Beaver/180

Driving Rain · Post by **Driving Rain** » Mon Feb 13, 2006 10:59 am

Don't wish to open a can of worms here but reduced power is not recommended at anytime. The killer isn't the boost MP it's the temperature. Retarding the power a couple of inches needlessly lengthens a take off run and subjects the engine to a longer high heat cycle. It could be argued that if your pouring less gas in the engine there would be less heat. This is only true to a point, believe me 2 inches won't make one bit of difference in the heat generating department. Air cooled engines need forward speed to cool properly reducing power just when you need it the most is self defeating.
It's been my experience that overloading and the resulting long takeoff runs are what kills the 985 or any engine for that matter. I've found that over a summer of high temperatures and big loads it's not unusual to get 5 or 6 flat jugs, keep up the abuse and she'll swallow a valve.

185_guy · Post by **185_guy** » Mon Feb 13, 2006 2:13 pm

How about guys yanking the power back to climb power the very instant the plane breaks the water?? the engines are rated for what....2 minutes at max power? (the 1340 is 5 minutes)
Pulling the power back so soon, only makes ya take a bit longer to accelerate, and airflow cools the engine, not to mention fuel. I leave her run full power till i got my 100mph climb speed, (keeping mind limatations) I believe this helps to cool it, by airflow, and fuel.
Maybe i'm wrong, cause i see lots of people scrambling to get the power back asap! (maybe they are coming off the water at 100mph?

)I say let her go, it aint gonna hurt! Espically during a critical phase of flight, you should be concentrating outside, not in at the tach.

phillyfan · Post by **phillyfan** » Mon Feb 13, 2006 3:13 pm

I'm guilty of powering back right after takeoff, not going to the redline if possible and not climbing the Beaver to altitudes above 3,000ft. I figure those are inches in the bank for when I need'em.

CLguy · Post by **CLguy** » Mon Feb 13, 2006 4:30 pm

There is certainly no reason to power back immediately after take off but I am not sure I would let it roar to a 100 mph either.

The one thing to remember though with a radial, in most cases if you are going to develop engine problems it will be on the first power reduction.

I agree with Driving Rain, it is temperatures not power that will kill a radial. Keep them cool and don't ever do reduced power take off's as this just defeats the purpose of why you have lots of horsepower.

185_guy · Post by **185_guy** » Mon Feb 13, 2006 7:43 pm

well i guess i probally dont go to exactly 100 mph, just let it accelerate a bit, making sure all is well, then get the power back. And in the beav, it dont take long for it to accelerale anyways, not near as long as the ole Norseman!

Driving Rain · Post by **Driving Rain** » Tue Feb 14, 2006 4:19 am

The only time it's recommended to reduce MP on a take off run in boosted engines is when it's very cold. This is to compensate for the colder denser air charge.

Airtids · Post by **Airtids** » Tue Feb 14, 2006 10:44 am

Or boosted with fixed wastegates.

bronson · Post by **bronson** » Wed Feb 15, 2006 11:03 am

If you look at the ailerons as you go past T/O setting you will see that you no longer have any "up" aileron. Important when it is gusty, nothing like having it roll at 50' and not want to recover. I also found it best to use climb flap on the t/o in some -2s as they wanted to go left even with full r rudder just as you start to get on the step. As for power settings, I had a P&W rep. tell me that if it was on the chart it was safe to use, and I generally ran 29 and 1750 unless really heavy. High boost and low RPM also puts a "cushion" in the cylinder, and reducing the RPM reduces the stresses that come from instantly reversing the piston travel at the end of the stroke. Thus it was explained to me.

MUSICMAAN · Post by **MUSICMAAN** » Wed Feb 15, 2006 10:05 pm

29 and 1750??? wow, that's a little like climbing a hill at 30 km per hour in 5th gear in your car. That to me is lugging the poor engine. But hey, that's just me...

bronson · Post by **bronson** » Thu Feb 16, 2006 8:28 am

Well if you try 28/19 and then pull the prop back ( I think 29.7 /1750 at sea level) and watch the oil and cylinder head temps, you'lll see that things cool off. the point is that high boost and low RPM are GOOD for the engine, the reverse isn't. The other key is to be smooth, sudden changes make for high torque stresses.

MUSICMAAN · Post by **MUSICMAAN** » Thu Feb 16, 2006 9:50 pm

An old timer once told me about this guy somewhere out east (back in the day) that ran his 938 at full power all the time, only pulled the prop back. This guy actually complained after an engine overhaul that it only got 40 inches. Anyway's I guess he made it passed TBO every time. One of the oldtimer enginer's told me just this summer, that the engine was designed to run at full power. Don't know how much truth there is to that but he must know something. The way I see it, there haven't been parts made for these engines for a long time and the old parts are really getting OLD. I'll baby the engine any day.

