Bearhawk STOL mods
- Thread starter schu
- Start date
AKKen07
Well-known member
Pardon my ignorance but can you please explain what you are saying about the first notch not being “blown†due to the pocket being imperfect? Do you mean that the slot won’t get extra airflow at that setting as the lower skin blocks it or something to that effect?
Battson
Moderator
Yes you have it Ken, I assume that both sections of the flap needed attached airflow right around their surface to generate maximum lift. However the truth may be different, it all depends on how the design has been done though.
I have always thought they worked like this, so that the airflow was blowing smoothly over both segments of flap:
However, in researching this response, I found this literature which suggests that the double-slotted flap still works without a streamlined flap pocket. So-call Douglas double slotted flap.
I love this stuff
Battson
Moderator
This has been tried and the results are known.
It makes a large difference, but there were some unintended consequences which were more annoying than the benefits were worth. I believe it made the plane really floaty in the flare.
Battson
Moderator
I am excited to confirm the new Airframes Alaska double-slotted fowler flaps have flown on the Bearhawk 4-place.
Positives:
Positives:
- There was a significant improvement in approach speed. Yet to be confirmed, but we are talking about a reduction of 6 knots or more and a 'rock-solid' approach.
- Reduced stall speed, improvement yet to be confirmed.
- There was an even more significant improvement in deck angle and forward visibility when landing. Angle is yet to be confirmed, but more importantly the point of touchdown was clearly visible even at the stall speed, no neck-craning required.
- There was a small reduction in elevator effectiveness at extremely low airspeed. This only occurred at speeds previously unreachable by a 4-place on final approach.
- When the plane stops flying, it really stops. The transition was sharp.
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Isilverone
Well-known member
Great news, are you waiting on permission from the builder?
Cguy
Well-known member
I talked with MicroAeroDynamics about this (more vg's in front of the flaps, a month ago, as my Rans S-7S also has "plain" flaps, like the BH designs. I have been using their vg's for 20 years on my wings, and had my credit card out and was hot to trot. They talked me out of it, I'd be messing with the ALREADY vg-ized (energized maybe was the term) airflow caused by the existing vg's on the LE, no need to put more on plus there was something said about "control reversal possibilities", and that's when I tagged out. The idea comes up from time to to time, but near as I can tell there is a good reason why we don't see vg's in front of the flaps.
Way to go Battson on the Keller flaps! I too look forward to your numbers on how they work.....
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Battson
Moderator
I have gone through the details more carefully and revised the approach speed reduction from 4 to 6 knots less.
The stall attitude appears to be about the 3 point attitude, or slightly tail low - same as a Maule with slotted flaps.
The plane is question is about 1,630 lbs empty weight. Initial flight tests were done with 20 US gal of fuel.
The results I have shared are quite literally from the first three approaches and landings. They are subject to change as test flying continues.
The pilot remarks that while it was possible to approach in the mid thirties [knots], it was a sporty regime and was accompanied by a loss of elevator control and reduced visibility. High thirties was rock solid with good visibility.
The stall attitude appears to be about the 3 point attitude, or slightly tail low - same as a Maule with slotted flaps.
The plane is question is about 1,630 lbs empty weight. Initial flight tests were done with 20 US gal of fuel.
The results I have shared are quite literally from the first three approaches and landings. They are subject to change as test flying continues.
The pilot remarks that while it was possible to approach in the mid thirties [knots], it was a sporty regime and was accompanied by a loss of elevator control and reduced visibility. High thirties was rock solid with good visibility.
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Battson
Moderator
There is some aft movement, chord length increases by several inches, so technically they are semi-fowler, like a Cessna flap. It's an advertising thing I guess.
I have laid this out before over at BCP, and it was argued out by the panel. Same conclusion was reached.
svyolo
Junior Member
I don't think there is a carefully worded definition on Fowler flaps. "True" ones I guess have sliding tracks, and translate aft as well as rotate down. Very complicated and heavy, and usually have external tracks, but not always.
Jon;
Your description makes it sound like it stalls at a much lower AOA. Does that seem to be the case?
Jon;
Your description makes it sound like it stalls at a much lower AOA. Does that seem to be the case?
