Vector 850 V Tail - Wing Problems, very unstable - resolved with increased airspeed - RC Groups
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Feb 21, 2012, 11:40 PM
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Vector 850 V Tail - Wing Problems, very unstable - resolved with increased airspeed


Any folks that fly V tails similar to the Vector, could you please comment on the flight characteristics on my Vector 850? I got it from HK a few months ago, took my time assembling and checking it out. The stock ESC was bad, it would drain the battery to zero, replaced it with a HK 20 amp and it works fine and the ESC runs at about 90F under full power.
But the big problem is instability - I can't fly the plane. I have a FlySky FS-CT6B radio setup for V tail mix according to F111John using the Digital Radio software ($2), V tail mix settings found here:

Works well, everything is mixed properly. CG seems about perfect, wing tip balance is good, control surfaces are set to "no adjustment" for the 1st flight. This means that I could fly the plane without any major control surface tweaks implying that the assembly was ok - no misalignments. Now for the 1st flight, hand launch was ok for the 1st few seconds and then it would snap roll and head for the earth. I went to a large field and sent it up under power (2/3 throttle) and it was a circus, 3 of 4 flights were throttle off emergency landings to get it on the ground without damage. 1 flight was somewhat controlled and it was ok but short. I was sweating.
Out of the box I noticed that the 1 pc wing was cambered down about 1/2" either side of center creating a negative dihedral. Being new to foamies and 21st century RC model flight I let it go hoping that this was not a mold defect. Now I am going back to basics and I am suspecting this as the cause of the instability.
Any suggestions?
Thank you very much,
Last edited by JohnStef; Mar 05, 2012 at 06:31 PM.
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Feb 24, 2012, 10:42 PM
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Doubletap's Avatar
It sounds like you are experiencing tip stall, which can happen when your AOA is improper with insufficient forward speed when entering a turn it has nothing to do with V- Tails or your perceived anhedral of your particular model the pictures of your model looks normal. It's a common mistake, carrying insufficient speed into a turn.
Feb 25, 2012, 11:01 PM
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Tip stall makes sense, I know that the flying speed was never very fast, I was holding back because it was the 1st flight. From what you say Doubletap, the wing needs more speed to create the lift it required.
Fly Faster!

Thank you Doubletap
Feb 25, 2012, 11:26 PM
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Doubletap's Avatar
Originally Posted by JohnStef
Tip stall makes sense, I know that the flying speed was never very fast, I was holding back because it was the 1st flight. From what you say Doubletap, the wing needs more speed to create the lift it required.
Fly Faster!

Thank you Doubletap
Yes, that is correct, especially when you are entering into a turn, that's why it is snapping on you as one tip stalls first before the root of the wing does. when flying sailplanes, you must always watch your forward speed relative to your angle of attack if initiating a turn too slow and if you pull too hard after banking it will snap on you. This i why that if I want to make a turn with low or no power, I will quickly first put my nose down in effect diving into the turn, with velocity to fly through the turn which is just second nature with us slopers especially because we fly VERY heavily loaded slope sleds which will snap violently if slowed too much going into a turn.
Feb 26, 2012, 05:08 AM
I like mine a lot.
About the easiest plane to fly I've owned.
Just run it wide open full time.
That's my only complaint.
Wish it was a bit faster.
I may try to run it 3s but the nose is really cramped for room for it.

And throttle off landings should coast and land like a butterfly.
This thing is smooth as glass.
Flies just like it's big brother.

All i can suggest is to take your plane up high to give yourself room for corrections.
Make sure you're not tail heavy. You need a slight down angle at the nose when at the cog.
Last edited by IFlyRCs; Feb 26, 2012 at 05:22 AM.
Feb 29, 2012, 10:38 AM
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Both of you gentlemen are spot on. As Doubletap said, I was experiencing tip stall - exactly right. I made a stand to more carefully check CG, it was off - tail heavy, I added about 23g to the front of the battery compartment. Total flying weight 330g - no mods except I threw the stock prop in the trash (used a 5.1 x 4.5). 1st hand launch test was better, 2nd was good - time to fly!
I gave it a good shove into the air with full throttle and let it climb into the wind, it wanted to go up too quickly but it was manageable, (thats what 15+ mph wind does!). At 150' to 200' I put it thru a few maneuvers and was very pleased. It seemed to bank very well, no diving, and turn without tip stall now that the flying speed was where it needed to be.
Thank you!
Rookie working out the bugs!
Last edited by JohnStef; Jul 18, 2012 at 11:37 PM.
Feb 29, 2012, 12:22 PM
Now you should be able to comfortably fly with no throttle.
It's a nice glider.
Not quite as good as the big one though.

