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Old Aug 02, 2002, 06:27 AM
(aka Cliff Lawson)
Wright Flyer's Avatar
United Kingdom, Essex
Joined Oct 2001
1,897 Posts
Switchback 3D - a bit odd, but I survived!

Hi,

Although I got the Switchback 3D wing kit a couple of weeks ago and had built it within a day or two, I'd put off covering it for a while as I think I was a bit scared that it might end in complete disaster but on Wednesday night I finally covered it and attached the ailerons and last night I fitted the pushrods and the wing spacers. But it was about 8:30pm when I was ready to fly and it's now got to the stage where it's not long after 9pm when it gets dark here in the evenings so I ventured out with some trepidation for the 3D maiden flight.

It didn't help that there was a large group of kids in the park where I was about to try the 3D wing for the first time but I thought, what the hell, and went for it anyway.

Well it was actually quite surprising. From FMS I'd expected it to have a lightning roll rate compared to the Sport wing and be very tricky to control so I had progammed in REALLY low rates but after a few circuits I flicked the dual rate switch to the higher rates and even then it didn't have the performance I was expecting.

I wonder if I've got something wrong because, apart from anything else I found a really weird effect where if I push the aileron stick hard over expecting a quick roll it tends to roll (but just at about the same rate as the sport) but once inverted the roll would stop and instead the plane would start to climb out of the inverted. This is really weird! I don't know what's causing this??

While exploring the performance a couple of times, because of the marginal light, I actually completely lost orientation (even though I have a high vis colour scheme) but I was really lucky that I managed to recover without the inevitable happening!

I landed it and then, with some level of confidence, I tried to fly it a second time but this time it would hardly climb and I kept hearing a clunking noise so I just landed immediately and gave up because I didn't want to risk marginal power with a plane I could barely see!

It turned out that the gear shaft was loose so I put a packing washer on it. I'm certain that the first flight landing had not damaged the gearbox in any way so can only assume that the gearbox was loose when I first fitted it. After fixing this I had a third flight this morning, it seemed much easier to fly but after only a minute or two the power system stopped and I just couldn't get it to restart.

I brought it into work but a quick test shows that it's now working fine so I don't know what that problem was but I guess I may well find out as I'm going out to try and fly it again at lunchtime as the air here is dead calm and great for trying out the new wing.

Here's hoping...

Cliff
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Old Aug 02, 2002, 07:34 AM
(aka Cliff Lawson)
Wright Flyer's Avatar
United Kingdom, Essex
Joined Oct 2001
1,897 Posts
Still completely flummoxed!!

Hi,

Well I went and had another 3 flights on the 3D wing and there's is definitely something wrong with it but the problem is that I don't know what!

It climbs fine, it's quite a bit faster than the Sport. I can get it up to height (about 4 mistakes high) in no time and fly nice sedate lazy 8 circles in what feels like a very nicely controlled fashion. Loops don't seem to be too much of a problem either but I simply CANNOT get it to ROLL properly.

Even if I enter a roll in a slight nose up and whack the stick hard over it takes an ETERNITY to roll and, while it's doing it, it simply "falls out of the sky" and a single roll takes about 3 of those four mistakes to complete (which is pretty hairy!!).

I've looked at the wing and it looks as flat as a ruler - not a sign of any warps that I can see. I've looked at the movement of the ailerons and they seem to be extremely close to that on my Sport wing that flies successfully and there's no slackness in the pushrods.

So does anyone have any idea what would be stopping it from rolling??

As I can only make gentle turns and it's flying faster, it takes much more "room" to land so I'm going to have to think long and hard about trying to fly this much more unless someone has an idea as to what is wrong.

Yours in desparation,

Cliff
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Old Aug 02, 2002, 07:40 AM
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Don Sims's Avatar
Outside of Dyer, Tn. USA
Joined May 2000
7,135 Posts
Hey Cliff, is your CG correct with the new wing? The wing may make no difference but if your CG got off that would cause wierd rolls. The other thing that comes to mind is do you have the same deflection on both of your aelirons??
Good luck solving the problem, there are many SB experts out there including the Guru himself....Doug!
Later,
Don
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Old Aug 02, 2002, 07:56 AM
(aka Cliff Lawson)
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United Kingdom, Essex
Joined Oct 2001
1,897 Posts
CG is correct

Don,

Thanks for the quick reply - I'm just waiting for the States to "wake up" in the hopes of getting some more relpies from the SB gurus (if Dreamer or Doug doesn't know the answer then I could have a problem!!)

