Questions for an Old, Bold Pilot...
 

I am a young chap who recently enough gained a Private Pilot Licence, and I have started this thread in the hope that I might gather some wisdom from some of you more experienced flyers in the general aviation field!

Now then, the question I have tonight is this :

A Cessna is flying from Airport Alpha to Airport Bravo at a cruise altitude of 6,000ft. When the Cessna is 20 miles out from Airport Bravo, how do you calculate in your head quickly the Rate Of Decent ? Is there some quick way of doing this in your head ?

Thanks.

I prefer to do it the other way.

Plan on a 500 ft per min descent. Then work out how many miles you will travel while descending 1000 ft. Ie in two minutes.

It will probably be between three and six miles per 1000ft. Remember that for your aircraft and now it becomes a simple calculation.

That figure* number of thousand ft you need to lose gives the distance you need to start your 500ft per minute descent from.

I don't bother. I just shuv the nose down, accelerate to VNE and break into the circuit at 500 ft, ensuring I don't rot anyone up ;)

Remember to look with your ears and get a mental picture of where everyone is.

Glad I don't pay for your new engines when you shock cool your cylinders :}

As most above, plan for 500'/min rate of descent, this will suit most SEP aircraft, nursing the engine down gently.

Based on a typical SEP speed of 90kts, that's a mile and a half a minute.

So 500' in 1.5 miles, or 1000' for every 3 miles, multiply the height you need to lose by three, and that's your distance in nautical miles.

You can adjust this distance into the wind, with a headwind you need less distance, with a tailwind you need more.

This also works for larger aircraft, onto jets, since the proportions stay the same. Forward speed of 250kts, rate of descent 1500'/minute.

I tend to view it slightly differently and use a generalised 3 degree descent plan (adjusted to provide a steeper final).

For any aeroplane descending at around 85-100kts I use 3 miles for every 1000ft descent required minus a mile or two for base leg or circuit slowing/flapping.

So from 6000ft above the threshold I'd begin a 500fpm descent from about 16 - 17 miles out. I.e. (6 x 3)-2.

IMO this provides a comfy descent to a height somewhere near to a good joining or final position with enough time to slow and add flap before the steeper final approach. Of course during the latter stages you can fiddle with power and speed to put you wherever you like. When I've done this reasonably well it makes for a smooth straight-in and rather satisfying.

Edit: Looks like RTN11 beat me to it!

Calculate the amount of altitude you have to lose in your case 5000 feet (so that you arrive at the airport at 1000 feet AGL to join the circuit). Then take the number in thousands and double it, 10 in this case and so you start your descent when your GPS time to airport reads 10 minutes. This will give you a 500 feet/min descent and self corrects for wind.

Don't have a GPS ? Well go buy one! Anybody who does not take advantage of the real time navigation information a GPS provides, not to mention the fact that the nearest airport feature may literally save your life; is IMO foolish

Oh and when you start your descent don't smash the mixture knob to full rich like your instructor probably told you to :rolleyes:

Isn't that red knob just for turning the engine off? That's all my first instructor ever used it for :}

'Glad I don't pay for your new engines when you shock cool your cylinders '

Who said I shock cooled the engine? That only happens if you close the throttle from high power! I keep the throttle where it is and convert speed to height, then when slow drop land flap! ;)

ps, you did pay for my engines... with your taxes

Don't I just love having my Flightplan HD app running on my iPhone..... Open the App. Select Navigation - Rate of Descent, enter current altitude, distance to fly, ground speed and required altitude and it tells you exactly what rate of descent you need to hit.... However, after entering 6000ft, 25 nautical miles, 110 knots and 1000 ft, I'm wondering which of us here would be able to hold an exact 366.7ft / minute descent :E:E:E

Big Pistons Forever wrote
Hi BPF, must admit that the instructors at the club I'm a member of still teach that, they claim that the excessive fuel entered into the cylinder aids internal cooling. At the club we have a couple of 172s with fuel injection and PA28s with carbs so would love to hear your reasoning.

Could this be something to do with the heights, the club trainers only instruct at heights around 2000 feet so when descending to a circuit height of, say, 1000 feet, would pushing the mixture full rich have such an impact as say, descending from FL95 down to 1000 feet and pushing mixture full rich, to avoid the need to look at EGT, fouling the plugs with an over rich mixture, etc?

