Jump to content

Sign in to follow this  
NeilC

Steeper descent profile

Recommended Posts

I had another go in the DC-3 (I appreciate this is the DC-6 forum, but I love both), and with a light load, full flaps, gear down, props at landing setting of about 2400rpm, if I kept the MP above 24 I could not descend (in fact, it was accelerating a little in level flight).

What am I doing wrong? If I reduce MP to about 20, it flies fine on final, but then the props are windmilling!


beta.gif

Share this post


Link to post
Share on other sites
10 hours ago, NeilC said:

If I reduce MP to about 20, it flies fine on final, but then the props are windmilling!

How do you know that they are windmilling the engine?  I've got no experience with DC3 but it's normal to see 20 inHg MP in the DC6 on final. 


Dan Downs KCRP

Share this post


Link to post
Share on other sites

I thought that if the MP is less than the RPM, you are driving the engines. So with the RPM at 2400 on final, a MP of 20 would not be ideal. Have I got this wrong?


beta.gif

Share this post


Link to post
Share on other sites
4 minutes ago, NeilC said:

I thought that if the MP is less than the RPM, you are driving the engines

That is something you can test for yourself in the DC6.   You are still pulling about 80 in of BMEP with 20/2400 I think... it's been more than a few days and my memory...


Dan Downs KCRP

Share this post


Link to post
Share on other sites
12 minutes ago, NeilC said:

I thought that if the MP is less than the RPM, you are driving the engines. So with the RPM at 2400 on final, a MP of 20 would not be ideal. Have I got this wrong?

Dan is certainly more qualified than I to comment on the nature of constant-speed piston props (and of course when it comes to the DC6/DC3 we're talking radials so even further outside of my knowledge areas!) but I would say that in general it is difficult, if not impossible, to make any connection between manifold pressure and engine torque.

Manifold pressure is simply a measure of the pressure in the intake. When the engines are shut down on the ground, the manifold pressure will be circa 30 inches... engine torque output, zero. Indeed, the general advice (albeit arguably an old wives tale for precisely the same reason) traditionally, at least with naturally aspirated piston engines (although, not radials specifically) was that one should avoid operating "over square" - i.e. with manifold pressure > RPM.

Without a torque gauge I can't think of any reliable way to determine whether negative torque is being generated, but I'm happy to learn otherwise!


Simon Kelsey

sig_FSLBetaTester.jpg

 

Share this post


Link to post
Share on other sites
14 hours ago, skelsey said:

Dan is certainly more qualified than I to comment on the nature of constant-speed piston props (and of course when it comes to the DC6/DC3 we're talking radials so even further outside of my knowledge areas!) but I would say that in general it is difficult, if not impossible, to make any connection between manifold pressure and engine torque.

Manifold pressure is simply a measure of the pressure in the intake. When the engines are shut down on the ground, the manifold pressure will be circa 30 inches... engine torque output, zero. Indeed, the general advice (albeit arguably an old wives tale for precisely the same reason) traditionally, at least with naturally aspirated piston engines (although, not radials specifically) was that one should avoid operating "over square" - i.e. with manifold pressure > RPM.

Manifold pressure in a supercharged or turbocharged engine is actually a very good indication of the power that the engine will produce.

The relationship between manifold pressure and rpm will depend on the engine design so I agree that a rule of thumb relating the two can surely only apply to one engine or family of similar engines. 

Edited by kevinh

ki9cAAb.jpg

Share this post


Link to post
Share on other sites

Neil, remember you need your first and last name in the PMDG support forum 🙂

 

Hi guys, just thought I would add my thoughts on this topic,

For some background: I have been flying high performance propliners for a while in FSX, using the wonderful freeware aircraft and handling techniques available at California Classic Propliners

To get the best experience from aircraft such as the wonderful PMDG DC-6B, I recommend reading (and practicing) all of the wonderful 2008 Propliner Tutorial. There are a lot of misconceptions that can be answered by this document, but be warned it is very thorough (read: lengthy)! In fact I use the "handling notes" of the freeware Tom Gibson/FSAviator DC-6B CB16 to provide for easy handling of the PMDG version (supplemented by the provided PMDG charts).

