HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 06, 2013, 12:26 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
If the booms are causing the wag via turbulence, I doubt that any fin size would help much.
It would possibly help... but only a small percentage improvement. Because length is still not going to get them out of the turbulence anyway - the real issue would be no nice flow to even have a fin gain 'linearity' from.
eg Imagine a nice flow of air, as per a normal fin would have... but in this case there is turbulence and 'void' either side of the fin(s) anyway, so the fin will never have 'solid' air to guide it straight anyway. A bigger fin would gain a BIT from its area, but still never has a solid flow either side.

It is very hard to measure, but I am guessing it does NOT even get better with speed. Though it LOOKS better.
Because it is moving much faster, the yaw amount becomes a smaller percentage of forwards travel distance anyway - thus looks less. The greater turbulence effect at higher speed, versus a bit more 'laminar' direction flow to the fins (also thanks to higher speed) might swing the dominant factor a bit one way or the other - and by visual, maybe that bit less look in yawing.

When I had it go a bit psycho on landing correction with aileron, that aileron use probably caused a bit of yaw too, which then brought the boom's effect more into play (they wouldn't really care about roll change), creating turbulence, which then causes more yaw (which way?).... and then a form of see-sawing yaw and roll motion unfolded.
Luckily it was a reducing pattern, not an escalating one!! But I am sure that if there was a resultant that escalated, a LOT more people would have found out by now! (crash!). LOL

Maybe it is linked to those boom front ends being AHEAD of CofG... thus a rightwards yaw at the tail, is a leftwards yaw of that 'up front fin' of the boom... totalling to the bit of weirdness we see. (yawing/wagging).
And the real one not doing it, because the root cause is at the boom thickness of the Durafly, which the real ones don't have and thus this issue never even gets 'started' in the real one. Or they may have other flow factors added that already account for it, if it had ever happened in their testings.
And maybe it was why there weren't many twin boom high-tail jets really.....
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: Skyzone Goggles - Button Shield
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 06, 2013, 12:49 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
You can fit about 50mm wide and 44mm high... length is less critical - 136mm is fine.. probably to 150mm region, but depending on your RX etc in there too.

BUT you might not be able to place a particular weight battery well enough to balance correct CofG.
If you break off the rear end vertical plate in the battery area then you can go a bit more rearwards into the plane (for heavier batteries).
But note my use of VELCRO on the floor and under batteries!! To assure they cannot move laterally or longitudally.

You can use this 6S as a size and weight reference of something that can sit to the rear end of the tray, and easily fit, plus balance out well.
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

This 4S 3300mAH should be close to the same sort of thing:
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

This 4S 4000mAH would probably get away with it really (much like the 3300mAH 6S can)
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
Note the 4S 4500mAH 45C Nano is CHEAPER! But a bit larger (still fit) and heavier too.
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: Skyzone Goggles - Button Shield
Reply With Quote
Old Nov 06, 2013, 02:31 PM
Registered User
MD AUTO's Avatar
United States, CA, Paso Robles
Joined Apr 2013
565 Posts
Quote:
Originally Posted by PeterVRC View Post
If the booms are causing the wag via turbulence, I doubt that any fin size would help much.
It would possibly help... but only a small percentage improvement. Because length is still not going to get them out of the turbulence anyway - the real issue would be no nice flow to even have a fin gain 'linearity' from.
eg Imagine a nice flow of air, as per a normal fin would have... but in this case there is turbulence and 'void' either side of the fin(s) anyway, so the fin will never have 'solid' air to guide it straight anyway. A bigger fin would gain a BIT from its area, but still never has a solid flow either side.

It is very hard to measure, but I am guessing it does NOT even get better with speed. Though it LOOKS better.
Because it is moving much faster, the yaw amount becomes a smaller percentage of forwards travel distance anyway - thus looks less. The greater turbulence effect at higher speed, versus a bit more 'laminar' direction flow to the fins (also thanks to higher speed) might swing the dominant factor a bit one way or the other - and by visual, maybe that bit less look in yawing.