Yup CG was one of my first thoughts but I checked and it's right on the recommended location. When I found the plane was behaving "odd" my first thought was a rearward CG so on the next flight I put the battery as far forward as it would physically go and brought the CG so it was on the main wing spar and not the usual 1/4" behind it but the plane STILL had the same problems?!?

(I daren't put it further back because the plane is already tricky to fly and I fear I could make it completely uncontrollable - on the other hand, maybe THIS is my problem??)

Cliff
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Old Aug 02, 2002, 09:27 AM
Fly
Veracitarian Muser
Tempe, Arizona USA
Joined Dec 2001
582 Posts
Just a guess, but do your wings twist easily? Your ailerons could be acting like trim tabs to twist the wings, negating most of the roll torque.
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Old Aug 02, 2002, 09:35 AM
(aka Cliff Lawson)
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United Kingdom, Essex
Joined Oct 2001
1,897 Posts
Fly,

Thanks for another great suggestion but the wing feels just as "solid" as my Sport wing. It's covered in Solarfilm which is quite a bit tougher than some of the lighter covering that I know others have used on Switchback wings so, if anything, I think my wing would be even less susceptible to twist than most others.

I've left the wing in the trunk of my car but when I get a chance I'll pop out and give it a quick twist to see if I've missed something. But that shear webbed wing spar does make it a pretty solid item and even if a rib had a crack I think it would remain pretty solid.

Cliff

Later..

Just took a couple of minutes to pop outside and check the wing and there is virtually no movement available in it whatsoever despite trying pretty hard to flex it.
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Old Aug 02, 2002, 10:37 AM
Mountain Models Wannabe
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Ithaca, NY USA
Joined Mar 2001
4,371 Posts
What Fly meant was can you grab the wingtip and twist it. On an early UrbanFlyer, I put Reynolds food wrap on a wing. The wing was so flexible that the ailerons would twist the wing and the plane would roll the opposite direction.

What servo are you using? What holes in the horns are you using? What is the maximum deflection of the aileron - end to end?

We'll figure it out.

Doug
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Old Aug 02, 2002, 11:15 AM
(aka Cliff Lawson)
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United Kingdom, Essex
Joined Oct 2001
1,897 Posts
Doug,

Thanks for coming to the rescue but I did try twisting the wing from the wing tips and there's virtually no movement possible mainly because of the heavy(ish) SolarFilm that I've covered it with.

On my Sport wing I used a Multiplex MPX-2 servo but for the new 3D wing I'm using an HS-55 because, if anything, I thought it was a HIGHER quality servo and I figured the 3D wing could do with the best servo I could get (the selection at my LHS for "small" gear is really pitiful). As an experiment, just in case it's the inability of the servo to provide enough force to operate the ailerons I might well try switching the known good MPX-2 in there over the weekend and see if that fixes it.

The 90 degree servo arm on the servo itself is pretty similar to that on my MPX2 and I'd say the holes must be about 7-8mm out from the centre. At the aileron end you've just made me think of something (hope this is the problem!!) and that's while on the Sport wing I have the rods in the centre of the three holes on the 3D I put them on the outside hole to deliberately reduce movement before I first flew it cos I thought it would be "twitchy". I hope that explains it but in terms of actual movement at the outer edge of the ailerons I'd say that, just like the Sport wing, I've got about the 5/8" complete movement that you recommend.

Cliff

I just hope it's the control horn thing!! I'll report back when I've had a chance to try changing this but "er indoors" has dictated that we're "going out tonight" so I won't get a chance until Saturday.
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Old Aug 02, 2002, 11:46 AM
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Tres Wright's Avatar
Forney, TX
Joined Mar 2002
15,165 Posts
My SB is still awaiting covering, but based on my other aileron flyers 5/8" deflection at the ailerons is not much. I've got the high rates on my Tiny and Wing-E set to 1-1/2" deflection!! Talk about insane roll rates! Especially the Wing-E, It rolls with almost no loss of altitude. My low rates on the Wing-E are about 3/4" and it rolls much slower with an accompanying loss of altitude.

I know Dreamer had some really high deflection set on his SB, probably more than the average flyer would want but it's an indication of just how far the SB throws can be taken. I'm guessing you might want more like an inch on your high rates.
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Old Aug 02, 2002, 11:51 AM
Leave me alone!
Martin Hunter's Avatar
Kamloops, BC, Canada
Joined Feb 2002
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Cliff, this is really strange. First of all, when you come down after a normal flight, where is your elevator trim? ie when you look at the stab and elevator from the side, do you have excess either up or down or is it pretty much neutral for level flight?