Gerd Mannsperger
Well-known member
Great to see the flap Mods work as well as I would have expected.
The first thing I would do though is to instal VG's on the leading edge wing and on the tail surfaces as well as gap seals to maintain controllability at the slower speed.
One of the most important and usually overlooked benefits of VG's is how they help to maintain control at the slower speeds not just the reduction in stall speed.
One of the negative side effects of lowered stall speeds usually is reduced control at that slower speed, only VG's enhance control while reducing stall speed.
We had the same issues with Robertson stol equipped 180and 185s and the addition of VG's made the aircraft very controllable at the slower stall speed.
The first thing I would do though is to instal VG's on the leading edge wing and on the tail surfaces as well as gap seals to maintain controllability at the slower speed.
One of the most important and usually overlooked benefits of VG's is how they help to maintain control at the slower speeds not just the reduction in stall speed.
One of the negative side effects of lowered stall speeds usually is reduced control at that slower speed, only VG's enhance control while reducing stall speed.
We had the same issues with Robertson stol equipped 180and 185s and the addition of VG's made the aircraft very controllable at the slower stall speed.
Westward_Flyer
Well-known member
I'm eager for some news as well, this is one of the coolest BH mods I've ever seen.
Westward_Flyer
Well-known member
Gerd Mannsperger
Well-known member
VGs on the leading edge of semi fowler flaps work extremely well but you can do either that or the VGs on the leading edge not both.
The leading edge VGs give the benefit of better control while the VGs on the flaps just lower stall speed with a reduction in slow flight control.
The reduction in stall speed is very close to the same in both instances, if in doubt go for improved controllability.
I believe the Cessna Caravan comes with VGs on the flaps stock.
The leading edge VGs give the benefit of better control while the VGs on the flaps just lower stall speed with a reduction in slow flight control.
The reduction in stall speed is very close to the same in both instances, if in doubt go for improved controllability.
I believe the Cessna Caravan comes with VGs on the flaps stock.
Battson
Moderator
This is the latest I heard about the Fowler flaps modification:
Final approach - estimated prevailing deck angle was in fact about 7 degrees. Ample visibility over the nose till the last couple of seconds and the round out.
This compares to about 14 degrees in a Bearhawk 4 place A model flown at the same approach speed / profile. This is a big deal, and the main benefit which we would hope for - as well as the speed reduction. We are talking flying at the slow speed limit here, certainly nothing like a 50kt approach.
That touchdown actually was concurrent with a full stall just as the stick hit the stops. It will take more time to really master it, results are still preliminary.
The roll-outs are now very benign from the reduced energy touchdowns, the pilot has said it makes the roll-out a very relaxing experience.
He is trialling some crosswind landings, noting the icy condition at the time this was reported. The pilot's view is that with the slotted flaps there is much less weather-cocking than the 52 degrees of barn door flaps. Crosswind control appears to have improved compared to the normal flaps.
I've touched base for a further update.
Final approach - estimated prevailing deck angle was in fact about 7 degrees. Ample visibility over the nose till the last couple of seconds and the round out.
This compares to about 14 degrees in a Bearhawk 4 place A model flown at the same approach speed / profile. This is a big deal, and the main benefit which we would hope for - as well as the speed reduction. We are talking flying at the slow speed limit here, certainly nothing like a 50kt approach.
That touchdown actually was concurrent with a full stall just as the stick hit the stops. It will take more time to really master it, results are still preliminary.
The roll-outs are now very benign from the reduced energy touchdowns, the pilot has said it makes the roll-out a very relaxing experience.
He is trialling some crosswind landings, noting the icy condition at the time this was reported. The pilot's view is that with the slotted flaps there is much less weather-cocking than the 52 degrees of barn door flaps. Crosswind control appears to have improved compared to the normal flaps.
I've touched base for a further update.
Gerd Mannsperger
Well-known member
That is correct
Gerd Mannsperger
Well-known member
One bit of caution on fowler and semi fowler flaps. They generate a lot of force into the back spar and attachments. The early Cessna 206 aircraft used to bend the back spar , never a issue with the less powerful 185 flaps, later versions of the 206 had spar doublers. On the Found Bush hawk we used to have Barn-door flaps that were activated by a simple lever--when they build the semi fowler flap the stall speed dropped by 7 knots and the approach was nice and flat, but it was impossible to activate by hand and a 2 tone electric flap jack( a bit of overkill) was installed.
