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Old Jan 17, 2013, 12:59 AM
Whiskey Tango Foxtrot
guitarcher's Avatar
Australia, QLD, Maryborough
Joined Jan 2013
151 Posts
Question
Topsky 2M Manta Ray spiral dive

I have had one flight of this new flying wing. It flew very well and thermalled nicely but scared me a couple of times when for no apparent reason it went into a spiral dive that I was very lucky to recover.

Do I need to move the ch forward or cut down the massive winglets?

I would have thought the designers had ironed out any inherent problems but it also suffers from wing flutter. I can't find much on the internet and topsky won't reply to my requests. No info at all was supplied with the kit.

Iove the wing but its likely to crash if I can't cure the problems.

Thanks for any suggestions.
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Old Jan 17, 2013, 01:21 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,282 Posts
http://www.topsoaring.com/index_pro_EPwing.htm

A link to the vendors site,not a lot of info.May help if you can add a few construction details.
Stuart.
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Old Jan 17, 2013, 02:34 AM
Registered User
miniphase's Avatar
Kent, UK
Joined Nov 2004
869 Posts
dial down your elevator throw on the elevons before you start adjusting the CG

make sure there's minimal play in the wing joiners as any slop will promote fluttering
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Old Jan 17, 2013, 07:47 AM
Herk
HerkS's Avatar
Virginia USA
Joined Jun 2007
1,645 Posts
Overlarge vertical surfaces can contribute to a spiral dive tendency. I notice that one of the photos in the link Stuart provided shows smaller fins.

However you didn't provide enough info to really get much help. Most spiral dive tendencies are easily prevented or controlled by the pilot. How does it develop? Are you sure it's not a spin? When does the flutter occur? Is it just the control surfaces fluttering or is it the whole wing? How is the model balanced? Do you have difficulty with visual orientation? etc.
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Old Jan 17, 2013, 02:47 PM
Whiskey Tango Foxtrot
guitarcher's Avatar
Australia, QLD, Maryborough
Joined Jan 2013
151 Posts
Thanks to Stupot, Miniphase and Herk for your suggestions guys.

Her's a bit more info.

I will post a photo when I work out how to do that.

The wing was a very straightforward build even without any form of instructions. I built it without any of my own modifications. A recommended cg would have made me a lot happier. I'm running the recommended battery and had to add 130 grams of nose weight to get the cg where the flying wing calculator advised. The plane came in at the recommended auw before adding nose weight.

The spiral dives came out of nowhere when in a gentle bank. As it was the first flight I was handling it like a new born baby. It was probably in a slight down attitude as I was trying to get it get it to lose altitude to land was flying it back and forth with it just floating up there not wanting to land. The spiralling happened 3 or 4 times. I will dial down the throws as suggested. The throws are 12 mm , 1/2" up and down. Have 70 percent expo.



The wing flutter occurred when in a shallow dive ( maybe 10 degrees )while trying to reduce altitude after losing sight of the plane in a thermal, even though it was flying quite slowly. The whole wing fluttered. The cf wing joiners as supplied measured 7.8mm and were fitting into 8mm cf wing spars so there was a bit of slop there. I had strong tape on the wing / fuse joint both sides of the wing. After reading miniphase's post I think the flutter may have been caused by this slop in the joiner. I snapped one of the cf joiners when I tried to launch for the second flight. The wing hit my head as I heaved it and it flipped over and hit the deck....DUH !!! I cut an old cf arrow shaft that was slightly smaller in diameter and wrapped extreme tape around it and it is a very snug fit in the wing spars now.

I will triple check the cg this morning and will fly it today. Its going to be 37 degrees here today with very light winds so there will surely be thermals around.

Can anyone suggest the throws for crow braking.? The wing floats so well it will be a must or I will lose it in a thermal as I had great great difficulty on the first flight trying to coax it down.

Thanks for your quick replies fellas, really appreciated.
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Old Jan 17, 2013, 03:44 PM
Herk
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Virginia USA
Joined Jun 2007
1,645 Posts
The whole wing fluttering immediately brings attention to the joiners. I believe I'd go straight to steel rods if it was mine.