How new is your servo? It's possible that it's perfectly fine in the center but stripped or partially stripped towards the extremes in movement. Try moving your ailerons all the way one way and then physically try moving the aileron with your hand. Don't push too hard, but you'll be able to see how determined it is to stay there. Check how solidly glued in your aileron control horns are (that is, the light ply horns in the ailerons themselves).

Basically what I'm getting at is that the throw might be ok on the ground, but possibly there's something not allowing full deflection in the air. With the recommended throws, I get just under one roll per second, and cranking it up yields about three per second. The bottom line is that it's not the airplane but something specific with your setup. For equal deflection, the 3D wing rolls quicker than the sport wing, or should in any case.

Let's get this fixed!

Martin
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Old Aug 03, 2002, 09:44 AM
(aka Cliff Lawson)
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United Kingdom, Essex
Joined Oct 2001
1,897 Posts
Temporary setback

Hi,

Thanks for the replies guys. Unfortunately I was too eager to test some mods last night that I first tried to fly the Sport wing but the wind was so strong it was virtually unflayable so, rather than do the obvious thing and pack up for the night I tried to fly it using the already "questionable" 3D wing but with the aileron servos horns re-positioned. Well after a hand launch I had about 0 control and before long I nosed it in and borke the plane clean in half.

It'll just be a quick glue job to put the two fairly clean bits back together but this is going to introduce a bit of a delay as I'm going to put a sheet of strengthening 1/16th balsa as an "outer skin" on the front half of the fuse to make it a bit more robust (and help to strenthen the joins).

I'll report back when I've had a chance to try the 3D again in calm conditions (wouldn't you know it the air here is TOTALLY calm because I don't have a flyable plane at the moment!!)

Cliff
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Old Aug 03, 2002, 09:26 PM
Deep Sea
Navy Diver's Avatar
OFallon, MO
Joined Jul 2001
609 Posts
Cliff,
I'm in the middle of building my second Switchback after numerous crashes with my first and have found that 1/64 ply doubler on the fuse is a great way to add strength with very little weight. Below is a shot of my new fuse with the doublers attached.
Eric
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Old Aug 04, 2002, 02:55 PM
(aka Cliff Lawson)
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United Kingdom, Essex
Joined Oct 2001
1,897 Posts
My worst weekend for flying - ever!

Hi,

I think the aviation gods must have got angry with me or somthing because I've just spent an entire weekend watching some of the calmest air we've had here for months and not being able to fly a Switchback in it!

After gluing the two halves of my Switchback together and sheeting the outside I must have since tried to fly it about 15 times and for some reason that alludes me it just will not fly. On the odd occasion it actually sustained flight for more than a few seconds it has returned to earth with a bump and is slowly but surely working it's way through my collection of GWS props!!

I think it's a power problem because even if I try to ROG and not even fly it just doesn't move across the ground as well as it did and holding it in my hand and throttling up it doesn't seem to have the usual "pull". But I have independently changed the Rx, the ESC, the motor, the gearbox and the prop on separate test "flights" and no matter what I do it simply will not fly.

I'm now at my wits-end as I don't know what is faulty or what has changed to make it unflyable. As I write that it strikes me that the ONLY thing I haven't been able to substitute is the Tx - but I don't see how a setting in that could have mysteriously changed??

About the only thing other I haven't tried replacing is the plane itself and because I have a spare fuselage kit I'm about to try that too except, wouldn't you know it, I have run out of both thin and medium CA and only have some thick available so I'm gonna wait until I can get to the LHS tomorrow and pick up some thin CA. Meanwhile the air outside is DEAD CALM!

Exasperated
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Old Aug 04, 2002, 03:07 PM
Mountain Models Wannabe
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Ithaca, NY USA
Joined Mar 2001
4,371 Posts
I hate to suggest this ... but ... Are you sure the prop is on facing the right way?

When the motor is at full throttle, does it sound like it's going the speed you remember from when it was flying?

Doug
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Old Aug 04, 2002, 06:25 PM
Leave me alone!
Martin Hunter's Avatar
Kamloops, BC, Canada
Joined Feb 2002
15,106 Posts
To paraphrase Alice: "Curiouser and curiouser"

You didn't mention you battery packs. Also, what is the plane's flying weight? Is it possible you have more than one sick motor? I'm guessing more than advising, at this point.

Martin
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