Vy and Vyse

[stlcards]

Does anybody know why and what advantage an airplane would have when Vy and Vyse are the same. For example in the Piper Seminole Vy and Vyse are the same speed, 88kts.

 

[flyboyike]

Well, we know that Vy is that speed at which there is the most excess power available for climbing. On most light twins Vy=Vyse or at least Vy~Vyse, because it is at that speed that there is that excess power, albeit from the only remaining engine.

 

[MauleSkinner]

Does anybody know why and what advantage an airplane would have when Vy and Vyse are the same. For example in the Piper Seminole Vy and Vyse are the same speed, 88kts.

The biggest advantage would be that you don't have to remember as many numbers

Fly safe!

David

 

[sleddriver71]

I think the Seneca II I used to fly had the same Vy and Vyse numbers (89 kias if I remember correctly). I would agree, the biggest advantage is that you don't have to remember as many numbers.

 

[SBD]

Just remember, if you lose an engine below Vy or Vyse good luck. Chances that airplane will still climb is about 50/50.

 

[Metro752]

Just remember, if you lose an engine below Vy or Vyse good luck. Chances that airplane will still climb is about 50/50.

who told you that?

 

[sleddriver71]

Just remember, if you lose an engine below Vy or Vyse good luck. Chances that airplane will still climb is about 50/50.

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.

 

[Tonala2k]

Sleddriver,
Thank you for your input. Very well delivered. You hit a lot of very good points.

As to the original question. I'm sure it is incidental to design and not designed that way. With smaller engines we don't have must thrust in the first place with both engines operating. I'm looking to get check out in a CE-425 Turbo prop. Lose an engine on this bad boy an that's a lot of power loss. Still plenty of excess power, but now where near as much as before. I think that if we really crunched the numbers, true Vy would be slighted different than Vyse, but hey, as it was said before it easier to remember one number, especially when they are so close together.

(Please note, this is opinion only. I have no authority on the matter)
$0.02

 

[Metro752]

you pitch for level flight, not a number, and if you can, get a climb rate after you clean up the airplane, if you can get Vyse, super dooper,

there is no set number since it changes with all variables/conditions

in the seminole its anywhere from 75-80s after you get cleaned up, initially, for level flight, and maybe 100fpm climb

 

[UndauntedFlyer]

Great Post

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.

The above information from Sleddriver is 100% correct and very well said. These are concepts that most multiengine pilots are not taught and do not know. This information can save your life but with some skill involved too. While this concept of pitching to near Vmc can save your life, it can also kill a pilot that doesn't know his airplane. Stall characteristics of the wing is a big factor here. Thanks for posting this information.

 

[MauleSkinner]

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.

Now THAT's one of the best things I've seen in print since I read the "Safety Information" section of Beech POH's...

Know, BEFORE YOU TAKE THE ACTUAL RUNWAY (I think the emphasis is mine...I took this quote out of my Baron Powerpoint presentation), whether you can maintain control and climb out if you lose an engine while the gear is still down. It may be necessary to off-load some weight, or wait for more favorable temperatures.

The rest of the multi-engine flying portion of this document is pretty good, too, btw...I recommend it.

Fly safe!

David

 

[SBD]

" in the seminole its anywhere from 75-80s after you get cleaned up, initially, for level flight, and maybe 100fpm climb," My thoughts exactly. On a hot humid day where you are carrying some weight, the Seminole climbing while under Vyse or Vxse is really a crapshoot. The PIC's skill and knowledge will determine what events will play out. We can all calculate the best Single Engine Climb performance with the charts, but can you honestly tell me that you feel comfortable with that information. There have been times while performing a Vyse demo for students that we couldn't maintain altitude to save our lives.

 

[SBD]

This maybe a little off topic but since we are talking about Vxse and Vyse this might be a good place to ask this. On my MEI FAA ride the DPE asked me this scenario based question. After you rotate on the takeoff you lose an engine on let's say a 4000 foot runway and the only thing beyond the end of the runway is fields and grass. You are below Vxse and Vyse, do you
A) Continue on the climb and try to clean it up, feather, and return for landing?
or
B) Close the throttles and try to plant it straight ahead?

 

[SBD]

Fields grass and trees. Sorry.

 

[MauleSkinner]

This maybe a little off topic but since we are talking about Vxse and Vyse this might be a good place to ask this. On my MEI FAA ride the DPE asked me this scenario based question. After you rotate on the takeoff you lose an engine on let's say a 4000 foot runway and the only thing beyond the end of the runway is fields and grass. You are below Vxse and Vyse, do you
A) Continue on the climb and try to clean it up, feather, and return for landing?
or
B) Close the throttles and try to plant it straight ahead?

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

 

[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.