Flight planning in Seminole

kevmor99

kevmor99

Well-Known Member
How much preflight planning do you guys do for the Seminole? I'm used to a 172, and with all these charts, it literally took me hours to calculate every single chart (time/distance/fuel to climb, time/distance/fuel to descend, single engine service ceiling, rate of climb gear up/down, etc).

For this particular flight, it's only 50nm. Since I know I won't be needing any short field techniques, I can skip those and just use the normal takeoff/landing ground rolls, but do I really need to calculate the time/distance/fuel for climbs/descents (we'll be at about 4,000-5,000)? In the 172 because it didn't have these for climbs/desc. I would put a slower speed for the first few miles of the leg on the flight log to account for the climb. Doing it this chart way, I subtract the distance between my first waypoint and put that as an entry in the flight log with the climb speed used.

(Also, the climb in the book is at 2700 RPM/full throttle, so my CFI told me to estimate with 25-50% of that for a 2500 RPM/25")
 
kevmor99 said:
do I really need to calculate the time/distance/fuel for climbs/descents (we'll be at about 4,000-5,000)?
Click to expand...

No, way overkill. The error is pretty small if you just a assume a constant GS from origin to destination.

<<(Also, the climb in the book is at 2700 RPM/full throttle, so my CFI told me to estimate with 25-50% of that for a 2500 RPM/25")>>

Personally, I'd climb FT/2700.
 
For Climb:
At ATP we use a 24" MP 2500 RPM setting. By about 5/6000' your not able to maintain that 24", and it will just have to be full throttle. We where supposed to climb at 100kias, but after that 5/6000' you cant even maintain 500fpm. So you would start bringing it down to almost 88kias.

-Rob
 
v1valarob said:
For Climb:
At ATP we use a 24" MP 2500 RPM setting. By about 5/6000' your not able to maintain that 24", and it will just have to be full throttle. We where supposed to climb at 100kias, but after that 5/6000' you cant even maintain 500fpm. So you would start bringing it down to almost 88kias.

-Rob
Click to expand...

Hey v1valarob~

If you want the Helm of a Beer Warrior, you need one of these!
 
kevmor99 said:
How much preflight planning do you guys do for the Seminole? I'm used to a 172, and with all these charts, it literally took me hours to calculate every single chart (time/distance/fuel to climb, time/distance/fuel to descend, single engine service ceiling, rate of climb gear up/down, etc).

For this particular flight, it's only 50nm. Since I know I won't be needing any short field techniques, I can skip those and just use the normal takeoff/landing ground rolls, but do I really need to calculate the time/distance/fuel for climbs/descents (we'll be at about 4,000-5,000)? In the 172 because it didn't have these for climbs/desc. I would put a slower speed for the first few miles of the leg on the flight log to account for the climb. Doing it this chart way, I subtract the distance between my first waypoint and put that as an entry in the flight log with the climb speed used.

(Also, the climb in the book is at 2700 RPM/full throttle, so my CFI told me to estimate with 25-50% of that for a 2500 RPM/25")
Click to expand...

Calculate using the short field T/O's and Landing charts, no need to calculate the "normal" takeoff/landing rolls, and just because you calculated it that way dont mean you have to do a Short field takeoff if you got plenty of runway.

You would probaly get a better Fuel and time econamy if you climb at around 100 KTS 25/25, vs the 88kts-full/2700

A good rule of thumb: You will either lose 5 knots, or 100 FPM for every inch of MP that is reduced. so every thousand feet you go up, you will lose around 5 knots, until you get to blueline, then you will lose roughly 100 FPM per thousand.
 
the seminole PIM i have doesn't even have normal to/landing charts in it!

before every flight i make my students calculate:
1. Accelerate stop
2. TO
3. S.E. Climb Rate
4. S.E. Service Ceiling
5. Landing

I do this because it aids in learning how to properly plan for every flight in the event you do lose an engine, you know what you can expect for performance as well as have a plan of action "ready" (not that i dwell on it, but at least it has been looked at and thought about for a few minutes)

we climb out at 25/25 105kts (pretty sure that is piper recommended) for visibility and engine cooling reasons, and the time/fuel/distance charts are just guestimates anyway.
 
