Vy and Vyse

[UndauntedFlyer]

Here ya go...the answer is in there somewhere
http://forums.flightinfo.com/showthread.php?t=74653

Another great post from MauleSkinner.:beer:

 

[greyhound]

I would first have to ask the following....

Why are you below VXse or VYse after 4000ft of rwy have passed?

The #1 priority after the airplane breaks ground is to let it accelerate to either one of those speeds. Takes 4-5 seconds at the most.

Now,(assuming I'm above those speeds) if I'm at a sea level field on a cool day, I would feather it/ climb to a safe altitude and turn back.

In the seminole with two people and full tanks I've gotten 500 feet per min. rate of climb with a simulated engine failure. (Avg is 300ft/min).Airport was practically at sea level though.

If I was departing from an airport or in conditions that cause DA to be above the aircraft's single-engine service ceiling....then I would go for the grass on the field.

And as for the advantages of having the same #value for VY or VYse?

It's easier on the brain but I believe the real intention when they publish speeds is so the pilots fly the proper attitude and angle of attack that will result in the best rate or angle of climb. The speed they publish coincidently provides the proper attitude required for that situation.

Same with Best glide speed on singles.....It's the speed that puts the wings at the best angle for LD/maX.

They try to trick you with speed values but it's really to put you at a certain pitch.

It's a dirty secret that cessna and piper did not want you to know.

 

[UndauntedFlyer]

In the seminole with two people and full tanks I've gotten 500 feet per min. rate of climb with a simulated engine failure. (Avg is 300ft/min).Airport was practically at sea level though.

Since I am sure you would not have feathered an engine for real for this test while training, you must have been using "simulated" 0-thrust. Never believe the performance results from such tests because you can never really "simulate" zero thrust. In this case unless there were probably some serious up-drafts to help performance that may have given the appearance of 500 FPM climb, it is impossible to outperform the S/E climb chart by that much just because you were maybe 400 pounds below MGW. 300 FPM climb, maybe, but not 500 FPM in the Seminole under those conditions. For accurate performance results do this test with the engine really feathered at 3000 feet AGL. The Seminole will climb about 200 FPM there, so then 300 FPM at SL would be about correct as the POH says for that weight.

 

[greyhound]

That is correct undaunted...We can never really simulate zero thrust exactly.
And we can't always get the airplane in an exact zero side-slip condition.

I did get the 500ft/min on that particular day. Used about 3 degrees bank max, ball 1/2 out. But in a real engine out situation I would not count on replicating those results.

 

[UndauntedFlyer]

That is correct undaunted...We can never really simulate zero thrust exactly.
And we can't always get the airplane in an exact zero side-slip condition.

I did get the 500ft/min on that particular day. Used about 3 degrees bank max, ball 1/2 out. But in a real engine out situation I would not count on replicating those results.

Since real 0-thrust can only be duplicated by an actual feathering of the engine, simulated 0-thrust will always give unreliable performance results. Since the results are guaranteed to be wrong, the simulated 0-thrust test is WORTHLESS. Please don't believe anything from such tests.

If you feather (real 0-thrust) at 3000 feet AGL and get 200 FPM climb, then it will be about 300 FPM at a 3000 feet lower density altitude. That's what can be figured from the POH for a PA-44.

 

[sleddriver71]

I would first have to ask the following....

Why are you below VXse or VYse after 4000ft of rwy have passed?

The #1 priority after the airplane breaks ground is to let it accelerate to either one of those speeds. Takes 4-5 seconds at the most.

Now,(assuming I'm above those speeds) if I'm at a sea level field on a cool day, I would feather it/ climb to a safe altitude and turn back.

In the seminole with two people and full tanks I've gotten 500 feet per min. rate of climb with a simulated engine failure. (Avg is 300ft/min).Airport was practically at sea level though.

If I was departing from an airport or in conditions that cause DA to be above the aircraft's single-engine service ceiling....then I would go for the grass on the field.

