Mini-Review 70mm Velocity-RC Slingjet - Sling Shot

[mode101]

Digging into this one, thought I would do a mini-review on it while it's assembled since it's relatively new in the US.

Velocity-RC 70mm Velocity Slingjet - Sling Shot

Available in the USA from http://www.ductedfans.com


Span: 41.54" (1055mm)
Length: 40.95" (1040mm)
AUW RTF: approx. 37 oz (1050g)
70mm Fan Unit

Mainly Balsa construction with some lite-ply with foam core wings, vac form plastic nose cone, canopy and nacelle/ducting.

Designed around the WM400 fan unit, I don't know much about the fan other then it's a pusher style, but it appears the Wemotec MF480 and/or Het 6904 would work as well. On the maximum performance view, whether or not a inlet ring adaptor is an advantage, is another question?

For the power system, I'm still unsure? A 4S-5S pack should fit nicely but the fuselage appears tight in the length department, ample space for the RX and ESC aft, but need some room for the steering servo in front.

Overall first impressions, nice quality ARF with decent covering job. No particular styling but falls into the category as a trainer style jet, I read it was influenced by Star Wars.

There is another thread with more pics and the manual in pdf format for more details.

http://www.rcgroups.com/forums/showt...light=slingjet

I will adding more pictures and details of the build, as time allows.

[monkamarm2000]

looks nice and straight forward. I like those wheels too.


Barry

[Whistling Watts]

Looked at the configuration of the Slingjet, and you can be pretty certain that if you built it out of the box as per, its going to work well, worth waiting for the WM400.

Have some ideas for you if you would like to consider them?

Firstly, always worried that if flown without wheels, most will be I think. the aileron horns mounted on the underside of the ailerons are a bit vunerable to damage. Might be an idea to mount the aileron horns on the top of the wing. (Fig 1) save the horns being caught on a grass hump.

As you have to bore a hole through each wing for the aileron servo cable. Using some wire and wheel collets. Perhaps you can make a Torq rod with some wire and Ali tube instead? Keeps the wing nice and clean and you only need one good servo. (Fig 2)

Also, the plastic inlet has a sharp edge. I will think you will find if you line the inside of the front duct with a simple sanded polystyrene "Lip" in an airfoil shape, the static thrust will improve. You might think by doing this you are restricting the inlet, not so, Bob Kress proved otherwise. (fig 3)

Sorry about the crap diagrams

[mode101]

Originally Posted by monkamarm2000

looks nice and straight forward. I like those wheels too.


Barry

Yes it appears to be so, some good design thoughts and the wheels are nice indeed. I think the 90mm version has retracts, but don't quote me.

Originally Posted by Whistling Watts

Looked at the configuration of the Slingjet, and you can be pretty certain that if you built it out of the box as per, its going to work well, worth waiting for the WM400.

Have some ideas for you if you would like to consider them?

Firstly, always worried that if flown without wheels, most will be I think. the aileron horns mounted on the underside of the ailerons are a bit vunerable to damage. Might be an idea to mount the aileron horns on the top of the wing. (Fig 1) save the horns being caught on a grass hump.

As you have to bore a hole through each wing for the aileron servo cable. Using some wire and wheel collets. Perhaps you can make a Torq rod with some wire and Ali tube instead? Keeps the wing nice and clean and you only need one good servo. (Fig 2)

Also, the plastic inlet has a sharp edge. I will think you will find if you line the inside of the front duct with a simple sanded polystyrene "Lip" in an airfoil shape, the static thrust will improve. You might think by doing this you are restricting the inlet, not so, Bob Kress proved otherwise. (fig 3)

Sorry about the crap diagrams

Good ideas, I really don't care for the current servo set-up (mounted on the top of the wings) since I'm using fixed gear anways). The Single servo idea is one to consider, with a strong servo it should work. I actually thought about just flipping the servos on the bottom like the Keecat/Lingcat.

Yes I wondered about the inlet that should help on the nacelle/duct now does the WM400 even come with any type of inlet ring adaptor for the fan like the MF480? I don't see a offset for the fan to fit into, bascially looks like there will be a sharp step right into the fan.

[Whistling Watts]

I am sure that someone from Velocity will post a picture. Because of the fans design, don't think it will a problem. They might post one in the other thread, they seem to post to that one.