6,000'? A series of loops, rolls, and stall turns will burn off a chunk of that in the Chippy :E .

I'd be at 1,500' or so for Zone Entry, and most of that would be converted into speed in the last couple of miles to fit in with the commercial traffic having been cleared to final, only slowing and trimming to Vfe on short final, then back to 60 max stabilised for landing by very short final.

One of the options available in the GNS430 and successors is "Rate of Descent Required". You tell it that you want to be at altitude X at a certain point, and it tells you the ROD required. You can set that up 100 miles away.

Going to an unfamiliar airfield, I would set it up and wait for "500" to show. Then select a 500fpm ROD, and check it occasionally. It never failed me.

If you fly with the kit, learn to use it: there's an amazing amount of clever stuff in panel-mount GPS units these days.

If you don't have that, then as others have said: a little mental arithmetic works fine - which is how I do it these days in an antique taildragger.

Thanks for the replies guys. I think I have it now.

Mixture was mentioned above. Now, my instructor told me to always lean, even when I was just doing circuit training I would lean the 172 about 2 finger thickness out in between crosswind leg and downwind leg.

I flew a 200NM cross country to an Island not so long ago with a PPL freind. I went up to 7,000ft (For some reason I feel safer when I am higher) and I had the mixture back half way on the PA-28. He was shocked as he was taught to never touch the mixture, and only pull it out to shut the plane down! I was shocked to hear that. It freaked him out when I leaned it but he soon found out that in fact the engine does not stop when you lean it. It seems, the higher I fly, the more I can lean it.

So far I have 95 hours total time of which 61 are Pilot in Command. All of my training was done on the Cessna 150 and Cessna 172N.

Since gaining my PPL I have mainly rented a PA-28 Archer and a Rallye 110ST.

My next question is this :

If the wind is at almost at the cross wind limit for the aircraft at the runway in use with gusting reported, is it possible for say a Cessna or Piper to get off the ground and make it out or will you smash it back into the ground ? From your experience now I am looking for advice. I know what the manual says.

Any advice for landing a PA-28 on a 400 tarmac metre runway ? The shortest runway I have landed on was 550 metres!
I know how to do it but the nerves get to me just think about how small it is.

Thanks

One thing you need to remember is that this is a rule of thumb thing rather than a precise science so be ready to adjust.
Taking still air all these calculations work but we are flying in moving airmasses!
Ie do you have a 40 kt tailwind or a 40 kt headwind very different results in a 120kt TAS aircraft!
One gives you 160 kts over the ground the other 80 kts! Remember too that as you descend the winds will probably change direction too.
You may also experience pockets of sink or pockets of lift.
With GPS or DME or even mental distance to run calculations it easy to work out you have 10 minutes to run and of course GPS will calculate the time to point X! but be aware of moving airmass and prepare to increase or decrease the descent rate as things pan out!

Not sure why this is a question for old bold pilots?:}

Pace

Talking of strange noises..... any strange noise that occurs whilst passing close to Carla on a cross channel crossing in a PA 28 without the necessary altitude to glide to the nearest airfield.....

And yes, I'm pretty sure the planes have a knack of knowing when you are out of glide range from a field and they tend to say "hey, let's get him wound up, let's misfire for a second or two". :eek:

The way in which the American spam cans you are describing were certified was with a max demonstrated cross wind landing.

When the test pilot flew and then certified that cross wind landing, he would have been taking into account the average pilot on the average day being able to handle this amount of cross wind.

With low hours like yourself, you may want to limit yourself to say 15kts cross wind, rather than the 17kts demonstrated in the PA28 POH. As you gain more experience of cross winds, and are current on type then you can start to experiment with more challenging cross winds.

I have comfortably landed a PA28 in around a 23kt turbulant cross wind, and that was still nowhere near the absolute limit of the aircraft, but I was very current on type at the time.

Ultimately the more cross wind you have the more difficult it is to maintain directional control, eventually you will just run out of rudder. This varies significantly on type, as I say I know the PA28 well, and am happy with it in a x-wind, having hardly any time on say a C152 I wouldn't push the limits nearly as much.

But to answer your question, no it won't just fall out the sky because you're a few knots over the demonstrated cross wind speed.

