Multiplex Fun Cub

[Tony Smith 7]

Posted by Tony Prince on 17/06/2011 13:14:04:
It's too late for me but she does like a lot of aileron differential.

That's not really too surprising. I've had some time flying a high wing microlight (Rans S6), that has about 2:1 differential on the ailerons but still needs a good boot full of rudder to initiate or roll out of turns. I think the dihedral on the Fun Cub means some rudder is always going to be needed - you'll never quite get rid of adverse yaw and the dihedral will couple that back and resist the roll input.

[Steve W-O]

Posted by Tony Smith 7 on 17/06/2011 16:33:46:

Cheers. With flaps down the steady-state attitude of the model would be more nose-down than normal so its funny that power should make it nose up. Maybe its increased airflow over the wing roots.

 

I'm going to set the geometry so the flaps do down as far as possible, then limit the travel with transmitter settings.

 

Steve - are you using yours with the TH9x radio? Just wondered what you use to operate the flaps. I was thinking to use the three way switch with the travel for each stage set by one of the pots.

 

Thanks,

I use the three way switch for three positions, then the gear switch to select either no flaps or one of the three positions, ie the three switch will normally be right forward, say 10deg flap, and the gear switch up, then if I put the gear switch down, the flaps go to 10deg.

 

I find this convenient, as if the three position switch is right back, ie full flap, and I want to lose the flaps in a hurry, I just flip the gear switch up.

 

I used to use a pot to set the travel, but found it to be a pain, as i only use one of three positions, a little bit, medium, and a lot, but with the pot, could never be sure I was in the same position as last time.

[Tom Wright 2]

Tony surely the effect of the dihedral ,when rudder is applied skids the nose in the opposite direction to the effect of adverse yaw ,caused by the downward going aileron.?

[Tony Smith 7]

Posted by Tom Wright 2 on 17/06/2011 16:51:50:

Tony surely the effect of the dihedral ,when rudder is applied skids the nose in the opposite direction to the effect of adverse yaw ,caused by the downward going aileron.?

 

Yes that's correct that's why the rudder is needed. To understand these interactions its sometimes helpful to imagine the effects happening in sequence. So in your scenario some rudder into the turn slips the nose in the correct direction, then the dihedral causes the leading wing to lift more than the trailing wing, giving roll in the correct direction.

 

Consider adverse yaw in a left hand turn. Roll to the left generates some adverse yaw, to the right. The yaw to the right then causes the left hand wing to lift more than the right, giving a roll to the right which opposes the commanded left hand roll.

[Tony Smith 7]

Posted by Steve W-O on 17/06/2011 16:48:02:

I use the three way switch for three positions, then the gear switch to select either no flaps or one of the three positions, ie the three switch will normally be right forward, say 10deg flap, and the gear switch up, then if I put the gear switch down, the flaps go to 10deg.

 

I find this convenient, as if the three position switch is right back, ie full flap, and I want to lose the flaps in a hurry, I just flip the gear switch up.

 

I used to use a pot to set the travel, but found it to be a pain, as i only use one of three positions, a little bit, medium, and a lot, but with the pot, could never be sure I was in the same position as last time.

 

I'll maybe do something similar. Shame the three-way isn't on the left hand, I had a vague idea about wiring in a multi position switch in place of one of the pots.

 

My idea with the pot was that if I set a switch to command say 50% flap travel, then I need to get into the menus and edit the mixer to try something else. If I set the pot to command flap, with the switch enabling it, then I can try different settings a bit easier. I don't think moving the pot to actually deploy flap would work for me.

[Stephen Grigg]

All the batteries are charged up just wating for a window in the weather.Must check my C of G just checked it was a bit nose heavy and off I went.Dont bother with the flap.I do fly with aileron rudder mix on all my models for take off,not that I need ii when taking off with the Fun Cub...Have been practising take offs with rudder only because I have 2 models with 91 2 strokes and I need to learn to counteract the thrust.,

[Steve W-O]

Posted by Tony Smith 7 on 17/06/2011 18:18:09:

Posted by Steve W-O on 17/06/2011 16:48:02:

I use the three way switch for three positions, then the gear switch to select either no flaps or one of the three positions, ie the three switch will normally be right forward, say 10deg flap, and the gear switch up, then if I put the gear switch down, the flaps go to 10deg.

 

I find this convenient, as if the three position switch is right back, ie full flap, and I want to lose the flaps in a hurry, I just flip the gear switch up.

 

I used to use a pot to set the travel, but found it to be a pain, as i only use one of three positions, a little bit, medium, and a lot, but with the pot, could never be sure I was in the same position as last time.

