Keeping the Merlin running smoothly on descent

Arguably the finest fighter aircraft of World War II.
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EnDSchultz
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Keeping the Merlin running smoothly on descent

Post by EnDSchultz »

So I splurged and picked up this gorgeous bird and have been racing her around the Alaskan wilderness for the past few hours. One thing that's constantly causing me problems is keeping the engine running nicely at low altitude...she's so clean she just doesn't want to slow down and if I pull the power back below around 50% the engine starts sputtering something fierce. Once on final approach with all the flaps out, things are pretty nice, but when approaching the pattern, I'm constantly having problems. I've made sure the prop is set for the recommended 2600-2700RPM. I thought maybe carb ice could be an issue so I hit the carb heat per the described procedure, but that didn't resolve the issue. Am I just being too aggressive with the descent?

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DHenriques_
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Re: Keeping the Merlin running smoothly on descent

Post by DHenriques_ »

EnDSchultz wrote:So I splurged and picked up this gorgeous bird and have been racing her around the Alaskan wilderness for the past few hours. One thing that's constantly causing me problems is keeping the engine running nicely at low altitude...she's so clean she just doesn't want to slow down and if I pull the power back below around 50% the engine starts sputtering something fierce. Once on final approach with all the flaps out, things are pretty nice, but when approaching the pattern, I'm constantly having problems. I've made sure the prop is set for the recommended 2600-2700RPM. I thought maybe carb ice could be an issue so I hit the carb heat per the described procedure, but that didn't resolve the issue. Am I just being too aggressive with the descent?
Shouldn't need carb heat with a Merlin unless icing conditions are present.
Approaching your landing airport in a Mustang takes a little planning ahead. Medium power settings are usually the way to go. I use around 25 inches and control airspeed with pitch. Patterns flown in the Mustang are usually flown off an initial using a break to bleed off airspeed to drag entering the downwind off the initial break turn.
If you fly a normal pattern, keep it in close and use flaps. Important point here is that by using flaps you bleed off airspeed requiring power to compensate. This keeps the manifold pressure up in the range where the plugs won't foul and the prop doesn't start turning the engine.
Remember you can start using 10 degrees of flaps all the way up to 400 mph and 20 degrees at 275. All down under 165. Flaps will help with airspeed loss so use them when needed.
The only time you idle a Merlin is over the fence through touchdown. On the roll out after landing you will eventually have to increase the power a bit to around 1000 RPM to avoid rough running.
Takes a bit of practice but worth the effort to do it correctly.
This is the way we fly the actual P51 and all of it is accurate in the A2A version.
Dudley Henriques

EDIT: I would add to this that on approach the best time to "bring up the prop" is on final when the MP is low enough that the prop is beneath the governor range. This way you don't get a surge in RPM as you make the change. I would note also that for the Mustang specifically there are several Dash 1's that state a 2700 RPM figure for the propeller on approach. This is fine and can be done easily while the MP is high enough to keep the governor in adjustment range. If you wait as I have suggested to bring up the prop on final below the surge range you will be bringing up the prop to the full 3000 RPM level which is fine as the RPM won't show on the tach due to the governor not being in range to actually change the pitch until power is applied. At 2700 you would be using 46 inches on a go around. With the prop all the way up you can use anything you like up to and including 61 inches if the fuel is 130 octane or 55 inches if you're loaded with 100LL.
Last edited by DHenriques_ on 05 May 2014, 13:20, edited 2 times in total.

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NAA551WB
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Re: Keeping the Merlin running smoothly on descent

Post by NAA551WB »

I echo what Mr. Henriques stated and my rule of thumb is when I start the break I'm usually between 200 and 225 and being absolutely never below 20 inches of manifold and the RPM set at 2700. As soon as I make my break I will take out two notches of flap and usually about the time I turn base I can drop the gear down and still make the airfield if I have an engine failure. Also with the added drag I'm having to actually increase on the power to keep my approach speed where I want it.
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EnDSchultz
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Re: Keeping the Merlin running smoothly on descent

Post by EnDSchultz »

Thank you, sirs, for the prompt and excellent advice. It always brings a smile to my face to see how passionate the A2A community is about sharing their experience and helping out a poor student pilot in need! Anyway, after about 25 hours I'm starting to get the hang of it!

