KW,

I wasn't clear (enough).

Cold bucket of water time.....

At Gross Weight (in any PA-31), accelerate-go isn't going to be possible under normal operation.

Here's why:

S/E climb performance is going to be reduced by the extended gear and flaps (if used), and when you retract the gear, the doors are going to reduce performance even more during the retract cycle.

IF you rotate at VYse + 30, MAYBE you'll have enough momentum to climb and remain clear of the surface long enough to get the gear and flaps up -MAYBE. It is very possible that to have enough kinetic energy you will have to exceed the rated speed for your tires (maybe by a lot).

Bottom line: The reason you don't find accelerate-go charts is light twin engine aircraft were not required to demonstrate that level of performance for certification.

As an owner of one, I assume I will be landing straight ahead until gear is up and airspeed is over 100KTs. You should too. If that risk isn't acceptable. You need to raise your sights to a turbine aircraft with adequate performance.

Side note: Based on what you want to do (accelerate & go), you need more HP not less..

One of these, weight limited to 7,000 or 6,200# would meet your accelerate & go requirements with a reasonable runway length and rotation speed.

http://www.wingstream.com/aircraft/turb ... -1753.html
http://www.controller.com/images/contro ... s/1516.pdf

Hi Forrest,

Just last week, I did my semiannual Airbus simulator recurrency training. I had four or five engine failures, fires/explosive failures, all of them, except for one, at the most inopportune time, at V1, or just past it. One was at max take-off weight. I'll tell you what, that is one airplane I need! At max weight and max thrust this baby slides on up at 900 fpm! on one engine. A Navajo can't match an Airbus, but it will hold it's own, assuming you did your "homework" during the flight planning phase. I'll show you how next time. Now I have to slowly lollygag on down to the airport to "practice what I preach".



KW

This accelerate/go issue is only of major importance on a short runway. If that is an issue, fly it well under gross or buy a standard length Navajo with a Panther conversion. It will fly out on one at heavy weights with no problem. Otherwise, just always use long runways. EVERY plane is a trade-off in some way.

http://www.marvgolden.com/downloads/dl/ ... safety.pdf

~~ Mark

Thanks for your input Mark, and an interesting link.



KW

Hi Forrest,

That is not true. Some manufacturers do provide accelerate-go graphs. Below you have two such graphs, plus one engine inoperative take-off climb gradient graph.

KW

Further response to your post Forrest,

At Gross Weight in a PA-31, accelerate-go is not only possible under normal operation, in the hands of a proficient pilot, at decision or just past decision speed, he is expected to continue the take-off. Flaps are not used for normal operation. The landing gear retract cycle is just few seconds, the landing gear doors being parallel to the airflow do not increase the drag much, the open wheel wells create more drag, so this is also a moot point.

Accelerating to Vyse + 30? How about getting a JATO rocket? That would certainly propel one up and away.

More HP? Not necessary. The Piper T-1040's single engine rate of climb is the same as Normally Aspirated Navajo's, so why bother.

Last but not least, if you don't have the confidence that your airplane can continue a take-off on one engine, then landing straight ahead might be the best option for you, indeed.



KW

How about this for single-engine performance.

In May of 1951, the Aero Commander company flew their new aircraft at full maximum takeoff weight from Oklahoma City to Washington, D.C. with one propeller removed, and stowed in the baggage compartment. The record-breaking single-engine flight was such a success that the company found itself in a backorder situation. The first production Twin Commander delivered was the Model 520 with two Lycoming engines. The second production version was the Model 560 and 560A which had a slightly larger cabin and more powerful engines. In 1955, the Air Force was so impressed with the single-engine capability of the 560, that fifteen were ordered, with two for the exclusive use of the then-President Dwight Eisenhower. It was the first civilian aircraft ever approved for Presidential use.

K

You want to accelerate and go, go light.

That's all I'm going to say about that.

Have a great week!

Forrest

Sounds like you need a commander!

Beautiful airplane though the Aero Commander is.

KW

Great week to you as well Forrest.

KW

Here is an optimum technique for a light twin engine airplane departure. It requires longer runway, but provides higher energy, better margin above Vmca, and higher level of safety. I don’t get into this “I believe, I don’t believe, I think, old wife’s tales, etc.”. This is calculated science. You calculate the book performance, then execute it. For this purpose, I will use a Piper Turbo Navajo performance graphs, take-off weight of 6200 lbs., flaps 0, sea level, dry, level runway, wind calm, standard temperature. Vmca in the Navajo is 76 kts. There is no V1 speed concept in the Navajo, but I will use an equivalent speed, and call it a decision speed, to handle an engine failure. For the Navajo, let’s call it 89 kts., well above Vmca. This will also be our rotation speed. Blue Line Speed, Vyse, is 94 kts., only 5 kts. higher than decision/rotation speed. The “window of vulnerability” is a very short six second event, from rotation speed of 89 kts. to Blue Line Speed of 94 kts.