 

I'll maybe do something similar. Shame the three-way isn't on the left hand, I had a vague idea about wiring in a multi position switch in place of one of the pots.

 

My idea with the pot was that if I set a switch to command say 50% flap travel, then I need to get into the menus and edit the mixer to try something else. If I set the pot to command flap, with the switch enabling it, then I can try different settings a bit easier. I don't think moving the pot to actually deploy flap would work for me.

 

 

Before I settled on my settings, it was really only the middle setting I was adjusting.

 

Full down was just that, all the way down, and the first setting was around 15deg, not to much extra drag, but extra lift and lower stalling speed.

 

The Funcub was the first one I experimented with, and I found once I had it like I wanted, it was easy to transfer the Funcub positions to the others as a starting point.

 

The Funcub is by far the most sensitive to throttle with any amount of flap down, so it really is the right one to test on

 

There is no reason why you could not put a three way switch in place of the hover pitch pot, or even swap them over (though I would prefer the extra switch and not the pot)

 

I use the rudder dual rate switch to switch all my rates, so a three way switch could go where the elevator dual rate switch is.

 

The problem is to find a decent switch. I have a couple of four position switches, but they are PCB mount, and slightly too big.

 

I also thought of putting a slider pot or slider switch just to the left of the badge, if I used a switch, I would have a preset for each position and use the hover pitch chanel. That is still my preferred way if I could do it neatly enough, I have the case looking butchered, which is why I put my programming connection in the battery compartment..

 

 

Must admit on the Funcub I normally only use the rudder on take off and landing, unless it is a very still day, when the un-coordinated turns look obvious, but in our normal breezy conditions, you don't notice

I also find that if the wind is not too gusty, I just hold in a constant amount of rudder, and then land with ailerons. So long as the rudder input is about right for the cross wind, the Funcub seems steadier that way. (tht comes from my lazy method of side slipping, where I hold the rudder almost constant)

[Stephen Grigg]

Windy again today but after lunch took the Fun Cub to the field.Need to give it more downthrust.The shaft diesnt appeared to be the problem.On full power the motor is making a lot ofnoise,more like vibration than anything.Throttle back slightly and its fine.had 3 good flights in between rain showers,very pleasant time

[Tom Wright 2]

Steven.

We have a couple of Fun Cubs at the field both fly fine with the standard thrust line ,but both have suffered noisy motors, one turned out to be a cracked bearing housing ,and the other was cured by using a different prop and spinner.

[Steve W-O]

Also find the motors vibrate on the mounting if only held on by two screws.

 

Easy enough to put two more in, doesn't make it any stronger or more secure, just stops it buzzing

[Tony Smith 7]

Just noticed some run-out on the prop of mine, I'm not sure if its the shaft or the prop adapter, but it needs some investigation.

[Tony Smith 7]

Posted by Steve W-O on 17/06/2011 16:48:02:

I use the three way switch for three positions, then the gear switch to select either no flaps or one of the three positions, ie the three switch will normally be right forward, say 10deg flap, and the gear switch up, then if I put the gear switch down, the flaps go to 10deg.

I've just blatantly copied your idea. I wanted to slow the movement as well, and that didn't seem to totally work, some of the switched movements would be instant. I'm not completely sure I got to the bottom of that and it may be a configuration error. The work around was to apply all the switches to a virtual channel, without slows, then to mix that virtual channel at 100% onto the real output and apply the slow at that level.

[Steve W-O]

Posted by Tony Smith 7 on 23/06/2011 16:55:25:

Posted by Steve W-O on 17/06/2011 16:48:02:

I use the three way switch for three positions, then the gear switch to select either no flaps or one of the three positions, ie the three switch will normally be right forward, say 10deg flap, and the gear switch up, then if I put the gear switch down, the flaps go to 10deg.

I've just blatantly copied your idea. I wanted to slow the movement as well, and that didn't seem to totally work, some of the switched movements would be instant. I'm not completely sure I got to the bottom of that and it may be a configuration error. The work around was to apply all the switches to a virtual channel, without slows, then to mix that virtual channel at 100% onto the real output and apply the slow at that level.

 

 

 

I have found I have done things in a round about way before to, then sent the file to one of the experts who have promptly simplified it!

 

I think the slow difference may be in the code, as I found the same thing

 

 

But, if it works, that's fine.

 

Just wondering how many other makes of TX that could have been done on?

[Kozmyk]

Have you seen the ER9X tutorials by richardmrazec on YouTube?

Lesson 4 includes conditional flight mode switching very similar to what you were after.

 

ER9X Tutorial #4

 

I'm learning loads from these vids.

