Thread: Mini-HowTo Ramps for Hotliners / F5B
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Old Jun 03, 2012, 03:36 PM
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Ramps for Hotliners / F5B

So i thought i would share a little secret sauce from the F5B world for those who have no idea what all this stuff is about. Save you some work, make life a whole lot more easy. Some people don't want me to post this, and it is indeed a lot of invested time and effort i am about to share with you. You can buy me a beer some time.

End points;
For starters you have to realise that whatever you do with the signal coming from the TX is going to be between the end points you have set on the TX. If those end points are a long way beyond what the ESC is looking for, then your ramps will not take the amount of time / have the effect you expect them to have. So you might want to figure out where the end points need to be for your ESC before you start dialing things in to much. You can test this on the bench with a couple of cells less and no prop. When you have found the end points you need, you want to add a little extra for reliable operation.

Forward speed vs RPM;
The angle of attack (AOA) of a prop is what makes or breaks performance. Just like a wing, get the AOA to high and it will stall. There are two factors that determine the AOA during normal operation, the RPM and the forward speed of the plane. Fortionately unlike a wing, when the prop starts to stall it will only start to stall near the root of the prop blades and not stall completely. This means you still get a lot of thrust and just a small loss in efficiency. The bigger the part of the prop stalled, the lower the efficiency.

Max start power;
The maximum power you can put into the prop at the start of the climb is determined by the pitch of the prop and the forward speed of the model. A prop with less pitch can take more power at this point. Flying slower means you can put less power into the prop before it starts to stall. Keep that in mind when you rig your ramps for duration mode when you are flying far slower then when flying legs.

Roughly speaking, you can put about 4KW into most modern F5B props at the start of the climb before the prop starts to stall. This excludes the launch and assumes you are doing the distance task with a reasonable return speed from the last set. The forward airspeed is somewhere around 120 to 150 Kph.

In duration mode, your plane is only flying about 60 to 80 Kph and so you can only put about 1.5 to 2 KW into the prop before it starts to stall.

Since these planes accelerate very fast, the power you can put into the prop also increases very rapidly. However, if you put in 500W, the plane will accelerate much slower then if you put in 4000W. So you are looking at a sort of exponential deal where the faster the plane goes, the more power you can put in and the faster it will accelerate.

Two stages;
With the Futaba 8FG, 12FG, 12Z and similar TX's you have a motor menu that works perfectly for what we want to achieve. It will allow you to do simple strait line power ramps with 2 stages. The first stage is how fast you get the power up to the start power of the climb, the second stage dictates how long it takes for the rest of the power to feed in.

Hope it all makes sence so far.

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Last edited by jjmouris; Jun 04, 2012 at 10:00 AM.
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