800A DC relays are massive.

As Jesse said, this was big stuff in initial/recurrent. Not sure how much info stayed with the crew after that training, but it was well covered where I went.

800A DC relays are massive.

That is effectively what you have with the Battery Relay. The problem is you can't use that path to power the starter since you have 225 Amp current limiters in that circuit. So you need to bypass the current limiters with the Start Relay. It carries 800 amps from the battery bus to the starter. Carrying 800 amps is why the start relay fusing closed is a failure mode trained for.

Here is the electrical schematic for the CJ2+. Much of Cessna's approach has not changed. You will see the Battery Disconnect Relay on the ground side of the battery. That is what lets you fully disconnect the battery from the cockpit, if necessary for a few different failure situations.

Just what I wanted to always be: an electrical engineer

Truthfully I love this stuff. But I need a tutor like BT and Allen, jj, MH,...etc

Riddle me this Batman: When is it possible to have a V1 that is higher than Vr? If so what do you do if you lose an engine before V1?

On an extremely long runway V1 could exceed Vr. It has to do with the somewhat strange definition of V1 (which I’m sure you know). To me in an aircraft that is capable of routinely flying away from an engine failure once I’ve rotated we’re committed to fly.

In my plane I don’t have a single V1 (or V1 point since a piston twin really has no true V1). I have three decision points.

First Vstop. It’s the highest speed at which there is no chance of an overrun even if the brakes don’t work. On a normal 4000’ runway length in my plane it’s about 80. Anything at all unusual that happens before this speed and we’re going to stop.

Second is Vr. Same meaning as it normally has. Rotation speed.

Third is Vgo. It’s the lowest speed that I can be sure I’ll have directional control and be able to fly away from any failure. For me this is blue line with the gear up. After that speed I’m taking any problems into the air to deal with there.

In a piston twin the sequence is
0-Vstop were gonna stop for anything.
Vstop-Vgo were only gonna stop for a major problem. Engine failure, engine fire, loss of control, notion the airplane won’t fly.
After Vgo we’re taking it into the air to deal with in flight.

As you can see these are in the wrong order in a piston plane (or a jet on a short runway) and there is a time where you can’t be sure you can stop but you also probably can’t go. For me the answer is usually to try to stop and accept the overrun and crash at 30-40-50 off the departure end of the runway. The only caveat is if there is something really bad on the departure end that makes and overrun unsurvivable (think KSEZ) then it’ll get briefed before entering the runway and we’re taking any problem after Vstop into the air.

In a jet you’ll generally hit Vgo (the speed where accelerate go can work in the full runway distance available) before you hit Vstop (the speed at which it’s no longer possible to stop in the full runway distance).

If it were me in my own jet it’d go as follows

0-Vgo were gonna stop for anything
Vgo - Vstop / Vr whichever is lower we’re gonna stop for major things
Above Vr /Vstop we’re flying

To me the idea of a single V1 balanced field speed has never made sense. It only works on one length of field and will have you stopping when you can go on fields that are shorter than that and going when you should stop on ones that are longer.

I always thought that Cessna reduced the V1 to match Vr so we didn’t have to think in this situation

Andrew

I flew a V this week (borrowed) for 6.5 hours. It burns so much gas compared to a II that it's not really a practical airplane (for me) for personal usage. It's 50kts faster for an extra 50GPH. OUCH. Awesome airplane but the II really is a sweet spot in the Citation range.

At what altitude?

Curious...how do you “borrow” a jet for 6.5 hours? Truth in Lending, LOA’s, insurance etc. Seems impractical.

What’s the fuel burn and of the V compared to the II. Woulda thought they were close on a per/nm basis.

At what altitude?

Curious...how do you “borrow” a jet for 6.5 hours? Truth in Lending, LOA’s, insurance etc. Seems impractical.

CJ2 at FL450 burns about 700#....total.

Can a CII go to FL430? I only flew it few times but I think I remember that it preferred being in the 30s.