They're probably thinking carb ice. The wet grass is a sign of the dewpoint spread.

Yes. The Continental engine in the C150, esp. the O-240 fitted to some of the Aerobats is notorious for icing up whilst taxying over wet grass.


MJ:ok:

Thanks for the enlightenment :)

The O-200 gets a bad rap for carb ice, which I think is undeserved. Though I have had carb ice in them, it has been no worse than any other engine type. In conditions which are conducive, I'll use carb heat. Otherwise, I never touch it. Carb ice is not a reason for an engine to go from full power to no power suddenly. And, if you have managed to actually get the engine to quit because of carb ice, start looking for a place for a forced landing, 'cause it's too late for carb heat to do any good!

The ice which has caused me instant full engine failures (twice on O-200, and once on O-470) was ice crystals in the gas, because I had not used alcohol in the fuel to dissolve them out. That is just totally random, though an application of full power increases the odds.

The fuel quantity problem is really the focal point of a sudden engine failure in a 150, they are otherwise pretty well bullet proof. I noted the remark of "incorrect dipstick". With due respect, if it is long enough to touch the bottom of the tank, while still emerging from the top, it's the right dipstick. I am not aware of any formally approved dipstick, or marked dimensions for one for any Cessna (other type do have them). So if you're relying on markings of unapproved origin on a home made dipstick, you're playing with fire. I have seen commercially available after market ones for Cessnas, an my experience has been that if you are using the one made for the aircraft model and tank configuration, they are pretty good, but they are still not "approved", leaving the user of the dipstick responsible for the determination of quantity.

If you have anything stuck into the tank, which will touch bottom, and show a wet mark, good for you. Put your thumb and fore finger at the place where it enters the tank filler, and pull it out. If the wet spot is less than a quarter of that distance, buy some fuel before you fly, and buy more accordingly for your planned flight. Anything more complicated than that may be leading you down the garden path, and to a forced landing....

Absolutely !

It appears the OP was lucky to get away with flying with insufficient fuel and his lesson is a good one to hoist in for every pilot.....

I find the after market dippers for the 152/172 to be pessimistic (which is good). I flew a 152 back from somewhere yesterday and dipping the tanks before take off gave me 4 galls per side or 30 litres. I put 40 in before take off and then another 29 to full when I got back. I probably burned around 20 litres on the trip so taking into account unusable fuel it was around 13 litres out on usable fuel when I initially dipped it.

I was indeed thinking carb ice, not for the OP, the one at Wellesborne. Taxi-ing on wet grass will get most engines a good dose of ice in humid air, and at low ( one hopes ) RPM. I have had this with an O-320, and more than once with a Limbach ( aka Volkswagen ) in an SF 25. Now that one is REALLY known for icing up. :-)

Full rich cut
 

Early in my training my instructor was demonstrating touch and goes in a 150.

Wheels on ground, flaps retracted, throttle straight forward, only to completely lose the engine.

Once we'd coasted to a halt it fired straightaway so not icing, he concluded it was a full rich cut, the first he'd seen in 30 years. We were around 3/4 full tanks and the rest of the lesson was fine

Ever since I've been a bit gentle on advancing to full throttle

Don't know whether facts could be similar ?

In my (very limited) experience with (Lycoming) Cessnas and their acceleration pumps, you can make it stumble, but once the extra fuel goes through the engine, it'll roar back to life. I find it a little odd, regardless of engine maker, that it came to a complete stop due to accelerator pump over-rich.

On the other hand, carb ice melts remarkably quickly in a hot cowl with the engine stopped. Especially with Continentals with the carb attached to the sump.

But I have almost no time and I am probably wrong.

If the accelerator pump is U/S, and the pilot jams the throttle open, you can make it quit, but it will do so the instant that the throttle is opened, if it's going to. If you have made an engine quit with rapid application of the throttle, the engine handling is verging on abusive, and the accelerator pump needs maintenance (unless it is one of the rare engines which does not have one).

Grass was dry and piece of paper I jotted down temps is somewhere in the bin.


a/c had been sitting on the grass a couple of hours in outside temp of 24+C. 10ft taxy from grass to hard taxiway.


Wasn't taking any chances and on powercheck left the carb on for a couple of minutes.... just in case.Don't know why just gut feeling maybe

vun fifty driva.
on the marvel schebler carby there is an accelerator pump.
in the linkage is a little triangular plate with 3 holes in it. the holes have different distances between them.
when you push in the throttle the little pump gives a squirt of fuel up into the manifold. how much of a squirt depends which way around the little intervening triangle is positioned.

if the little triangle is set up wrong you will probably get too much of a squirt.

the other option giving not enough squirt would probably be picked up straight away when the carby was being worked on.
too much of a squirt is subtle though. you really only see the way over rich mixture cut out when you push the throttle in suddenly. push it in gently and the engine may flag a little but will keep on running.

I know about this because I encountered it when I reconditioned my carby.
I eventually got it completely right.

I'd suggest that the carby may not be set up quite right. easy circumvention is to just gently increase the power each time. don't slam it to full throttle.

Think I read somewhere that aircraft engines generally do not like abrupt power changes too much, e.g., compared to most car engines. In any case, since then 1-2 seconds is the minimum time I take for going from idle to full power or v/v.