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Old Mar 26, 2012, 01:50 PM
Grumpy old git.. Who me?
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Aberdeen
Joined Mar 2006
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Originally Posted by NJSwede View Post
Actually, as long as you have some forward speed, you're going to have a headwind vector that's at about 15 A-o-A. When you add that to the prop wash, you'll have a true A-o-A that's greater than zero.
Yep, I hadn't overlooked that, I just don't think it's significant.. Also bear in mind that as the AoA increases toward 45 deg the 'lift' generated by the wing due to prop wash and forward vector is actually working to slow the plane as much as to lift it upward because the lift vector is incline about 45 deg rearwards.

BTW.. look up the 'Custer channel wing' planes for an idea of what's possible using prop wash, when you design the plane to exploit it.. A fundamentally flawed concept but interesting non the less.
Custer Channelwing in Flight (0 min 44 sec)


Anyway.. this probably belongs over on the aerodynamics forum.. I still need to fix my Slick before i can test any of this stuff out.
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Old Mar 26, 2012, 02:16 PM
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Grass Valley California
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Steve

I think you have an excelent understanding and correct observation of the difference between the 3DHS and HK Slick's

For harrior you need a wing design that stalls quickly and stay's stalled, Hence the thin airfoil and sharp leading edge.

Wing rock is caused by the stalled air trying to retach itself, easier on a fat round airfoil.

That wing then generats more lift and starts to fly and the other wing drops picking up speed and then it starts to fly.Then you get wing rock

Most airfoils can be forced to harrior, but may have a very small sweet spot, AOA, that they will do it at. That is where pilot skill can make a bad design look good.

In harrior lift is not generated by the airfoil but by the upward thrust of the prop and preasure on the bottom of the wing. the airflow over the top of the wing is stalled generating no lift.

In watching Michel fly the HK slick it appeared to have a fairly wide envelope that it harriored in The rudder was not being over used and with the right balance of power and elevator it seemed to do well.

It also looks like the 3DHS designes are much more forgiveing. there is some voo-doo magic involved with their airfoils and designes.

I think any discusion about full scale will be irelevent. Just not looking for the same things.

Most pilots that have a problem with a model that others seem to be able to harrior well either have not trimed the model correctly( CG , elevator throw and expo on rudder ) or are useing to much rudder. You are already holding full up elevator and adding to much rudder is a snap roll command.

I did the review on the 3DHS 72" Extra and that is one easy plane to harrior. And I still saw posts that the flyer comlained about wing rock. Problem solved when he was advised to set a neutral CG and more expo on rudder.

You will generally need at least 45* of elevator and 55* may be better. almost imposible to harrior with 20* to 35* of elevator throw.Not enough to keep the wing stalled

And last If you think you are trimmed because you set the factory recomended CG and trimed for level flight you will be fighting a lot more than just wing rock. Spend some time to get the model correctly trimmed.

Steve I would probably say get a little more flight time and trimming before I started to change things, but it would be interesting to see what the stall strips would do

Dennis
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Old Mar 26, 2012, 02:21 PM
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OOps my bad

Most of the last post was in general response to posts other than Steve's
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Old Mar 26, 2012, 02:43 PM
3D Wannabe
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United States, NJ, Mendham Township
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Originally Posted by Dennis C View Post
OOps my bad

Most of the last post was in general response to posts other than Steve's
But very interesting, so we forgive you!
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Old Mar 26, 2012, 02:50 PM
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Originally Posted by Dennis C View Post
Most airfoils can be forced to harrior, but may have a very small sweet spot, AOA, that they will do it at. That is where pilot skill can make a bad design look good.
This would be any time Michael Wargo flies a HobbyKing model for a video.
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Old Mar 26, 2012, 03:56 PM
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Some more some less

He did not look very busy with the Slick

Dennis
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Old Mar 26, 2012, 04:00 PM
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Originally Posted by Dennis C View Post
Some more some less

He did not look very busy with the Slick

Dennis
Maybe I just missed that, I couldn't see his thumbs .

Cheers!

Gary
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Old Mar 26, 2012, 07:01 PM
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Originally Posted by JetPlaneFlyer View Post
Wow you are pushing that 840kv motor HARD running it on 4s with a 14x7.. you must be pulling over 70A on a fresh battery.. no?


