks flying, we might expect to see a couple at some point. That said, I suspect you are more likely to see a Bearhawk bouncing around back-country strips with the local group of PA-18 clones, Maules, and tailwheel Cessnas.

[@EllipsisAircraft]

@@MDLuthier stall speeds are quoted at cited gross weight. That is literally the definition of VS0/VS1, which is clean or landing configuration, at max gross weight. To go out with a medium sized pilot and an illegally low fuel quantity (30 minutes reserve is at cruise power setting, not a significantly reduced 40% power level to attain those 30mins at best L/D with zero margin). As my math showed, these numbers are fairy tales and are not attainable in the real world by any builder or operator of these aircraft, in practice. That is my complaint: These claims are bordering on lies. If a super-lightweight aircraft was flown by a medium American sized pilot with only 2.5 gallons (15lbs*) of fuel to attain the claimed performance numbers, then my original calculations still stand. That these aircraft achieve a CLmax somewhat above 1.8 but well below 2.5. Leading to a stall speed of around 50mph at gross weight. And that tracks very close based on these numbers. Vans have metal wings, 50% of trailing edge is a 20-22.5%-chord flap. And they are slotted. Airfoil shaped, and slotted. None of which is true of Bearhawks. Which have plain flaps. Plain flaps attain a maximum CL around 2.5 in a wind tunnel with infinite wall end-plates. No matter how wide they are on the airplane, spanwise effects reduce the attainable performance below the maximum theoretical. And VGs wont improve it much, as q goes up at the square of speed. No VGs in the world are going to shave 5mph off a 46mph landing speed, unless the airfoil has a very poorly designed upper surface. An RV-8 has an honest CLmax of over 1.8, and will attain this number at published landing speed, at maximum gross weight, and most forward CG. Not counting the tail down-load to overcome forward CG or the wings negative pitching moment due to flap deflection. They publish not the most favorable that could ever be attained in practice; quite literally the least favorable condition found inside the design envelope. Cessna 180s having their very effective fowler-action slotted flaps, seem to attain slightly above 2.0: CL of 2.1 actually. The bearhawk is not much better than this, and probably a little worse than a Husky. There is zero chance any bearhawk wing can ever attain a CLmax of 3.35+ ever never. And I doubt it could get as slow as the 32-36mph range published, at maximum gross weight, by hanging on the prop at 100% power on a 59 degree day at 0MSL. Nope. Not going to happen. Not at maximum weight. These wings are middling-mediocre. Just big enough to work well enough for most people.

[@MDLuthier]

​@@EllipsisAircraft We both agree that airplanes stall at higher velocity as weight increases, and manufacturers tend to quote takeoff and landing distance, as well as Vso, at something other than max gross (see Aviat's Husky for another example). The Husky is a nice package that I have time in and a nice divot in my skull from a rushed preflight... anyone with time in one understands the trades to get those slotted flaps are the six head-knockers for passengers and those loading cargo. Not sure what a semi-Fowler is as claimed by Aviat; maybe they were going for Fowler-action but the ad folks got a hold of the word and decided to go Fowler-adjacent? Perhaps a nice post on their sales video bemoaning their misleading ad copy? In any case, the B is still rag wing and tandem lift struts, so those single slotted flaps are a good choice for an older airfoil like the Clark Y. That said, any plain flap hinged at or near the bottom of the surface ends up with some slotting effect without the head-knockers, so avoids braining the uninitiated at the cost of a knot or two at the low end and a gain of the same on the high end. Having spent way too much time in skinny little airplanes (6'2" and 210... so shoulder width matters), that 26" cabin on the Husky is a little narrow... I'll look for at least a 32" cabin width on the Ellipsis Model ... ;-)

[@MDLuthier]

On Vso - stall speed in landing config is landing config dependent. Should manufacturers quote Vso at max landing weight? ICAO Standard at sea level, etc? Nice, but also worth knowing what the aircraft will likely do when I am out solo (my usual jam) and not tanking fuel. Weight, flap config, landing gear config (on aircraft where that matters), and atmospheric conditions all matter. I think that - unless stated - you can assume Vso is minimum flying weight with min fuel and payload. Complaining that manufacturers are misleading the consumer is a valid bitch across the industry, so we consumers do due diligence, look at all the other factors (gear design, cabin width and access, cruise speed, cost to build, will our designer or kit manufacturer evaporate before project completion?) and pick a winner.

[@EllipsisAircraft]

@@MDLuthier manufacturers should provide reliable data the pilot can fly by. Citing a number the pilot will never see in reality is dishonest. He will never see this number, because he always flies with more than 2.5 gallons in an airplane that burns 12 gallons an hour. Stall speeds are always assumed to be at maximum gross weight. There is no other weight to assume. As that is the number all other factors are taken (g limits, climb rate, power to weight ratio, wing loading, etc, etc). If stall speeds just happen to be quoted at some other weight than maximum gross weight, it should be specified and clarified. Gross weight stall speed should be declared. As this is literally the most important factor in aviation. The ASI includes the green and white arcs for this reason, which are also defined at maximum gross weight in every airplane ever. How would you like to fly an airplane having the green arc extending 20mph below the stall speed? If the manufacture states an aircraft stalls at an unbelievably low speed, but is basing it on an unrealistic low payload, just to puff up their performance numbers. Then they brag about how their airplane is a 4.5g airplane... Yeah, but at what weight!? And what CG? Aft most CG greatly improves G-rating due to several factors. Are they quoting these numbers at the most favorable position? They seem to lean that was in all other areas. So yes, we can assume this is in some optimal test and may not coincide with reality. Carbon Cubs quote two speeds, 2 climb rates, and 2 weights. Because if they only publish gross weight performance, like Cessna or Vans, then some of these other fly-by-night kit companies will win over sales due to untruths and make believe. If you look at the performance of a carbon cub flown at minimum weight and maximum performance, it blows the BH lineup out of the water. There are many reason for this. Not that BH are bad designs. They are Utility planes, Bush planes, cargo haulers, and even qualify as STOL planes having takeoffs and landings under 1,000' which most Cessna's also qualify for. But they are being marketed as some sort of extreme STOL monster with dishonest numbers and false expectations, the reality is something else. They are mediocre; middle of the road lift, drag, speed, range, climb performance. The fact the manufacturer resorts to lies in the performance department is evidence of this fact.

[@gregbruner1918]

Thank you for posting this!