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Sep 10, 2016, 08:52 AM
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Build Log

Viper Jet - 90mm EDF - 1400mm HSD (Rating 8/10)

I always wanted a Viper Jet....

Something made me decide to get one. But there are a FEW choices you could make!
At least:
1) HobbyKing Viper Jet 90mm
2) Taft Hobby Viper jet 90mm
3) HSD Viper Jet 90mm

The HK one is a composite, quite heavy and thus the costs of having that weight. Tip Stall potentials, and just needs more space to fly around in really.
The Taft Hobby is 1450mm span, a bit bigger than the HSD 1400mm span. But they are essentially the same design really - by the same foamie designer.
The HSD costs more!! But the HSD is also the newer of the pair, and has some improvements that add up to the higher cost.

Eeeny, Meeeny, Miny.... (no Mo)
The HK one was off the list quick smart. But the Taft and HSD were neck and neck!
I chose the Taft Hobby one as it costs less, and the main issues with it are the PNF stuff, so I would get the KIT and put in 'good' stuff!
I ordered that.... THEN saw something I had missed....
The Taft uses 'straight' oleos, and the HSD has Trailing link oloes - much better for GRASS use! WAY better!
Plus the HSD uses a top mounted cheater duct, and the Taft an underside one. Again, the HSD is better for GRASS use!
The HSD is also better finished - better painted, better decals...

So I changed the order to the HSD kit.... AUD$70 more... the extra benefits of it were well worth that really.

THEN after thinking about the KIT, with NO servos, NO Fan, NO motor, NO ESC...which I did not want anyway... BUT for "just" AUD$160 more... it is worth getting the PNF really!
Plus ALL videos show a fantastic flying 6S jet, in stock form! So maybe I could just Plug And FLY as per PNF means!
All the reviews, write ups, forums etc added up to "It is a great plane, even good/great in its PNF form".
Versus the TAFT having servo issues... blowing up ESC/Motor issues. The Taft also has a way weaker fan/motor/ESC setup anyway. You would NEVER get the Taft as a PNF!!
But the HSD... fine to do the PNF!

And I can always change the EDF/ESC setup anyway, and use theirs in something not needing much Power - the FlyFly Mirage for EG.

I chose the "Benz" colour scheme (Silver/Red)... but in some ways I wanted the "Brown" (Bronze/Black) as that it the main known colour of the full scale Viper Jet. But that is just a bit bland, sort of.. and not overly "orientation friendly"!! So the Silver/Red won.

I am not sure how long it will take to get here.... but I am eager, as it sounds like it is a FANTASTIC jet... hopefully an 11/10 like the Dynam Pitts Model 12 is!!
It is also going to be my "jet version' of the Pitts FULLY AEROBATIC capable aircraft.

Last edited by PeterVRC; Jan 13, 2019 at 11:58 PM.
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Sep 15, 2016, 03:37 AM
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Well, a "delay" turned up. They do not have any "Benz", silver/red, scheme Viper Jets at the moment! Booo! And it could be a many week wait for one!
But an alternative, which actually grew on me very quickly, was the "Ferrari" scheme (pics below).
It has a few slight negatives.... advertising....
But it also has some positives! A very distinctive, different, and cool looking, YELLOW underside! Great for Orientation!

Is there a REAL Viper Jet painted up in the Ferrari scheme? I have not found any information about one, But if there WAS.... I guess it would/could look like this HSD one.... or rather, it would look like the picture below of the Turbine version someone has! With Scuderia and Ferrari decals.

If you buy the VJ from Banana Hobby it has Banana Hobby advertising decals on the Wing, Tailplane and a small one on the fuselage.
If you buy it from Dragon Hobby then it 'had' (when??) Dragon Hobby on the wing and tailplane instead, yet stil the BH logo on the fuselage(!!). But apparently theirs now comes with no DH logos, but replaced by Viper Jet stickers.

That is the format mine will be... well I am pretty sure that is what they MEANT when they explained it to me, in hard to understand/communicate Chinglish emails!
It seems they HAD the BH and DH specific versions, but reverted to them ALL now being just "HSD Hobby" and "Viper Jet" - but still with a small BH decal on the fuselage. That small BH decal is a nice Advertisers logo anyway.

Yet to be SEEN what mine truly will be! But it SHOULD be as per in the picture of the boxed VJ below!
If those stickers can be removed without damaging the paint, I will take those off and put on 'better' suited wording! Though not sure how yet. At worst... Callie Graphics!

Sep 15, 2016, 03:44 AM
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HSD versus Taft Viper Jet

Both look very good....

The Taft is a BIT larger. But note its inlet duct is also a bit larger and not as well shaped.
But in their FOAM terms, both are very good.