I am fortunate enough to to work as an airline pilot, and as such, I go through all sorts of training you can imagine, including failure management, and 16 hours of simulator time per year. I have to stay sharp and proficient. For living I fly an Airbus, whose performance is substantially better than the Navajo’s, but similar principles apply. As we are dealing with marginal engine out performance to begin with, we want to start with the best performing airplane, at least 300 fpm single engine rate of climb, or better. Besides the Normally Aspirated Navajo, the Beech Baron, Geronimo, and some models of the Aerostar, there are not many airplanes that can do this. Somebody mentioned the Chieftain, with a stated 240 fpm rate of climb. This is insufficient, as we have just given away about 75 fpm of our already marginal roc, as comparing to the NA Navajo.

First I calculate the accelerate-stop distance. It works out to 3100 feet, accelerating to our decision speed of 89 kts. I will add 500 feet as a safety margin. That comes to 3600 feet.

Now I will calculate the accelerate-go distance. Under the above conditions the accelerate-go distance works out to 4600 feet, to cross the far end of the runway at 50 feet, and 94 kts. This 4600 foot runway would be safe for take-off under the given conditions. Shorter runway would not be acceptable. At lighter weights of course, the performance gets better. If you go blindly “I think this runway is long enough” you might be surprised. Let’s assume that we have checked everything else, and are ready for take-off.

We are in position on this 4600 foot runway. Set the runway heading bug, as it might come in handy as a reference heading. Every time I push the throttles up, up to the decision speed, I am ready to pull them right back, STAND on the brakes, and stop within the calculated accelerate-stop distance. You have to be ready. In fact you should outright EXPECT it. It’s a mindset. You won’t be surprised. If everything is normal at decision/rotation speed of 89 kts., I instantly revert to the FLY MODE. I rotate. As the airplane achieves lift-off attitude, we are right at 94 kts., Blue Line Speed, Vyse. Should an engine fail, apply rudder to maintain your bugged runway heading, finesse the stick to maintain Blue Line Speed, at positive rate of climb – retract the landing gear. 50 fpm is good enough for this life saving purpose. 50 or 100 fpm is not much, it’s only half or one graduation up from zero on the VSI. Not much at all, strange… We are not used to retracting the gear at this low vertical speed, and there is a “psychological barrier” trying to prevent us from doing just that. There is a tendency to pull back on the stick, and get on up in a hurry, we don’t have time for this… do we. Don’t, as this will be your last pull-up. Feather the dead prop. Roll the airplane into the good engine. Close the cowl flap on the dead engine. The rate of climb slowly increases to 200, then 300 fpm. Trim it. This is dicey. No room here for mistakes. If you’re proficient, you will handle it. Now cleaned up, the worst is behind us, the Earth is slowly dropping away. Perform the “engine failure during take-off” checklist. In few minutes we’ll be at a thousand feet, autopilot on, and sweating beads!

Now we start thinking again… Runway heading to 1500 feet, that’s only another 500, okay, duh… Then we turn to LUCKY! intersection, climbing to MSA of 2500 feet. If in VMC, and obstructions in sight, we can start turning back towards the departure airport at about 400 to 500 feet, while continuing to climb. Start preparing for the approach, instrument or visual. LG, Life’s Good.

Summarizing it, fly the airplane, retract the gear, feather the prop. That’s all we have to do! The critical period lasts only about 30 seconds. Everything else is beer foam…

That’s how you coax-up a sick angel.

This has to be practiced often in order to maintain proficiency, until you never have any doubt as to the outcome of such a scenario. You might spend your whole life flying, and never encounter such event, but if you’re not ready, it only takes one, single event, to ruin everything.

Departure with flaps is more complicated. You have to accelerate from Vxse to Vyse, while incrementally retracting the flaps. I will use it for training purposes only.

If one is not ready, or not proficient in these procedures, perhaps the safest option during engine failure, even after lift-off, would be to close both throttles, and land straight ahead.

KW

There is no decision speed. You don't "GO" with wheels down and a windmilling engine at 90kts. You NEVER go with wheels down except in situations like Sedona or Catalina imho.

You will never get a positive rate at blueline OEI with wheels down.

Did I somehow misunderstand this post?

If everything is normal at decision speed, I instantly revert to the FLY MODE. I rotate at decision speed of 89 kts., and as the airplane achieves lift-off attitude, we are right at 94 kts., Blue Line Speed, Vyse. Should an engine fail, maintain your bugged runway heading, finesse the stick to maintain Blue Line Speed all along, at positive rate of climb – retract the landing gear.

When you lift-off, you are effectively going up - climbing, maybe at 50 fpm, but climbing nevertheless. Instantly, hit the gear up, then immediately afterwards feather the prop. This has to be done spontaneously, without undue delay.

KW