Slope Monkey

[mikey100]

Got my Monkey set as per instructions and it is perfect. Diff is 50%. My onty problem is I keep breaking wing spars!

[Pij]

Thanks for the feedback, Mikey. Do you find it extremely sensitive? How does it respond if you use aileron only for a turn, with no elevator to help it along?

I wish I could apply some exponential to reduce the sensitivity, but can't do that with the basic radio.

[felix]

Hey pij bank and yank turns are pretty normal to slope planes,even moreso when they are as small as the monkey, and not many turn like a ruddered dihedral plane.a few things might help though:
I think decreasing the differential will have the opposite effect on what you are trying to achieve, think of the pitching and drag moment on the wing instead of lift….. try increasing the diff quite a lot with very LITTLE down movement but a LOT of up. Reasons behind this is that it will greatly increase the drag on the inner wing skidding the plane around in the turns a lot like a rudder without the need for roll, the upward pitching moment of the wing with up aileron will help in keeping the nose high in the turn and you will have the added bonus of little chance of aileron induced tipstalls. If your monkey has dihedral it should work quite well. Another tip is to move the CG back too. I could be wrong here though as this is only aerodynamic theory at play lol
As for softening the controls you can achieve a type of linear mechanical type expo with the servo/control horns. Trick is to move the control linkage on the servo on the lowest hole possible, this provides less control rod movement for every degree the servo turns, you may need longer servo horns to still get large enough throws. i worked this out on my last modded bee that was near on impossible to fly on my old non computerized tx.
hope some of my rant makes sense and is helpful

btw mikey did you replace those spars with solid fibreglass yet? if my bee couldn't break them your monkey wont either


Edit* a quick thought on creating a flatter turning monkey –if you find that more up helps create a more level turn another Idea could be to cut up some new ailerons that are a lot wider at the tip then root. This should create more drag than lift and really “wheel” her round the wing tip? Will require very little down movement on the down going aileron to avoid tip stalls though.

[Pij]

Thanks Felix - you've given me some things to think about:

think of the pitching and drag moment on the wing

I didn't think about either of those at all. I am now.

try increasing the diff quite a lot

I have a little more room for increased differential - maybe one spline on the servo arms. That could have quite some effect, though. Plenty of spline positions available in the other direction, to reduce the diff.

Does an up-aileron really make much more drag than a down aileron? Why?

upward pitching moment of the wing with up aileron will help in keeping the nose high in the turn

I see! The up-aileron on the outer wing has greater deflection (than the inner wing), so there's more pitching moment from that wing, and that pitching moment is nose-up. Got it!

little chance of aileron induced tipstalls

Why?

Another tip is to move the CG back too.

What effect will this have?

you can achieve a type of linear mechanical type expo with the servo/control horns.

I've already done that, using the innermost hole for the elevator, and the 2nd innermost for the ailerons. Perhaps I could go that one step further. Isn't linear exponential a contradiction in terms?

With all that to chew over, it seems the CG change is the easiest to try, then I can tweak the differential in either direction to see what effect there is. Thanks Felix.

Just saw your "edit", Felix. That seems scary. Putting all that surface out near the tips seems a radical difference. The Monkey currently has tapered ailerons. I suppose I could swap them, left for right, or perhaps make some un-tapered ones. But I had been thinking about increasing the taper after your earlier suggestion on avoiding tip-stalls. I don't have an unlimited amount of differential setting available to sidestep that problem, as I'm achieving the diff by fitting the servo arms ahead of centre (so the pull stroke is less effective than the push stroke). If I go much further, they won't pull at all, then if I go even further, they'll push instead of pulling.

[Pij]

An idea: The aileron trailing edges are about 1.5mm thick. I could sand the underside of the outer 7cm or so of each aileron, to create a little wash-out. This would have a bit of effect in avoiding tip-stall, and also would slightly reduce the effectiveness of the down-aileron (slightly changing the angle of the undersurface, thus deflecting the air slightly less) while leaving the up-aileron unaffected. I'm not sure however how much I can achieve with a little bit of sanding, without weakening the balsa too much.

[felix]

When I did theory instruction I used models and diagrams but this is ALOT harder so sorry for the next rant in answering your q’s but you asked for it pij

*your differential problem- you have the potential for as much diff as you need….. you can offset the control horns on the flying surfaces by spacing up the front or back of the horn base plate- pain in the @rse but it worked well on fine tuning the beelix when I run out of options.

*your aileron question- normally an up aileron is never going to produce as much drag as a down aileron as the golden rule of “if you increase lift you also increase drag” has that one covered. By lowering an aileron you have created more camber/higher AOA, created more lift and therefore more drag……this is only if the throws are EQUAL. A much larger movement of an up aileron compared to down will create more drag on that side (won’t explain that one as I’ll be typing all night lol).

