Couple basic questions

[LewisU_Pilot]

1. Slaved HSI. How exactly does this work?
2. Vsse. Why is this good to know? Say you do encounter an actual situation where you need to shut down an engine. Why does it have to be at or above this speed.
3. Stall warnings. For the piper Seminole there are two electric stall detectors located on the left wing. Why are there two of them? One works when flaps are 0-10? The other 25-40?

 

[Clutch_Cargo]

"How's a posi-track on a Plymouth work?? It juuussssssttttt dooooeeessssss!"

Ummmm... I'd love to help you out here but I am entirely too tired right now... please just consider this a friendly bump.

cc

 

[DrewBlows]

1. Slaved HSI. How exactly does this work?
2. Vsse. Why is this good to know? Say you do encounter an actual situation where you need to shut down an engine. Why does it have to be at or above this speed.
3. Stall warnings. For the piper Seminole there are two electric stall detectors located on the left wing. Why are there two of them? One works when flaps are 0-10? The other 25-40?

1. Solid state electronics (a "flux gate" whatever that means, seriously), it's the same thing that's in you late model caddie (or any car with a digital compass).

2. If you really need to shut down an engine, shut it down! Vsse is the result of instructors in Apaches doing V1 cuts. Not very smart. So, the manufacturers of light twins (namely piper, as a result of bad publicity from the twin comanchee) decided to set a minimum speed to intentually cut an engine.

3. You answered your own question. The Seminole (as well as every other airplane) stalls at a different angle of attach with flaps than without, so you have different lift detectors to determine your stall condition. Not to say that every airplane has seperate lift detectors, but yours does.

 

[User546]

Very well put Drew...

Let me chime in on the Slaved HSI / Flux Gate Compass question.

Back in the tailcone of the aircraft, away from all ferrous metal, is a magnetic compass. The output of this compass is electrically "enhanced" and amplified through a flux gate.

This signal is fed to the HSI to drive the DG portion of the unit. What this means is that the reading is very accurate, not subject to the vagrancies of the regular magnetic compass, and is constantly being corrected for drift.

The "Flux Gate" in particular here is what senses the direction of the magnetic field of the earth and continuously gives that information to the gyro. The gyro will take that information and correct itself when it tries to precess or drift.

Click below for the "Novice Guide to the HSI" and it should answer any and all other questions you have concerning the HSI and components!
http://stoenworks.com/Tutorials/HSI, the complete.html

 

[DrewBlows]

"How's a posi-track on a Plymouth work?? It juuussssssttttt dooooeeessssss!"

"How's an airplane fly?" It just does.

Joe Dirt.

 

[DirtyBeech]

a flux gate, whatever that means, seriously

the earth's magnetic field has these things called lines of flux. one of their useful properties is that when a line of flux crosses a wire a current is induced. a flux gate (which btw looks like the flux capacitor from back to the future) is able to measure these changing currents and interpolate a heading which is then presented to you on the hsi's compass card. there's a little more to it than that, but that's all you really need to know.

consider the angle of attack on your seminole and how it changes when you lower the flaps. you'll probably get your answer right there.

 

[freeflyer14]

and have fun in 33N...

 

[lawfly]

Chiming in on Vsse: I don't think it was V1 cuts in an Apache. Light twins, to my knowledge, don't have a V1 speed, which is a speed calculated before takeoff for existing conditions, notably weight. I mean I did V1 cuts in the Citation, but not in the Seneca. Twin Comanches, I have heard through the years, had a relatively high Vmc. The effects of Vmc can occur at lower speeds as altitude increases in a normally aspirated light twin. Horsepower/thrust output is decreasing with altitude (no turbo) and so is the asymmetric thrust. At some point, effective Vmc and Vs can coincide and that is a bad thing. That aside, I read that Vsse was primarily a safety margin above Vmc, to allow for student reaction time in an un-announced engine fail in the training environment.

V1 is not about a loss of rudder authority and directional control, as is Vmc, although one does have to use the rudder in a V1 cut, but there is adequate rudder authority. V1 is principally about runway length considerations and stopping distances. It is my understanding that in the interest of safety, most instructors/examiners will announce a V1 cut beforehand. In fact, there is a Vmc ground for the CE-500: something like 55 knots in the early takeoff run. But there is no Vmc in the air, as the airplane would stall before it reached Vmc, probably due largely to the relationship of the engines to the aircraft centerline.

 

[CapnVegetto]

But there is no Vmc in the air

There is a Vmc air, it's 4 knots above Vmcg in the Citation, but it is below stall, so we don't care. I'd have to look up the actual numbers, but like I said, we don't care. Every speed you really need to know is marked somewhere in the cockpit.

For an explanation of V1, it's a jet thing. It's the speed at which it is officially safer to continue a takeoff after an emergency rather than abort the takeoff, and it varies with weight, airport elevation, temp, etc. I've never heard of anyone climbing at Vsse in ANYTHING....you always climb at Vyse. In jets, you climb at V2, which is basically the same thing as Vyse in light twins, except once again, it varies a lot with altitude, temp, pressure, weight, etc. Before you go fly, you figure out V1, Vr, V2, Venr and return Vref whenever you fly a jet. You can't just mark a 'blue line' or something on the a/s indicator because when your speeds are higher and you're engines are stronger, the speeds vary much more greatly, and they need to be figured on a leg by leg basis.

 

[tarp]

Law:

Think the author was being funny about V1.

What he was referring to is the desire of overzealous instructors to "simulate" an engine failure on takeoff. Doing this at 100 agl in an Apache, Seminole or Seneca which may be just marginally above Vmc and no where near a Vsse or Vyse speed yet can be conducive to death. (i.e. it feels like a V1 cut in a jet - happening just after the point of no return / useable field)

And I have no basis for the next comment, but I thought it was Beech that created the "Vsse" rather than Piper. LewisU will find that instructors "play" in that area between the redline and the blueline to keep the student thinking about blueline - doing it close to the ground? -let's just say the instructor should not be having an "off" day.