I will post a picture of the one I have if they don't, can't see why not though?

[absolute-zero]

Originally Posted by mode101

Fixed gear is optional for those who want to bungee, not sure about handlaunching?

Handlaunching isn't a problem.

The link below is from one of the prototype-tests, and showing a handlaunch.
It's powered by a Mega 1615-4, 5s LiPo in a Wemotec MF480 350W

In flight video. (4:39 min 76.1MB)
http://www.az-net.dk/projekt/slingje..._in_flight.avi


If you want to see some speed, I have made this little clip. (1:51 min 14.6 MB)

It's the production model, with Mega 1615-3, 4s LiPo, WM400, 400W
Take note this is only 50W more with a shift to WM400
http://www.az-net.dk/projekt/slingje...K_Slingjet.avi

The video say static 450W, but further test tells it's only was 400W, becouse of higher voltage-drop, than expected.

[Whistling Watts]

As I said, wm400 is worth the wait.

[mode101]

Very impressive videos, looks like a great set-up to go with.

4S what? 2100 or 3000+?

Waiting for the WM400, on Ducted Fans "wait list", I'm a slow builder anyways so I can wait.

[Joe 1320]

If I were doing this build, the aileron servos would have their actuator arms positioned upward into the wing with the actuator rod going through the wing and connecting to the control horns on top. That puts everything inside the wing except for the actuator rods that would exit the top.

[absolute-zero]

Originally Posted by mode101

Very impressive videos, looks like a great set-up to go with.

4S what? 2100 or 3000+?

Waiting for the WM400, on Ducted Fans "wait list", I'm a slow builder anyways so I can wait.

The 4s setup was powered by a 2200mAh (15-20C), but I will recommend a 3000mAh (20C) for higher watts (less voltage-drop).

The 5s setup was 2000mAh Kokam

[mode101]

Originally Posted by absolute-zero

The 4s setup was powered by a 2200mAh (15-20C), but I will recommend a 3000mAh (20C) for higher watts (less voltage-drop).

The 5s setup was 2000mAh Kokam

So is there a Wemotec MF480 vs WM400 comparision, thrust, amp draw and etc? I'm curious to see the results for 4S and 5S. Also can you tell me if the WM400 benefits from a intake lip, I don't see it in the picture(s).

[clausxpf]

all fans benefits from intake lips / clean ducting .
But how do one do a real fair test?
first of all ... power surply with no voltage drop....
the same motor set up in each test.
simultanously messuring of volt and Amps.
some kind of standard for the intake lips.. i would go for something like a harmonic nacelle that could be used for airliners or so
and then a standard duct similar to what happens when we build in the fan in a jet model.
that i think will give a fair picture of each fan and where it haves its strength
Claus at area 52
Denmark
Velocity-RC team.

[Whistling Watts]

Originally Posted by Joe 1320

If I were doing this build, the aileron servos would have their actuator arms positioned upward into the wing with the actuator rod going through the wing and connecting to the control horns on top. That puts everything inside the wing except for the actuator rods that would exit the top.

Wow, that's a good idea! Someone should post a diagram explaing that

[absolute-zero]

Originally Posted by mode101

So is there a Wemotec MF480 vs WM400 comparision, thrust, amp draw and etc? I'm curious to see the results for 4S and 5S. Also can you tell me if the WM400 benefits from a intake lip, I don't see it in the picture(s).

As Claus so greatfull tell, it's hard to make a fair comparision, and static-thrust messuring doesn't tell the hole story. You need dynamic-thrust-tests as well, and pressure-ratio over the fan too, to create the most correct comparision.

I fly with a WemoMF480 intake-lip in the speed-video.
The prototype, flew with a very small 3mm lip inside the ducting.


You asked me about the benefits from a intake lip.

I have just made a bench-test with WM400 at around 700W, with and without the intake-lip.
Then I removed the intake-lip the static-thrust decrease 15-20%

[Haze_b]

Absolute-Zero,,

Would you please post an example of the available color schemes? I would greatly apprieciate it.

www.ductedfans.com lists 4 choices, however their website is not very well maintained, and the links are dead for the photos.

I sent them an e-mail but got no response.

Thanks

Haze