RobertL18C wrote:
Close, but actually the Seneca V has a Vmca of 66 KIAS and the short field technique has a Vr (technically a lift off speed for a puddle jumper) of 73 KIAS, so meeting the 1.1x requirement.
I never flew the V but only the one and II, on which we did the short field training approx 1990 or so. I’d have to look up the short field procedures on that one, but I recall my instructor to be very clear on this.
RobertL18C wrote:
My PA-30 POH is at home so will compare notes on that. Helpfully the PA-30 POH is paranoid about asymmetric operations (the revised PA-30 POH introduced the FAA concept of Vsse), with full page warnings on there be dragons there, etc
For good reason I suppose. I think this had to do with the FAA insisting on demonstrating VmcA effects in low level, killing a good bunch of people and airplanes in the process.
The PA-30 has a Vmca of 78 KIAS, and you are correct short field take off is Flaps 15 with a lift off between 61 KIAS and 70 KIAS, but then accelerating to 78 KIAS. Flapless has a lift off of 78 KIAS so no safety factor to define Vtoss.
I searched older POH and they show Vmca at 78 KIAS. The Twin Comanche has a strong tendency to want to wheelbarrow, so the design does seems to require lift off around Vmca.
Some years since I flew a Twinkie.
The Seneca V Vmca may be lower than the earlier versions. This is a quirk of the definition of Vmca. The allowed bank of around 3 – 5 degrees towards the live engine relies on horizontal component of lift to improve/lower Vmca (less rudder drag and fuselage drag). Horizontal component of lift is proportional to weight and therefore, counter intuitively, the Seneca V having the highest MAUW has the lowest Vmca, admittedly by only a couple of knots.
RobertL18C wrote:
The Twin Comanche has a strong tendency to want to wheelbarrow, so the design does seems to require lift off around Vmca.
I think there is a mod to get a smaller nosewheel to counter that tendency. Not sure what that does for prop clearance though.
RobertL18C wrote:
Some years since I flew a Twinkie.
It’s on my bucket list to fly or even own one. Won’t happen most probably. And for my low training status I think it would be safer to go for a Seneca anyway, the fuel system of the Twinkie appears to be quite interesting… I felt very comfortable in the Seneca at the time.
And you are right, also the Seneca II has Vr at Vmca of 66 kts, also on short field. I wonder what my FI was on about at the time.
RobertL18C wrote:
This is a quirk of the definition of Vmca.
I think it as much to do with the certification rules which have been augmented over time, while the are generally the same if you include certain assumptions that are not spelled out in the rules. For example the original rules don’t mention weight.
A seneca is a Part 23 aircraft certified in the 60’s and the POH may had bee updated “voluntarily” to keep up with FARs as they were enhanced. A twinkie is a CAR 3 aircraft that probably had its POH updated to reflect more stringent versions of the FAR 23, because they got some pressure to do so because of number of accidents. Some other twins may still just rely on the original CAR 3 definition, especially if they stopped making them in the 50s or 60s.
This is CAR 3 at the end of 1959, I don’t think the concept of Toss existed for this type of aircraft at that time. See pg 27, 3.111. AFAIK This is the last version of CAR 3 before Part 23.
Ted wrote:
I don’t think the concept of Toss existed for this type of aircraft at that time.
It still doesn’t in the US, I had never heard of it and had to Google it. In both twin types I fly Vr is a few knots above Vmca, but well (about 20 kts) below Vyse.
I had the impression VMC also applies on the ground? not sure what delaying rotation VR would offer to save the show as one could also lose control on the ground if their VMCG is high, the only way out is cut power and fly glider above VS 
Some ATO use very high VR for the demo of engine failure after takeoff (as briefed), it’s scary even 20kts above VMCA, especially the slow first climb at +100fpm…
Vmca is minimal control speed in the air, Vmcg is the same on the ground, not taking front wheel steering effect into account.
Vmca is also a minimal speed in worst configuration, CoG full aft and mtow. And most planes don’t flip over when Vmca is reached, they just start to turn. But if ball is not centered, which is easier on a twin running on 1 engine, asymmetrical stall is not very far.
If your twin is light and correctly centered, asymmetrical stall may come first.
No planes don’t normally flip over at Vmca you just can’t stop them turning even with full rudder on the live engine. The way to stop it and gain a but more travel on the live pedal would be to reduce power on the live engine the consequence of that is that if you are still trying to climb you reach stall speed very quickly. Nose down helps but you are now heading towards the ground like you would in a single except that if you have any power on the live engine you are still assymetric and you will be landing with some power on. Better instead to reduce the live engine fully and land as.you would in a single.
Vmcg should be avoided by aborting the take off by closing the throttle at the first sign of ANY problem. Even if that turns out to be as has happened to me, an examiner listening to the controller’s message on the DA42s recorded radio messages facility.
Notice that Vmca is measured under ideal conditions when you’re banked about 5 degrees into good engine. If it happens in any other scenario, Vmca is much higher. 5 degrees makes a huge difference. So don’t take that number to the bank – have some margin.
gallois wrote:
With the Twinkie having such a fan base of support and smaller engines it is quite a bit cheaper to operate than the Seneca for the time being anyway. The counter rotating props PA39? version and the addition of vortex generators makes it a pretty decent go anywhere light twin.
Yea, it is pretty ideal, particularly the turbo normalized version is quite amazing. Huge range, good speed and decent payload. I’ve been a huge fan of this airplane particularly since having watched some of the Pilot und Flugzeug documentaries of what this airplane is capable of. When that particular plane (N7311Y ) came up for sale several time in recent years, my “want it” reflex was huge but in the end, realism prevailed. Yes, it is quite cheap to operate but still twice the cost of my Mooney.
Where it can bite pilots with mediocre currency is the fuel system which is quite complex. Hence for myself I prefer “dumb” systems like the Senecas over the up to 6 tank setups of a C310 or Twinkie (or certain Bonanzas as well for that matter.)