When I had it go a bit psycho on landing correction with aileron, that aileron use probably caused a bit of yaw too, which then brought the boom's effect more into play (they wouldn't really care about roll change), creating turbulence, which then causes more yaw (which way?).... and then a form of see-sawing yaw and roll motion unfolded.
Luckily it was a reducing pattern, not an escalating one!! But I am sure that if there was a resultant that escalated, a LOT more people would have found out by now! (crash!). LOL

Maybe it is linked to those boom front ends being AHEAD of CofG... thus a rightwards yaw at the tail, is a leftwards yaw of that 'up front fin' of the boom... totalling to the bit of weirdness we see. (yawing/wagging).
And the real one not doing it, because the root cause is at the boom thickness of the Durafly, which the real ones don't have and thus this issue never even gets 'started' in the real one. Or they may have other flow factors added that already account for it, if it had ever happened in their testings.
And maybe it was why there weren't many twin boom high-tail jets really.....
I will say that mine is rock solid on landing no wag at all . Now I do tend to come in hot and use most of the runway...I hate to tip stall.
MD AUTO is offline Find More Posts by MD AUTO
Reply With Quote
Old Nov 06, 2013, 04:46 PM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
Hopefully my Hatcam videos turn out ok. Boy was it waggling around today.
And right into touchdown too.

Had a close call with using an already flown battery by mistake, oops!
Got full power take-off and circuit back to me and then 'Brrrrrrrrr' LVC........
Luckily that occurred just as it passed overhead at about 20ft and I heard it clearly, plus instantly went into "emergency landing mode" with no "thinking time" to guess what might be wrong.... because that was the one chance to immediately do a short base run to come around for landing right away!

One boo-boo was choosing to belly land!! In hindsight I could have got the gear down but I think in the very short time frame to rapidly assess the path and wind etc, I didn't think the main gear (Lander's that run SLOW) would get down in time - but really, in the time frame that unfolded (20secs or so?) I am sure it would have.
It is very slick underneath, so it skated WAY across the oval - from mid oval touchdown to right off the other end of the field - plus because of the high speed that immediate turn to land had.
It skated through the boundary line water pipe fence 'gap'!! Phew!! It if had hit a vertical pole it would not have been happy! (or me)

So it lived for another day... and a few more flights, with charged batteries!

But I did walk away, after the next two flights, thinking I wish I had not bought one and would not recommend it to anyone - it is just a bad flying plane. (versus my other 30+ as references)
If you weer tossing up over Vixen or Vampire... VAMPIRE wins hands down!
Even though the Vixen is just a bit larger, up market plane really..... very nice to look at....
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: Skyzone Goggles - Button Shield
Reply With Quote
Old Nov 06, 2013, 05:44 PM
Registered User
MD AUTO's Avatar
United States, CA, Paso Robles
Joined Apr 2013
565 Posts
Sorry to hear that Peter mine is a joy to fly. I have a Free Wing B17 that everyone raves is a fantastic flier .. Smooth graceful .....PHOOEY I hate it, it wags all over the place even with a stabilizer ...Always drops it's nose in the turns ... And the retracts are bad.
MD AUTO is offline Find More Posts by MD AUTO
Reply With Quote
Old Nov 06, 2013, 06:16 PM
Canadian Bacon
flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
13,057 Posts
Yeah. Mine doesn't wag on landing, or calm wind for that matter, just gusty wind.

Gord
flypaper 2 is offline Find More Posts by flypaper 2
Reply With Quote
Old Nov 06, 2013, 06:48 PM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
I tried into the wind, down wind, across wind (quite light wind this morning).... it occurs in all directions. I guess I would say cross wind is worse - banking cross wind is clearly worst. It is a huge amount... like 20deg peak to peak at times! It almost seems to escalate to a harmonic, if you have not done something different to shake it out of it. (eg end of that bank to level flight)
As long as you use any roll (bank) it wags more... but even in a straight line it is wagging, just less. So I would say that the standard 'bank and yank' yaw result you get, triggers its start and makes it worse.
The slower you go the more it does it.... at least in visual terms you see it more. Even at high speed passes it is wagging some amount still.