As a bit of a segue, the flare has been especially challenging to perfect, coming from training in a putt-putt little tricycle Cessna. In that plane, you just try to hold off with the flare, applying more and more back pressure as you bleed off speed until the plane settles onto the runway. I have discovered through a number of rather...graceless landings that this is not the way to do it in the Mustang, and videos I've seen of how actual landings are done seem to corroborate this. It seems best to carry enough speed and meter the deceleration after the threshold such as to kiss the pavement with maybe only 5 degrees of pitch. So by now I'm to the point where if I'm on my toes I can pretty consistently set her down with little to no bounce...it really is priceless to hear the tires scrub the pavement and not be immediately met with the silence of rushing air.

Just thought I'd share. Thanks again for the help!

budo
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Re: Keeping the Merlin running smoothly on descent

Post by budo »

Dudley, What altitude do you use on initial ? I know WW2 fighters used various altitudes on initial returning from missions usually very low then pulling up sharply to bleed airspeed but that is beyond my ability :oops:
Budo

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DHenriques_
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Re: Keeping the Merlin running smoothly on descent

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budo wrote:Dudley, What altitude do you use on initial ? I know WW2 fighters used various altitudes on initial returning from missions usually very low then pulling up sharply to bleed airspeed but that is beyond my ability :oops:
Budo
There are two types of military initials flown; one from altitude and the other as a fan break off the deck.
The fan break began during the war as a quick means of breaking up a formation from echelon, spacing the aircraft in the pattern, and getting them on the ground quickly for mission turn around.
Today, unless in a show or display environment, the break from pattern altitude is the preferred method for a high performance airplane like a Mustang.
With tower authorization, I flew my initials in the Mustang with a little offset parallel to the runway so I could see it at 1500 agl using a break speed around 225 indicated at cruise power setting as I reached the far end of the runway. In the break turn I'd go to 20 degrees of flaps and leave the prop where it was coming back to around 23 inches or so. The pattern should be fairly round and close in. I configured as needed to put me over the fence at 120 indicated with full flaps.
DH

budo
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Re: Keeping the Merlin running smoothly on descent

Post by budo »

Dudley, thanks for your explanation of initial approach methods. You gave me great details on what I had been curious about for quite a while. Appreciate it.
I do remember when the Delaware ANG was flying the P-51H and watching them on final with the Merlin Popping. 8)
Budo

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DHenriques_
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Re: Keeping the Merlin running smoothly on descent

Post by DHenriques_ »

budo wrote:Dudley, thanks for your explanation of initial approach methods. You gave me great details on what I had been curious about for quite a while. Appreciate it.
I do remember when the Delaware ANG was flying the P-51H and watching them on final with the Merlin Popping. 8)
Budo
When I was a kid the tower at New Castle was on the other side of the field behind what is now K taxiway. It was over beside the old Zim's Diner on the base. It had an open stairway steel structure that ran up to the top "house" where the tower was. I sat up there many a day with the operators there. This goes all the way back to the 142'nd Jug days.
Memories ! :-))
DH

EnDSchultz
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Re: Keeping the Merlin running smoothly on descent

Post by EnDSchultz »

So if I understand correctly, you'd basically fly a far displaced upwind leg parallel to the runway, then pull a 180 degree turn towards the runway to enter into the downwind?

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DHenriques_
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Re: Keeping the Merlin running smoothly on descent

Post by DHenriques_ »

EnDSchultz wrote:So if I understand correctly, you'd basically fly a far displaced upwind leg parallel to the runway, then pull a 180 degree turn towards the runway to enter into the downwind?
I liked to have the aircraft just enough off to the right or left of the runway (depending on the downwind direction) so I could see it pass under the inner part of my wing. In the Mustang that was right through the guns.
DH

EnDSchultz
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Re: Keeping the Merlin running smoothly on descent

Post by EnDSchultz »

So effectively the opposite of what I said. You want to fly upwind tight in over the field and then do a 180 degree break -away- from it to build distance.

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DHenriques_
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Re: Keeping the Merlin running smoothly on descent

Post by DHenriques_ »

EnDSchultz wrote:So effectively the opposite of what I said. You want to fly upwind tight in over the field and then do a 180 degree break -away- from it to build distance.
Yes. Making it tight (but not too tight) is good for the Mustang. The drag rise in the break helps bring it down to gear speed fast, carrying 20 degrees of flaps increases pattern visibility over the nose (safety) and subsequent more flap equals more power and more power equals less fouling and keeps the engine driving the prop and quicker smoother spool up time if a go around.
DH

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