Need some tips for DESCENDING

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boilerhead
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Need some tips for DESCENDING

Post by boilerhead »

Hello friends :)

Do you have some tips generally for descending, what should I follow? Descending with trim down or throttle to idle or what is right .
Descending is only phase of flight which I do not know about.
I'm fly with WW2 aicrafts A2A (B-17G, Spitfire, P-40, Texan ...)

Thanks for tips from experienced pilots! :D

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Oracle427
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Re: Need some tips for DESCENDING

Post by Oracle427 »

Well first you need to know when to descend and the rate of descent.

I was taught the 3/6 guideline for planning.

That is you multiply the number if feet to descend, in thousands, by three to determine the distance to begin descent.

For example, if you are at 10,000 feet and need to descend to 1,000 feet, you would need to descend 9,000 feet. 9 x 3 = 27 miles out to begin descent.

Next you multiply the ground speed by 6 to determine the rate of descent.

For example if you are making 150 knots GS, then you would need to descend at 150 x 6 = 900 FPM.

Then you just learn to configure your aircraft for a stable descent with the above parameters.

I do not know if this rule makes sense for very fast aircraft. The rates do seem reasonable to me.

Descents begin with power reductions, the amount and rate at which power is reduced will vary by aircraft.
Last edited by Oracle427 on 09 May 2018, 16:02, edited 1 time in total.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

boilerhead
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Re: Need some tips for DESCENDING

Post by boilerhead »

Thanks for good info ! :wink:

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Jacques
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Need some tips for DESCENDING

Post by Jacques »

As Oracle pointed out above, each aircraft descends according to different profiles, but a couple of important things to watch are

1) shock cooling the engine by cuttting engine power while also increasing the rate of descent. This causes the cylinders to start rapidly cooling which can result in engine damage.., and

2) avoid letting the propeller drive the engine ( high propeller RPM with low Manifold Pressure) This will also damage the engine.

For fighters, keeping the two pointers above in mind, I try to descend in a controlled manner that allows me to reach my destination (see Oracle's excellent information above). Since fighters are slippery, they will gain speed. Once at your destination, you will need to "break" as you cross the airfield to rapidly bleed off speec, so you arrive at the approach end at a slow enough speed that you can lower flaps and gear and land safely.

The B-17 can be safely descended by keeping the turbo boost dial at 8, ensure mixtures are in auto rich, and fuel boost pumps are on. I try to maintain 25" of manifold pressure and 2000 RPM while descending initially at 500 feet per min and increasing that to up to 800-1000 feet per minute at lower altitudes. Remember as you descend to dial back the boost to maintain your desired manifold pressure.

The manuals that came with each aircraft usually comes with speed recommendations for various conditions (flap speeds, gear speeds..)
The internet can often provide genuine .pdf manuals for most A2A aircraft...in addition, there are loads of WW2 era training videos that can be found by searching youtube!

Spitfire Mk II:

https://www.dropbox.com/s/73vrsgzqeyxw2 ... 0.pdf?dl=0

T-6G Texan:

https://www.dropbox.com/s/7c5jvuxcaonzn ... 1.pdf?dl=0


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DC3
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Re: Need some tips for DESCENDING

Post by DC3 »

10,000 to 1,000 ft @ 150kts gs

Remember to keep ground speed at 150 kts during descent or 3/6 formula will not work.

(10,000 - 1,000) * 3 = 27 miles to descend

150 * 6 = 900 fpm descent rate

(27 miles / 150 mph) * 60 minutes = 10.8 minutes to descend

900 fpm * 10.8 minutes to descend = 9,720 feet down altitude -- so -9000 feet with room to spare.

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Oracle427
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Re: Need some tips for DESCENDING

Post by Oracle427 »

"Modern" opposed engines like the Lycosaurs don't suffer from the issues caused by insufficient lubrication when the prop drives the engine.

On the older engine designs and especially radials, the prop driving the engine causes the crank bearings to experience loads from the piston rods at different angles than designed for. The result being that the oil film is not not in the correct place on the bearing surfaces to take the load resulting in metal to metal contact.

This carries over to shock cooling. If you try to reduce power gradually and keep the engine warm, you'll never let the prop drive the engine in the first place. Plus you're being gentle to engine which is always a good thing.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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Aymi
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Re: Need some tips for DESCENDING

Post by Aymi »

In the big radials like the Connie, I found that keeping the MP/RPM needles parrallel as a rule of thumb did the trick to prevent prop windmilling the engine. At very low RPM, something like 1500RPM - 20"InHG, you can keep descending at 250 IAS for a hundred nautics while eating almost no fuel.
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shortspecialbus
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Re: Need some tips for DESCENDING

Post by shortspecialbus »

Also, don't fly the plane with trim. Fly the plane with the yoke/stick, and use trim to relieve the need to apply pressure (this isn't quite right but it's a start). Not saying you were, but it's a common thing with sim pilots. Remember, throttle controls altitude and pitch controls speed :)

-stefan

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Oracle427
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Re: Need some tips for DESCENDING

Post by Oracle427 »

Some detailed infromation from Mr Deakin on why prop driving the engine on some types of engines is bad.

https://www.avweb.com/news/pelican/186778-1.html
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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