Ideals to reduce Johnson bar force

[Battson]

I am finding it hard to pull the last notch of flap during backcountry ops. Especially when I might be turning in a tight space, or focussing outside, when I need more flap. You really have to get your body in behind it. I have actually pulled a muscle in my arm on two occasions now! I use a high seating position to see clearly over the nose for STOL ops which makes the problem worse, it's really only the last notch which gives grief. I am observing the Vf speeds, and in most cases going slower than necessary before adding flap.

Has anyone though of ways to improve this?

One idea I had was lengthening the bar, to reduce the necessary force and make the bar handier for the last notch. I have long arms so the reach isn't a problem, and you can simply grab the bar lower down for the first two notches.

I also thought of using a larger grip as part of such an extension. That little 3/4" tube is pretty hard to grasp firmly. In summer with hot hands, my hand has slipped off the top a couple of times.

I also considered installing a large spring to reduce the force required, although a spring would provide less force the further up you move the bar - when you really need more force, not less.

Has anyone spoken to Bob about this kind of mod? Any other ideas?

(please don't recommend that EZ-flap product.... )

P.S. This is also an issue because my financee can't fly the Bearhawk herself, she's not weak but also not strong enough to work the flap handle. Maule flaps take almost no force at all, why is there a difference??

[DesertBearhawk]

Could you modify the input arms on the flap torque tubes, making them longer for more leverage?

[Battson]

Good lateral thinking - I hadn't considered that.
Trouble is, there's practically zero room left in the wing root for improvement. Flap drive set-up is exceptionally tight as it is, virtually touches the forward and aft limits already. But thanks for the idea!

[Zzz]

Eager to see the responses, as my impression of pulling the last notch was about the same. Quite the effort! If your hand is sweaty, forget about it.

The Maule lever is not really longer if I recall, so there must be a geometry issue somewhere? Perhaps it has to do with the leverage afforded by the torque tube arms as they rotate into a less "powerful" position near the end of the flap travel?

[Battson]

Yeah I would really like to know why. In the Maule and the Cessna's I've flown with manual flaps, they can have full flaps pulled on by a youth without difficulty, even with the aircraft above the flap speed for full flaps. There must be a significant geometry difference somewhere?

[DesertBearhawk]

Thats an interesting point about the flap arms. I bet you could get some advantage if you changed the geometry to give you the best leverage at the full flap position. This, of course would require you to re-index your torque tube. As I have not yet drilled my tube for the drive arms I'll be watching this thread closely!

[John Rheney]

I've been doodling around on this question for a couple of years. I'll probably work on it in earnest now that I'm about to move the fuselage back to the shop. In my napkin sketches, I have replaced the inboard arms with a fixed cams. The problem with the arm is that once it passes the straight 'up' position the leverage the cable can apply is continually reduced as the arm moves rearward. Replacing the arm with a properly shaped cam that keeps the cable at the maximum height above the axis of the torque tube may provide some relief. I haven't put together the numbers and ground them through any analysis yet, but I intend to. The shape at the bottom of the handle may also provide some opportunity, but I think it is closer to being correct for the transmission of arm power to the flaps as is.

Them's my thoughts. Call me crazy.

John

[DesertBearhawk]

I agree, you want the input arm 90 degrees to the cable at the full flap position. As I said, Im in the process of wing building and have yet to drill my drive arms yet….Ill have to noodle on it….

[Battson]

That is a great idea with the cam, hopefully there's room in there for one if cleverly designed.

I alreadyrotated my drive arms further forward than normal, so they are close to 90 degrees with full flap applied - the first two notches are still easy to pull, even with the very shallow cable angle, but being close to 90 degrees for the last notch hasn't alleviated the problem.

I think the largest part of the force increase at the handle is coming from the aerodynamic force increasing. With the larger change in momentum of the airflow, bending around the flap, comes larger force upon the flap - proportional to the sine of the angle of the bend the airflow is being forced to make.

I had a talk with Bob about this tonight. His view was that it's largely an issue of the reach to the handle making it seem harder than it really should be.
He said that provided the flap speeds are observed, solutions like lengthening the bar, moving the pivot point higher, etc would be ok to try. He is happy to take a look at any drawings people might create.

He did mention the geometry and position of the outboard drive is designed to reduce the spring resistance at full flap.

[Gerhard Rieger]

I do not know about the Maul, the Cessnas have 40 deg . Bearhawk at 50 deg and it is a huge flap. I do not think Bobs design is bad, we must just get some wisdom to improve on it. If you have a winch on your truck, you put the cable to a tree you have xx pulling power, if you double the cable through a pully back to the truck you increace the pulling power to xxxx I did not yet looked at the possibilities for this but will look into it.

[Battson]

Doubling the cable over a pulley is much like doubling the length of the lever arm - you get twice the force, but you have to pull twice the distance too - which takes space.

[Gerhard Rieger]

Thanks, Battson, point taken,

[kestrel]

Perhaps my electric flaps aren't so bad after all? The Bearhawk's flap has a very wide chord and that is probably a factor. Gerhard, force times distance will remain constant. The problem with reducing force is finding more distance. The ideas of cams or changing arm angles work by increasing force/reducing distance at small flap angles when the task is easy anyway, and doing the opposite at the other end of the range. Other than that, more distance is needed. -- Bearhawk

[Battson]

RE: electric - at least you know you're getting the extension angle you've asked for!
To be honest, I don't see how electric flaps would be any real hindrance. I never dump the flaps on landing, too much else to do if you're landing somewhere that it could actually make the difference.

