RPM control in turbulence or pwr on stall? PA30

[N8632Y]

In the past there have been posts, about the limitation in the twin, listed in the POH, Killough, 2nd issue, page 2-6 saying,
"When performing power on stalls, do not exceed 2100 rpm."

Also there has been mention in extreme turbulence to slow and set RPM similar.

Question, maybe stupid, BUT,
to get RPM's back to 2100, for the stall, I am setting throttles at 19" MP, and then pulling the props back to 2100, using the prop controls, not by reducing throttles alone, is this HOW it is done?

Looking for proper technique, in NJ,
steve

[Bernie Mazurek]

The 260C has a similar requirement for turbulance. I reduce prop rpm to 2200 and manifold pressure to 22" or lower to reach manuvering speed (150 mph)

[steen]

[N8632Y]

Steen,
That argument makes fantastic sense to me. That is one reason I avoid extreme rates of climbout on departure, in case of engine out, traffic too among other reasons.

Yes, a lesser power gives less pitch attitude and a more subtle maneuver.

But I thought it was due to the prop shaft extension and the loads that were incurred, possibly exceeding limits? Isn't that why we do not have 3 bladed props on the twins?

That is why the 260C model has the same limitation?

I can see pulling the MP back to about 19" and slowing to Va in turbulence or departure speed prior to a pwr on stall, but are we not pulling the props back to limit the RPM's to 2100 after that, then of course the mixture gets reset if too rich?

[steen]

Steve,
The use of 2100 rpm to enter stall practice is done by pulliing throttle to the rpm. This gives good deceleration that is fast enough you don't go to sleep but not so fast as to enter a deep stall inadverdantly. The twinkie is a gentle staller anyway, but a gentle entry is a good way to do it. I generally set the props to 2500rpm prior to the pull back so that if needed I have a lot of power available on the recovery. (I also do touch & goes with props set at 2500rpm as this gives good "go" performance without the trauma of 2700rpm. Personal preference at a home elevation of 860'msl.)
The twinkie is a marvelous performer with so little horsepower but has some handling characteristics that make it a little bit of a "pro" airplane too. For instance I can do a near vertical departure climb down to no airspeed showing and then "unload" by applying rudder and aileron so as to gently roll out into a level flight condition from 0 airspeed indicated just by using the prop blast over the wing for lift, but I had better know what the consequences are if an engine coughs during this manuever. The airplane can perform amazing things but it will bite you bad if you don't understand and fully "fly" it mentally as well as physically.
Landings are easy if you know how, too. Except strong crosswinds, where it can be a bear on a slick runway.
Steen

[steen]

Steve,
Forgot your comment about pattern work and climb speeds. I know what the POH says, but I use 150mph as my climb speed with full MP and 2500rpm all the way to cruise, in my case usually 8000-11000' where the airplane just shines (170k @ 15.8gph leaned 75rich of peak by my Shadin fuel flows which are dead accurate}. This almost always works out to 68% of power in cruise.
In a C-150 or PA-28 180 or whatever with a fixed pitch prop these engines routinely are full throttle to cruise with less than 2500rpm so they are being more overboosted than what I suggest and go to TBO!
I use 150mph to about 5000', then fade to 140mph to about 8000-9000'
then never lower than 125 on up to my cruise altitude. This allows me to get lots of cooling and cover a lot of ground during the climb. I start leaning to 100 rich above 4000' With the additional airspeed comes additional lift (and drag of course but this is a slick airplane) so my rate of climb virtually mirrors the book values but I cover more miles.
Steen

[N8632Y]

Steen,
thank you for the explanation, sounds like a plan.
Climb outs for me are the same, I will set my JPI to show the 3rd cylinder, which i know the left engine peaks around 1540, and on departure, monitor it and lean to keep it about 1400 for about 100-150 ROP on climbout.
The digital EGT, CHT, Fuel Flow is a wonderful tool.
Thank you again,
steve

[Zach Grant L1011jock]

Steve,
WOT is the way to climb the plane, period. You can certainly pull the prop back a bit for noise, but 2700/2600/2500rpms are all good settings. There are many reasons for this, not the least of which is that it is the most efficient setting, and allows for the most even airflow to the cylds. Climbing at higher power settings allows good climb rates, at higher speeds, keeping the engine cool, minimizing the time to climb, and staying at the high fuel flow altitudes for the minimum amount of time, and if looked at in a truly scientific way, the engine spends much less time at what is considered high stress power settings if run hard and climbed fast at lower temps, than by pulling power back to "baby" the engines. Why pull the power back, only to add it back a little at the time in the climb?

As for a climb profile, my pesonal technique is a bit different than Steens. I look more at climb rate than airspeed. I like to get 750 fpm up to about 5K, and then I just set 500 fpm and let it rip from there on out. Speed translates, depending on weight and temp to roughly 125-140 mph indicated initially, and then 140-155 mph indicated. Turbos and Robertson birds will be on the slower side of these speed ranges, but the turbos will hold the speed to a higher altitude. With these speeds it is easy to keep the CHTs below 400, even on the turbo birds while running at best power mixtures in the climb. I state this as it is another "technique" that may be useful to think about.
-Zach

[Zach Grant L1011jock]

On the RPM "limitation" (which it is not, just an advisory) for the power on stalls, as well as the turbulence, it originally existed as a load reduction for the gyroscopic forces on the crank. There were many concerns initially as to how the prop hub extensions would affect the longevity of the engines. It has not proven to be a big issue, hence the relative obscuity of the aformention "limitation". I agree the lower power setting for power on stall practice is a good practice for safety, but this was not the original intention of the advisory.
-Zach

[N8632Y]