Take-off aborted
 

I hired a club a/c at the weekend. On runway, opened throttle to full RPM. RPM didnt get past 2100. Glanced at remaing TODA, gave it a few more seconds, still 2100. Throttle closed. Taxied back in. Spoke to an inst who had a look at agreed RPM was too low for full throttle. Spoke to CFI. "Oh thats normal for that a/c...didnt you see the placard above the RPM guage?". Went back to a/c. Ducked under instrument panel and lo and behold there is a little piece tape saying "ADD 80 to RPM". Nicely obscured under lip of instrument panel (esp. for my height). Felt like a prat, but still glad I did what I did.

Made a mental note to open this up on PPRuNE for discussion as am curious as to opinion of others on this one - so here it is. Is it acceptable for engine guages to have little notes on them saying "dont forget to add X to whatever is shown here"? and should I have launched on the basis acceleration was normal? (my gut answer is still no on this - but other opinions invited)

Club didnt charge me - and were very good about it. The CFI also flew the a/c for a circuit to double check all was okay.

Well, as with everything, it depends. If it's privately owned or only a small number of people fly it, I'd say it's no problem at all, as long as it's consistent. I would say it's still only a minor annoyance if it's flown by a lot of people. I used to be in a group with a Taylorcraft. We knew the replacement tacho was duff but we also knew the airplane. We flew it by engine sound and airspeed and didn't worry too much about what the tacho read in absolute numbers, just what it normally read in climb and cruise and anything that was different from that. You could tell from the engine noise if it was getting close to redline, so that was never really an issue.

However, for a club aircraft that I'd be hiring at a fair market rate, I'd expect everything to work as advertised. And, if it were placarded, I'd expect it to be really obvious so no one would miss it.

Now, as to whether you were right to go or not, only you can decide that. As you're still around to tell the tale, I'd say you made a good decision. Remember that any guage can fail and that, as you get more hours in any particular aircraft (specific one, not just a type), then you'll find yourself flying it more by feel and sound than anything else. When I take off in the Pitts, I know what it should sound like, how it should move, I have no idea what the tacho says as I've never bothered to check. But I'll know instantly if something isn't right.

How's that for a definitive answer, eh? :)
Pitts2112

i think it was right action and there is nothing to shame about it. It was better choice as to takeoff and not be sure about what happend;)

Nice reply - cheers.

The engine sounded normal and everything felt normal which is why I didn't instinctively chop the throttle immediately as a reflex reaction. I just didnt see what I expected to see so consciously and deliberately scrubbed it purely based on the numbers not looking good and completely ignored the physical indications (sound, speed etc) which were normal.

I wonder if my decision would have been different if I flew the a/c day in day out and knew it intimately as you describe with your Pitts. Interesting point....!

Gee,

I wonder that the club would be willing to dispatch the aircraft with an error allowing the engine to rev 80 RPM over the red line if so operated by the unwary pilot.

In Canada the following applies:

"The accuracy of mechanical drag cup type tachometers, for fixed wing propeller driven aircraft, shall be checked on site annually, and be accurate to within the tolerances established by the aircraft manufacturer or, where no tolerance has been specified by the aircraft manufacturer, to within +\- 4% of engine RPM at mid-point of the cruise range."

As tachometers are not generally adjustable, replacement is implied for a non-compliant instrument. The placarded error you report, however, would still comply with this requirement.

That said, reassure yourself for future occurances, by trying the occasional partial power takeoff, when you have lots of runway available. You may be surprised to find that takeoffs with as little as 75% power still seem fairly reasonable. This would be what you would experience at a high altitude airport, or the more common occurance of a sticking exhaust valve, or fouled plugs, on a 4 cylinder engine. When that happens, you'll be just airborne, and it'll startle you in a not so nice way. Yes, you'll be thinking of landing again real soon, but there maybe a lack luster performance circuit ahead of you first...

There are numerous recorded accidents where a sudden partial power loss has happened, the pilot surmised an engine completely failing, and crashed, instead of continuing to fly an at least manageable aircraft.

Cheers, Pilot DAR

Bandit - Out of interest, what aircraft type was this?

It might have been, but it might not. Caution is no bad thing when applied to something in aviation you haven't come across before. I've stayed on the ground loads of times in perfectly good weather, already at the airport, because, when I got there, something just didn't "feel right" about flying that day. Usually have a cup of coffee and a chat with mates when that happens and think about the fuel money I just saved. The airplane'll be there next time I want it.

You do get to know an airplane the more you fly it, and it eventually becomes instinct in the same way your car does. You can immediately tell when something's not right with the way your car is tracking or braking, or a noise the suspension wasn't making yesterday, that kind of thing. Eventually you'll find you don't really need most of the instruments, you're only using them to confirm what you know already by the engine note, the sound of the wind against the fuselage, the feel of the controls, the motion of the aircraft (except holding altitude. I'm rubbish at that!). I didn't get that feeling until I'd had about 30 hours in the same machine, most of it spent in the circuit under all kinds of flight conditions and maneuvers.

Keep flying and making judgements the way you are. You'll slowly and gently add to your experience and stay well alive to carry on doing so well into old age!!

Pitts2112

Whatever the cause or whatever you missed, it was a good decision; nothing broken.
Not a case of having had a coarser propeller fitted, is it?

I wonder if you have given thought to seeing how much space you need to stop and whether you make note of a particular marker to have reached a certain speed by.

PA28-161 Warrior II

I certainly hope so! - thanks and happy landings :ok:

That aircraft presumably has a Lycoming 0-320. I can't believe that its max revs are 2180rpm (2100 + the 80 the tacho was supposed to be under-reading).

Correct observation. The CFI pointed out that you often don't see full RPM until well down the roll / just after rotation. This surprised me as I've always seen a health 2400 RPM in my modest 210hrs (~100on type) fairly rapidly after throttle advance. Comments?

Your airspeed will make a difference to the max RPM you get out of the engine. Max Static RPM is measured with the aircraft stationary and full throttle. On the Pitts, with an AEIOU-360, I can only get about 2400 RPM with John Tempest laying over the tail. In straight and level flight, she'll max out at about 2700 RPM as there's less drag on the prop. But, as you noticed, you may not get max RPM from the start of the takeoff roll, but whatever you do get you should get consistently. If you don't get it one day, time to abort and go have a look, just like you did.

You made the right call, no question. :)

Pitts2112

Ooooooh - Suit You Sir - was he dressed Sir ?, was he ? :E

You certainly did the right thing by not going anywhere till you were happy.

Remember these are old tech instruments and are often more than 5% inaccurate (135rpm at 2700rpm). Car speedos were thought acceptable at 10% error.

The aircraft flight manual will normally give a max static rpm which on a fixed pitch pro is always less than red line max rpm. The test is normally conducted crosswind to reduce the effects of the wind.

Warriors should pull between 2330 and 2430. In reality they normally pull 2200-2400 depending on the instrument. We test the accuracy with a strobe tester through the props if we have any suspect problems.

CS props should obviously reach max rpm static.

Bandit

Thanks for the reply. PA28-161 is my usual choice and I would have thought that even 2180 would seem a little low hence my query.

We live and learn.