[DesertBearhawk]

Can you give more details on the electric system you are using?

[Helidesigner]

I agree there can be quite a pull to get the flaps down. Remember force increases by the square of velocity. The Bearhawk flies well with one notch of flaps all the way down to ~65 kts, I pull the second notch around there, and the third below 60 kts. I find at the lower speeds the flap pull force is OK. It would be nice if it was less but I think it would take a lot of modifying to make it better. A thicker handle is an idea to at least give a better grip.

Mark

[Mark Goldberg]

I just have not had any problem lowering flaps if the airspeed is where it should be. Mark

[Battson]

We did quite a lot of off-airport flying in the weekend. Again I was grappling with "the 4th notch".
Once I and then my friend too, each had to use two hands to get flaps when we needed them while flying PIC. This is never above 55kts. It's just that last inch of travel which is the problem.

An example:
On short final I was dealing with frisky wind and mechanical turbulence off trees. Descending steeply through a gap in willow trees at 2000ft/min to hit my spot, branches less than 20 feet from the wingtip and undercarriage. The aiming spot is quite close to the trees, there is no room to land long (or you end up in the water), the surface is exceptionally rough and the flare needs to be at low airspeed and perfectly executed given the high rate of descent. The situation requires full flaps, and the 4th notch needs to be applied at a certain moment (sometimes at 55kts) because you can't wait a few seconds for airspeed to wash off to 50kts, to reduce the pull force, as you'll be busy with other things by then. I couldn't really have applied full flaps earlier, because of the canyon turn I just made 10 seconds ago (too much drag) and I was busy with the throttle the rest of the time from then until this moment. My palms are a little sweaty given the pressure, and my hand tries to slip up the bar during the last inch of pulling #4 notch. This can be the last straw for a go-around. Plus I want to get my hand back on the throttle quickly in case the wind gusts/lulls. Overall it's just a nuisance during a high-workload phase of flight, and has resulted in go-arounds.

I had a similar situation happen at least 3 times in as many hours, yesterday But we got some great video!

I agree that just playing about on a 600ft grass airstrip, where you have lots of room, there is no problem.

Currently I think it's a geometry issue. The Maule has a comparable system, similar length of handle, but you are never pulling truly aft, always a mixture of upwards and aft, which is much easier as you can use your whole torso and not just your upper arm. Also the grip is larger.

[bestbearhawk1231]

As far as the hand slipping when sweaty goes, have you concitered gluing a bit of skateboard tape to the bottom of the lever? I know this is done with certain types of handguns used for competition to keep the handgun in place during the recoil. I have also done this to a rifle I use for hunting, the synthetic stock was just too slippery when it was wet or heavy gloves were used...glued some skateboard tape to the stock in a couple places and the slipping problem was solved.

[Battson]

I though about this solution. I decided I would end up with red-raw hands after doing 3hrs of back-to-back landings and take-offs, like we did this weekend. I think a larger handle with a tang would be the best. although I feel I need something stronger than glue to attach it - which I haven't solved yet.

[bestbearhawk1231]

When I mentioned glue I was referring to the industrial strength stuff made by 3m that is used under the adhesive backed wing walk material, but if you are doing 3 hours of tight touch and goes your had would be pretty sore. Welding a tab onto the end of the flap bar would also prevent your had from slipping off...similar to what they do on the rudder pedals.

[S Lathrop]

Instead of having a lever arm on the torque tube that operates the flap, you could have a wheel/pulley for the arc that the arm travels.. The leverage of the cable on the torque tube would be constant over the travel of the flap.

I have taken a quick look at the layout of the torque tube and the wing rib, and I think that it is possible to have an arm that would resemble a pulley. What I don't know is how far the arm has to travel to operate the flap or how many degrees does the torque tube rotates to operate the flap.. I think that the effective arc could start 50 degrees forward of the vertical position of the flap arm. My guess is that the pulley might have an arc of 70 degrees or more degrees. The drawing has 90 degrees.


I have built this type mechanism to operate throttle shafts on carburetors on race cars. I would need to scaled things up for the cable size we are using. This would be like having the cable pass around a 8" diameter pulley. This is a lot larger than the pulleys in the flap system. The cable end would most likely be a ball type.


Here is a drawing for an alternative the the actuaing arm on the flap torque tube.

[S Lathrop]

Here is a better drawing of a possible way to reduce the forces involved deploying the flaps as the flap angle increases. This may be more obvious than what I posted before.

When the flaps are first applied, the lever arm is 4" but as full deployment is approached the lever arm decreases to 3.5" resulting in an increasing mechanical advantage of the flap handle relative to the flap. The change in the lever arm is just a guess. The advantage of this device is that it can simply replace what is there now. The cable end could be a ball type or a simple Nicopress stop sleeve.

It will be close if something like this can clear the rear spar.

[JCD23]

Where did this ever end up? This seems like a good approach.

[jim.mclaughlin924]

I like this, it reduces the load on the whole actuation mechanism rather than just making easier to put more force on the lever. I think I will see if i can make it work.

[Battson]

To close this thread out, I ended up extending my Johnson bar as long as possible considering the panel clearance.
This has been a fantastic modification, definitely worthwhile.
See the details here. https://bearhawkforums.com/forum/bea...om-flap-handle