N7 fuel tank capacity

[troasb]

I am wondering a bit about the fuel tank capacity of the N7 as I am only getting 5.30-6 minutes running time on my O.S. 105 HZR. I am going to install a Lynx MOAS clunk to maybe improve my safe running time a bit.

[Chris Sexton]

The N7 has a 22oz fuel tank. I run the MOAS magnet and it will help with the confidence going deep into the tank for sure!

Flight times are very subjective.  Depending on motor, head shims, tune, fuel, weather variables(heat, humidity, etc), flight style, etc are all examples of things that will effect flight time.  The two biggest being motor tune and flight style (in my opinion).

I run a 91HZ-R Speed Black with VP PowerMaster 30% and the extra .2 shim in the head.  My flight style is sport, big air with some learning 3D in the middle.  I can run 7 minutes easy, 8 with some auto practice.

I know guys with 105s and 20% fuel getting 7 minutes too.

I would recommend not getting too caught up in the number though.  Trying to get every last second out of the motor is great, but it is very easy to tune yourself into a corner and possibly burn up a motor.  If you are flying hard 3D and maxing the engine full time, 5-6 minutes is very respectable in my books!

[Kevin Dalrymple]

I am running a fuel magnet and a 105 HZ-R with 20% and I am getting 7 minutes at 1950 head speed

[troasb]

The N7 has a 22oz fuel tank. I run the MOAS magnet and it will help with the confidence going deep into the tank for sure!

Flight times are very subjective.  Depending on motor, head shims, tune, fuel, weather variables(heat, humidity, etc), flight style, etc are all examples of things that will effect flight time.  The two biggest being motor tune and flight style (in my opinion).

I run a 91HZ-R Speed Black with VP PowerMaster 30% and the extra .2 shim in the head.  My flight style is sport, big air with some learning 3D in the middle.  I can run 7 minutes easy, 8 with some auto practice.

I know guys with 105s and 20% fuel getting 7 minutes too.

I would recommend not getting too caught up in the number though.  Trying to get every last second out of the motor is great, but it is very easy to tune yourself into a corner and possibly burn up a motor.  If you are flying hard 3D and maxing the engine full time, 5-6 minutes is very respectable in my books!

Hi again Chris!
Thank you for your useful reply.
I use Optifuel heli 20% on my O.S, 105 HZ-R. Although I had to use some Byron 15% Aero Gen2 4-cycle fuel due to unavailability of my standard fuel. Not much difference in running time..
I am a sport flier trying to learn some 3D and I do much flying on Idle up 1.
Why do you run a 91 engine and not a 105, flying time?

[Chris Sexton]

Hi again Chris!
Thank you for your useful reply.
I use Optifuel heli 20% on my O.S, 105 HZ-R. Although I had to use some Byron 15% Aero Gen2 4-cycle fuel due to unavailability of my standard fuel. Not much difference in running time..
I am a sport flier trying to learn some 3D and I do much flying on Idle up 1.
Why do you run a 91 engine and not a 105, flying time?

I started with an OS 105 but I had one of the bad luck engines that needed a new seat. But I got tired of chasing the tune before they released the fix.  RonLund.com had 1 of the 91 speed blacks left and I ran with it.  It's a power house, most people who fly it think it's a 91 until I tell them.  The 105 for sure has more torque but the 91 is plenty for my taste.

[troasb]

Hi again Chris!
Thank you for your useful reply.
I use Optifuel heli 20% on my O.S, 105 HZ-R. Although I had to use some Byron 15% Aero Gen2 4-cycle fuel due to unavailability of my standard fuel. Not much difference in running time..
I am a sport flier trying to learn some 3D and I do much flying on Idle up 1.
Why do you run a 91 engine and not a 105, flying time?

I started with an OS 105 but I had one of the bad luck engines that needed a new seat. But I got tired of chasing the tune before they released the fix.  RonLund.com had 1 of the 91 speed blacks left and I ran with it.  It's a power house, most people who fly it think it's a 91 until I tell them.  The 105 for sure has more torque but the 91 is plenty for my taste.

Thank you for your reply Chris. I guess a 91 could have been plenty for me also. I am wondering about trying the O.S. GT15HZ gasser engine in another N7. My fuelbudget is about to go skyhigh! But the gasser has about 30% less power then, but again fuel costs would be neglictible, Do you have any experience with the O.S. gasser?