My point is better make sure the engineering on the attache structure is up to the task. Extra weight (Attach structure and the flap) as well as added complexity are the negative side effects of fowler flaps.
My point is better make sure the engineering on the attache structure is up to the task. Extra weight (Attach structure and the flap) as well as added complexity are the negative side effects of fowler flaps.
Gerd Mannsperger
Well-known member
As long as there are known upgrades and fixes for known problems you are good togo.
Fatigue is a tough target to design for when dealing with aircraft that need to be light.
Just keep that in mind when you build, take extra care when you build the attach structure to save yourself a repair later.
This is just a heads up for anyone upgrading to bigger more powerful flaps.
Also watch your flap extension speeds especially in rough air, a few MPH lower Flap extension speed dramatically drops the induced forces on the flap,
These Forces on your flaps increase exponentially with speed they go down the same when you slow down.
Fatigue is a tough target to design for when dealing with aircraft that need to be light.
Just keep that in mind when you build, take extra care when you build the attach structure to save yourself a repair later.
This is just a heads up for anyone upgrading to bigger more powerful flaps.
Also watch your flap extension speeds especially in rough air, a few MPH lower Flap extension speed dramatically drops the induced forces on the flap,
These Forces on your flaps increase exponentially with speed they go down the same when you slow down.
Cguy
Well-known member
That is also what MicroAeroDynamics told me. A long time, 20 years, user of their VG's on two different Rans S-7's, on the wings and the bottom of the horizontal stab., I had an idea to use them to "enhance" my flaps, and was told in no uncertain terms that it was not a good idea, and was not needed as the LE VG's were already "getting the job done."
FastLaneAK
New member
I have a Lake Buccaneer. The VG’s are on both the leading edge and the huge slotted flaps as per STC. I’m not sure who said that they don’t work on both as they do. Also used on Shane Madison’s cub slotted flap hangers with great success.
FastLaneAK
New member
Gerd Mannsperger
Well-known member
Yes that was my information as well
500AGL
Low & Slow & Door Open
I've not installed VG's nor test flown various settings on the Ribblett airfoil of the Bearhawk. But regarding VG's in general, Jerry Burr is pretty much the authority on them, having spent likely hundreds of hours testing, learning and understanding what worked the best. I believe the graph below from him was on a SuperCub wing. The most common installation error in my opinion is simply that they are mounted too far back on the chord. The idea is to keep the airflow attached at high(er) AOA, and as his graph shows, it's almost impossible to put them too close the leading edge.
Attachments
Gerd Mannsperger
Well-known member
The most effective of all STOL mods is also the cheapest one.
Weight -- less is more.
If you want STOL capability exercise discipline build simple and light.
Just got back from a Photo / training flight on some local sandbars with light aircraft and it is so easy.
Usually I am always at gross weight ( for work) and it is a whole different world --weight should always be the first consideration for a STOL aircraft.
Weight -- less is more.
If you want STOL capability exercise discipline build simple and light.
Just got back from a Photo / training flight on some local sandbars with light aircraft and it is so easy.
Usually I am always at gross weight ( for work) and it is a whole different world --weight should always be the first consideration for a STOL aircraft.
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Gerd Mannsperger
Well-known member
Yes been there done that.
But I pulled 160 pounds of misguided perceived needs out of my last Cessna 206 and 120 pounds out of my last M7 all in Vacuum systems Avionics auto pilots and heavy interiors.
The Airframe and powerplant are still all stock.
Paint is a big one too, more so on fabric aircraft.
On the Maule I saved 25 pounds alone on the paint when I painted it and did the fabric.
Both Aircraft already had lightweight Starters and Alternators but still have stock Batteries. If this is on the table on certified aircraft imagine what is possible to the builder of homebuilt aircraft.
If STOL is your game watch the Weight
But I pulled 160 pounds of misguided perceived needs out of my last Cessna 206 and 120 pounds out of my last M7 all in Vacuum systems Avionics auto pilots and heavy interiors.