bronson · Post by **bronson** » Thu Feb 16, 2006 11:23 pm

Well another analogy would be that running high RPM and low man. press. is like running around with one foot on the brakes in your car. Consider that any engine runs at its most efficient when the throttle ( butterfly) is wide open. Obvious enough when you're talking T/O power, maybe less obvious, but still true at cruise. Ideally the throttle will be at the stop and the boost will be where it should be on the chart. You don't have to go very high with a 985 to achieve this situation! The higher your RPM, the faster the supercharger turns, the more power it sucks up. Any excess "boost" as the Brits call it is also wasted H.P. Slow the engine, utilize all the boost. If you are producing 2000 H.P. at T/O power ( at the prop), you are also using 2-400H.P. to drive the supercharger.
To quote an obscure manual..." the stress imposed on an engine is twofold- thermal and mechanical. The magnitude of the thermal load is indicated by the cylinder head and oil temperatures, and that of the mechanical load by the RPM.....mechanical loads fluctuate with RPM...a stress is initiated at the piston, gudgeon pin (wrist pin), connecting rod and big end bearing...by centrifugal force resulting from rotation, and the inertia force on the piston caused by its acceleration and deceleration on each stroke....centifugal force which causes the major part of the loads, varies as the square of the speed, and therefore if a force of 1500# occurs at 1400 RPM, the force will be 6000# at 2800 RPM..the golden rule of " high boost-low revs" gives not only economy but conditions conducive to long engine life...at highRPM and low boost the gas pressure in the cylinder may be insufficient to hold the rings on the lower portion of their grooves. as a result the rings vibrate or "flutter".....oil consumption increases about 6 times when the RPM is doubled, since it varies at a rate between the square and the cube of the RPM.....cruising a motor car at high RPM in one of the lower gears is unthinkable, so why run the aero engine that way?"
There's lots more but I can only stand to type so much. I gues the upshot is that to really baby the engine you should reduce the RPM and put a good cushion at the top of the stroke.
As for reduced power T/Os, look thru the service bulletins and you should find a page or two from Pratt that explains why the do more harm than good, it's a couple of pages long and you'll find it hard to argue with their logic when your done. Best I can recall is that you lose some of the fuel cooling and " cushio" but the mechanical loads are unchanged, and as someone already pointed out you'll have to stay at that setting for a longer time.
hope this helps...

Edo · Post by **Edo** » Fri Feb 17, 2006 11:57 am

Regarding powering back immediatly after you leave the water.

Ive had this discussion a few times:

option 1: set climb power immediatly after breaking water and lowering the nose slightly, then set climb flap

option 2: break water, lower the nose slightly, set climb flap, then climb power.

Assume you are getting airborne with a full legal load and are not exceeding the recommended time at max power

what is better?

angry inch · Post by **angry inch** » Fri Feb 17, 2006 1:28 pm

I always reduced power, while holding nose down to pick up speed & then set flaps to climb when loads were'nt a big deal, or when their was lots of room. When it's heavy, and/or space was a concern though... I'd leave the power on longer definitely. My experience is only modest however. What do the "High Times" boys say??

bronson · Post by **bronson** » Fri Feb 17, 2006 2:06 pm

I just hold the attitude, set flaps to climb (same attitude) and then reduce power, safest thing when it's gusty.

Cat Driver · Post by **Cat Driver** » Fri Feb 17, 2006 2:12 pm

(1) Rotate

(2) Accelerate ( after safely airborne and no fear of flying back into the water when surface is hard to see )

(3) Climb ( set climb flap and reduce to climb power & trim )

Edo · Post by **Edo** » Fri Feb 17, 2006 3:41 pm

I agree flaps first then power.

I have seen a few guys who always want to get the power back first to "save" the engine but these are also the guys who seem to believe in reuced power takeoffs.

MUSICMAAN · Post by **MUSICMAAN** » Fri Feb 17, 2006 7:41 pm

Hey Bronson...........wow!! lot of big words in there..haha.. I see your point. I agree with the hight RPM and low boost theory. It was explained to me as, "cavitating"... if that makes any sense. But at 18 and 28, or 19 and 29, could that really be called low boost?

As far as Take-offs. It's almost standard procedure to lower the nose after take-off in most De-haviland's, isn't it?

I use EDO,s option 1. It all depends on the situation though. I like to get the nose down, pick up speed and get the flap up so that if an engine failure does occure, I've got some speed to play with. Can't think of an occasion that I ever held the take-off attitude after leaving the water.

bronson · Post by **bronson** » Mon Feb 20, 2006 10:16 am

well I guess the point is that knocking a 100 RPM off will only help. T/O attitude has to be roughly optimum climb angle I think, so if you just ease the flaps up and hold the attitude you'll have max altitude to play with in the event of a failure. I like that even better than speed. Nice for the passengers too, try it sometime and see what ya think. "nother subject, if you do blow a jug, don't touch the throttle. If you have lifted a jug and the intake has come off, the engine will quit as soon as manifold pressure drops below ambient pressure and the engine starts to suck. Another reason for high boost in cruise, over ambient is good.

Intentional Left Bank · Wed Feb 22, 2006 10:49 pm

The guy that taught me how to fly insisted on reducing power literally the instant that the floats left the water. Years later, I checked him out on a Mk III. Boy, that habit sure took a looong time to break.

It's nice to have to pull back on the column to keep your airspeed below red line.