Throttle on takeoff



  • Apologies for the potentially dumb question but, are you supposed to use full throttle for takeoff? I tried flying some traffic patterns today but when climbing at the recommended 90KIAS, my vertical speed would be +2000 or more (maxed out indicator) and then come rapidly down to like +500 before eventually stabilizing around 10-1500. I can dampen the oscillation and make it settle sooner with some forward pressure on initial climb, but forward pressure during takeoff seems so counter-intuitive.

    As for conditions, this is at around 800 pressure altitude and 15degC.



  • Hi, it's normal behavior of the plane. After takeoff you have to adjust two things: trim and speed. Each time you change the speed you have to set proper trim. It needs some practice. Good luck.



  • I can share with you how I was taught to manage takeoff and climb power. There is no single "right and only way" to do it, but I think its a good idea to have a routine and to stick to it. Here is what I do;

    This is for a normal (neither short nor soft field) takeoff;

    • If density altitude is > 5,000 ft, then lean to 100F rich of peak EGT, otherwise set mixture to full rich.
    • Set RPM to full forward position.
    • Advance throttle to full
    • The plane will let you know when its ready to fly, usually around 60-65 kts IAS the nose will start to get light. Rotate and pitch to maintain 90 knots.
    • When its no longer feasible to land straight ahead on the runway you are departing, raise the gear.
    • At 700 ft AGL reduce RPM to 2500 and MP to 25 inches.
    • Adjust rudder trim if necessary to center ball for climb speed of 90 knots
    • Check MP every 1000 ft and increase throttle to maintain 25 inches (Once you climb through about 5,000 ft there is insufficient atmospheric pressure to maintain 25 inches of MP, just use full throttle if you can't get 25 inches of MP)
    • Level off at cruise altitude (actually I climb to that plus 200 ft and then descend. It helps get to cruise speed faster. I am less likely to do this if on an IFR flight plan as in the U.S. you can get "busted" for altitude deviations > 300ft.)
    • Reduce RPM and MP to desired cruise performance. (eg 2400 rpm & 24 inches of MP)
    • lean to desired fuel flow for the power you are trying to achieve (eg 12 g/h)
    • adjust rudder trim to center ball after airspeed stops increasing.
    • trim elevator to maintain level flight at desired cruise altitude. This is an iterative process. Each time you trim nose down you will increase speed, which increases lift requiring more nose down to maintain a constant altitude. Each time you increase speed, you may need to re-trim rudder. In real life as in the sim, this takes a bit of time. If you want to cheat in the sim, engage altitude hold.

    When descending, I can just trim nose down to get 500 ft / min decent and then check MP every 1000 ft to keep it at 24 inches MP.

    On the way down you should try avoid abrupt power reductions for cylinder health. Try to keep MP reductions to 1 inch per minute.

    -bv



  • @BernieV Hi Bernie thanks for this info🙂
    Does it matter on the order of adjusting RPM and MP in real life?
    -Lee.



  • @captain744 If you decrease MP first, that's probably the easiest way to avoid combinations of MP and RPM that are discouraged by Engine Operator guides (supplemental publications from the engine manufacturers.) From memory, I think my io-360-b1e engine guide says no more than a difference of "3" between MP and RPM (e.g. 24 inches X 2100 RPM is ok, but 24 inches X 2000 rpm should be avoided). If I was set to 25 X 25 for the climb and wanted to cruise at 24" X 2100 RPM, reducing MP to 24 first would avoid a momentary setting of 25" X 2100 RPM. Would the world (or the prop!) stop if I reduced RPM first? Of course not, but again I make it a habit of doings the same way every time and prefer to change MP first.

    I should mention mixture as well. A simple rule to follow (on the arrow) on making power changes is

    1. To increase power, adjust controls from right to left (mixture, prop, then throttle)
    2. To decrease power, adjust controls from left to right (throttle, prop, then mixture)


  • Thanks Bernie. All makes sense, thanks for giving us all a better understanding of power management.



  • @BernieV Thanks for this info. For some reason I am still having trouble. Right after I retract the gear the vertical speed rockets up to like 2400 fpm. Isn't that a bit extreme for such a small aircraft? Maybe that is what's supposed to happen, I'm not sure. The problem is I blow through my pattern altitude in like 20 seconds and level off twice as high as I want to. The alternative is trimming down/applying forward pressure to yoke but then I end up going like 110 knots instead of 90.



  • @vcapra1 said in Throttle on takeoff:

    @BernieV Right after I retract the gear the vertical speed rockets up to like 2400 fpm. Isn't that a bit extreme for such a small aircraft?

    It does seem excessive. Try rotating around 60 knots and lifting off about 65. Pitch up as required so you don't exceed 90 knots. Don't raise the gear until you can no longer make a safe landing straight ahead and reduce throttle to 25 inches MP & RPM to 2500 at 700 ft AGL.

    You will see the absolute best climb performance as soon as you lift off. You are generating close 100% power, so 1000 - 1500 fpm until you reduce power for the climb at 700 ft (at sea level) is reasonable. If you allow the aircraft to exceed 90 knots just after takeoff and then pitch up to get back to 90 knots, you will also see a momentary increase if climb rate (as you are trading speed for increased clime rate).



  • @BernieV Thank you for your help. I think I was letting the speed get too high initially like you said, then pitching for 90 and seeing that high VS. If I keep it at or below 90 it only goes up to around 1700 fpm



  • @BernieV said in Throttle on takeoff:

    If density altitude is > 5,000 ft, then lean to 100F rich of peak EGT, otherwise set mixture to full rich.

    For those that want to know more, here is the inimitable Rod Machado explaining this in great detail (to only your left ear, unfortunately): https://youtu.be/eBUfWI4C6sE