The 2008 Propliner tutorial explains what I believe is the fundamental error Neil is making regarding his DC-6 handling (as I too know from personal experience).

Quote

Most flight simulation users fail to plan TOD correctly, fail to vacate cruise at TIME = TOD, and then fail to manage their energy state competently after their mistaken TOD. Consequently most flight simulation users soon loose control of drag altogether, because they descend too late, too steeply, and with too much power applied.

Neil, I believe your problems fundamentally state from a late descent from cruise altitude which result in you carrying way too much speed on approach, likely combined with incorrect power settings which result in you being unable to meet the targets of a charted instrument approach. The humble CalClassic page gives a great deal of information on how to handle these demanding aircraft, and I will only give a very quick (IMHO) tips and suggestions for the thread. The goal of my post is only to give a very quick overview of the problems and concepts in this thread as I see them.

1) Neil, you need to start a descent MUCH MUCH earlier than you would expect to in a turbine aircraft (prop or jet). Plan and execute a 500FPM descent all the way down from cruise altitude to the IAF.

2) The recommended configuration of a DC-6B CB16 when you cross the IAF (at the lowest legal altitude) is as follows.

Quote

COWL FLAPS = 1 degree

2000 RPM

MINIMUM 20 INCHES MAP

FLAP = STAGE 2

MAINTAIN 140 KIAS

with these targets in place, at less than MGLW, the DC-6 (PMDG or freeware) has no problem descending on the overwhelming majority of IAP's in the world, despite mountains or other obstacles. This aircraft is designed for those approaches, and those approaches are designed to be flown by this type of aircraft.

3) Full IAP's flown in the PMDG DC-6B are certainly possible by following the MAP>(RPM/100) operating restriction. I find the justification for this restriction compelling, and choose to comply with it in these aircraft.

4) Do not go below MAP>(RPM/100) until you reach the runway threshold (the PMDG manual states 15" for the flare, and I think that works just fine).

4) Modern STARs are not relevant for propliner operations. While I have no experience flying large high performance piston airliners in the modern environment... it makes no sense to put the two together. As previously discussed, the 500FPM descent will not allow you to meet crossing restrictions oriented for turbine aircraft anyways. In the example of the MOTIF6 STAR to KMDW, notice that those charted altitudes are "Expect" only, meaning they must be assigned by ATC. Your response would very likely be "Unable" to such restrictions, and this descent angle is much too steep (and late) anyways. Also, consider that in the modern world a DC-6 is affectionately known as a "flying roadblock" to the turbojet/turboprop aircraft barreling down on it at 200KIAS+. You would either be rerouted off a STAR, or given vectors to get out of the way. Routing is likely to be very similar to the period correct procedures used at CalClassic.

5) I also disagree with Simon, in that MAP (considered with RPM) is a very good estimation of engine torque or power. Remember that while MAP only informs us of the amount of air delivered to engine, it is the carburetor's job to deliver an appropriately metered amount of fuel for combustion, based on the density of the air at the manifold. If I know MAP and CAT, then I know the density of the air charge, and thus can infer exactly the metered amount of chemical energy being delivered to the combustion chambers based on the setting of the automatic mixture controls.

There is yet MUCH MUCH more to these wonderful aircraft, and I would highly recommend dedicated users check out the resources available in the Propliner Tutorial and at CalClassic, and hope you guys can experience the satisfaction from mastering these demanding machines.

Robert Toten

Share this post


Link to post
Share on other sites
13 hours ago, randomTOTEN said:

4) Modern STARs are not relevant for propliner operations. While I have no experience flying large high performance piston airliners in the modern environment... it makes no sense to put the two together. As previously discussed, the 500FPM descent will not allow you to meet crossing restrictions oriented for turbine aircraft anyways. In the example of the MOTIF6 STAR to KMDW, notice that those charted altitudes are "Expect" only, meaning they must be assigned by ATC. Your response would very likely be "Unable" to such restrictions, and this descent angle is much too steep (and late) anyways. Also, consider that in the modern world a DC-6 is affectionately known as a "flying roadblock" to the turbojet/turboprop aircraft barreling down on it at 200KIAS+. You would either be rerouted off a STAR, or given vectors to get out of the way. Routing is likely to be very similar to the period correct procedures used at CalClassic.

