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Nov 04, 2016, 07:17 AM
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Build Log

Giving the HK 90mm Viperjet a try

Finally started my own HK Viperjet, which had been waiting in the garage for a year now. I plan on doing it pretty straight forward, on 8S and with only minor modifications

First step I took was weighing the airframe and components I've collected so far:
Fuselage incl. canopy, covers, wing and stabilizer tube, radio plate: 1,179 gr.
RH/LH stabilizer: 63 gr. each
Rudder: 18 gr.
RH/LH wing: 121 gr. each
Total airframe: 1,565 grams.
EDF unit (aluminum), 8S, 1300KV, incl. mounting: 603 gr.
DLUX 120 HV: 171 gr.
BEC 4A/5A: 21 gr.
4x TGY-211DMH servo's: 15 gr. each
4x MG-14 servo's: 15 gr. each
3x SBUS decoder: 14 gr. each
Receiver: 11 gr. each
Total equipment (so far): 968 grams.

Total weight so far: 2,533 grams. But this is without batteries, landing gear and a few minor modifications I plan on making:
-change split flaps to full flaps
-add the ventral fins the original has as well

Second step was checking the dimensions and installation of the wing tube (which broke out the first attempt to insert the wing tube.....)
The measurements I took also had me stomped. I let the picture speak for itself. I can only conclude that the fuselage must be slightly bend sideways
Well, you get what you pay for, I guess

So far for now. I look forward to your comments.
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Nov 04, 2016, 07:43 AM
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Mine is in a semi complete state with prob 90% of the work done.

Decided to play with a few smaller edfs before jumping in to the big one. My flying is not what it was after missing alot of field days last year.

Working up to it, subscribed.
Nov 04, 2016, 01:26 PM
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Same goes for me, not a lot of flying this year. But last year I flew the Durafly MK100 Vampire with 70mm EDF (my first EDF). That was so much fun, I decided to get the Viperjet, because I wanted some more speed.

Love to see your Viperjet, put some pictures on if you will.

Also thinking to put some wing fences on, like someone on another thread I read. Everything possible to minimize the risk of that death spiral I read so much about.

By the way, did you install retracts and if so, which ones ? I'm struggling with the max. depth the wing has and can't find a retract set low enough not to stick out of the wing at least 5mm. Any tips would be greatly appreciated.
Nov 27, 2016, 02:12 PM
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Got a bit of work done on the fan today. As I don't trust the factory balancing of any asian manufacturer, I took apart the fan today to check.

Behind the fan I discovered there is an integrated cooling fan (which needed some fine burrs removed). The intention behind this idea is good, although not of much use if you don't have any exit holes for the cooling air So I'll see if I can make 4 pcs of 6mm (1/4") in the tail cone.

In order to be able to fit the fan in the Viperjet, I had to take of the inlet ring. Boy, was that thing tight on there. I had to make a cut with a Dremel in order to get it off of the housing. Before cutting I tried to also remove the motor from the fan housing....not a chanche. It's in there for eternity. So no chance to upgrade to higher KV

Balancing the fan turned out to be impossible. The center hole is not straight in there, so the fan was wobbling all over the place when I spun it by hand. I'll order a seperate JETFAN 90-V2 fan and put it in this aluminum shroud. Should be awesome.

I also decided to go with an S.Bus cable harness in order to reduce cabling as much as possible. As I am only using non-S.Bus servo's I'll have to put in some decoders. The first one went into the tail section today.

Next weekend another update.
Nov 27, 2016, 03:05 PM
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Going to get back to mine soon, next on the list.

I also have a complete jetfan 90 v2 now but its not going in the viperjet as it has epf 90mm 1600kv fan in it that is really nicely balanced and only pulls 95 amps on 8s installed already.

Be interesting to see what power you get out of the jetfan rotor on 1300kv and 8s.
Last edited by raydar; Nov 27, 2016 at 03:20 PM.
Nov 27, 2016, 06:31 PM
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What thrust do you get from the jetfan at 8S and 1600kv ?
Nov 28, 2016, 06:47 AM
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Originally Posted by madray66 View Post
What thrust do you get from the jetfan at 8S and 1600kv ?
Reread my post the jetfan does not have a 1600kv motor in it the epf fan does. The jetfan is still in its packet.

My jetfan will eventually have a het 1400 kv motor in it I think for 10s for another plane, not quote decided or pulled the trigger on a motor yet but the figures on paper look good.
Last edited by raydar; Nov 28, 2016 at 06:52 AM.
Nov 28, 2016, 07:24 AM
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I see now, misread your post. Just looked up the EPF fan, very nice indeed !