*your aileron induced stall question- (this will take a bit lol). A wing ALWAYS stalls at a given ANGLE OF ATTACK . this is explained as the chord line’s relative angle to the airflow (stalling has absolutely no connection to any other factors ). Easiest way to see this one is to draw an aerofoil and draw a line from the very front point of the aerofoil to the very rear point you will have what’s called the chord line. Now draw the same aerofoil with the aileron lowered and compare the relative angles and you’ll see the latter has a much larger angle! Soooo if we cut this story short and say by decreasing the possible amount of down travel to our aileron we have greatly limited the ability to change our chord line to the airflow therefore created a very large buffer before a tip stall can be induced. Of course there are contradictions to this but that is another much larger topic

*your CG question- To keep it very simple (to stop delving into another drawn out explanation) by moving the cg back you basically are reducing the nose down tendency that flying surfaces of the plane need to compensate for. This may help the plane to hold a flat slightly banked skidding turn and reduce altitude loss –this is a very tricky one though as it can be a vast improvement or make the plane tricky to fly for a beginner.

*oops, yes linear expo is definitely a contradiction lol. What I was trying to explain it that you are slowing the control movement down over the servos entire range instead of just a proportion of it.

*the alternative ailerons I mentioned are a little scary but perfectly safe as long as the downward travel is limited or taken away altogether. just another way of solving a problem but also possibly causing anotheeeer……


...ah cr@p now I’m fried haha

[mikey100]

I just set mine up by the book....and bank then elev to turn, then flatten out. There is a bit of nose down, but this keeps the speed up, so increased lift.
Felix..I went lookin for the Kiteshop at3/462 Beaconsfield Tce, Brighton 2day after flyin at SC...but couldnt find it. Am interstate till nxt wk, so will try again then. In the meantime, the Noodle is fun. And I got the Bee....

[Pij]

You instructed in flight theory, Felix? I didn't know that. I'm interested in the when & where of it, if you'd like to PM me.

You did pretty well without diagrams or models. I followed almost all of that.

By offsetting the control horns to get differential, do you achieve this as a result of slightly shifting the connecting hole ahead of, or behind, the hinge-line? I considered getting my diff by placing the horns with the holes ahead of the hinge-line (horns are under the wing), but I couldn't picture in my mind how much diff I'd achieve that way, so I did it with the servo arms instead.

I now understand what you meant with the drag of the ailerons, the aileron induced stall, and the CG effect on turning (partly). Thanks again, Felix.

Mikey, it sounds like my Monkeys do actually perform much like yours. I suppose my problem stems from wanting to change the characteristics to suit my sons. For myself, I love flying the Monkeys. It was very hard today to force myself to stop re-launching, and drive back to town. Do you have any pictures of your Monkey?

[felix]

Yeah pij I did theory instruction at both cab flight training (GA school/charter op.) and wings flying school (ultralight training), mind you that that was when I was 16-18 and I’m now 27 lol. Glider theory on the other hand is very new to me but I’m learning bit by bit

*the horn Q- if you TILT rather then move the whole horn backwards away from the hinge line you will (generally) get more up than down travel and vica versa for towards the hinge line……oh your horns are under the wing? Reverse what I just said lol.

*the cg on turning- that side of things as they relate to turning is a complicated subject with a hell of a lot of variables that need consideration and flight testing. Best bet is to just experiment here and see what the results are and see if you can figure out why.
A quick disclaimer here though mate, I’m no expert and my approach could fail. I’m just looking at it from the perspective that I wanted to produce a dedicated trainer out of a monkey.

Another idea that may work is to reduce your fin area bit by bit. This should reduce the fins ability to counteract the adverse yaw and help in skidding the plane around flatter turns a little more. This is redesigning a plane to do something that it wasn’t originally intended to do, can actually cause a poor flying model and on the same note this is going against what one normally tries to achieve but is fun all the same lol.

Mikey next time you’re at sc I’ll show you on the map where that shop is

[Pij]

Dec 9, 2008 21:47:23 GMT 10 felix said:

I wanted to produce a dedicated trainer out of a monkey.

reduce your fin area bit by bit. This should reduce the fins ability to counteract the adverse yaw and help in skidding the plane around flatter turns a little more.

A trainer from a Monkey - that's exactly what I'm using them for! So you've been thinking about this for a while... since seeing Mikey's Monkey fly?

I started thinking about adverse yaw late last night (as I asked myself what I'd learned in the past about the reasons for differential - but this related to truly high-wing trainers), and considered increasing the fin area experimentally. I don't want to allow a little more adverse yaw, I want a little more proper-direction yaw. Doesn't decreasing the fin's ability to counteract adverse yaw mean allowing a bit more adverse yaw, meaning when you bank left, it tends to yaw right? I think I'm trying to achieve bank left, yaw left.