[Tony Smith 7]

Posted by Steve W-O on 23/06/2011 17:12:12:

Just wondering how many other makes of TX that could have been done on?

Not even Multiplex I would guess!

[Tony Smith 7]

Posted by Kozmyk on 23/06/2011 17:32:52:

Have you seen the ER9X tutorials by richardmrazec on YouTube?

Lesson 4 includes conditional flight mode switching very similar to what you were after.

Nice one

[Tony Smith 7]

First flight with the new radio, and the ability to use the full range of flaps. It's a hoot! Full flap gives me just under 90 degrees, and at that it needs something over 1/2 throttle to maintain power. Sort of like a carrier deck landing. It also seems like the elevator is super sensitive with flap down, which made it a bit of a handful on take off.

 

I'm a bit challenged with take off and landing for the next few weeks, we have the hay sold but its not yet cut. First three attempts I didn't keep straight enough and went into the rough, before I started using the very end where its a bit wider (but then it needs to get off the ground in a steep climb). A few other times the wheels or even prop clipped the uncut grass going over the end of the strip.

 

Ready for take-off !

 

 

Edited By Tony Smith 7 on 01/07/2011 20:45:58

[Klippy]

Gee Tony, I thought I had problems! I hand launch without flap, I tried 80% but as you've discovered it's not really useable. I reduced to 20% and will see what happens next time out.

[Andy Mc]

I've been reading through this thread over the last week or so with great interest. I was in Ipswich last week so popped into Galaxy and they had a couple of Fun Cubs on the shelf, after a quick look in the box I walked out with one under my arm (after paying for it of course )

 

I decided to get the recommended Multiplex power-set to save trying to match up motors, props, ESCs etc, as well as trying to balance the CofG with differing weights of motors. And I've just ordered some Hitec servos from Steve Webb.

 

Once the servos have arrived in a day or two I'll commence the construction.

I'm undecided as to which battery to go for as I'm relatively new to electrics.

So......

Should I stick with the recommended 2200 or go for a bit more duration with 2500 or 2600 packs?

 

Will a larger pack fit in ok, and will the CofG be effected?

 

Has anybody else gone with the Multiplex power-set? What duration do you get with your set-up?

 

I hope I'm not asking too many questions here guys.

T.I.A

Andy

 

[Klippy]

Hi Andy, go for the 2200s' I find they give me 15 to 20 mins = tired and have yet to hit the LVC.

With the Mpx setup you're going to battle to get the CoG back far enough, cut a tunnel in the back of the fuselage before you fit the halves together, about 50mm should do it, cutting into it afterwards is nigh on impossible.

The Mpx setup up will only give you about 130watts on its 13x4 propeller, this is one of the reasons for the long duration. To get more watts you'll have to go to a much bigger prop. I've tried a 15x6, excellent power and very quiet, but, I seemed to get some form of gyroscopic precession with the big prop so took it off.

A 13x8 works Ok but can be a bit noisy on full power, and it pulls the plane around VERY fast!

If you're going to enable the flaps she pitches very nose up when you select, I used 75degrees. Don't deselect without getting the nose down, she loses about 20feet if you don't.

All in all, a great plane, I love mine, and she bounces pretty well too!

[Klippy]

I use 2200s and 2450s, there's almost no change in the CoG

[Andy Mc]

Thanks for the reply Tony.

I'm now a bit concerned that this (expensive) power set won't have enough power for what I need. It states 350watts in the paperwork but you say it pulls around 130watts on a 3s pack.

The paperwork also states 26amps on this setup, but my calculations using what I learnt at school say that 11.1v (3cell) x 26amp = 288watts.

 

If this power-set isn't suitable then it needs to go back, I was prepared to pay a little more to get a good set up without too much faffing about, but it seems that taking this direction hasn't worked.

I want the fun cub to be able to go vertical shortly after take off, and unless I'm mistaken, I won't be able to do that with 130 watts.

[Tim Mackey]

At the very best, you will only see around 10.5V under load on a 3s lipo.

10.5 X 26 = 273

Still a long way short of 350 though, so sounds like you need a bigger prop.

[Lazygit]

I can't get the pesky hyperlink tool to work so here it is longhand. For those who think chunky boots don't look scale, visit Old Warden and you might see "www<dot>airplane-pictures<dot>net/image134299<dot>html.( You'll have to copy, paste and edit until someone makes the link tool more intuitive).

 

Tony's skis, (many pages back) that kept digging in, you have to have the mount point BEHIND the mid point, then the loading at the front is lower than the back, so the front tends to rise. You need a bit of elastic to hold the front up in flight of course.

[David Ashby - Moderator]

Here you go Lazygit