According to data from E-jets I should get around 2.9-3.0 kg thrust with a 1300 kv motor at 8S. Would suit me fine at a model weight below 4 kg.

Alternatively, I am also looking at a 12-blade CNC aluminum fan from Dr. Mad Thrust (HK). Any thoughts on that ?
Nov 28, 2016, 08:52 AM
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I am not experienced enough to be giving advise on fan selection but all my future 90mm edf purchases will be tried and tested jetfan setups.
Dec 10, 2016, 01:42 PM
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Made a little bit of progress today. It's going to be a slow build, but hey, I've got the time, not in an hurry.
Got the rudder servomounts in place and the servo screwed on. The edge of the cut-out in the vertical fin will need some work in order for the servo to fit properly.
Also put in the fan for a trial fit. Looks like the ducting will need a fair bit of work...

One thing I'm a bit worried about though is the motor, only rated for 56 Amps. At 29,6 Volts that comes down to just 1657 Watts
I don't think that's going to produce a whole lot of thrust....I think I'll make a test bench first before putting it in.
Getting that motor out of the aluminum housing is going to be a challange, should I have to replace it with a stronger one. Probably going to have to heat the housing so it'll expand and release the motor...
Dec 10, 2016, 04:56 PM
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That motor will take way more than 1670 watts, I push 29mm dia can motors to that wattage, fit a heat sink.

Hold off trying to marry that ducting to the fan till I have flown mine, if my amps don't go up a fair bit in flight then your are wasting your time with the ducting and will be as well to just hack that little off the front and fit your fan with inlet lip.

Was hoping for a proper maiden of mine tomorrow but when fine tuning the linkages I realised my flap programming was poorly done. Unfortunately when reprogramming a better way I fried the flap servos!!, hey ho fitted new ones tonight.

Hope will get a real flight mid week, won't have made all the tweeks I want by then but should be good for a flight or two.

Not going to post in this thread anymore as there is already a good thread out there.
Last edited by raydar; Dec 10, 2016 at 05:21 PM.
Dec 10, 2016, 09:54 PM
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Cabledawg1's Avatar
I am fuzzy on the Futaba Sbus. You end up with less wiring, but you have to add decoders. It doesn't seem to be about weight then. What do you perceive the benefit is?
Dec 11, 2016, 03:23 AM
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Actually you do save a little weight as the decoders are light, well the Frsky ones are but your right saving weight was not the prime objective.

Benefits for me where one wire going to each wing with one connection with the decoder in the wing itself, much neater install and my single x8r 8 channel receiver is now a full 16 channel capable receiver by using the two 4 channel sbus decoders.

I have used 12 channels on this jet so far.

So much for not posting here anymore lol.
Last edited by raydar; Dec 11, 2016 at 04:06 AM.
Dec 11, 2016, 07:45 AM
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@Raydar: I'm hoping it will handle a lot more amps as, ideally, I would like to fit a Jetfan rotor, which will give me around 3kg of thrust but will pull 80-90 Amps. As for the ducting, I will cut the ducting part that protrudes past the fuselage former anyway and make an intermediate piece to connect the ducting with the fan. For this reason I actually removed the inlet lip (had to cut it off, as the thread had seized, so not possible to re-fit).
Looking forward to hearing the results of your upcoming maiden. I know there are other threads on this bird (read them all, more than once ) but these mainly deal with the older, copper coloured, version. Plus I want to share some modifications I have planned. I hope you will keep sharing your experience in this thread.

@Cabledawg: I don't think there will be that much weightsaving, since this plane is relatively small. On a bigger plane the weight benefits would probably weigh in more [pun intended ]. The main advantage I see is a much reduced number of cables. Plus, I simply want to give it a try. I am using three Corona SBus decoders CSBD-1: one for the three tail servo's and one for each wing. The Corona Programming Card CSBP-1 works very easy. If this works well, I'll be using it on other planes as well.
Mar 05, 2017, 08:55 AM
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The project continues...

So, after 2 months of silence, finally some progress again:
- got the fan unit ready for installation, cut cooling air outlet holes and fitted part of the ducting.
- programmed and installed all three S-BUS decoders.
- installed all control surface servo's.
- cut part of the wings in order to make full flaps, just like the original.

With programming the S-BUS decoders you just have to take care to give each elevator and flap servo it's own channel number as one of each needs it's direction reversed (due to mirror installation left/right). But other than that, the S-BUS system works excellent and really simple, saving a lot in wiring, as you can see from the pictures. My advise: don't leave home without it !
Last edited by madray66; Mar 05, 2017 at 09:00 AM.

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