It's hard to give recommendations for your request about crow. I looked at the photos but couldn't make out the size of any of the control surfaces. Still, based on wings I have and have flown I suspect that you can use the inner surfaces as pure flaps with very little correction needed on the elevons. As flaps they should be quite effective - get as much deflection as you possibly can. Oh and yes -- retract them before landing

If you provide the dimensions of the model, I'd be glad to give a CG recommendation. From your description it sounds as if it's balanced pretty well. A dive test would tell more.

And yes - those fins look to be huge. For a model with that much sweep, you probably don't need for the total fin area to be much more than 5% of the wing area. If you decide to trim the fins, I'd just do a bit at a time.
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Old Jan 17, 2013, 08:50 PM
SlingWinger
San Bernardino, California, United States
Joined Oct 2004
1,629 Posts
While snug fitting joiners are good, we all need to keep in mind that swept wings often need more torsional rigidity than straight ones.
Some years ago I had the pleasure of helping a guy with a swept aft combat type glider. It was fine at low to moderate speeds, but at higher speeds it would get divergent and at really high speeds would flutter like mad.
He had fins that were only above the wing, like the subject plane. I reasoned that possibly drag from these fins were twisting the wing toward a wash-in condition so we cut the top half off the fins and added them below the wing.
This helped, but didn't cure the divergence. I reasoned the elevons were twisting the wing, so we used some brightly colored stiff paper to cover the forward area of the wings from the high point forward. That did the trick.
Apparently Boeing experienced this with the B-47, their first swept wing. The ailerons could twist the wings enough to cause "wrong way" roll response.
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Old Jan 17, 2013, 09:15 PM
Whiskey Tango Foxtrot
guitarcher's Avatar
Australia, QLD, Maryborough
Joined Jan 2013
151 Posts
Thanks Herk,

Wing measurements as follows,
Span 2M, Root chord 200mm, Tip chord 150mm, Sweep 445mm.

I recalculated the cg using bruder at 20% came up with 247mm instead of the 237mm I had been using.
When I tried a hand test launch this morn with the cg set at 247 it wallowed really badly then down and flipped over on its back, even with all the reflex taken out.
By the way, there is no inbuilt twist in the wing and no dihedral, so I assume it needs reflex on the elevons.
Elevons are 40 mm wide.and are nearly half the wingspan with the flaps being the same size.
I kept adding weight again until I could get it to glide satisfactorily with 6mm reflex, which brought the cg back to where I started. Then I tried the motor to get some altitude and tried the glide, motor off. It was stalling a fair bit and I had to remove about 12 clicks of the up trim ( reflex ) to get a stable glide. I didn't experience any wing flutter with the tightened wing joiners but the spiral dive was just as bad. At times it would glide nicely ( very slow ) but then it would seem to sag tail down ( stall ? ) and sometimes in the middle of a bank it would just roll over and spin vertically down. Luckily I had plenty of altitude and the spin wasn't too fast so I could opposite aileron to stop the spin then pull it out of the dive. It did stall on landing tho' and nosedived from several metres up with no damage.

It floated nicely and nosed up as it passed through thermals. Was very easy to gain height in the bouyant air and proved a challenge to stop it climbing out of sight.

Will play with the flaps when I get the rest of it sorted if it doesn't smash before then!!!

I have balanced the wings, so it seems to me to behaving as tho' it needs more forward cg.

Cheers.
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Old Jan 18, 2013, 01:03 AM
Whiskey Tango Foxtrot
guitarcher's Avatar
Australia, QLD, Maryborough
Joined Jan 2013
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More flight tests this arvo.

Had 2 half hour flights. Spiral dive is still an issue. Anything more than a moderate bank angle produced a very quick transition to nose down attitude. Wings like to be kept very level. Large thermal turns are ok but tight turns are not and opposite aileron must be employed very smartly.

A dive test leveled itself very quickly so that indicates cg could possibly go aft but would be very difficult to fly like that.

Flutter is diabolical in anything other than moderate air speed even while climbing under gentle motor. I'm sure its not from the wing joiners now and I think its the whole wing not the control surfaces. The plane has to be slowed quite a lot to get the fluttering to stop.

On final approach a wind gust lifted the nose of the plane and flipped it over smashing into the ground nose first. Wing has snapped and fuselage has split along the mold join line.

