sskianpour

My Feedback: (2)

Will be starting a new Viperjet build as well. Also interested in anybody's input. I lost my last one on maiden. Flew like a trainer, put her into landing flaps with 2 passes no problems. Turning to baseleg with 3/4 throttle on P-120 with FULL flaps, it was admittedly a shrap turn but not THAT sharp!!!... Se snapped inside, dove to the ground, almost got her back late, but then she bounced off the ground. Totalled! Ouch.

Will build new one. Will be aware of this particular tendency from now on. Any ideas anybody? Thoughts?
TIA Shaz

InboundLZ

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OK she is under way...

Some background on this Viper...I got her used. She was "built" (and I use the term built very loosely) but never flown.... I traded for her but thats another story... It is a Viper Jet II so it has the updated spars and whatnot.

Anyway...I just started working on what ever problem I found first (actually I found several). The original builder put 8 holes in the bottom of the fuse for access to the spar locking bolts. I believe he used the "pin the tail on the donkey method". This would never do, so I have set to fixing the holes so I can locate them properly. Some glass mat and I am on my way. I took a second to index the bolts so I know where to drill the new holes.

The second thing I did was remove the crooked engine rails. Thankfully the "builder" used crappy glue so ripping them out was easy.....

I also worked on the bypass. I wanted to get an idea of how all that works as I have never done a bypassed engine installation before. That has left me scratching my head...anyone have any input on this?

OK some pictures....they should be self explainatory....

SinCityJets

Dave,

What is your question about the bypass?

Chad

Miguel Santana

My Feedback: (6)

Nice surprise to see this thread alive.
The Viperjet is to heavy for its size...so the stall speed is higher than normal...keep that in mind, especially during turns...you have to add a few clicks of throttle before turning
Speed breaks are not needed, and you'll safe weight without them. Instead, program the crow setting in your transmitter.
With all the factory modifications to the last edition, it has a big tail heavy tendency, so displacing the turbine about 1" forward will help, but also will require an extension to compensate the tail pipe length.
Proper installation of the hinges for the flaps is a critical issue,,,and all models I had seen build by other has this same problem. The hinge pivoting point shout be located flush with the bottom of the slots to ensure proper travel.
This is very critical for the flaps in order to obtain 45 degree deflexion without over riding the servos. In addition ..at the bottom of the wing you'll have to cut about 2 mm of the trailing edges right behind the flaps to allow them full deflexion.
At the end...I had to use 2 Nicads 6.0 Volts 2400 Mamps packs at the nose cone for balance.
Good luck...is a fun to fly jet.
Regards,
MS

InboundLZ

My Feedback: (10)

Hey Miguel, good to see you posting to this again. I look forward to any and all suggestions.

The airplane is for my son (he is 12 5/1). He has the eyes and skills for a small fast jet...he really wants a Bandit but I think this is a good way to get his skills sharpened.

Anyway, I fixed the mess with the holes in the bottom of the fuse and they look much more acceptable now. I will post some pictures soon.

I am going with a 120 in mine and I am going to use a half bypass. Two reasons for this. 1) the bypass cover is a POS and does not fit well at all and 2. it has been suggested that a half bypass actually runs cooler and its less weight/hassle too!

The next thing I am going to take on is the inlet cowl rings. They are complete crap and if I can not get factory replacements I am going to make my own, either way i hope to have them cleaned up quickly.

More to follow!

Miguel Santana

My Feedback: (6)

For my taste I prefere to use the full bypass on this kind of jets...Never had cooling problems and it make the jet go faster. In this thread I think you'll see pictures of the way I close mine...I made some trimming to it...

Removing the inlets cowls is a good idea that also will give the model with more scale look.

One thing that will help you to distribute the weight propelly for balance, is to use JR 2721 in the Ailerons and Flaps with 3/4" arms....these are light weight servos...not heavy like the 8611's. These servos locations are behind de CG...

InboundLZ

My Feedback: (10)

Miguel, would you have any pictures of your inlets so I can see what you did (if anything)????

Miguel Santana

My Feedback: (6)

Sorry, did not find any picture about it.
Anyway is simple...just take off the rings, put some carbon fiber at the slots opened at the fuselage after removing the rings, and the rest is common sense... is not big deal at all

E.N.T.