[Mike Spano]

I am a gasser guy, I love my gassers. I would never, I repeat never, install a GT15 in any 700 size machine ever. the motor generates too much heat in a 700 platform. the motor is very well known to eat itself in less than 3 gallons, and does not have the power a 700 needs. stick with nitro on this bird, that gt15 has its place, but its not in a 700 bird. sucks, I was really hoping it would work out too, I really wanted an N7 gasser.

[troasb]

I am a gasser guy, I love my gassers. I would never, I repeat never, install a GT15 in any 700 size machine ever. the motor generates too much heat in a 700 platform. the motor is very well known to eat itself in less than 3 gallons, and does not have the power a 700 needs. stick with nitro on this bird, that gt15 has its place, but its not in a 700 bird. sucks, I was really hoping it would work out too, I really wanted an N7 gasser.

Hi Mike
Thank you for your very useful reply. But I almost find it difficult to believe. As far as I understand the GT15 is intended to go in a 700 helikopter to be a direct replacement for a 90. engine. If this does not work where is the place for this engine? And O.S. must for sure have a lot of trouble with dissatisfied customers with broken engines in 3 gallons!

[Mike Spano]

you are exactly right. it has a horrible reputation and no one buys them now. at least for a 700 size. they actually re-designed the mounting pattern and crank OD for the motor to accommodate a 600 heli when they finally came to the realization that this was a real problem, and it still isn't working well. the only heli it seems to work well in is a 570 size conversion that leviathan has made for a goblin 570. it took him (the designer) 6 months of trial an error to design a cooling system that would actually cool that motor too. the 570 just taxes the motor less, and generates less heat.

what happens is this. gas gets much much hotter than nitro when burned, I do not know the exact BTU's, but it is like 3-4x as much. that motor is a nitro motor converted to run off of gas with very limited "gas specific" traits. it was not originally intended for gas, thus the tolerances and such where not what they needed to be. it even uses a needle bearing on the crank....so first thing that happened was the piston was sticking in the fist gallon bc the thermal expansion was too much for the little piston to handle. then the made the piston smaller. so much in fact, that with a cold motor you can actually shake it and hear the piston slap the liner.....  the main thing now that gets guys is the wrist pin retainers. they get too hot, lose their strength, and come flying out inside the motor causing it to eat itself. the longest running motor I have seen (outside of the ones in the 570 conversion) has been 6 gallons. that is what I have seen personally..... what guys have been doing to help the retainer issue is take the brand new motor apart, and install spiral wrist pin retainers. this really needs the retainer groove to be enlarged for it to properly fit, but you can get away with it without doing this machining work also, just a little riskier.

in the beginning OS was fixing motors and replacing them, but I don't know about now. seems like about 3-4 months of that and then OS started blaming the users for the issues.

this is a typical stock GT15 motor after a few gallons - http://www.helifreak.com/showthread.php?t=500684&highlight=gt15

this is an email from an OS rep regarding the "new" piston they designed to "lessen" the damage to the motor, not fix the problem..... - http://www.helifreak.com/showpost.php?p=5547087&postcount=38

another customer - http://www.helifreak.com/showthread.php?t=531148&highlight=gt15

another customer - http://www.helifreak.com/showthread.php?t=535144&highlight=gt15

another..... - http://www.helifreak.com/showthread.php?t=535061&highlight=gt15

read the threads also. looks like most of these guys had issues using OS needle settings, and OS fuel/oil recommended mixes......this is a very real issue, and why you do not see these motors everywhere. a good gasser motor is a Toxic (TRM) VX300SE, now THAT is a gasser motor. http://www.trmpower.com/html/vx_300_tt.html

hope this helps.

[troasb]

Thank you Mike for useful information. I am not going to try the O.S. GT15 now!

[Mike Spano]

Thank you Mike for useful information. I am not going to try the O.S. GT15 now!

LOL...yea man, just trying to save you some headaches and money!   that motor sounded very promising. and I think with more time behind the drawing board, maybe it could have been. but in the end, it wasn't, and that stinks. I really wanted this motor to be successful too!