 

I had no problems with sticking to the MOTIF6 STAR with the PMDG DC-6, I was able to comply with all the "expected" altitudes displayed on the charts, but I had to plan way ahead and make some calculations for it to work. Most of the time I use the "VCALC" function of the GTN650 installed on my DC-6, works quite well when you set your required altitude at the IAF as target altitude, then a descend rate of 500 FPM and lastly a 10NM offset before the planned waypoint, so that you are able to slow down below max. flap extension speed before passing the IAF. But you have to make sure that you won't descend below MSA in order to thet to the IAF (e.g. in a mountainous area). If I'm face with such a problem, I request a hold with descent clearance to the IAF's minimum required altitude before continuing the approach.

If you're searching for an interesting and challenging approach for the DC-6, try BGBW (Narsarsuaq, Greenland). I've landed there last week. Did the NDB/DME-1 approach for runway 07. Aircraft that are not able to fly the steep approach path (5.6°) have to overfly the threshold and then make a 360° turn to the left. That was fun in the DC-6, as you don't have much time to lign up to the runway on short-final after flying that 360° turn!

Edited by TheFinn88

Matthias R. Schwab

Intel i7 7700k @ 4.8GHz, Asus Maximus IX Hero, Asus GTX 1080ti OC 11GB, G.Skill Trident Z 32GB @ 3200MHz, Samsung 960 EVO M.2 1TB

Share this post


Link to post
Share on other sites
On 9/17/2018 at 3:04 AM, TheFinn88 said:

I had no problems with sticking to the MOTIF6 STAR with the PMDG DC-6,

That's great to hear. What was your IAS on the arrival?

On 9/17/2018 at 3:04 AM, TheFinn88 said:

Most of the time I use the "VCALC" function of the GTN650 installed on my DC-6... request a hold with descent clearance to the IAF's minimum required altitude before continuing the approach.

I do the same thing. I haven't brought myself to install a GPS unit in the aircraft yet, and got intimately familiar with the panel mounted clock on my most recent flight. 😎

On 9/17/2018 at 3:04 AM, TheFinn88 said:

try BGBW (Narsarsuaq, Greenland)... NDB/DME-1 approach for runway 07.

This looks like a wonderful little approach, and I can't say no to a scenic NDB approach such as this. Thank you for the suggestion. As you've mentioned, and others might not realize, despite the very close proximity of 5,500'+ mountains to the airport, this is not categorized as a "steep approach." At most, it is "optionally steep" and I would agree with your decisions regarding this approach. The DC-6B likely cannot comply with the 5.6 degree glide slope for a straight in from the 1,800' minimum descent altitude. It also likely cannot achieve the required 4% minimum climb gradient for a missed approach from 1,800'.

But even with such close terrain, it certainly can comply with standard descent gradients to the 3,500' MDA, and then descend via a normal 3.0 degree path in a casual circle under visual flight to the runway. Should a missed be executed from 3,500' the DC-6B will meet the required climb gradient for a safe return to 6,800'.

I noticed that the chart doesn't list visibility minimums for any category, so I found them in another document. Regardless of either a "steep" straight in or "normal" circling procedure, 6,000 meters of visibility (about 3.75 sm) is required to descend below the chosen MDA. If the approach is conducted at night, then only the straight in is authorized. This means that the the PMDG DC-6B is likely only authorized to arrive at BGBW during daylight hours.

Somebody would need to test to see if the steep approach is possible (Real operators would likely calculate the possibility), but I have full confidence that normal gradients can be met.

Are there any operators/routes which would have flown a DC-6B into this airport? I'd like to make this approach part of a complete flight if I can.

Robert Toten

Edited by randomTOTEN

Share this post


Link to post
Share on other sites
6 hours ago, randomTOTEN said:

That's great to hear. What was your IAS on the arrival?