The Airframe and powerplant are still all stock.
Paint is a big one too, more so on fabric aircraft.
On the Maule I saved 25 pounds alone on the paint when I painted it and did the fabric.
Both Aircraft already had lightweight Starters and Alternators but still have stock Batteries. If this is on the table on certified aircraft imagine what is possible to the builder of homebuilt aircraft.
If STOL is your game watch the Weight
Gerd Mannsperger
Well-known member
You are correct Kestrel weight is not everything, I would not want to weaken the airframe or landing gear for example.
However if you add more weight you will need to go to heavy duty landing gear and brakes for the higher weight - adding more weight - eventually you will need more HP = Bigger engine More weight now your stall speed goes up and you need to extend your wings to make up for it and on it goes. I hope you get my point.
However if you add more weight you will need to go to heavy duty landing gear and brakes for the higher weight - adding more weight - eventually you will need more HP = Bigger engine More weight now your stall speed goes up and you need to extend your wings to make up for it and on it goes. I hope you get my point.
JimParker256
Bearhawk Enthusiast
Kitplanes has been running an excellent series of articles on aircraft design. It has given me a lot of insight into the compromises and trade-offs made during that process. More fuel -> more weight -> stronger wing structures -> more weight -> more power needed -> more fuel, repeat ad nauseum... Understanding those trade-offs a little better have given me even more respect for Bob and his designs... No design is perfect, but Bob's designs produce some pretty incredible airplanes!
Westward_Flyer
Well-known member
With the increased gross weight of the model 5 are the more extreme (plan altering) STOL mods off the table? Such as fowler/slotted flaps, wing extensions, etc.
I'm assuming the other mods will be fine since it uses the same wing as the model B.
I'm assuming the other mods will be fine since it uses the same wing as the model B.
Dave Roberts
Member
Are there any updates on the double slotted flaps? Thanks Dave
Battson
Moderator
Sounds like they have done what was expected, small reduction in stall speed and much flatter deck angle (about 50% closer to level). From what I understand, testing finished a long while ago.
I expect this plane will come up for sale sometime in the future, for unrelated reasons.
Even if you got no reduction in stall speed, getting the deck angle down when flying slow would be a tremendous stol mod.
Dave Roberts
Member
Thanks. Yes deck angle would be a big deal.
I was over at Carbon Concepts the other day and he has some really interesting new flaps on his cub. Single slot with a kevlar based compliant hinge for the second. I think the install would be wildly simpler on our airplanes.
I guess through testing they were finding the second slot was doing nothing at all for keeping the airflow attached at our slow speeds.
I really want to get the deck angle down to. I'm landing tail first about 100% of the time if I want to be slow. A water landing acceptable deck angle is around 50kts. Pretty fast.
I guess through testing they were finding the second slot was doing nothing at all for keeping the airflow attached at our slow speeds.
I really want to get the deck angle down to. I'm landing tail first about 100% of the time if I want to be slow. A water landing acceptable deck angle is around 50kts. Pretty fast.
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Pbruce
Member, Patrol QB
Is it the slot between the wing and the first section of flap or the combined angle of the sections which allows for the lower pitch attitude for a given speed, or what? Is there any video or photo documentation available to show this simpler installation with this Carbon Concepts flap? It’s pretty neat stuff. Planning big wheels on my Patrol, and I’m thinking the pitch attitude will determine what can be done within my comfort zone. I’m going as stock as can be done to start, but I’ll be paying attention to thiS thread with much interest.
500AGL
Low & Slow & Door Open
You may want to consider looking at Shane Madson’s hinges. Although perhaps Randy’s may be similar?
https://madcustomcubs.com
(https://madcustomcubs.com/product/fowler-flaps/)
If you look at some photos of his cub you’ll see how the hinges roll the flap aft as they deploy.
https://madcustomcubs.com
(https://madcustomcubs.com/product/fowler-flaps/)
If you look at some photos of his cub you’ll see how the hinges roll the flap aft as they deploy.
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svyolo
Junior Member
It looks like the bird hit the market. Looks nice. Interesting cowl flaps as well. I wish he was on the forum to discuss his build. I hope all goes well for him.
