Minimum acceptable self-launch climb rate

I've had two Rotax 912 seizures in a Pipistrel Sinus.Â* In each case I
was at or below 200' AGL.Â* In both cases I turned back and landed safely
without undue concern other than being extremely ****ed off. In the
first case, the engine seized so quickly that the 6 bolts holding the
prop onto the hub sheared and the prop windmilled like a pinwheel almost
separating from the aircraft.

In the second event, I noticed reduced climb rate, and reduced pitch.Â*
Then the RPM dropped slightly.Â* At that point, again at or below 200'
AGL and still over the runway but too far down to land straight ahead, I
started to turn back.Â* About half way through the turn it threw a rod
through the crank case, filling the cockpit with smoke and covering the
windscreen with oil.Â* I landed on the parallel taxiway.

The root cause for both failures was that Pipistrel replaced the hose
from the oil cooler to the oil pump with one with internal wire bracing
and did make note in the Illustrated Parts Breakdown.Â* When the hoses
were replaced with Rotax recommended hoses at 5 years, the hose in
question, having a tight bend, collapsed when it heated up starving the
engine.Â* The wire braced hose would not have failed that way.

On 4/28/2020 3:56 PM, wrote:
On Tuesday, April 28, 2020 at 10:25:27 AM UTC-7, Eric Greenwell wrote:
wrote on 4/28/2020 8:16 AM:
The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.

My experience is much different than yours. I think self-launch in my ASH26E is
safer than towing or winch, because I am in complete control. There is no chance
miscommunication, no chance of entanglement with a rope or parachute, no need to
fly formation or operate at a very high pitch attitude.

At the places I fly, I can land straight ahead from less than 100' agl, and do a
180 back to the runway over 200' agl - the same numbers I would use for a typical
tow. At 600 fpm climb, that's only 10 seconds of "aw snap!" if the engine stops
between 100' and 200', same as for a tow. If the engine quits (never has), I will
just nose down to keep the speed correct, then use my pre-determined plan for the
situation, same as if I was being towed. I've practiced this at altitude, examined
the IGC file, so I'm confident it would work as well as it would with a tow failure.

I've flown at Minden, Ely, and Parowan many times over 25 years with the 26E, and
never had a problem with handling turbulence on takeoff; I do land as you do in
the often much more turbulent afternoon.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
Hi Eric, your points are all true, and on balance I prefer a motorglider. But just not for the first minute of takeoff. Although I don't feel personally endangered, an engine failure would probably force me to sacrifice my motorglider to preserve my safety. From 200ft, starting nose up at best climb speed (51-54kts), flaps +2 and engine windmilling, I very much doubt I could do a safe 180 in my glider (Ventus 2cxm). I've I've never dared try it, and I've never heard of anyone trying it. In contrast, simulated aerotow failures from 200ft in gliders is practiced as part of standard training. Similarly, a winch failure at any time should be able to be safely handled.


--
Dan, 5J