In PNF terms, the Taft is junk! Whilst the HSD is very good in PNF form.

The HSD uses Trailing Link landing gear, the Taft uses 'Straight down' oleo pistons - fine for hard runways, but bad on grass!

The Taft has very THIN Elevators.... and they are really unacceptably thin. The HSD has decent Elevators.

All in all the HSD is a better plane, in a number of important ways.... and worth the extra that it costs. BUT a Taft can be made up to be a great plane still - more so for non grass use.


Taft Viper Jet Banana Hobby link (Info and pics etc)

HSD Viper Jet Banana Hobby link (info and pics etc)

Last edited by PeterVRC; Sep 15, 2016 at 04:04 AM.
Sep 25, 2016, 06:22 PM
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Tail assembly design

I have seen/heard of two HSD Fin failures - one for the Viper Jet and one for the Super Viper.
But when I looked at the VJ tail assembly design, it is STRONG and robust! Though it does have one potential shortfall area....

HSD are using a LOT of 'especially made' plastic parts for their aircraft. Lots of good ideas used!
It is actually so much like the Avios Sea Fury that I would expect "Avios" is HSD!! They even have the exact same types of shortfalls!

So the Fin "Box" (mount) is a large piece that has lugs going down through the tailplane, to be screwed into a fuselage mount. The fuselage mount is a large plastic part, mounted up from inside the fuselage exhaust ducting. So screw these two things together and tey are never really going to come apart or fail!
Very well done!

The potential shortfall is in the FIN.
It has two embedded plastic blocks to take screws from the large fin mount "H" piece. The H piece more or less also clamps the fin. In those terms it is strong and well done again! BUT.... those fin blocks could tear out the END of the fin, as they are quite close to its base.
Most likely they would not.... but they surely COULD.
The foam used is very dense EPO, but the blocks could still tear out. So I suspect any failures seen would have to be from that aspect.

To me it looks fine, and strong enough... yet a worry seeing it HAS happened, though not clear on the exact physical failure - that was never mentioned.
I think HSD should have made a one piece fin block, and a bit larger area to keep it going further from the edge.

This could be done as a mod now - 3D print a replacement one piece, larger part there. I will think about that idea....

Last edited by PeterVRC; Sep 25, 2016 at 06:30 PM.
Sep 25, 2016, 06:30 PM
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Spars, spars, spars...

This plane is made extremely well !!
As mentioned, just like "Avios".. err Avios/HSD...

Every surface has spars! Wing, Aileron, Flaps, Tailplane, Elevators, Fin, Rudder!
This is a very robust and 'solid' plane! No flexing or flimsiness..... but HEAVY thanks to that!

It uses a very thick walled aluminium spar for the wings. (10 mm?).

Once it is all assembled it is SOLID! And heavy...
Even a composite aircraft is not this solid! Possibly not even a balsawood aircraft! Well, both would be close to the same end result.

This, like the Avios Sea Fury, is a good/great thing - but you have to pay for it in weight.

Sep 25, 2016, 06:33 PM
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Some crinkles

Both Flaps were 'crinkled' in the same place and way. It seems to me that they might STORE the Flap at some stage, rested on its rear edge!? Or during some parts fitting process.

The fuselage has some areas of that - very slight - also. Suggesting it is rested on a surface that is too hard, during assembly.
It is only very slight, but you CAN see it in the paint sheen.

It is only a bit annoying, but it would be nicer if they took a bit more care for it to be 'perfect'!

Sep 25, 2016, 06:40 PM
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AS150 Anti-Spark connectors

The VJ come fitted with AS150 connectors. These are a built-in Anti-Spark connector. Nice! And costly.
BUT they are not a lot of use to most people, seeing not many people use AS150 connectors anyway! Though they ARE of good use with a bit of alteration....

I removed the black/Negative connector to use it a the mate for the red/Positive one. Thus you have an Anti-Spark 'link'. Then adapt that down to your own chosen battery lead connectors.

I also shortened the ESC leads quit a lot, as they are way longer than required. But it is good they are too long, not too short!

In the end, on the ESC leads, you have a black/Negative XT150 connector and a red/Positive AS150 connector.
And a short AS150 to XT150 adaptor piece - so that you still get tot use the AS150 Anti-Spark function.

Sep 25, 2016, 06:43 PM
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Some 'features'....

All the hinging is done with plastic pinned hinges. Quite nicely done. Easily adequate, 'airworthy'.
But GLUING is dubious seeing they look to have glued in things ON PAINT in most cases! For a lot of things this does not actually matter, but for some it DOES matter.

The Flap Hinges looks like a 'flat plate' but they do also have 'keyed edges' - the plate is really a 'square U' that embeds into the foam also. Whilst this give more area, and extra contact/bite, I would bet they do NOT glue into those slots! They would only put glue onto the flat face - which would then be on paint....