Wow, and for a price! I mean, I hope he gets it. I'd sell mine tomorrow for something near that.
Battson
Moderator
Show ponies have previously fetched north of $140k for looks alone. This plane has tangible value in terms of a long list of real modifications which cost the seller a lot of money to purchase and install, plus countless time in literal research and development as discussed here in this thread. I believe this person doesn't have the repairman cert and started with a stock plane, so needed to have these installed by others - as would anyone else buying a completed plane.
Therefore the price reflects the real cost to create such a highly customised and extremely high performance machine, without starting from scratch / kit.
For comparison, take a look at Greg's new videos of Bushwacker II on his YouTube channel "mauleguy". This Bearhawk 4-place has every mod which Greg included on Bushwacker and a lot more, apart from the extended wingtips (which you will soon be able to bolt on for next to nothing in the scheme of aircraft price tags). To me this plane is worth about what he's asking. I too hope he gets something close. Our plane isn't too dissimilar to this machine - in terms of performance I think we do a little better as we're lighter, but I am not selling
Just gonna put these here for the record:
Note the revised gear design.
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Show ponies have previously fetched north of $140k for looks alone. This plane has tangible value in terms of a long list of real modifications which cost the seller a lot of money to purchase and install, plus countless time in literal research and development as discussed here in this thread. I believe this person doesn't have the repairman cert and started with a stock plane, so needed to have these installed by others - as would anyone else buying a completed plane.
Therefore the price reflects the real cost to create such a highly customised and extremely high performance machine, without starting from scratch / kit.
For comparison, take a look at Greg's new videos of Bushwacker II on his YouTube channel "mauleguy". This Bearhawk 4-place has every mod which Greg included on Bushwacker and a lot more, apart from the extended wingtips (which you will soon be able to bolt on for next to nothing in the scheme of aircraft price tags). To me this plane is worth about what he's asking. I too hope he gets something close. Our plane isn't too dissimilar to this machine - in terms of performance I think we do a little better as we're lighter, but I am not selling
Just gonna put these here for the record:
Note the revised gear design.
In the US you only need the repairman cert to do the condition inspection. My grandmother can do all the mods and mx to my airplane she wants. Just can't do the condition.
whee
Junior Member
I looked at the ad the day it was listed and a few days later the ad was gone. I was stunned. Awesome for the seller if it sold and awesome for the buyer who got a cool airplane.
If there was a buyer that was a day late...I’ll sell ya mine for a deal. Or I’ll build me another and sell it to you in a couple years.😜
Battson
Moderator
I don't know if I would sell mine at that price, once the chips were down...
Once you value your time (fair value) the plane owes you a lot of money. You probably couldn't build one for that money if you were paying for skilled labour and all those mods. This leads to a discussion about pricing a custom STOL build with third party labour - probably a different thread!!
Once you value your time (fair value) the plane owes you a lot of money. You probably couldn't build one for that money if you were paying for skilled labour and all those mods. This leads to a discussion about pricing a custom STOL build with third party labour - probably a different thread!!
Battson
Moderator
The other point I want to reflect on:
Many expert observers speculated that the Bearhawk would run out of elevator authority if slotted flaps were installed. With elevator gap seals and elevator VGs, this was not a problem on this particular machine. This is great news for anyone else wanting to enhance their flaps. I think this is the only real weakness of the Bearhawk family of designs, high nose AOA at landing because the flaps aren't slotted (whereas a Maule's flaps are). Converting to Maule style flap hinges would be an easy and literally bolt-on modification.
Further thought:
This Bearhawk had a stock trim system.
As far as I know, the (former?) owner never thought the plane pitch-sensitive in the cruise, noting that his cruising speed was about 115mph given he liked to run LOP and has 35" tires with a cabane L/G. I suppose a faster cruising plane would become pitch sensitive with those gap seals and elevator VGs installed. I am tempted to install those items.
Many expert observers speculated that the Bearhawk would run out of elevator authority if slotted flaps were installed. With elevator gap seals and elevator VGs, this was not a problem on this particular machine. This is great news for anyone else wanting to enhance their flaps. I think this is the only real weakness of the Bearhawk family of designs, high nose AOA at landing because the flaps aren't slotted (whereas a Maule's flaps are). Converting to Maule style flap hinges would be an easy and literally bolt-on modification.