Its repairable with glass and epoxy, but is it ever going to possible to turn it into a predictable and reliable flier...???!!!
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Old Jan 18, 2013, 02:43 AM
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Kent, UK
Joined Nov 2004
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did you reduce your elevator throw? I would also suggest removing the expo setting, you don't want a large amount of throw coming in at the extreme of the control surface movement; I can't help but think this is the cause the spiral diving you describe.

edit; also check to see that you're not getting any radio problems, eg interference, brown outs (I see carbon in that wing) and power loss (are you running with BEC?)
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Last edited by miniphase; Jan 18, 2013 at 09:04 AM. Reason: radio thoughts
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Old Jan 18, 2013, 07:25 AM
Herk
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Virginia USA
Joined Jun 2007
1,645 Posts
My CG calc shows the same numbers that yours does. It says that you are flying the model with a 10% static margin which should be more forward than necessary for a wing with fins.

The only sense I can make of your experience is that the inner wing is stalling when you initiate a turn. The only way to avoid that is speed/low AOA. If I'm correct the wing needs twist to fly well at low speed. You might try turbulating the outer third of the wings upper surfaces. (assuming that you decide to repair it)
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Old Jan 18, 2013, 10:06 AM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
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Quote:
Originally Posted by guitarcher View Post
Its repairable with glass and epoxy, but is it ever going to possible to turn it into a predictable and reliable flier...???!!!
Now the fun begins......

Of course it's repairable and after the repairs you can be more daring because it's not a new model any more. At least that's the way I think.

Just for fun, I'd move the CG back and limit elevon deflection at the outer panel to 15 degrees max. With a rearward CG, that will be plenty of deflection for basic control. Do a dive test to check the CG.

Also, check the wing for washout by clamping sticks across the airfoil at the root and at the tip, then sighting down the wing to check the alignment of one stick to the next. Who knows, maybe something went wrong in production and you actually have washIN....which would explain a lot.

Also, isn't it true that in conventional aircraft a rudder that is too large can cause spiral instability? Maybe those tip fins ARE too big?

I've got some planes that are quite simply difficult to fly due to a handful of built in bad behavior "features". I still fly them. They just have a smaller flight envelope than a super stable trainer. It's part of the fun. As Herk says, just fly faster (low AOA) and you will not have a tip stall. I regularly tip stall my Hortens by flying slow while trying to thermal, but it's not a problem because I'm already 500' AGL.

Let's us know how round #2 of flight testing goes.

Kent
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Last edited by Knoll53; Jan 18, 2013 at 10:26 AM.
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Old Jan 19, 2013, 04:35 PM
Red Merle ALES
Curtis Suter's Avatar
United States, Mt, Helena
Joined Apr 2002
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I would like to see you try no expo or say 10% max. What may be happening is that you are not getting the response you desire and keep applying up elevator, still nothing, then you apply even more and then all of a sudden you get a massive amount of throw and the AoA is exceeded and she snaps or stalls.

Curtis

Oh, I would trust Herk on tiplet size.
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Old Jan 20, 2013, 01:18 PM
Whiskey Tango Foxtrot
guitarcher's Avatar
Australia, QLD, Maryborough
Joined Jan 2013
151 Posts
Thanks to all for your suggestions.

I will work on repairs today.

I don't believe that the expo is causing the problem as when the dive begins the sticks are often in the neutral position or with very little input but I will remove it any way. I have already reduced the throws.

The plane will happily circle repeatedly with low bank angles ( is this angle of attack ? ) but if a wind gust lifts one wing tip past about 15 - 20 degrees or I tighten the turn slightly , that's when it noses over. This is occurring at fairly low speeds, is it tip stall ?

Herk, how do you suggest I put I install turbulators?

I have checked the wings and there is no twist at all. The wings are blue foam with a full length carbon tube spar and glassed skins. Very rigid, so why the wing flutter?

If I move the cg back to the recommended position I will have to take out all the reflex and I'm concerned this will increase tip stall issues. When I tried this cg with hand test launches the wing seemed to fly nose up , tail sagging with a tendency to roll over.

Thanks again fellas.
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Old Jan 20, 2013, 01:46 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,282 Posts
Sorry to here about the mishap,at least it's repairable.I'll leave the tech stuff to those who know what they're talking about,but re the pics- do you have or access to any sort of smart phone?If so install the Tapatalk app.You can get on the forum with it and upload your pics,which are worth a ..............
I only have an iPad ,all my pics from that app.
Stuart
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