It also falls out of turns very notably. More than a typical jet - even more than F-16, F-22 etc which have even less wing/lift per bank angle. Possibly having waggle, as it banks even more, makes the lift even lower than it otherwise would have been. Maybe the 'centre of waggle' is not aligned to flight path, but leans towards the turning direction a bit (??)... thus making falling out of turns that extra amount worse.
With its quite large wing area I would have thought it would fall out of turns LESS not more.
It is not sensitive to control at all, so maybe I can go more rearwards in CofG to test what that changes. I had to use High Rates for elevator, which is something towards 45deg angles at max! And need to use that at times.

Inverted I don't need much down elevator, so the CofG is probably in a good spot really. Plus it rolls very axially.
Also the elevator trim is dead level to tailplane for level flight - it seems a quite narrow range of pitch error per airspeed too. No ballooning.... no 'WOT cheater suckdown' etc. at all.

I am balanced at the very front edge of the main gear wheel bay - pretty much right where the curved edge of the bay finally is 'flat' wing (4mm ahead of the bay vertical wall?). But with larger batteries it is up to 10mm ahead of that.
All positions (the various batteries) still fly the same as far as I can tell - anything that falls in that 10mm range I have used.

But the waggle is the only bad point about the plane really... all other aspects are passable enough, or even very good.... and it is a bad enough aspect on its own to totally destroy it being anything like a clean flying scale jet. BAH.
So a gyro on Rudder (only) better cure it!

7 flights now, landing on grass, and the LG legs are still all perfectly straight! The Vampire, which uses the same legs, does not last as long before some re-bending is required. The Vixen is from 1.78Kg to 1.88Kg AUW (battery dependent). The Vampire typically flown at 1.6Kg or so (1.65Kg?)

I'll head out again this evening, otherwise in the morning again....
I have 10 batteries suited for it.... but I didn't even want to fly it again after the 2.5 flights..... it is no fun at all really - being non-linear flight, and looking "weird", ruins the view/atmosphere really. For now it is just testing interest.... and if I can work out the waggle (fix), then GREAT. Or maybe it would have to be a "Dead calm day ONLY flier".... or.... the first plane I ever actually SELL.
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: Skyzone Goggles - Button Shield
Reply With Quote
Old Nov 06, 2013, 08:19 PM
Registered User
MD AUTO's Avatar
United States, CA, Paso Robles
Joined Apr 2013
565 Posts
Very strange Peter my Vixen has none of those bad traits . In fact everyone at the two clubs I fly at comment on what a smooth flyer it is. And how nice it banks . Maybe a stupid question do you think changing the outlet sizes on the exhaust could make it fly bad I.E one nozzle has more flow than the other????? Or maybe the changes to the splitter area of the outlet ducts is causing some sort of abnormal flow ???? Its weird mine really flies like a pussy cat.
MD AUTO is offline Find More Posts by MD AUTO
Reply With Quote
Old Nov 06, 2013, 08:23 PM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
I guess that would be nice if it was something like that (exhaust thrust-line).... fixable then!
But exhaust sanding 'errors' mainly give a bit of mis-directed thrust (eg up thrust, down thrust, side thrust... a bit of two...) and that doesn't typically create a waggle... BUT, with the booms and their portions ahead on this, maybe it is a special case(?).

Also, pretty well everyone else has waggle in the Vixen anyway - of X amount, at varied times. Whilst most other aircraft never have any at all..... I think it is typically a twin fin issue. eg Even the Radjet800 flying wing (with twin fins) does it. Mind you even that little screamer only does it a small amount, and a mere fraction of my Vixen's.

Oh..... I have dead neutral RUDDERS to fly straight..... so I expect that means there is no side-thrust error.
The Elevator also dead level for level flight..... so no detrimental (even if it is different to stock) up/down thrust result either.
Ailerons... also dead level trims.

It is extremely clean and 'perfect' as per how it was moulded.
Though I do have a few coats of WBPU and it is very glass-like and thus very slippery. But I don't see how that would bother it tracking fine. (more drag in all directions means another same plane would 'drag' more and resist going off alignment, for a same given speed)
And any building error (which it has nothing askew here anyway) should also just cause a 'direction error' like a yaw, or roll... which you then would trim out via surfaces - but mine must be dead true in every axis, to have trimmed dead level roll, pitch and yaw surfaces.