But anyway, overall it seems quite good - but yet to be seen what 'failures', of glue, could occur!

The servos are all Digital Metal Gear, and have nylon clevises with metal pins(!). The servos go into servo 'trays' and have cover plates. All very nicely done!

HSD have produced a "Controller unit" which does all the "stuff" the plane needs done electronically. You just plug your RX into that and it does the rest.
Things such as, route all the wiring - single Pitch RX input out to dual Elevator servos, and the same for Flaps and Landing Gear, the LED lighting, the gear door sequencing, the power source for the 7.4V retracts(!!!)... and even a few unknown things!

7.4V retracts!!???
Yes, they have their 'own' design two wire retracts. What this means is that the retract only has a motor and no 'servoless' control circuitry. That part is in another Retract Controller Box. So the retract are just fed 7.4V... in one polarity direction or the other... to make them open or close. There are no limit switches etc, the controller box just senses a current rise whenever they are physically 'stopped' by something and then it stops driving the motor. This stop occurs when they hit an end, for opening or closing... or jam earlier for some reason. It is actually a very good system and servoless retracts, which also have microswitches inside them, have issues with the switches often enough. So making 'decisions' just based off 'over current' is of more use.

They are all alloy retracts... very hefty and well made!! With 5mm oleo pins too. So they are excellent, and would be worth a lot in cost!
The oleos are well made BUT they have springs that are so hard you can almost not compress them by hand! WAY too hard for the plane - effectively no spring!

One issue with 'controller boxes' is their are custom, and if they fail I bet they cost a fair amount!
You can easily enough go around the controller and do things the more 'conventional way' - but not for the retract controller. You NEED that for those retracts!

The Gear doors.... sigh.
They are well done, and even have the function of "Doors open, main gear goes down, doors close to seal the large wheel wells"... nice.
BUT, they drive the gear door servos just like the retract system. The servos are actually "continual rotation"type... they have no end stop.. the rotate 'forever' if told to. Again, just like the retract motors do. They also use that same 'check for over-current' as the way to stop them.
This is actually a GREAT way to open and close gear doors because it means they will drive them UNTIL they hit a stop and are closed for sure! Or open for sure.
The PROBLEM is that the over-current setup ONLY works in the doors OPEN direction for some reason! This means the doors hit the stops when closing, and the servos KEEP driving forever.... stalling and buzzing then!

I pulled out a door servo and ran it.... they are that 'continual rotation'. If you force it to stop, in ONE direction it senses the over-current and then stops! This shows the over-current is done WITHIN the servo. But they only stop for ONE direction of travel!! It should work for both directions really. But it doesn't.... so this is a big problem! You do not want Digital Servos being driven incessantly, to stalling, for the entire flights!
This needs to be looked at and corrected!

Last edited by PeterVRC; Sep 25, 2016 at 07:28 PM.
Sep 25, 2016, 07:36 PM
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Battery tray and area

The internal room inside the VJ is HUGE...or so it would SEEM.
It is huge, but it is not all of much use! A 6S battery needs to go all the way to the rear of the battery area anyway!

I use pairs of batteries. 2x 3S for 6S. These are a heavier total weight than using one 6S. Almost 100g more. And with those you cannot balance the plane out - you can't move them rearwards any further!

Another issue is the 'nice' foam covered plywood battery tray they have in stock form. It LOOKS nice, but it is really not an effective way to hold a battery in place!
If you strap a battery down against it, it has SOME friction.. but not enough for something 800g or so!
So I made up a new battery tray plate, that allows TOTAL use of the floor area - not just a narrow strip down the middle - so then I can have a Velcro Floor, which 'locks' onto velcro I use on all my batteries.
You still use a STRAP because the velcro is manly to lock it down horizontally, and the vertical direction is done by velcro AND the strap. This method makes for a 100% secure battery placement!

But it did not solve the balancing issue of 2x 3S for 6S....

Sep 25, 2016, 07:44 PM
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Extended battery tray

After some investigating and thinking, I decided to EXTEND the battery area more rearwards!
That would be a simple enough task - cut the rear bulkhead to suit, and make up a battery tray to epoxy in place.
It also then allows 7S and 8S battery setups to be used and positioned effectively to balance it all out.

This had a small unforeseen flaw....

In this manner one battery goes into that new rear area, as it can't be made wide due to the inlet ductings on either side there. But if the batteries have to go in line, the final balancing result is STILL not that great in the leeways it gives - not as hugely flexible as I was expecting. Though it does 'make it' possible to balance it with SOME leeway now.