PS.. there was nothing wrong with the set up on mine, extended arms on all servos, ball linked pushrods on all servos, sealed hinges, CG set so inverted was hands off. Slightly slow servos was the only thing that I'd say had room for improvement.

i have discovered why i think the HK Slick rocks more (in my hands) than current 3DHS or Ef models; it's in the airfoils used on the wing. Current planes from both 3DHS and EF use thin airfoils with quite sharp leading edges, they all use pretty much the same airfoil from root to tip. so the airfoil at the tip is thin and sharp nosed.


The HK Slick uses a similar sharp nosed thin airfoil at the root but it uses an old trick to prevent tip stall.. the airfoil % thickness (that's thickness over chord x100) increases from root to tip and the airfoil at the tip gets a much larger leading edge radius. The difference in the airfoil at the tip between the HK Slick and ,say, my EF Edge EXP is quite marked. The Slick has a thicker airfoil and a much more rounded nose to the airfoil.
Now while this is accepted aerodynamic practice for 'normal' airplanes to improve stall behaviour (it stops the tips stalling before the root) it seems that both 3DHS and EF have turned their backs on it for 3D models. I assume what 3DHS and EF are looking for is an airfoil that when it stalls, it stays stalled, and you dont get any unstable part stalled/part un-stalled flow regimes (this is my guess but whatever way there must be a reason).

So what i think I'll try is some temporary leading edge 'stall strip' (google it) extensions that will alter the airfoil behaviour. Adding stall strips at the tips is the opposite of what conventional wisdom says because they normally go at the root, but it seems that that is what 3DHS and EF are effectively doing with their airfoil choice.


Steve,

PS.. Don't worry she will be repaired, but you can bet your bottom dollar that there wont be any popsicle sticks used; they are best used for supporting popsicles IMHO.. I'll be using wood from my mountain of balsa (I scratch build too). I just ordered the covering I need, I'll have to jig the fuselage to get it straight because it's banana shaped right now.
Nope it actually is only pulling 46 amps and just under700 watts. doesn't even break a sweat! This info comes from flying with a watts up meter installed. This is the setup Will3Dforfood recommended on the other thread . Its been working good for me. Below is his recommended setup.I first started out with a Vox 13x6.5 prop but, it was only pulling 42 amps and 524 watts, so I went with a 14x7. Maybe my SK3- 35x48 was wound differently. I just don't know but , this is what it reads after a flight with the watts up meter.
Things to buy for ULTIMATE Setup:
Turnigy Aerodrive SK3 - 3548-840kv Brushless Outrunner Motor
Turnigy Aerodrive SK3 - 35-XX Spare Accessory Pack
TGY-390DMH High Performance MG Digital Servo (Extra Strong) 5.4kg / .11sec / 22.5g - QTY.4
Turnigy Super Brain 60A Brushless ESC
Turnigy USB Linker for AquaStar/Super Brain
Turnigy nano-tech 2650mah 4S 35~70C Lipo Pack
Turnigy nano-tech 2200mah 4S 35~70C Lipo Pack- For Lighter setup
Polyester Velcro Peel-n-stick adhesive side V-STRONG (1mtr)
Battery Velcro Strap (2pcs/bag)
Insta-Flex Flexible Thin CA 1. oz
Turnigy 5mm Heat Shrink Tube - BLACK (1mtr)
Nylon XT60 Connectors Male/Female (5 pairs) GENUINE
Charge Cable w/ Male XT60 <-> 4mm Banana plug
Polymax 5.5mm Gold Connectors 10 pairs (20pc)- I was going to put these on my battery and esc to motor for less resistance
Turnigy Heat Shrink Tube 10mm BLACK (1mtr)
Cable Ties HS3.6x250mm 100pc (Natural White)
SELF TAPPING SCREWS W/SHOULDER M2X12 (10PCS/SET)- I always lose them
Ball and roller link 3.9x2x16mm (10pcs)- MUST HAVE!!!
Ball and roller link 4.8x3x17mm (10pcs/bag)- Wanted to try these out too.
HobbyKing 4-6min Epoxy Glue- I use this to glue the ball-link to the pushrod, scuff metal rod first before glue(I only use on small planes)
Twisted 15CM Servo Lead Extention (Futaba) 22AWG (5pcs/set)
Futaba/JR Connector caps (5pcs/set)-Need atleast 2 bags
Spinner 48diam / 5mm shaft
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Last edited by bonner; Mar 26, 2012 at 07:13 PM.
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Old Mar 26, 2012, 07:07 PM
Team 3DHS
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Nashville , Tennessee
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I really hope I get to fly one of these wonderful airplane.