So all in all, I can't see ANY possible construction, or special-case, situation in mine. I would say it would have to be as close to a perfect Durafly Sea Vixen as any could be.
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Last edited by PeterVRC; Nov 06, 2013 at 08:32 PM.
Reply With Quote
Old Nov 07, 2013, 12:11 AM
Registered User
anlucas's Avatar
Greece, Attica, Athens
Joined May 2011
3,503 Posts
Quote:
Originally Posted by PeterVRC View Post
So all in all, I can't see ANY possible construction, or special-case, situation in mine. I would say it would have to be as close to a perfect Durafly Sea Vixen as any could be.
Peter,
Given that most of our unmodded Sea Vixens don't have these vices (at least to this extent), it must be something that was introduced afterwards.

Is there any slop(even sub mm) in your rudder linkages?
Is it possible that the rudder servo and wires protrude and create drag on one side thus creating a side force on the tail?
anlucas is online now Find More Posts by anlucas
Reply With Quote
Old Nov 07, 2013, 12:26 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,544 Posts
Oh yes...
Well the Rudder servos are flush, but the linkages do run perpendicular to the RUDDERS, which is quite an angle off horizontal.
I can't imagine they cause it... but maybe....
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: Skyzone Goggles - Button Shield
Reply With Quote
Old Nov 07, 2013, 11:32 AM
Registered User
Bulgaria, Sofia-city, Sofia
Joined Aug 2012
177 Posts
It is from the plane - Me and my Friend have it on our flying field. Mine has rudders mod - his is 100% stock with motor and so. Both had tail wag - especially at slower speed - tail goes left right . This is on a very calm day with no wind at all. We tried also in wind - same thing.
cdmanbg is offline Find More Posts by cdmanbg
Reply With Quote
Old Nov 07, 2013, 11:46 AM
Registered User
MD AUTO's Avatar
United States, CA, Paso Robles
Joined Apr 2013
565 Posts
I can see it coming now WAGGLE GATE !!!!!!!!


I will see if I can shoot some video this weekend of mine doing some slow and fast passes and post it , to see what you guys think about how much it waggles.
MD AUTO is offline Find More Posts by MD AUTO
Reply With Quote
Old Nov 07, 2013, 11:58 AM
Registered User
Joined Aug 2011
297 Posts
Quote:
Originally Posted by cdmanbg View Post
It is from the plane - Me and my Friend have it on our flying field. Mine has rudders mod - his is 100% stock with motor and so. Both had tail wag - especially at slower speed - tail goes left right . This is on a very calm day with no wind at all. We tried also in wind - same thing.
Well, FWIW mine is totally stock, with all underwing stores fitted, and gets flown in winds up to about 15mph. It shows occasional very slight waggle, maybe 5-10degrees side to side, but only for a couple of seconds at a time, and it only does this say once in every second or third flight.

I think it happens when the plane encounters turbulent air.
Mark 2 is offline Find More Posts by Mark 2
Reply With Quote
Old Nov 07, 2013, 12:17 PM
History Eraser Button?
pomroyj's Avatar
United States, AZ, Phoenix
Joined Aug 2010
1,090 Posts
Where are the aero Phds? There's a thesis/research paper in here somewhere
pomroyj is online now Find More Posts by pomroyj
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Durafly Sea vixen TLMARK Electric Warbirds 9 Nov 24, 2012 07:24 AM
Sold New Durafly D.H.100 Vampire Mk6 EDF Jet w/retracts PNF OCLightning Aircraft - Electric - Jets (FS/W) 11 Jun 12, 2012 01:36 PM
Discussion Search for Chris Golds DH 110 Sea Vixen review jettrainer Electric Ducted Fan Jet Talk 2 Jul 17, 2011 04:17 PM
Build Log first build ever DH 110 Sea Vixen uggymoo Foamies (Scratchbuilt) 3 Nov 19, 2009 10:47 PM
Question DH 110 sea vixen twchdyn Electric Ducted Fan Jet Talk 10 Jul 01, 2007 10:30 PM