I really appreciate the chance to think this through with you Felix. I hope I'm not irritating you? I know some flyers do anything they can to avoid conversations like this - which is part of the reason it gets so hard sometimes to figure things through.

edit: I've just been reading through Model Aircraft Aerodynamics, topics relating to our discussion here, and the book reminded me again of Pitching Moment. My undercambered setting on the ailerons will be giving a nose-down pitching moment, so I might be best to remove all or part of that setting before I start making changes. I might otherwise end up fixing something that's not broken.

[Pij]

I'm making a "shopping list" of things to try:

Certainly to be done

Reduce undercamber
Cover gaps in aileron hinge line
Fly with good quality transmitter to see difference
No more changes until I've tested it in better lift conditions. Then...

Possible to be done, may experiment

increase or decrease fin area
move CG backward a little
increase differential
sand wash-out into aileron tips


There's a good piece in Model Aircraft Aerodynamics, section 13.5, Adverse Aileron Drag, relating directly to my problem:

Since a soaring sailplane is likely to be operating already close to the stalling angle, it is necessary to increase the flight speed in a turn to avoid a 'wing drop' caused by the inner wing in the turn stalling. This implies a steeper glide angle in the turn, and a higher sinking speed. The steeper the turn, the greater the loss of efficiency. In thermal soaring, since the model must turn to remain in the thermal, some penalty in performance has to be accepted. In hill soaring, the loss is small and in good or moderate conditions is hardly noticeable. However, in weak lift, the height lost on turns may be just enough to make soaring impossible. In such conditions it is common to find small patches of better 'lift' here and there along the slope, with weak or even nil lift between. If the turns are made in the better spots, not only is the increased sinking speed in the turn more likely to be overcome, but the model remains in the rising air longer than if it were allowed to fly straight through it. The 'beat' worked on such a day, if possible, should thus begin and end in rising air, with straight flight between through weaker areas. Note that all turns must be correctly banked. A flat, skidding turn creates excessive drag and increases sinking speed.

[felix]

Pij I’ve never thought about turning a monkey into a trainer until I seen your post and no your not irritating me one bit –aerodynamics and theories is something I’m very interested in

*adverse yaw is not always in the way that it causes a plane to slip in a turn, it can also refer to a plane skidding as well (just that we nearly always run into slipping on most designs). So what I mean is that if you can increase the drag on the inner wing of the turn you will be able to keep a much flatter turn by wheeling (skidding) the wing around the turn. So yes you want to bank and yaw/skid in the same direction.

*as for reducing the fin? The fin is there to help counteract any yawing tendencies. If the fin is large and effective you will have a lot of stability but very little chance of holding a flattish skidding turn. An easy temporary way to test the effect I guess here would be to put a small removable fin on the nose of the plane and see if it makes any difference and remains flyable.

Another couple of hints, get rid of the camber and really try and get as little down travel as possible. One of the main problems of skidding through a turn on a dihedralled wing is that the outer wing has a higher angle of attack to the airflow compared to the inner so it can be very easy to stall the outer wing. Easiest way to visualize this is draw a basic front on view of the plane, then draw a line across the front view from where the airflow will come from….you’ll see the angle on the outer is greater then the inner wing.

quote: “Note that all turns must be correctly banked. A flat, skidding turn creates excessive drag and increases sinking speed.”
This is an interesting phrase that is absolutely correct but needs to be compared taking into account a beginners skill level. A beginner will take a lot of time to learn how to do the best turns and will more then likely lose a lot more height/speed in a “bank and yank” turn then a flatter skidding turn where everything happens a lot more slowly.

Once again there is so many variables in doing this in the end you may not end up with a better trainer at all, could just end up with a pig lol. Still fun to try and once I get the fleagle repaired and my landing speed issues sorted I think I’ll play around with these theories and see if I’m right lol

[Pij]

Dec 10, 2008 17:49:11 GMT 10 felix said:

Once again there is so many variables in doing this in the end you may not end up with a better trainer at all, could just end up with a pig lol. Still fun to try and once I get the fleagle repaired and my landing speed issues sorted I think I’ll play around with these theories and see if I’m right lol

That's why I'm going to only try reversible ideas at first Yes, there is a kind of fun to working it out, isn't there?

[Pij]

Done
Reduce undercamber
Cover gaps in aileron hinge line (better looking too, since re-hinging)
Sand wash-out into aileron tips

To Do Soon
Fly with good quality transmitter to see difference
No more changes until I've tested it in better lift conditions.

The wash-out was supposed to be a later experimental effort, but there was a conflict between 2 principles: The "make one change at a time so you can see the effect" rule was defeated by the "while you've got the engine out you might as well overhaul the gearbox too" rule.

[Pij]

Back to test chucks today in the park. At first, the reduced undercamber seemed to detract from the glide-ability, but as I increased elevator trim, it eventually became flyable again. The elevator is now trimmed to be just noticeably UP, so I might move the CG back a touch, and get the elevator trimmed flat, and then I might have the trim correct. Son #2 had some chuck-flying practice today, and his mostly correct responses to very rapidly occurring situations, and his improvement over 20 chucks or so, were a credit to his youth.