Question about VMC Roll

labbadabba

labbadabba

Pattern Altitude
Joined
Aug 12, 2014
Messages
2,391
Location
Lawrence, KS
Display Name
Display name:
labbadabba
So, below VMC. If you are on a single engine you no longer have the control authority to override the turning moment of the good engine.

What if the good engine is not a full power? i.e., you lost an engine on climb out and the ASI is fast dropping to the blue line, couldn't you just conceivably pull the throttle on the good engine and make a power-off landing?

Wouldn't that be safer than trying to land with one engine making full power?

I fully intend to get my Multi, it's just a question that's been on my mind...
 
I don't know the answer, someone will be along, but in fast airplanes, things happen fast, you need to be up to the task. Remember that as you move up.
 
Yes the idea is to lower the nose and reduce power on the good engine until you regain control. But not much you can do 2-3 seconds after liftoff. I'm doing my CMEL add-on next week I'm hoping my wife doesn't see this video
 
Yes, you can lower the nose and/or pull power on the good engine to prevent a VMC roll before impact. Hitting the ground straight ahead and under control is better than loosing it before hitting and maybe rolling or cartwheeling. Assuming your question is that you are low and it's immediately after takeoff.

Blue line is SE best rate, red line is VMC.
 
I'm getting ready to finish up my ME and just did a simulated Vmc recovery today. You are taught to pull power to idle and nose down to gain airspeed. Once at 10 knots above Vmc, back too full power on the good engine and pitch for blue line. Obviously close to the ground, you can't do much of a pitch down, but pulling the power on the good engine will allow you to maintain directional control and not roll it in.
 
yes vmc lowers when you lower power. all the factors that change vmc are part of the usual stump the dummy questions during the oral portion of the usual ME checkrides.

yes, you gotta lower the nose and manage your speed to maintain controllability at the expense of altitude. in a low altitude scenario in a light piston you're likely going to meet terra firma and need to accept the fact the second engine doesnt make you better off than the single. people who waiver and hesitate in accepting this reality, often end up getting slow and rolled over as they stall with all that power induced yaw, or straight up getting rolled over below vmc while not yet stalled.

but remember, we didnt buy this twin to leave ass or bags behind, right? risk compensation is real.
 
Bobanna said:
Simply, yes. It's the good engine that's going to kill you: Vmc goes down as you reduce power on the running engine -- the trade-off is that you're throwing away the already-anemic climb performance on one engine.
Click to expand...

I’m not a twin person, but a question here. Assuming you reduce power on both sides, and you have room to troubleshoot, how do you tell which engine is dead? Now they are both not producing power and you are headed to the dirt.
 
That’s exactly how you recover from it. Reduce power, lower the angle of attack, increase speed and slowly feed power back in. Clearly, you would need altitude to accomplish this.

The funny thing about multi engine flying is that the light trainers have the worse performance. Heavy piston twins at best will have 300-400 ft/min rate of climb. Twin turboprops start having real single engine performance but that assumes the prop feathers and the crew does everything right. It isn’t until you get to the Part 25 jets where you start having the level of performance where you can lose an engine on the runway and continue the takeoff.
 
labb, if you really want to get into this, here is a video on the impact of power and density altitude on Vmc. It's Part 4 of a really good series on single engine aerodynamics and performance.

 
Yep, that's one reason why when really low and slow, you just chop the other one and ride it out.
 
labbadabba said:
So, below VMC...
What if the good engine is not a full power? i.e., you lost an engine on climb out and the ASI is fast dropping to the blue line, couldn't you just conceivably pull the throttle on the good engine...
Click to expand...
VMC is a Red Line. You shouldn't rotate below it in most if not all airplanes. Blue Line is the most optimum speed under certain specific conditions of weight, configuration, available horsepower, DA and CG, i.e., takeoff and climb. Anything other than those specified lower the optimum speed, so Blue Line is a maximum optimum speed—that's why it's inappropriate for landing. With all that understood, yes, you've nailed what you must do to maintain control before you lose it, but maybe a bit too soon.
 
Greg Bockelman said:
EGT, CHT, Manifold Pressure, Tach. It’s not that hard.
Click to expand...

And that takes seconds.... the 3-5 seconds of the OODA loop to sort it out is deadly. And that is assuming you are on point and actually expecting a failure like we do in training. Fly a few hundred hours and it ends up in the back of your mind. That’s when we become vulnerable.
 
I haven't flown a real twin... yet. My only experience with them is in X-Plane and other sims.

If I recall correctly, I read that when you lose an engine, you don't lose half power/thrust, but more like 80%. Is that correct?