There is a real possibility.
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Old Mar 26, 2012, 07:45 PM
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USA, VA, Fort Belvoir
Joined Jun 2008
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[QUOTE=bonner;21150830]Nope it actually is only pulling 46 amps and just under700 watts. doesn't even break a sweat! This info comes from flying with a watts up meter installed. This is the setup Will3Dforfood recommended on the other thread . Its been working good for me. Below is his recommended setup.I first started out with a Vox 13x6.5 prop but, it was only pulling 42 amps and 524 watts, so I went with a 14x7. Maybe my SK3- 35x48 was wound differently. I just don't know but , this is what it reads after a flight with the watts up meter.

I was actually going to ask this question today, but the whole wing shape issue was really going stong.

Bonner and I are using the exact same set up. Same plane, motor, ESC, Prop, and Batt. Only difference is Bill is using a Futaba system and I am using a DX8. Bill is getting 46 amps and 700 watts. I am getting 71 amps and 1046 watts...? I am really not sure what the deal is with this though. I replaced my first one because I thought it was not quite right, but the second motor is pulling just about the same numbers. I have a third motor for stand-by that I might install and test out. We are even using the same meter in both planes and our set ups are identical. I did set the throttle rage and tested it again, same numbers. Any thoughts?

Forgot to add, we are using a 4C2500 MA and after an 8 min flight I am putting 1600 ma back into it.
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Last edited by wblacker; Mar 26, 2012 at 07:58 PM. Reason: add more info
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Old Mar 26, 2012, 07:49 PM
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United States, NC, Hertford
Joined Oct 2007
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I have had 3 750KV motors on a 14x7 pulling around 900watts each. An 840 kv on the same prop should pull around 1K or slightly more. Somthing isnt right if you are only 700 watts with a 4s lipo and a 14x7 prop on a 840kv
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Old Mar 26, 2012, 08:03 PM
3D Wannabe
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United States, NJ, Mendham Township
Joined Jul 2011
849 Posts
Quote:
Originally Posted by wblacker View Post
Bonner and I are using the exact same set up. Same plane, motor, ESC, Prop, and Batt. Only difference is Bill is using a Futaba system and I am using a DX8. Bill is getting 46 amps and 700 watts. I am getting 71 amps and 1046 watts...? I am really not sure what the deal is with this though. I replaced my first one because I thought it was not quite right, but the second motor is pulling just about the same numbers. I have a third motor for stand-by that I might install and test out. We are even using the same meter in both planes and our set ups are identical. I did set the throttle rage and tested it again, same numbers. Any thoughts?

Forgot to add, we are using a 4C2500 MA and after an 8 min flight I am putting 1600 ma back into it.
If I were to guess, I'd say your transmitters have different throttle endpoint settings. There should be a way to calibrate the ESC to the tx. You may want to google that for your ESC (unless there's a manual, of course...)

14x7 @ 840kv should pull a lot more than 700W. I'm pulling 670W on a 700kv with that prop and the increase should be pretty much proportional to kv squared, so a relatively small change in kv should add a lot of watts. So your setup seems more "correct" than Bill's.
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Old Mar 26, 2012, 08:38 PM
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USA, VA, Fort Belvoir
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Originally Posted by NJSwede View Post
If I were to guess, I'd say your transmitters have different throttle endpoint settings. There should be a way to calibrate the ESC to the tx. You may want to google that for your ESC (unless there's a manual, of course...)

14x7 @ 840kv should pull a lot more than 700W. I'm pulling 670W on a 700kv with that prop and the increase should be pretty much proportional to kv squared, so a relatively small change in kv should add a lot of watts. So your setup seems more "correct" than Bill's.
Which Billl? . Thank you BTW
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Old Mar 26, 2012, 09:47 PM
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It's been real, its been fun, but for me, flying the HK Slick wasn't real fun. So... I sold it and I'm moving on to my next project, the PA Ultimate AMR
Good luck working the kinks out fellas, I'm out!
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Old Mar 26, 2012, 09:52 PM
Sippin the Koolaid!
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I guess I will be flying an hk slick sooner than I thought. Gary thanks for the deal
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