JET LEGEND VIPER BUILD THREAD
07-28-2014, 06:18 PM
#1176
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Hi Fredo
The main tank once the system is filled draws only fuel from the two rear tanks and then air once there empty, It must remain a sealed unit and not draw any air until the rear tanks are empty or the rear tanks will not empty at all.
This is why the lines from the rear tanks and there vents must be equal so they empty symmetrically, If one rear tank empty's before the other it will continue to slowly draw from the remaining "fuller" tank but at a much slower rate.
This is because air will then be drawn through the empty tank easier than fuel can be from the part full one, in practice and in my experience both rear tanks are usually dry at the end of the flight, lets hope the main one is not
An other option and one "I don't recommend" is to plumb all the tanks in series IE empty one after the other, this creates quit a high draw for the pump when all the tanks are full and a comparatively low draw when only the front tank is full.
I have tried it and even on a well plumbed and as free flowing setup as feasible, first makes the poor little on-board pump work hard and then confuses it as the draw reduces which can lead to an uneven run, so for me its never a first option.
All the best Mark V
The main tank once the system is filled draws only fuel from the two rear tanks and then air once there empty, It must remain a sealed unit and not draw any air until the rear tanks are empty or the rear tanks will not empty at all.
This is why the lines from the rear tanks and there vents must be equal so they empty symmetrically, If one rear tank empty's before the other it will continue to slowly draw from the remaining "fuller" tank but at a much slower rate.
This is because air will then be drawn through the empty tank easier than fuel can be from the part full one, in practice and in my experience both rear tanks are usually dry at the end of the flight, lets hope the main one is not
An other option and one "I don't recommend" is to plumb all the tanks in series IE empty one after the other, this creates quit a high draw for the pump when all the tanks are full and a comparatively low draw when only the front tank is full.
I have tried it and even on a well plumbed and as free flowing setup as feasible, first makes the poor little on-board pump work hard and then confuses it as the draw reduces which can lead to an uneven run, so for me its never a first option.
All the best Mark V
. I've made my decision. Thanks again.
07-28-2014, 06:33 PM
#1177
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Vettster, I wasn't reacting to him not using uat but to the fact he is using stock tanks without having any issues and the simplicity of his install...oh well never mind. In the mean time I've changed my mind and go for 3 tank set up for two reasons. CG doesn't shift that much and having just one tank in the front will gain more space for air tank and uat.
08-03-2014, 12:37 PM
#1178
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Well John Wright... Im sold!
I maidened the viper today and had 3 flights on it with no UAT. I did all the standard stuff plus some inverted, vertical flight.. etc and not even a sputter from the engine. Me thinks I see a future with no more UATs. Less weight and 4 less points of potential air leaks.
I maidened the viper today and had 3 flights on it with no UAT. I did all the standard stuff plus some inverted, vertical flight.. etc and not even a sputter from the engine. Me thinks I see a future with no more UATs. Less weight and 4 less points of potential air leaks.
Last edited by Vettster; 08-03-2014 at 12:46 PM.
08-03-2014, 11:36 PM
#1181
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Well John Wright... Im sold! I maidened the viper today and had 3 flights on it with no UAT. I did all the standard stuff plus some inverted, vertical flight.. etc and not even a sputter from the engine. Me thinks I see a future with no more UATs. Less weight and 4 less points of potential air leaks.
I maidened the viper today and had 3 flights on it with no UAT. I did all the standard stuff plus some inverted, vertical flight.. etc and not even a sputter from the engine. Me thinks I see a future with no more UATs. Less weight and 4 less points of potential air leaks.John
08-05-2014, 02:06 AM
#1182
Hi Guys
I took delivery of yet another Viper to assemble last Tue this time in the Vodapone/Mercedes colours.
Nothing out of the ordinary with this Viper but I note the flap hinge/horn is now inline with the slot in the servo hatch and it has the plug on tip fins.
A Jets Munt VT80, Futaba Rx and 7x Savox SC1256 servos were supplied. The servos are a little over kill at 20Kg but too much powers never an issue.
My usual 3 tank set up with 1x1500cc up front and 2x800cc to the rear were fitted this will give me less of a CG shift that will be very helpful at take off.
The VT80 is near the lower end of the power range but experience has shown me it will rise from grass with no problem now the CG is not as forward when fuelled up.
The turbine rails did have to be altered to take the smaller VT80 by adding a small extension to reach the turbines mount and its tail cone set at 22mm from the tailpipe.
A 125ml UAT is tucked along side the main tank , both air valves are on the same tray out the way, another advantage of just one tank up front giving a less clutterd install.
Total fuel load is 3.1lt which could be reduced at a later date by fitting a smaller front tank further reducing the CG shift and still giving good flight times.
I was given Carbon effect vinyl for the trays, I was sceptical at first but it looks quite good
, I also raised the front tray above the nose wheel to keep the crud out.
125g of lead right in the nose and the largest RX packs I could find were needed to correct the now usual CG at 35mm rear from centre of wing tube.
This Viper came out at 9.54Kg (21.03lbs) including its plug on tips at 45g each tips, scaleish cockpit tub and full UAT.
I took delivery of yet another Viper to assemble last Tue this time in the Vodapone/Mercedes colours.
Nothing out of the ordinary with this Viper but I note the flap hinge/horn is now inline with the slot in the servo hatch and it has the plug on tip fins.
A Jets Munt VT80, Futaba Rx and 7x Savox SC1256 servos were supplied. The servos are a little over kill at 20Kg but too much powers never an issue.
