Hobbyking Zulu - Page 3 - RC Groups
Thread Tools
Jan 09, 2016, 04:06 AM
Reap the wild wind
headlessagain's Avatar
Tucking under is scary. Have you tried a dive test
Dive test:
"First find a good level flight, at typical cruisespeed trim.
Then perform a 30deg dive, let it get a little speed then release elevator stick.
Pulls up sharply, you're model is noseheavy (you have up trim in to keep the nose up in level flight)
Pulls very gently up = optimum CG
Stays at path or increase dive angle you're tailheavy. (The model probably has down trim in to keep the nose down) Shift CG forward to your liking"
Hope this helps
Andy
Sign up now
to remove ads between posts
Jan 09, 2016, 11:58 AM
Registered User
Good stuff! This is all very useful info. I'll start mine in about a week hoprfully.
Jan 09, 2016, 06:23 PM
Registered User
Did some more fine tuning this morning. Now got it comfortable in a 50 degree (or so) dive. (No tuck-ins or pull outs).
The stats for my (motorised) Zulu are:

i) All up flying weight = 714 gms. (Includes everything below as well as ESC, motor, Rx, XT-60 connectors, wires, spinner/folding prop, etc);

ii) Battery (of 122gms), is held in place inside the kevlar nose cone 78mm back from the nose cutoff;

iii) Added an extra 22gms of lead externally (at the moment), on the fuselage nose, just behind the spinner. (Done to make sure it doesn't tuck-in during a steep dive).

iv) Items (ii) and (iii) above result in a CoG of 85mm back from a point on the LE measured 25mm from the fuse side (underneath). (The swept back wing really calls for another reference measurement when speaking about accurate placement of the CoG position).

v) Had to add 1mm of 'up' trim (reflex) after increasing the nose weight with the 22gms. This resulted in almost a dead level level glidepath under zero wind conditions (at the field).

vi) Expo is now at 35% Elevator and 30% Aileron.

vii) Surface deflections: Full up is 17mm, full down is 13mm.

Its now a lot of fun to throw around in the air. Loops at almost any radius desired. Aileron rolls are a bit trickier .. Doesn't like any elevator input during the roll (it comes way off axis doing this). Stall turns on the slope were pretty easy going and graceful. Landings on the slope requires some height losing manoeuvres .. (wish it had at taliplane and some flaps! )

Gotta do something about its colours too .. I'm told its one of the 'ugliest' planes on the field. (None of these folk are slopers addicts though, and none were ever into wings/planks when they used to slope).

Hope all this helps. Have fun .. the HK Zulu is definitely a fun sloper. I'm looking forward to good experiences with it!
Cheers

PS: Inverted is good and easy to maintain.
Last edited by Flightplan; Jan 09, 2016 at 06:28 PM.
Jan 09, 2016, 06:28 PM
Registered User
Quote:
Originally Posted by headlessagain
Tucking under is scary. Have you tried a dive test
Dive test:
"First find a good level flight, at typical cruisespeed trim.
Then perform a 30deg dive, let it get a little speed then release elevator stick.
Pulls up sharply, you're model is noseheavy (you have up trim in to keep the nose up in level flight)
Pulls very gently up = optimum CG
Stays at path or increase dive angle you're tailheavy. (The model probably has down trim in to keep the nose down) Shift CG forward to your liking"
Hope this helps
Andy
Thanks headlessagain .. much appreciated. Cheers.
Jan 10, 2016, 01:56 AM
Reap the wild wind
headlessagain's Avatar
No problem. The dive and inverted tests are the basic c of g tests but I've read that when you get into complex sailplanes different rules apply
I agree that some clarification is required re where the c of g mark is measured from. Last night I glued the internal ply pieces, rough installed the servos and popped the wing on. I then marked the c of g which will probably be too far aft so thanks for your revised position.
My final fitting out will have to wait until my DX8 is back from Horizon (elevator gimbal)
Ugly plane? Clearly not slope addicts. I think they were going for a finish that showed off the construction. Why cover a bagged composite wing as that would make it look like the cheaper Zupair Zulu.
Talking of being a slope addict, one of my local fb's asked me how many pure slope models I have aquired since getting hooked 14 months ago. I stopped counting at 20 and that's before I factor in the Pluto and Zackspeed wings that are on route. I think he now understands why I normally take 6-7 models to the slope each time
Andy
Jan 24, 2016, 04:07 PM
Mex
Mex
Registered User
Hello peeps,

I've been slow building the Zulu since Black Friday and it looks like it can go for a maiden flight soon the only thing i don't know is the 4 degree Down thrust it looks like so 'freakin' much to me. I have used the 'Jig' that is included to cut the nose of so a motor can be fitted.

