View Full Version : Don't change tanks before take-off
QDMQDMQDM
28th Apr 2004, 22:11
This may or may not have been a contributory cause of the accident which befell one of the Supercub.org regulars. Whatever the case, it is good advice and, I thought, worth highlighting:
http://www.supercub.org/phpbb2/viewtopic.php?t=3895&postdays=0&postorder=asc&start=0&sid=666cd18c2d389148e15aa468f7b9965d
QDM
IO540
28th Apr 2004, 22:24
I don't know the Supercub at all, but the general idea is that the checklist should be laid out so that you initially startup and taxi out on the less full tank and then (after a period of time during which, unavoidably, the entire volume of fuel in the pipe from that tank must have shifted) you change to the fuller tank and then during the power tests you unavoidably shift the entire volume of fuel in the pipe from that tank.
To do otherwise means you could be taking off with a tank selected, whose delivery has not been verified.
Even if one does a very short taxi before the power checks (too short to check that tank) one should easily use up enough fuel in the power checks to check out the tank used for takeoff. Does this make sense?
I suppose if the power checks were done very quickly...
Mike Cross
28th Apr 2004, 23:06
Doing my last renewal with Irv. Did the preflight, including draining the gascolater (the only drain in the system). The Luscombe has two wing tanks fed via separate taps to a tee piece and thence to the gascolator.
Taxied to the clubhouse, parked and found Irv. Got back in, started, power checks, everything OK, took off. At a height of about 20 feet sudden loss of power. Killed the throttle and landed ahead. Found the engine still running at idle so taxied back. Did the renewal in a borrowed C152. Subsequent ground runs showed no abnormality leading me to suspect that there was a small amount of water lurking in some corner of the tank that found its way into the feed pipe during taxying.
Mike
QDMQDMQDM
28th Apr 2004, 23:15
To do otherwise means you could be taking off with a tank selected, whose delivery has not been verified.
You can't guarantee to verify both tanks on the ground and switching just before take-off makes no sense. Better to find out that a tank isn't supplying at 2000 feet in the cruise than at 200 feet on take-off.
Here at Eggesford I could be airborne in under a minute from start-up and my Lycoming manual discourages ground-running for more than 4 minutes.
QDM
A and C
29th Apr 2004, 08:23
Carb ice !!!!!!!!.
"Monday Morning Quarterback".
Nice, by the way, to see that there exists such a lively Supercub board (from whence my first remark is taken). Nineteen fora dedicated to the PA 18!
QDMQDMQDM
29th Apr 2004, 08:41
Nineteen fora dedicated to the PA 18!
FNG, it's more a religion than an aircraft.
:D
Hallelujah.
QDM
Flyin'Dutch'
29th Apr 2004, 08:43
It all depends on timings but if as he says in the article he did the run-ups and left it running 'a bit longer as I did change tanks, something I would not do in my Mooney' it is may be a bit less likely that fuel starvation due to a feed problem from the tank was a problem.
This would further be supported by the fact that changing the tanks as attempted made no difference.
The way to assess what works best for your regular mount is to change tanks with different power settings and see how long it takes for the engine to start spluttering and how long it takes before it picks up again after resupplying the fuel.
Gladly the guy was OK, shame of the Cub.
FNG,
That is indeed a brilliant site, isn't it.
FD
More of an L4 man myself, but, indeed, Praise Be!
Flyin'Dutch'
29th Apr 2004, 08:52
From the posting that you wrote on 'shredding props by hail', can I take it that you fly one of these fine machines?
FD
IO540
29th Apr 2004, 09:10
FD
This would further be supported by the fact that changing the tanks as attempted made no difference.
What I've read happens occassionally is this:
Assume somebody runs a tank dry (or takes off with an empty tank and that tank is selected; yes, it's been done and I've seen the result) and the engine stops. The pilot does what he's been taught; pump on, switch tanks. You then have to wait some 10-20 secs (there is an FAA certification requirement on this max time in a SEP but it is hardly going to have been checked recently in a typical 30 year old plane) before the fuel from the other tank works its way through the system, and this feel like ages when you are going down at some 1500fpm. So people assume that wasn't the problem, and switch back to the original (empty) tank. Shortly afterwards, the fuel does reach the engine, which briefly restarts, but then stops because the tank now selected is the empty one. Which leads the pilot to assume it cannot be a problem with a particular tank....
Flyin'Dutch'
29th Apr 2004, 09:13
Indeed a very plausible scenario.
Information about fuel management can be gleaned at John Deakin's site.
FD
FD, I occasionally fly a pristine L4 belonging to a friend, and one of these days may get one of my own, but I wasn't in the Cub when I encountered (or, rather, ran away from) the prop-eating hail I referred to elsewhere.
I have only one hour on the Supercub (but a pleasant hour it was). I'd love to try one on floats.
Flyin'Dutch'
29th Apr 2004, 09:35
Jack Brown's in Florida is your man.
Great outfit and superb atmosphere.
Just found a nice Maule for our strip but in the search bumped into a rather nice looking L4.
They are veritable temptresses! May have to give in!
FD
scottish_ppl
30th Apr 2004, 11:03
You can try one (http://www.caledonianseaplanes.co.uk) closer to home than Florida..:ok:
Hoots awa! Does the wee Cubby run on Dalwhinnie?
Thanks for the link, I'll add it to my to-do list (along with the altiports, the gliding, the P 51 rental etc etc etc...)
Flyin'Dutch'
30th Apr 2004, 12:04
Looks a very nice place and the reports are favourable.
Just a PITA that you can not fly to something nearby to go and do 'it'
FD
Mike Cross
30th Apr 2004, 12:11
On a point of order FD:-
Is the correct medical terminology Proctalgia rather than PITA?
Mike
Flyin'Dutch'
30th Apr 2004, 12:30
M,
You are, not entirely correct.
The correct terminology would be proctodynia.
Proctalgia can be used.
I pride myself in use of 'chartermark clear English' to avoid all confusion.
Seems the punters like it that way.
;)
FD
BTW by something nearby I meant somewhere nearby the seaplane base. Nearest is Cumbernauld and that is 45 mins or so in a car.
Tell you what, Doctor FD, lets you and me buy the world's ropiest POS C150 or something for £zilch, fly it direct to Scotland via whatever airspace we can bust on the way, crash it in the lake (sorry, loch) and say "Hi, we're the guys come for the floatplane lesson".
PS: if we get something bigger we can give Pink Aviator a lift back to Scotland while we're at it. If she can't get out of the back seat before the crate sinks, well, life is harsh.