03/17/2016 at 1:03 am #42459AnonymousInactive
I have a Green Head 15 that I want to put on a T-Bird, what would be a good tank size? I have a Perfect 1/2 ounce and a Perfect 3/4 ounce. I am a occasional contest participant, not really sure about this, not a lot of room for a tank.03/19/2016 at 12:26 am #55846DAN BERRYParticipant
Almost all of us use a bladder tank.
On a .15 I’d Greenhead I’d guess you need 12-15 ccs of fuel to get it started and launched.
On my Nelson 19/21 setup I put 29 cc fuel into the bladder. It generally uses about 10cc for a flight.
The Greenhead would use….less… fuel than the Nelson.03/19/2016 at 12:52 pm #55847AnonymousInactive
Thanks, it’s a Nostalgia plane.03/19/2016 at 7:51 pm #55848George ReinhartParticipant
Seems to me it makes sense to use a bladder though.
Nostalgia? We were using them as far back as ’55.
More consistent engine runs and it’s a crude form of induction tract fuel injection.
Cheers!03/22/2016 at 5:14 pm #55849SIMON BLAKEParticipant
I think the 3/4 ounce tank should be okay. If you can, you might try bench running the engine with both of those tanks and see which one will give you about 35-40 seconds, which is generally enough to get the motor started and launch the airplane. I run some of my nostalgia models and my NFFS one design Bounty Hunter with a hard tank on suction and a pinch-off timer. It works fine and simplifies the starting procedure considerably. The performance disadvantage isn’t anything like what some people would have you believe and if you are starting the engine by hand it makes it a whole lot easier (and an electric starter can be murder on a Greenhead).
Right now I’m building a Top Banana 400 with a hard tank and suction so that I can use an AM 25 (15) diesel for the diesel duration event we have in Western NY Free Flight Society contests and then I can use the same airplane with an OS Max III .15 for nostalgia. (Starting a diesel is tricky enough without having it on pressure.)
In my larger models I use a hard tank with crankcase pressure and in some of the smaller models I use the red cap bladders. The main reason for using a bladder is because it’s simple and saves a little weight, but it’s not the only way to go. A green head .15 and a T-Bird sounds like a good combination!
Regards, Simon03/22/2016 at 10:59 pm #55850JIM MOSELEYParticipant
Starting a diesel is tricky enough
A prime, one or two flicks and it’s up and running. If they were hard to start would the teamrace boys be using them?
Don’t underestimate the difference in power between the AM25 and the OS Max .15 !03/23/2016 at 2:36 am #55851SIMON BLAKEParticipant
I meant for us mere mortals Jim… I was surprised at your comment that there was a substantial difference in power between the two engines, so I had to look it up and you’re right. I expected some difference but not that much. According to the Model Aircraft Magazine engine tests, the AM 25 (which is a .15 in North American sizes) puts out 0.225 bhp while the OS engine puts out O.43 bhp on high nitro fuel and with the pressure venturi.
The airplane is actually sized for the OS at 445 sq. in. I think the AM will work okay however, as the airfoils are quite thin and the AM spins a 9/4 prop at about 12,500 rpm versus a 7/4 and 17-18,000 rpm for the OS. And we get a 12 second engine run in diesel duration. I suspect I will have to add a little additional left thrust when I am using the diesel because of that big prop. The AM .25 is supposedly easy to start and weighs about the same as the OS, so those were the two big considerations.
- You must be logged in to reply to this topic.