Further thought:
This Bearhawk had a stock trim system.
As far as I know, the (former?) owner never thought the plane pitch-sensitive in the cruise, noting that his cruising speed was about 115mph given he liked to run LOP and has 35" tires with a cabane L/G. I suppose a faster cruising plane would become pitch sensitive with those gap seals and elevator VGs installed. I am tempted to install those items.
The bearhawk isn't pitch sensitive unless you're in the back quarter of the cg range. If you're flying around mostly empty like a lot of people do especially for max performance you'd never notice.
Dave Roberts
Member
I wouldn’t do any expensive mods to the Bearhawk. Extended wingtips, gap seals on the elevator (that one will create problems with the old style trim tabs),vg’s and bush wheels will get you in and out of any strip that you need to. Spend the rest of your money on av gas and learn how to fly it. You can get $20,000 in mods pretty fast. I can just about guarantee you the guy that spent that 20000 on av gas and practiced will kick your butt on landing and taking off. The Bearhawk is a good airplane and more capable than most pilots. Not that I haven’t toyed with the idea of improving the flaps. But in the end it just doesn’t seem worth it. This thread started out with wanting to land and take off light in 400 to 500’, heavy 700 to 800. A bone stock Bearhawk with a 540 will do that effortlessly.
As far as the Keller flaps go. I talked to the guy that has them on his bearhawk. All said and done that was a $20,000 mod. I can go find a strip a hundred feet longer and buy more Avgas for that. A lower deck angle would be nice, but with 900 hours and over 3000 takeoffs and landings somehow I’ve gotten by without them.
As far as the Keller flaps go. I talked to the guy that has them on his bearhawk. All said and done that was a $20,000 mod. I can go find a strip a hundred feet longer and buy more Avgas for that. A lower deck angle would be nice, but with 900 hours and over 3000 takeoffs and landings somehow I’ve gotten by without them.
whee
Junior Member
Awesome! Thanks. Those pics are massively helpful to me.
Sir Newton
Well-known member
I reviewed some flap modifications with 71yr old aerial spray applicator with 17k+ hrs spraying fields in the Alberta /BC foothills. My friend knows how to fly heavy low and slow. He looked at the flaps on the bearhawk model B wings & said there is no need to change anything. Plenty of flap for that little plane. You will not be able to use what you have. No need for more.
whee
Junior Member
Your totally right, it might not be worth the effort. I’ve been digging into texts that are focused on flap design and the difference in lift at the trailing edge between a slotted flap and a plain flap appears to be significant. To me this is what matters. I don’t need the plane to fly slower; being able to land at minimum speed without the tail touching first is what I’m looking for.
Battson
Moderator
Here is a video of a Maule and a Bearhawk flying the same speed, similar wingspan, similar weight, and within 30 seconds of each other - same conditions.
The main difference is the flap design, barn door Bearhawk vs slotted as shown above. Look at the difference in deck angle.... there is a noticeable difference.
The Maule pilot can see where he's going over the nose, the Bearhawk pilot has to look around the nose or use a little sideslip. Having flown both planes, I there is a difference in deck angle.
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schu
Well-known member
I can see a little difference, but not gobs as you can see the upper windshield of both aircraft all the way down, though the bearhawk seems to have gotten into a deeper flare.
It would be much easier to tell with a cockpit camera or even better flying the approach in both.
schu
It would be much easier to tell with a cockpit camera or even better flying the approach in both.
schu
Battson
Moderator
I have video of the Bearhawk with the double slotted flaps landing in a deep flare, you can easily see the difference in that case. At least 8 or 10 degrees flatter deck angle and a wonderful sight picture all the way in.
I have also flown slow approaches in both planes in that last video, as PIC, and the Maule is better - but not 8 to 10 degrees better. Just a handful of degrees. But then again, that does make a difference, especially given there is no weight penalty with that design of flap hanger - it should bolt straight on.
There is a small weight penalty, I think, with the double slotted flaps. However it was very small. You make up for that very small weight penalty by how much it lightens your wallet...