What do you guys think about it? I have no experience with slope gliders and it's also my first converted motor slope glider

(The black line across the spinner and nose is photoshopped so it makes the 4 degree down thrust move visible in the picture)

Edit: About the motor setup it's not the 'recommended' setup it's a power setup and it will go fast!
Last edited by Mex; Jan 24, 2016 at 04:12 PM.
Jan 24, 2016, 05:12 PM
Registered User
Quote:
Originally Posted by Mex
Hello peeps,

I've been slow building the Zulu since Black Friday and it looks like it can go for a maiden flight soon the only thing i don't know is the 4 degree Down thrust it looks like so 'freakin' much to me. I have used the 'Jig' that is included to cut the nose of so a motor can be fitted.

What do you guys think about it? I have no experience with slope gliders and it's also my first converted motor slope glider

(The black line across the spinner and nose is photoshopped so it makes the 4 degree down thrust move visible in the picture)

Edit: About the motor setup it's not the 'recommended' setup it's a power setup and it will go fast!
Hi Mex;
If you followed the guide it should be fine. Mine looks to be about the same as yours, (as best I can make out).

You'll be in for a surprise if you've 'suped' up the motor. Its a pretty slick airframe to start with, so I'd suggest launching from half throttle until you get used to it. (I actually started my maiden from just a hand-launched glide and slowly throttled it up). If you're planning on going fast, beware of the dive. It will tuck under and won't want to pull out until you get the CoG just right ... and its very sensitive to minor CoG changes.

I've recently cranked up the surface throws on mine and removed the expo (just for more aerobatic fun).

I've also come to the conclusion that inverted flight requires an almost perfect CoG (and trim) setting (for the prevailing conditions) and because it absolutely needs about 3mm 'up' reflex (remember to set this for the maiden .. otherwise it'll plough straight into the ground), it immediately dives when it goes inverted. This makes aileron rolls very tricky to perfect.

Let us know how it goes ... best of luck

Cheers
Jan 25, 2016, 02:10 AM
Reap the wild wind
headlessagain's Avatar
Good luck with the maiden Mex. Try to shoot some video if you can.
My slope version should be next on the bench to finish off now that my Wisel has been finished and had it's maiden
Andy
Jan 25, 2016, 04:09 AM
Registered User
Quote:
Originally Posted by Flightplan
Hi Folks;
I started out with a CoG right on 97mm from the LE. Overall, its a very docile well-behaved plane .. very graceful in light wind conditions (at the field) and responds well to controls (I'm running 35% expo on elevator and 30% on ailerons). However, when put into a high(ish) speed dive, it was very difficult to pull out. It more or less viciously porpoised its way reluctantly out of the dive, (although it seemed to have set its mind to drill its way well and truly into the turf). More nose weight was recommended, so I added another 20 (ish) gms to the nose and moved the CoG about 5-7 mm(??) forward. This seemed to make it much more controllable in the dive, although it still displayed the same general overall reluctance to pull out of it.
Wish i had seen this before i flew mine at the weekend. It flew well for 30min until I got a lot of height in some good lift. I decided to come out of it and pushed in a bit of down and got it into a shallow dive. It then tucked the nose and started to go vertical. I put in max up but it kept on going with only a couple of small wobbles to even indicate it was trying to come out of it. It never succeeded and a big thump was heard.