I once flew a Seneca Five twin into Denham the wind was 90 degrees at 40kts and that was about the limit with full rudder to maintain directional control.
I had no more intention than having a look and maybe a touch and go but settled with a landing when it surprisingly settled onto the runway.
So more than double the demonstrated!

Pace

The GPS time to station is recalculated every second so any change in the winds will change the time which will trigger you to slightly increase or decrease the rate of descent with no math required.

BPF : an old but definitely not bold pilot :ok:

Sigh, another example of a flying school urban myth mindlessly passed on from instructor to instructor. The excess fuel from full rich will indeed cool the cylinders which is good for long climbs at full power. However when you are descending you are increasing airspeed and/or reducing power both of which will lead to cooler cylinder temps. Dumping a whole bunch of fuel will exacerbate this cooling and potentially lead to cracked cylinders from shock cooling.

For the scenario posted by the original poster I tell my students to leave cruise power on lower the nose to an attitude which gives a rate of descent of 500 feet/min and slightly enrich the mixture from the cruise lean (ie push the knob in a quarter of the the distance from where it is to the full rich mixture). For aircraft with fixed pitched props you will need to occasionally reduce the throttle because the engine RPM will increase as you descend. The aim is to maintain cruise RPM throughout the descent.

new ppl guy
 

point one: if you are flying at 6000' you are flying at an IFR altitude...shouldn't you be VFR at 6500' feet? (assuming youare above 3000 agl)

point two...sometimes it is smart to overfly the field at altitude and descend after looking the field over.

point three, you haven't said if there is intervening terrain features, natural or manmade between yourself and the airport.

these are the things us OLD pilots think about.

a 500 foot perminute descent for a non pressurized plane should be considered the MAXimum for passenger/crew comfort. others have given you an idea how to calculate this...but you should enter the traffic pattern at pattern altitude and not higher ( you might descend on top of someone especially if youare in a low wing plane).

as far as the mixture goes...well, if you are concentrating on your mixture knob and not looking out for traffic you might die. if you enrichen the mixture before leaving 3000' or so, the engine will be fine and you can look out the window for traffic...YOU CHOOSE WHICH IS MORE Important.

AS TO CROSSWINDS AND WINDS OF ANY KIND. I've landed a piper arrow in a 60 knot wind, and it wasn't straight down the runway. I landed ''crabed'' and rolled about 40 feet and stopped.

So, for the new pilot, stay below the max demonstrated crosswind component. someone talked about landing a seneca...well, a twin engine plane can use assymetric thrust to enhance crosswind performance...indeed I've even used it on jet transports.

AS to landing a piper archer on a 400 metre runway( so that's about 1200 feet plus a bit). I suggest you do the following:

one...calculate the exact vref (approach speed)...using the exact weight at time of landing. fly at this speed using the techniques in the pilot operating handbook.

aim for a safe touchdown point (not right on the numbers as you might end up short)...I always told my students to aim for the SECOND stripe in the runway centerline...but you might not have the runway marked.

as soon as you touchdown, retract the flaps (the archer is a fixed gear plane...no chance of retracting the gear) and smoothly apply the brakes to a complete stop.

Landing and stopping this type in less than 1000' shouldn't be a problem PROVIDED there is a bit of a headwind...don't attempt with tailwaind or if in violation of the POH.

IF you can, go up and fly around in the landing configuration with the payload and fuel loading you expect on landing...at a safe altitude do a power off stall in the landing configuration. NOTE the airspeed of stall (recover of course) and use that speed to calculate 1`.3 times that speed for vref and use that as approach...it may be below the standard approach speed but use it and it is the proper speed for landing.

the standard speed is calculated for max landing weight, not the weight you may really be at.

the archer/warrior series is a very nice plane to fly...but if you take the time to read the POH and make the calculations based on real weight, you will get better takeoff and landing performance.

while instructing for commercial pilots, we used a turbo arrrow 3...by using the exact techniques and speeds we could make the thing jump off the ground and clear the 50' obstacle in a very impressive manner. but using the standard speeds it would be sluggish.

now, be careful, dn't stall...and you can't lose even one knot!!!! there is slop involved in the standard speeds and you lose the slop if you are ''right on''.

fly safe...try to read what I posted about unfamiliar airport entry patterns somewhere else on this forum