Bearhawk STOL mods

[Battson]

Oh - Full flaps definitely gets the plan flying slower, and popping full flaps gets it off the ground a little sooner.

When people talk about "best lift flap setting", I think they mean best lift:drag ratio for a given flight regime?

[Battson]

I'm asking because I doubt that the BH gives you much lift past 2 notches, just more drag.

Oh - I think I missed this part.

Full flaps definitely gets the plane flying slower, and popping full flaps gets it off the ground a little sooner too. The drag is much higher of course, but lift still increases considerably. The 540 machine just eats the drag.

Importantly, flap also lowers the deck angle and helps you see what you are doing. This pilot-element is key to STOL performance.

When people talk about "best lift flap setting", I think they mean best lift:drag ratio for a given flight regime?

The one time drag worries the plane is go-around / climb out.

[Bdflies]

Soon after beginning work on my Patrol project, I started thinking about the Keller double slotted flaps. The Patrol flaps are SO much larger than PA-18 flaps, it wouldn’t be a modification of the Kellers, but fabrication of a system, based on the Kellers. I continue to consider such. In my many hours, spent flying Huskies, I’ve grown quite fond of the single slotted flaps. If I ventured in that direction, I’d go with a single slotted flap, rather than the complexity of the double slot system.
Just this past week, I measured movement of the flap actuator pushrod. Full stroke is about 2 1/4”. The Husky has about 6” of travel. The Husky has a horizontal bellcrank in the wing, actuated by a cable, routed to a 'Y' harness. I think pushrod stroke is the key to a slotted flap system. I can build a set of fiberglass flaps. I can build a 'dropped hinge' system, similar to the Husky, to swing the flaps down and out. To build a bellcrank that would achieve 6” of pushrod travel, would require me to pull the wings and do massive surgery. I think the actuation system would require a complete re-design.
The Patrol flaps work fine. My experience with slotted flaps, on a similar airframe, makes me really curious about how the Patrol could benefit from such. The force required to deploy the hinged flaps is very high. I’d estimate flap deployment forces in Huskies to be around half of those in the Patrol. I think slotted flaps would be worthwhile, but I can’t see myself taking the plane apart to do the mod. If, on the other hand, anyone has a set of Patrol wings they'd feel like volunteering for development of such, I think it would be a great project!

Bill

[PaulSA]

Full flap may technically give a shorter TO roll but I suspect that most short strips are going to have hedges or trees at the end (that's why they are short!). The extra drag is going to severely degrade the initial climb performance. Sure, an IO540 powered aircraft is going to climb well anyway but it'll climb better with half flap. So, it's always going to be a compromise between TO roll and initial climb performance.

The generally accepted theory (certainly amongst the VANS forums) is that a flap setting equal to the down aileron deflection is optimum.

[Battson]

Full flap may technically give a shorter TO roll but I suspect that most short strips are going to have hedges or trees at the end (that's why they are short!). The extra drag is going to severely degrade the initial climb performance. Sure, an IO540 powered aircraft is going to climb well anyway but it'll climb better with half flap. So, it's always going to be a compromise between TO roll and initial climb performance.

The generally accepted theory (certainly amongst the VANS forums) is that a flap setting equal to the down aileron deflection is optimum.

A really interesting discussion point!

That aileron theory you're referring to is certainly a well known 'rule of thumb' for best lift:drag ratio. It does not work so well for high power:weight ratio aircraft. Refer to this backcountry flying source.

The Bearhawk 540 can pull itself off the ground fastest with three notches of flap set, or by pulling full flap at the right moment. Naturally you have to ease off the flap ASAP to climb efficiently. Best angle of climb is with half flap, and best rate of climb is with flap retracted. We can't really generalise and say half flap gives best climb, it depends why you are climbing... and according to this other backcountry flying source its a wash between Vx and Vy. Splitting hairs.

At minimum weight with flap retracted at 57kts, my Bearhawk climbs at greater than 45 degrees nose to the horizon, which is about 25 degrees climb angle. Obstacle clearance is almost never an issue for the 540 Bearhawk in my experience. If the strip is *that* tight for a 540 Bearhawk, then other planes are not going there. Think of situations like a gravel bar, tundra, mountain valley, or beach. Those situations probably cover 90% of STOL flying. In those places there is often a shortage of usable ground, but normally no immediate obstacles to clear. In fact, I can only think of four or five situations in the last 650hrs backcountry / STOL flying where immediate obstacles were an issue for me. These were places where few other planes short of a Carbon Cub could go.