And as for the advantages of having the same #value for VY or VYse?

It's easier on the brain but I believe the real intention when they publish speeds is so the pilots fly the proper attitude and angle of attack that will result in the best rate or angle of climb. The speed they publish coincidently provides the proper attitude required for that situation.

Same with Best glide speed on singles.....It's the speed that puts the wings at the best angle for LD/maX.

They try to trick you with speed values but it's really to put you at a certain pitch.

It's a dirty secret that cessna and piper did not want you to know.

That's a good thing to wonder, and you're right, in a normal situation, the airspeed should be at or above Vxse/Vyse. But that's not the point, after all if you're flying a properly maintained and preflighted airplane the engine shouldn't fail in the first place. This is more of a "what do I do if it doesn't go by the book" scenario as often emergencies don't care about "the book." Situations(emergencies) outside of the box do happen and it's important to think about how we are going to deal with them in the best possible manner.

 

[MauleSkinner]

I would first have to ask the following....

Why are you below VXse or VYse after 4000ft of rwy have passed?

I don't actually see where anybody said that 4000 feet of runway had passed...the way I read it, it's simply after liftoff on a 4000-ft runway, with no indication one way or another about how much runway was used to this point.

That's a good thing to wonder, and you're right, in a normal situation, the airspeed should be at or above Vxse/Vyse. But that's not the point, after all if you're flying a properly maintained and preflighted airplane the engine shouldn't fail in the first place. This is more of a "what do I do if it doesn't go by the book" scenario as often emergencies don't care about "the book." Situations(emergencies) outside of the box do happen and it's important to think about how we are going to deal with them in the best possible manner.

...I highlighted the key word here--"shouldn't"...unfortunately, properly maintained and preflighted airplanes DO have engine failures on occasion.

And while you're right, emergencies don't care about the book, the way I read the original 4000-ft runway question, it was asked as a "simple, by-the-book" engine failure (if there is such a thing).

Fly safe!

David

 

[UndauntedFlyer]

Why are you below VXse or VYse after 4000ft of rwy have passed?

Of course normal climb profile in any light twin is Vy to about 1000 feet AGL, and of course Vyse is usually not to far from Vy. (In fact on the Seminole it is the same.) So with an engine failure at 400 feet AGL I think it would be totally normal to see airspeed decay quickly to Vyse or Vxse. That would be a likely situation to be in following an engine failure.

Do you not all agree on this?

So in that case just pitch forward while applying corrective rudder, clean up and feather. Be respectful of Vmc and climb out if you're within the performance envelope.


Comments?

 

[JoaoD]

While Vyse may be the most efficient airspeed for rate once established at that airspeed, it is not always the best airspeed to attain in every situation, at least initially. If you are 5 or 10 knots below Vyse and single engine and lest's say 20 feet off the ground, if you pitch down for Vyse, you will most likely make contact with the ground. In this situation, it is better to initially maintain the slower airspeed (pitching up close to Vmc or stall may be required) instead of pitching down to Vyse. Make sure to immediately (in a controlled fashion of course) add max power (keeping controllability in mind), and clean the airplane up (don't forget zero sideslip - usually half a ball deflection and a few degrees of bank towards the operating engine). Be patient and let the airplane slowly accelerate back towards Vyse.
In regards to the chance of the airplane climbing below Vy or Vyse being 50/50, ummm, there is little to no chance involved. Depending on weight, CG, atmospheric conditions, and pilot technique, the airplane will already be in a condition to climb or not climb and it is up to the PIC to know the current conditions as to whether or not it will climb, it's not chance.

Thats a good point, but Vyse for a prop engine is lower than the normal Vy, so we would not pitch the plane further down, we would actually pitch up to achieve that lower Vyse

Maybe the most reasonable explanation is that Vy and Vyse are so close together that it better to have the standard Vy defined as Vyse

Padpilot -> New item by João