Originally Posted by
sheppey
There is no need to leave the gear down until blue line airspeed is reached although practically speaking it only takes a few seconds to reach blue line speed after lift off providing the aircraft is flown at the right attitude.
An engine failure right on blue line speed will almost certainly result in a rapid airspeed decrease below blue line due to the instant drag of the windmilling propeller. In any case,blue line means best single engine rate of climb and a typical piston light twin will generally still have a positive gradient of climb below that speed but a less rate of climb.
In fact some light twin POH publish a best angle of climb on one engine as well as best rate of climb and the former speed is usually lower than that for best rate. Blue line is not the be all and end all of light twin performance on one engine.
So blue line as a decision point for selecting gear up becomes meaningless - in other words you are fooling yourself.
Once the gear is retracting, the reduction of drag means the aircraft will accelerate faster towards blue line and this is why the gear should be retracted on reaching a positive indication of climb and not wait until blue line speed. . Pilots of these light twins should accept the fact that the certification rules mean there will always is an uncertainty period shortly after lift-off and the sooner the aircraft is allowed to accelerate through those few seconds of uncertainty, the sooner a safe single engine airspeed is attained and the next phase of the take off climb occurs.
The period from liftoff to blueline will obviously occur with the aircraft at a low altitude and over the runway. So if the engine fails the best thing to do is plop it back on the runway. Even if you can't stop by the end of the runway you are in a very survivable situation.
On one thing I am absolutely certain. It is a practical impossible for the average light twin to maintain altitude while retracting the gear and feathering the propeller
and then accelerating to blue line. The pathetic advertised SE climb rates of light twins all of which are only in the 200 to 300 ft/min. can only be obtained at
blueline airspeed, with the gear and flaps up, the cowl flap on the inoperative engine closed and 5 deg of bank into the good engine. Even a small deviation in airspeed, high or low, will wipe out the climb rate. A good example of this is from the PA 31 -350 POH. If the temp is above 30 C you can not fly the normal 106 kn blueline because the operating engine will overtemp. Instead the POH requires you to fly at 110 knots. This 4 knot difference reduces the climb by 50 FPM or 40 % of the available SE climb rate under these conditions.
As was noted by "whats next", most ME students will never see a light twin again as the next ME aircraft they will be in will have transport category performance. For those folks the concept of gear down until a judgement decision is made as to insufficient runway exists has no relevance to what they will be flying for the rest of their career. I would argue the idea that the takeoff had 2 parts with the first part being a mandatory reject and the second part an intent to continue mirrors how large aircraft are flown in philosophy although not in exact detail.
For those ME students of mine that were actually likely to fly light twins I insisted on two extra upper airwork exercises.
The first is SE climb at various airspeed to highlight how important it was to accurately fly at blueline to get the most climb performance. I would set only climb power on the operating engine to simulate the worst case hot day high weight case.
The second, and here I will use the Piper Seminole numbers (VMC 56kt, Vr 75kt, Vyse 88 kn) involves setting up with the gear down and slowing to 70 kts. Full power in applied on both engines and and as the airplane accelerates through 75 (ie Vr) retarding one throttle. The student is to retract the gear identify and feather the failed engine (I will set zero thrust 5 seconds after the student call for the feather) and accelerate to 88kts
without losing altitude. I have yet to meet anybody who can do it. The usual result is my taking control as the airspeed is deteriorating through 70 and the airplane is starting to sink. Even for the good ones who quickly clean up the aircraft find that the aircraft won't accelerate and they soon have to let the aircraft descent in order to stop the aircraft from deaccelerating. Having the aircraft just sit there totally bogged down and going nowhere is a very big eye opener.
The other thing I do is as part of the pretakeoff brief I insist that the student touch each of the controls as he/she is rattling off the drill. Having that muscle memory is extremely valuable when the excrement hits the fan.
A low altitude EFATO in a light twin is a desperate emergency and even after doing everything right you may still have to close both throttles and take your lumps straight ahead. Sadly the real world EFATO's often have a terrible but predictable sequence.
1) Shock freezes the unprepared pilot
2) The aircraft rapidly deaccelerates due to the drag of the windmilling prop and gear
3) The pilot unconsciously raises the nose as the aircraft starts to sink towards the ground
4) The pilot allows the airspeed to drop below VMC and or/stalls and the aircraft rolls over crashing upside down beside the runway.