In the STOL community it is widely accepted that popping flaps and lifting off as soon as possible is an important skill. It does depend on who you talk to, some prefer to set and forget. Refer to videos of any STOL contest to confirm this statement. In my view, optimising the wing shape for each phase of flight gives better performance overall, like birds do. However the margins are slim and it takes a lot of currency in the plane to get it exactly right. Done wrong, it adds workload and distracts the pilot for absolutely no benefit, and 50hrs a year simply won't get the pilot enough practice to ever get those skills. For intermediate skill levels, it's best to set and forget. Same goes for dumping flaps on landing.

[whee]

At minimum weight with flap retracted at 57kts, my Bearhawk climbs at greater than 45 degrees nose to the horizon, which is about 25 degrees climb angle.

This seems to indicate that using 19deg for fuel flow testing is not steep enough for big engine BHs. Are you saying that your level flight datum is at a angle great than 45deg during max climb? 45deg is crazy steep and far greater than the 19deg Russ Erb calculated for his flow testing.

[Battson]

This seems to indicate that using 19deg for fuel flow testing is not steep enough for big engine BHs. Are you saying that your level flight datum is at a angle great than 45deg during max climb? 45deg is crazy steep and far greater than the 19deg Russ Erb calculated for his flow testing.

Yes, the angle of the deck to the horizon can exceed 45 degrees at max performance. I should video it from the cockpit one time, it's impressive. Bearhawk 540's are just the best fun.

I suggest testing whatever works for you and your inspector, 45 degrees is not practical for a ground-based flow test. We did three point.

My system is pumped twice in those circumstances. However, we can take-off / climb that steeply with only one pump and with very low fuel pressure (like 12 psi), we've tested it.

That angle is for Vx, but I can go steeper just for the fun of it. The plane will climb steady state at over 50 degrees to the horizon "hanging on the prop" at about 50 knots. I have seen 55 degrees for short periods. You'd have to see it to believe it. This is practically useless though, just for fun!! Not many planes can do that kind of trick.
I wait for perfect weather to ensure safety, despite a huge margin over the stall showing on the AOA display, call me chicken.

[Mark Goldberg]

I do not think anybody calls you chicken Jonathan. Much to the contrary. Mark

[svyolo]

Wow. That is impressive. I have only flown one "overpowered" plane. By that I mean the engine can put out more power than the airframe can actually handle, and can actually drag it through the air at speeds greater than it can comfortably fly (or control). But the some of the descriptions of the 540 BH remind me of the same thing. Especially going fast.

I think it is a good generalization that more flaps is better for the shortest TO roll, but at the expense of climb. Higher flap settings on bigger planes also works, but at a large penalty in Max TO weight. The loss of performance is just to great. It does work well when fairly light.

[Rollie]

I thought I would go ahead and weigh in on this discussion on flap usage. Flaps for takeoff, for me, is situationally dependent. I don't like buying tires so I always want to get off the runway fairly short so I always start my takeoff roll with two notches of flaps. Sometimes I leave it there for takeoff, sometimes I pull it to the 3rd notch as I rotate to get off the ground a bit earlier. I haven't gone to the 4th on takeoff yet. The takeoff roll is short, but it is also quick. It starts rolling, the tail comes up, about a second later I can lower the tail and pull more flaps and I'm flying. A few seconds later I'm going back to 2 notches of flaps so I don't overspeed the flaps. I could just climb really steep to keep the airspeed down but after a few seconds I'll be above any nearby obstacles and then there isn't really a reason to stay in an attitude that would be difficult to recover from in the event of an engine failure that close to the ground so its time to accelerate which means its time to raise the flaps a bit. What I'm getting at is that no matter how much flaps you apply for a shorter takeoff roll, the extra drag from more flaps isn't really an issue for climb because you won't be leaving them down for more than a few seconds. I'm just flying behind about 200hp in my Patrol. In the 250 hp four place, you really have to be paying attention to keep the climb steep enough or reduce power to keep your airspeed down until you raise the flaps. Its a lot different than the Pacer I used to have. On my Pacer, which had two notches of flaps, I would start the roll with one notch of flaps, add the second as I rotated, get off the ground, climb slowly while waiting for the speed to build enough to raise the flaps back to one notch without stalling, then climb out with either one notch or flaps up. The drag of full flaps on the Pacer definitely hurt climb performance, but it was still the only way I could get out of short, tight strips.