cg as at 97mm and it seemed right prior to the dive. If anyone needs an underwing hatch i have one, it's the only undamaged part, the rest is a write off; snapped tail, front end is crushed all the way back to wing bolts, wing core is snapped. I've had some bumps before but this is my first proper write off. Glad it wasn't an expensive purchase.
Jan 25, 2016, 07:41 AM
Mex
Mex
Registered User
Flightplan, great thanks for the info! paul_mccaughey thats a bummer! So it has a couple of serious issues i'm not so happy about... Sounds like my plane is already doomed mine is pretty heavy 2200mah 3s 40amp esc 1500kv motor it will go unlimited vertical I thought around 600 - 700 watt
Jan 25, 2016, 10:41 AM
Reap the wild wind
headlessagain's Avatar
Sorry to read of your terminal crash Paul
Looks like a more forward c of g will be called for when I maiden mine. Was your's a powered or slope model?
Andy
Last edited by headlessagain; Jan 25, 2016 at 10:53 AM.
Jan 25, 2016, 12:42 PM
Registered User
Really bad luck. Seems strange that the manufacturer has recommended an too far aft cog!?
Jan 25, 2016, 02:07 PM
Registered User

must be in the airfoil, or?


actually, when you go down vertically, the CG does not play any role (which is why you should do just that when you want to test your decalage aka angle of incidence of an airplane with a stab, or the reflex with a flying wing).

therefore, it must be some bad behavior of the airfoil at higher speeds, or is there any other possiblity?

I certainly wouldn't have the nerve in such a situation to think about trying an outside loop to get out of this problem, but it might be worth a try to push instead of pull?

OT: During a test of the De Havilland Swallow, Geoffrey de Havilland was killed, as the (flying wing) plane got into pitch oscillations.
Jan 25, 2016, 03:12 PM
Registered User
Quote:
Originally Posted by paul_mccaughey
Wish i had seen this before i flew mine at the weekend. It flew well for 30min until I got a lot of height in some good lift. I decided to come out of it and pushed in a bit of down and got it into a shallow dive. It then tucked the nose and started to go vertical. I put in max up but it kept on going with only a couple of small wobbles to even indicate it was trying to come out of it. It never succeeded and a big thump was heard.

cg as at 97mm and it seemed right prior to the dive. If anyone needs an underwing hatch i have one, it's the only undamaged part, the rest is a write off; snapped tail, front end is crushed all the way back to wing bolts, wing core is snapped. I've had some bumps before but this is my first proper write off. Glad it wasn't an expensive purchase.
Aarrgghh! (Never good to hear that ..). Commiserations, Paul.

Not that it'll help your situation now, but the 'tucking in' issue seems to almost disappear with the CoG moved forward by as little as another 7mm. At this forward position however, I also noticed a loss of 'floatiness', (which would be expected, of course). Flight times between throttle-ups seemed noticeably shorter as a result.

Its a pity yours is a write-off. Its a very easy & fun plane to fly once the dive problem is sorted out.
Oh well ... the drooperoned foam Zulu is still a temptation for me, even though the carbon Zulu is still an active fleet member. (You might also now consider the foamy now as well?)
Jan 25, 2016, 03:45 PM
Registered User
Quote:
Originally Posted by mopetista
actually, when you go down vertically, the CG does not play any role (which is why you should do just that when you want to test your decalage aka angle of incidence of an airplane with a stab, or the reflex with a flying wing).

therefore, it must be some bad behavior of the airfoil at higher speeds, or is there any other possibility?
I'd certainly like to understand more about why it has this characteristic. I agree that if the CoG is in free fall, then I can't really see why the CoG position should make any real difference, nevertheless, it seems to.

I've had one sneaking suspicion that the needed preset 'up' reflex might be playing a role in keeping the wing in a kind of 'locked-in' stable position in the dive(?)

The dive isn't perfectly vertical either, so the control surfaces might simply be in the wind shadow of the LE of the wing in a say, 70 degree dive(?) In other words, they may simply be stalled, with the net result that up elevator becomes ineffective(?) But why the added nose weight makes any difference at all in this scenario, then becomes the main question(?) Maybe it pulls the wing more towards the vertical, and then re-exposes more of the control surfaces to the airflow(?) I dunno.

Quote:
Originally Posted by mopetista
I certainly wouldn't have the nerve in such a situation to think about trying an outside loop to get out of this problem, but it might be worth a try to push instead of pull?
Good idea .. I might give it a go if I can work up the courage!

Quote:
Originally Posted by mopetista
OT: During a test of the De Havilland Swallow, Geoffrey de Havilland was killed, as the (flying wing) plane got into pitch oscillations.
Hmm ... I haven't noticed any oscillations but I'll keep that in mind!

Cheers


Quick Reply
Message:

Thread Tools