My usual 3 tank set up with 1x1500cc up front and 2x800cc to the rear were fitted this will give me less of a CG shift that will be very helpful at take off.
The VT80 is near the lower end of the power range but experience has shown me it will rise from grass with no problem now the CG is not as forward when fuelled up.
The turbine rails did have to be altered to take the smaller VT80 by adding a small extension to reach the turbines mount and its tail cone set at 22mm from the tailpipe.
A 125ml UAT is tucked along side the main tank , both air valves are on the same tray out the way, another advantage of just one tank up front giving a less clutterd install.
Total fuel load is 3.1lt which could be reduced at a later date by fitting a smaller front tank further reducing the CG shift and still giving good flight times.
I was given Carbon effect vinyl for the trays, I was sceptical at first but it looks quite good
, I also raised the front tray above the nose wheel to keep the crud out. 125g of lead right in the nose and the largest RX packs I could find were needed to correct the now usual CG at 35mm rear from centre of wing tube.
This Viper came out at 9.54Kg (21.03lbs) including its plug on tips at 45g each tips, scaleish cockpit tub and full UAT.
Last edited by Mark Vandervelden; 08-06-2014 at 06:04 AM.
08-06-2014, 01:18 AM
#1184
I successfully test flew my viper on the weekend. It performed perfectly, with just a couple clicks of elevator and aileron. Landing was very smooth and predictable.
https://www.youtube.com/watch?v=27E6HyQ1eYo
https://www.youtube.com/watch?v=27E6HyQ1eYo
08-06-2014, 07:11 PM
#1187
Had a couple more flights today and with a slight headwind i would be only using 30 metres of runway to stop without using brakes, off my local grass strip. Getting better every flight. I have the 2 standard tanks and a 600ml tank at rear. I am getting 9 minutes with still just over 1 litre of fuel left on return to pits. Love this jet.
Jason
Jason
08-07-2014, 10:09 PM
#1189
Hi Fedo
The Rx packs in the Vodapone Viper above are a pair of 4000ma lipos, over kill to say the least but extra amps are more useful than dead lead.
Normally I would use no more than a pair of 18-2200ma.
I did stay with a 2200ma lipo for the ECU back on the turbine rail.
This is because a 700mm heavy duty lead to the front + the 105g pack up front worked out heaver overall than the lead it would in the nose.
Mark V
The Rx packs in the Vodapone Viper above are a pair of 4000ma lipos, over kill to say the least but extra amps are more useful than dead lead.
Normally I would use no more than a pair of 18-2200ma.
I did stay with a 2200ma lipo for the ECU back on the turbine rail.
This is because a 700mm heavy duty lead to the front + the 105g pack up front worked out heaver overall than the lead it would in the nose.
Mark V
08-08-2014, 01:19 AM
#1190
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Hi Fedo
The Rx packs in the Vodapone Viper above are a pair of 4000ma lipos, over kill to say the least but extra amps are more useful than dead lead.
Normally I would use no more than a pair of 18-2200ma.
I did stay with a 2200ma lipo for the ECU back on the turbine rail.
This is because a 700mm heavy duty lead to the front + the 105g pack up front worked out heaver overall than the lead it would in the nose.
Mark V
The Rx packs in the Vodapone Viper above are a pair of 4000ma lipos, over kill to say the least but extra amps are more useful than dead lead.
Normally I would use no more than a pair of 18-2200ma.
I did stay with a 2200ma lipo for the ECU back on the turbine rail.
This is because a 700mm heavy duty lead to the front + the 105g pack up front worked out heaver overall than the lead it would in the nose.
Mark V
08-08-2014, 02:02 AM
#1191
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You should just make sure that your plane does not have nose weight added by the factory. Mine must have had some because I only needed small batteries in the centre position (not in the nose) shown in my photos. I guess it depends when yours was made.
John
John
08-08-2014, 08:27 AM
#1192
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Good point John, my mate has one of the early ones and when I got mine it was assumed that the natural thing to do would be to simply copy the install across but that in turn led to disastrous balancing results after which we had to do some serious moving of gear about and add some lead to get it to balance, we just could not understand at the time ,It was only when he had an accident with his did he notice the lump of concrete in the nose !
08-08-2014, 07:06 PM
#1193
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Spot on John, I've been looking at all these installs and couldn't understand how can you guys have it all balanced with nothing much in front. I have tried mine and without turbine in place, only fuse with tail surfaces installed, still felt pretty tail heavy. Sure enough after your post, checked the nose and there's nothing. No weight. That's why I need big packs in the front.
08-08-2014, 09:31 PM
#1194
My viper is the newer model with removable wing tips and it has no added weight in it. I have 2 of 2s 3000 Mah Lifepos for Rx and 1 of 3s 2000 Mah for Turbine. The batteries sit on either side of nose wheel. No added weight required to balance model. I also have a pilot in front seat which is not all that heavy.
09-17-2014, 08:55 AM
#1196
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Hey guys, what switch is everybody using in this jet? I will be running dual futaba 7008sb My servos are not HV I would like to use Lipo Batteries, and I would like that each battery feed both receivers. Any Ideas?
09-18-2014, 09:27 AM
#1198
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09-18-2014, 10:03 AM
#1199
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I am using 2 A123 batteries for the Rx fed into a Powerbox sensor switch. The output at 5.9 v is fine for the electronic valves which work very well. Initially i was a bit sceptical about the thin airlines, but they work, no need to change them. Because I was using 20kg cm servos i added a Evojet Powerjack.
John
John