As for landing, I either use 3 or 4 notches of flaps. I'm still trying to work out the best way to land with 4 notches. With three I can glide in, flare to a nice touch down. With four, if I'm not right at the max speed for four notches, I don't get much of a flare, it will kind of drop through, which I attribute to all that extra drag. Now if I carry a bit of power with 4 notches and drag it in slow, and reduce power as I flare and reach idle about the time I touch down, I can get a nice landing and not use much runway. I haven't got to practice this much yet but I had it down pretty good in my Pacer and this plane is so much more capable.

[Bdflies]

I only use the 4th notch on short final. The 3rd notch is just as you describe. 4th is like air brakes! Great isn't it? I don't pull 4 above 65mph...then it's Game On!
Rollie, did you extend your flap handle? Or can you get the 4th notch with the standard handle?

Bill

[Rollie]

I didn't extend my flap handle. I have been able to get to the fourth notch one handed a couple times by slowing down to below 45 knots. Usually I just use two hands at just over 50 knots. My wife was having trouble getting to the third notch but once she started slowing down an extra 10 kts instead of trying to lower them right at the max speed she has been able to do it. The fun part is learning to pull that hard without pushing on a rudder pedal. I had done it a couple times during my test flying so I expected it when she did it. Not the best time to get way out of trim, especially if you slowed down close to stall to make it easier to lower the flaps.

[Bdflies]

I built a new extended handle, as long as possible without busting my thumb on the cross bar. The 4th notch isn’t easy, but way easier than before.

Bill

[svyolo]

I guess if I was planning on doing really short field work (I do), I would try to validate how the plane climbs at high flap settings and high weights before I was doing it for real. Load the plane up, get up to 2-3000 feet, and see how the plane climbs at 3 or 4 notches flaps. If it won't climb at gross weight or close, I would rather find that out with some altitude to recover.

Obviously density altitude is going to have a huge effect as well.

[schu]

That angle is for Vx, but I can go steeper just for the fun of it. The plane will climb steady state at over 50 degrees to the horizon "hanging on the prop" at about 50 knots. I have seen 55 degrees for short periods. You'd have to see it to believe it. This is practically useless though, just for fun!! Not many planes can do that kind of trick.
I wait for perfect weather to ensure safety, despite a huge margin over the stall showing on the AOA display, call me chicken.

Boy, that is interesting.... Sounds like your basic power on stall. Have you continued to the stall to ensure that your AOA is accurate in that situation?

I think Jon is right, makes me think differently about testing fuel flow.

[Battson]

Boy, that is interesting.... Sounds like your basic power on stall. Have you continued to the stall to ensure that your AOA is accurate in that situation?

I think Jon is right, makes me think differently about testing fuel flow.

Yes we have stalled it like that, call it "advanced stalls". We can fly around at maximum AoA doing turns up to 30 degrees bank left and right, well out of balance, and it just wont stall. You really need to mistreat it to make it stall.

When you are 50 plus degrees nose up and 30 degrees in a bank, out of balance, and the Bearhawk is holding everything together for you - you develop a deep sense of trust in your aircraft.

Of course all the discussion above is predicated on the plane being at minimum weight. With a load on it's a totally different ball game.

We did some stalls with a new pilot the other day, it was his first flight ever in a plane anything like this - after five minutes of turns we did the stalls, he was easily able to control / recover all but the deepest of wing-drop stalls. He is used to high wing loadings and nasty stall behaviour, so was really impressed. The Bearhawk really is an exceptionally safe plane for pilots.

[Battson]

For information, I am told the double-slotted Bearhawk flaps are now under production ("Keller Flaps").

For those who are unfamiliar with these flaps, see below for an install on a Maule.

full_flaps.jpg

[schu]

I wonder if airframes will sell a kit to keep the price down a little.... I think this with the other things mentioned would make the bearhawk into a much better bush rig.

[Battson]

I wonder if airframes will sell a kit to keep the price down a little....

I think they must. Once you've done all the engineering and tooling, you've done it all. The only thing remaining is to recoup your investment.
I expect a kit would be over $10,000 delivered, and it would not be "plug and play". You'll need to modify some of the wing parts.