Fly_Unity said:
You would probaly get a better Fuel and time econamy if you climb at around 100 KTS 25/25, vs the 88kts-full/2700
Click to expand...

What's time economy? Assuming that's the quickest trip, that will occur at the highest power settings, assuming it doesn't make you stop for fuel.

As for fuel economy, it's unlikely that the 25/2500 is optimal for any particular trip, except for coincidence. As the aircraft approaches its absolute ceiling for any particular power setting, the time to climb rises exponentially. Without running any numbers, it seems intuitive that there is a point where less fuel would be burned to climb at a higher power setting and actually arrive at the cruise altitude whereupon the aircraft could accelerate to cruise speed and complete the trip in less time.

Even prior to that point, the increased fuel burn rate is at least partially offset by smaller amount of time spent in climb and a sooner and quicker acceleration to cruise speed. An additonal factor in FT operation is the appropriate leaning for climb, once it's possible to do that, generally less than 75% power. At low altitudes, the power enrichment system can dramatically increase fuel flows for a given power setting.

The "piper recommended" 25/2500 is, most likely, purely arbitrary and not something the engineers calculated. I mean, how likely is it that the "best" power setting would work out to something so symmetrical and beautiful as 25/2500? These kind of suggested power settings generally state it's for the best combination of forward visibility, engine cooling, fuel flow, forward speed, but there really is no way to objectively optimize that diverse set of criteria. The right configuration will depend on the pilot value judgements.
 
When do you usually use the time/fuel/distance charts then? If you were climbing to a very high altitude?

I thought the reasoning for the power/rpm reduction was because of it running at red line (even though the Seminole doesn't have any restrictions based on RPM for a certain amount time...) It seems like the RPMs are really racing compared to a climb in a fixed pitch. I was told once you're at a safe altitude (500' usually) to put it at 25/2500.

tgrayson said:
No, way overkill. The error is pretty small if you just a assume a constant GS from origin to destination.

<<(Also, the climb in the book is at 2700 RPM/full throttle, so my CFI told me to estimate with 25-50% of that for a 2500 RPM/25")>>

Personally, I'd climb FT/2700.
Click to expand...
 
aloft said:
Is doing this pretty standard? Just a training practice?
Click to expand...
i use it as a tool to teach planning/decision making skills.

myself i know that in the summer the service ceiling is around 4000ft, in the winter maybe upwards of 6000 if it is really cold out. everything else is usually around 5000. same with the accelerate stop, i know how it changes and what it usually calculates out to.

i use that knowledge to apply to in the event of an engine failure in this area of flight these are my options, etc.

make sense?
 
kevmor99 said:
When do you usually use the time/fuel/distance charts then? If you were climbing to a very high altitude?
Click to expand...

In theory, yes, but in practice, I think most pilots just use some rules of thumb. Still, the original context of your question was a 50 nm trip. For a short trip, you're not going to climb that high so the amount of error you're likely to incur by not using your climb charts is very small (even assuming the climb charts are accurate for your airplane.) And your let-down at the end tends to compensate for the higher initial burn.

During training, however, I do have students do the calculations.

It seems like the RPMs are really racing compared to a climb in a fixed pitch. I was told once you're at a safe altitude (500' usually) to put it at 25/2500.
Click to expand...
It's extremely common, but you already discovered one of the problems....you're off the performance charts. Many knowledgeable engine guys argue it's actually better for the engine to keep FT. Reason being that there is a power enrichment system that keeps the fuel extra rich to keep the engine cool when the throttle is all the way forward. Fuel burns don't really appear to far off from the lower power setting, because you get to altitude sooner. Without a compelling reason to complicate things, I prefer to keep them simple.

If you don't like the high RPMs, by all means, reduce to some lower power setting. The point is to make an operational choice, based on your goals, rather than just doing a memorized procedure.
 
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