7S and 8S remain marginal, but if you upgrade the fan and ESC, they will be heavier (down the rear end) so that should make the 7S or 8S balancing all work out will then.
The rear extension is made wide enough to fit a 4S 5000mAH battery down here(!).

Sep 25, 2016, 07:53 PM
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No Banana Hobby Decals

The VJ came with no Banana Hobby, or Dragon Hobby, advertising. The Wing has a "Viper jet" decal and the fuselage places are left bare.
But they give you a set of Ferrari Emblem decals.
No info on WHERE to put those....
So I put one "Ferrari Shield" on the nose, one er fuselage side, and then the remaining "Ferrari Rectangles" onto the Fin.

Sep 25, 2016, 07:54 PM
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Ready to fly

Well it wasn't truly READY to fly, but it was "ok".... and a narrow window of opportunity arrived late on the Sunday afternoon, so I raced off for the Maiden Flight.
I had not Power or Thrust tested it, so when I got it ready to fly I did a run up to WOT and 'felt' the thrust.... it was not that spectacular and felt a bit weak for on grass. But I would find out if it could take off from grass!!

Oh... no I won't.....
When I set the plane aligned ready to go, I throttled up to WOT and.... the fan 'exploded'....
Blades shot out the back.... so it was very obvious.
FOD?? Well whatever did it, it managed to shred all blades off down to the hub.
So that was that .... no maiden. And probably good that it never got moving and took off!

Last edited by PeterVRC; Sep 27, 2016 at 10:36 PM.
Sep 27, 2016, 10:43 PM
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Upgrade to 8S

After getting the stock EDF out to check it, I found they use a 10mm shaft adaptor - which is pretty rare - so no other fan rotor can be used with it really.

Then a bigger surprise.... the motor uses a 6mm motor shaft!! "Normal" is 5mm or 8mm. This 6mm means NO other shaft adaptor can be used with the motor either! Great... not.

A very custom HSD EDF.....

To not 'waste' the setup it means I have to get a new rotor. So I ordered TWO.
The blades (I kept some) are quite soft and flexible, so it seems GRP (Glass Reinforced Plastic) was at a premium, so they used little or none = flimsy weak blades. Probably adequate for their task, as long as nothing makes them want to break off!
All 'decent' fans have a much higher percentage of GRP mix in them.

The 6S thrust did not feel that great anyway so I may as well upgrade the EDF setup, and just use that stock setup in another jet. Something that does not need much power.thrust! Like my Bungee Launch FlyFly Mirage! At least I will get to use the Fan, motor, ESC combo still....
Last edited by PeterVRC; Sep 27, 2016 at 10:58 PM.
Sep 27, 2016, 11:06 PM
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HET/Jetfan EDF combo

I had two main EDF combo choices...
The Fandrive 1500kv/Lander12 7S combo, or the HET/Jetfan 7S/8S combo.

The Fandrive combo is CHEAP but pretty good. About AUD$150 and can use a $35 ESC. But it is only around a typical 6S Power/Thrust level anyway. 2400W or less.

The HET/Jetfan is a AUD$320 combo. And then you need a HV ESC of about $130 too! AUD$450... but I already have those here too...
3000W and 4.0Kg Thrust!!

The HET housing fits straight into the Viperjet, but the Fandrive combo needs a fair bit of 'making fit', so that is another positive for the HET/Jetfan.
Except the HET inlet ring is HUGE and can't be used, but you NEED an inlet ring to blend the internal ducting into the fan.
After lots of inlet ring type tries... nothing was even near close to workable... I decided to design and 3D Print my own custom inlet ring for the task!
Without being able to do that it would have been a 'disaster'... there were no other inlet ring options! And with no inlet ring the fan would lose a ton of efficiency!

When I was designing the inlet ring I could see a coming problem....
Both 'ends' have 'overhangs', which 3D Printers cannot do properly. The stepped end that goes onto the fan housing, and the curved end of the inlet bell curve. I decided to print it front end down, as the stepped rear edge would never print in any useful manner if it was downwards.

The 3D printed inlet ring came out very good, with a bit of issue on the bell curve face but that can be 'filled' to make it all perfect and smooth. So that solved that inlet ring problem.....

Sep 27, 2016, 11:10 PM
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Retract Oleo "Suspension" issue

One thing I had partially forgotten about - but also ignored for the Maiden Flight attempt - was the Oleo SPRINGS. They are WAY too hard for the model and may as well be metal rods in there! There is pretty well zero suspension action from the oleos!

To fix this they would need new softer springs.
I am yet to get the springs out to check their dimensions etc and see what I can do about that.
In their current form - no suspension - it would be VERY BAD to operate this plane from grass! The hammering shocks would go straight into the retracts, mounts, legs... wing foam...
So they HAVE to be improved/fixed!

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