I'd also think that a Vmc roll would happen quicker if you lose the critical engine. yes?
 
redtail said:
I haven't flown a real twin... yet. My only experience with them is in X-Plane and other sims.

If I recall correctly, I read that when you lose an engine, you don't lose half power/thrust, but more like 80%. Is that correct?

I'd also think that a Vmc roll would happen quicker if you lose the critical engine. yes?
Click to expand...

Losing one engine is losing half of your power, but about 75% of your climbing ability.
 
Good thread as I always wanted to ask the question as well...have plenty of twin turbine time coupled to a single output and well versed in power issues when one of them heads south but never a true twin.
 
Saw a video once on a DA42 (can't recall if it was a NG, VI, or whatever) where they were demonstrating engine out on takeoff, and it looked pretty docile, and IIRC they continued climbing.

Any DA42 pilots here who can speak to an engine out on takeoff scenario?
 
LoneAspen said:
Saw a video once on a DA42 (can't recall if it was a NG, VI, or whatever) where they were demonstrating engine out on takeoff, and it looked pretty docile, and IIRC they continued climbing.

Any DA42 pilots here who can speak to an engine out on takeoff scenario?
Click to expand...
Don’t have any specific DA42 experience, but many light twins will climb on one engine if they’re light enough, the density altitude is low enough, and they’re cleaned up quickly enough.
 
Saw the result of this here about 15 years ago.
Hi DA (guessing 7K), well loaded light twin lost one on take-off as they were headed towards high ground.
Pilot chopped the throttles, landed almost straight ahead, everyone walked away.
I thought it was an awesome choice and vowed to remember it.
 
woodchucker said:
I’m not a twin person, but a question here. Assuming you reduce power on both sides, and you have room to troubleshoot, how do you tell which engine is dead? Now they are both not producing power and you are headed to the dirt.
Click to expand...

Without looking at the gauges, push both throttles back in. Whichever way it yaws is the dead engine.
 
BarryCooper said:
Yes the idea is to lower the nose and reduce power on the good engine until you regain control. But not much you can do 2-3 seconds after liftoff. I'm doing my CMEL add-on next week I'm hoping my wife doesn't see this video
Click to expand...
What Video
 
Bellanca_Pilot said:
Dead foot dead engine. No throttle change needed. Unless it a Cessna 337!


Sent from my iPhone using Tapatalk
Click to expand...

The premise was both pulled to idle. Both engines/props are acting as brakes in that scenario. I"m assuming the engine isn't seized because in that case it's easy to tell.
 
I wouldn't let VMC scare you. Know the numbers for the plane your flying, how it behaves on one engine and go from there and then practice, practice, practice to keep your skills up. The common theme coming from folks that have never flown a ME aircraft is that they are twice as likely to kill you if you lose an engine or it just means you'll fly to the scene of the crash after losing one (not saying that about anyone here doing that though... :) ).

I've flown my Travel Air just over 65 hours since February when I picked her up and that included a 15 hour "checkout" requirement from my insurance company, which is way more than what the FAA even requires to get your MEL - maybe they know something there?? My take, don't just jump into a twin without knowing what it's capable of. That becomes really important in my mind, when you start getting into the higher HP variants.

So guess what we did, almost 7 hours of single engine work - SE approaches and landings, SE failures enroute, failures on approach, failures on takeoff and then a long cross country down to Florida and back to Richmond to cover the last 8 hours. After doing all that, I feel pretty comfortable with how my plane will behave on one and can get her cleaned up and trimmed to fly OEI pretty quickly. She has no problem climbing OEI IF the DA is below 7000' (book says 8K SE service ceiling, but I don't trust that number...) - it may be slow, but she'll still climb even at gross weight. The later models have a higher MGW (B95/A, D95A/E95) on the same HP engines, but I would limit myself to 4,000 MGW in those versions as well.

The biggest thing is don't panic if you lose one on takeoff and just fly the plane by the numbers. Even if that means you are still low and need to cut the power to land straight ahead. I was taught and ABS backs this up, to not bring up the gear and start climbing until you hit blue line. Takes me about 3-4 seconds in ground effect to hit that mark then I start the climb, usually at about 1200' per minute at 120 mph, which is 20 mph over blue line.

If you read through all that, thanks! :)

Cheers,
Brian

P.S. I love flying the Travel Air. Lot's of rudder authority and is a delightful platform to hand fly in VMC or IMC (although having a nice STEC autopilot helps a lot in IMC).
 
You must log in or register to reply here.
Back
Top