I was cruising at 13'000ft, so I started my descend at the first waypoint with the first expected altitude at RENZO. But before I started my descend, I decreased my airpseed to 140 KIAS and dropped my flaps to 20° as soon as I was below 170 KIAS. With flaps set at 20° and an airspeed of 140 KIAS I had a descend rate of about 800 fpm, and I was able to cross MOTIF at 10'000ft and the Joliet VOR at 6000ft. I was also quite light with a LGW of about 72'000 lbs.

6 hours ago, randomTOTEN said:

I noticed that the chart doesn't list visibility minimums for any category, so I found them in another document. Regardless of either a "steep" straight in or "normal" circling procedure, 6,000 meters of visibility (about 3.75 sm) is required to descend below the chosen MDA. If the approach is conducted at night, then only the straight in is authorized. This means that the the PMDG DC-6B is likely only authorized to arrive at BGBW during daylight hours.

I use navigraph charts for my flights, and they state the minimum visibility (6000m) and minimum cloud base (1500ft) required for a approach into BGBW. And I actually didn't took into account the missed approach requirements, good that I didn't have to go around. :blush:  I landed there before the sun went down, and I wouldn't recommend to fly in there at night with the DC-6!

The departure out of BGBW is also very interesting. There are two options, one is to directly intercept the 277° bearing out of the NA NDB, and the other one is to fly a 360° to the right within the 3NM arc of the NQ DME. I flew the 360° departure, and after that you have to correctly lign up on that 277 bearing, as this will keep you over the water and between the mountains. So I had to fly about 7 minutes into the wrong direction and climb to 7100ft (MSA) before turning back to the NA NDB and continuing my flight to BIRK. Also don't take off below take-off minimums, as you desperatley need visuals for that 360° turn. I had few clouds at 900ft, where I punched through some of them while making that 360° turn. :rolleyes: But I always had visual to the airport and the surrounding terrain, still it was very marginal...

My next leg will be from BIRK to EGPK.:cool: And by the way, regarding the DC-6 at LSZH: I've found a video of the RB DC-6 landing in LSZH on runway 28 with live ATC. They called in "established ILS 28" on a nice sunny day, I think that answers my question of whether the RB DC-6 is flown VFR or IFR into LSZH. :rolleyes:

Edited by TheFinn88

Matthias R. Schwab

Intel i7 7700k @ 4.8GHz, Asus Maximus IX Hero, Asus GTX 1080ti OC 11GB, G.Skill Trident Z 32GB @ 3200MHz, Samsung 960 EVO M.2 1TB

Share this post


Link to post
Share on other sites

I have discussed and experienced may approaches with the DC-3 and also the Connie (which flies similar to the DC-6), but have no RW DC-6 experience. But we had great discussions with the pilots from the Red Bull DC-6.

The Rule of Thumb "MP > RPM/100" certainly has a safety marging included for the fact that you may have a wind change or gust which would short term impact the actual speed over the props. I also learned that ist is more important to stick to it when you flying during the approach with higher speeds, then on final.

Actually there are a bit different philosophies among the DC-3 pilots and the european pilots use a bit a different profile to slow down than the US ones.

The difference is that we try to avoid RPM below 2000 as the engines get a bit rough there. So we stick with minimum 20/2000, while US pilots also fly 17/1700, if needed.

Also important is that the rule is more stricktly to be  imposed on high speeds resulting in more torque driving an engine and damaging the gear versus when you are on final with just 100 kts.

In any case, we plan with 300 ft/min for decent and 500 ft/min as maximum in case of tailwind. Also as this is more convinient for passengers for a non pressurised plane. 

The DC-3 has very low flaps limits and we apply 1/2 below 100 kts. That is a big difference to the DC-6 with a smaller first step allowed at 174 and you can follow with steps to 20 and 30 degrees quickly if needed. Plus the limit of 170 for the landing gear.

So in essence for an approach into an airport you just need to slow down to 170 on a few miles horizontal during the approach pattern, but you need to set flaps/gear to follow a 3 degree glide.

  • Like 1

Happy flying!
Alexander M. Metzger

Share this post


Link to post
Share on other sites

Now that is both helpful and interesting in equal measure !  Many thanks.


Neil Burgess

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    28%
    $7,100.00 of $25,000.00 Donate Now
×
×
  • Create New...