My Feedback: (1)

Hola Miguel. Soy el Dr. Armaiz de Puerto Rico, el del L-39.
Cuando vienes para ac'a? Te esperamos.



Hector

laserbeam

My Feedback: (74)

Hi guys :

So Miguel ...what the end of this looooong ( 5 year old story) ? are you flying your 2nd viper by now ? are you happy ? .... i took Shaz Viper ( his 2nd ) i guess he doesn't want to deal with the turns-snap-landing issue ,,, to me is not a problem at all !! i'm only waiting on my engine to finish her ( modellbau 750 ) it'll be ready next week so i'll take some shots and video for all you nice guys that are interested in this nice looking american jet. I kept everything simple and light , just a little reinforcement on the gear plates, blocks that hold elevator tube and the formers that hold the wing spars, other than that was very easy, fast and simple to built ( no need for instruction manual ) it's defenitly tail heavy due to reinforcements they did but it no really a problem, i just put as much things as possible in the nose..still i'll let you know if after i got my engine and install it need or not additional weight in the nose.. i calculate the final weight will be around 23-25 pound because i'm at 19 without engine and pipe ( dry )...so let me know about you Miguelon !! ....................................

What about you guys ?

mu2driver
CARS II
MLaCoste

Are you flying your Vipers ?? or..............they're gone

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Miguel Santana

My Feedback: (6)

Marco,
I guess you had to use a drilling machine to dig this thread out of the center of earth...its been a long time.
My advise to you is to keep it as light as possible.

1.- No needs of airbrakes,,,,use de crow setting.
2.- Carefull setting up the hinges of the flaps BEFORE gluing them, to make sure you optain a 45 degrees deflexion. Yo need to have the pivot point of the hinges as much as you can inside the flaps leading edges. Also you are going to have to cut a few milimeter of the bottom lip at the trailing edge of the wing, and add 1/8" high density balsa block on each hinges hole at the wing trailing edge.
3.- No need to reinforce the tail or former at all. Keep it light
4.- Due batteries are going to be mounted on the removable nose cone, make sure to put some extra glue to the nose cone former just in case. Also changing the bolts location will be helpfull for better access to these screws.

Good luck and have fun. Is a good plane to fly.

MS

Robert_Ellis

So I picked up an orphaned ViperJet that I think is the first version. Composite fuse built up one piece wing, built up vertical and horizontal stabs. Opaque canopy. It's rough but I thought it would be a good first turbine jet. I only paid $325 for it.

Length and span are 80"

Empty fuse weight is 12.6 lbs (this does include rudder and 2 elevator and some lead in the nose I am still trying to get out).
One piece wing with 4 servos but no landing gear is about 3.6 lbs. The built up wing and stabs appear to have a light weight layer of fiberglass over the balsa sheeting.

It has some repair work in the horizontal stab area - I read that was an issue with the first version.

I am thinking of finding a good used 120 turbine to put in it.

Inlet ducting kinda just stops and is a bit busted up.

It had a ton of weight in the nose (most of it removed). I assume that with a more modern turbine (lighter) I can get CG without adding the weight back in.

It looks like the flap servos and retracts were installed before the wing was sheeting - no hatch for the flap servo. What the heck?

My Plan:
1. Reinforce the tail section with some carbon cloth,
2. Reinforce the main and nose retract mounts,
3. Redo or reinforce the turbine rail
4. Wet sand the exterior, then fill/sand and paint
5. Replace all servos
6. Source tanks and pipe
7. Use JP ER120 retracts 2m Viperjet
8. Find a decent used 120 turbine
9. For simplicity, I think I will just paint the opaque canopy black or something similar.

So my questions:

1. Is this a decent enough airframe to do this work to and get it flight ready?
2. What should I do about the inlet ducts?
3. Is this built up wing strong enough?
4. There seems to be a lack of formers inside - should I assume the thick hex cell fuse is strong enough?
5. There are no hatch covers for the flap servos - how the heck do I replace them? How were they installed in the first place?
6. Limited access to front because the full canopy is not removable - only the front gold section. Will it be strong enough to make the canopy removable?
7. Does anyone have any old Cermark ViperJet parts they want to sell? tanks, pipe etc.

Thanks in advance.