Congrats on your success.
Feb 29, 2012, 06:28 PM
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Congrats! It's a very nice flying mini glider!
Mar 02, 2012, 02:24 AM
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Jeebs77's Avatar

vector 850 mods

here are some pics of some mods to the vector 850. I am at about 340grams with a 11.1v 500mah or 7.4v 850mah battery. A little heavy but my whole reasoning for my mods are that this is my new backpack plane (needs to be sturdy and able to have the wing easily removed) and will be sloped at some cool off the beaten path sites, so we'll see how it does!!!
Mar 02, 2012, 10:44 AM
Good stuff Jeebs!
So the stock motor and esc handle 3s with no problem?
That's good news to me.
It performs Much better?
Mar 02, 2012, 03:22 PM
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Jeebs77's Avatar
hey IFLY i am not using the stock esc. i am using a hobbywing 18 amp. instead of unhooking the leads to the motor i simply unsoldered them and then re-attached to my hobbywing esc. on a 7.4v lipo i show about 6.5A and 45W- the 11.1v lipo is about 11A and 110w (not exact but pretty close to what i remembered when i checked). if the stock esc is 20amp though it should handle a 3cell fine. I know others said the esc was not the best, i knew i was going to run 3cells so i just changed it out of the box. i am using the stock prop since mine seems to be balanced fine (not to noisy). i flew it first with he 11.1v 500mah 25c and it had plenty of power and then some. i ran it pretty fast with no problems but i didn't have it at WOT for extended periods. the 7.4v 850mah 25c's were next and while they flew the plane fine i definitely had more fun with the 3cell. This plane likes to be flown with some speed for sure. i also tried a 7.4v 500mah 20c which decreased the weight by almost 20g and it still flew fine (My model is balanced per the manual for the heavier 3cell 500mah and the 2 cell 850mah batteries.) I now see why Johnstef was having problems with the initial flights, when you do stall it tip stalls pretty violently. i was also flying in about 10mph winds today and it handled them as well as some of my bigger planes. Fun plane though easy to build.
Mar 03, 2012, 01:35 AM
Well I'm soon to order some 3s 500s then!
I'll be very very happy with this plane at that point.
Thanks again for reporting the info!!!
woohoo happy days
Mar 03, 2012, 06:10 PM
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g00bd0g's Avatar
Does anyone know how to program the ESC to have the brake function enabled?
Mar 04, 2012, 11:21 PM
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[QUOTE=Jeebs77;20916784]hey IFLY i am not using the stock esc. i am using a hobbywing 18 amp.QUOTE]

Hi Jeebs77,
Good move, I posted a note in the HK discussion about the stock ESC - bad news - I ran the battery down to near zero to test the 6 volt cut off - no cut off! The airborn pack would be useless in the air - dead with no power.

I replaced mine with an 20A HK blue ESC (HKESC20A H-KING 20A Fixed Wing Brushless Speed Control) It works fine. I was just today wondering about the same thing - using a 3s to gain some speed! And here you are in this thread!

Now I plan on ordering a Turnigy Nano Tech 3s 850ma at 73g and take the extra lead out of the nose of my plane. Seems like an ideal tradeoff.

And Jeebs77 - Very Nice mod's! I like the spar down the fuselage, that may have saved my tail snapping off.
I put the plane down hard because it was out of sight and it did not want o climb any trees to retrieve it. Tail snapped off just in front of the tail fins - clean break - clean repair, but I drilled a 5/16 dia hole forward to the cavity in the body and rear ward about 1 1/2" and glued a 4 1/2" piece of carbon fiber arrow shaft into this. It added 5g total, as best as my cheapy postal scale can tell me.

Please post some beautiful pic's of sloping at this off the beaten path location!

Last edited by JohnStef; Mar 04, 2012 at 11:35 PM.
Mar 05, 2012, 01:21 PM
Registered User
Originally Posted by g00bd0g
Does anyone know how to program the ESC to have the brake function enabled?
I don't know if this will help or not but here is the manual for my HK ESC - proceed at your own risk.

You should be looking in battery/ESC/Power supply forums in the future for this stuff, you will get better help from their knowledge base.
Last edited by JohnStef; Mar 05, 2012 at 06:28 PM. Reason: add attachment, proceed at your own risk

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