Power Hesitation

[tenten]

Guys of the herks, need your help in this issue:

Is there any book reference, idea, or experience for power stabilization time limit during fast open power-touch & go-?

for I am having some engines(T56-A-15) during fast open power hesitate/lag for a moment (3-4 seconds) then back up with other engines, (hesitation taking place in some cases as momentarily cycling of TIT, TP, and somehow stagnation of fuel).

RPM in some cases hits the 104% then stabilized within the above mentioned time.

Cross-over correction during run-up check of some effected engine found to be 30⁰C cut back.

Flying crew advised to lock the TD and check engine behavior. Done, a little improvement, but the lagging comparing to other engine is persisting.

1-Prop main & standby filter changed.

2-All fuel filters changed.

3-CIP blown out with air.

No improvement.

Is it normal/accepted lagging?

What might be the cause of this?

Is the engine enters the Fuel Topping Range?

Is it an issue of valve housing (sevo/non servo/or age)?

Is it worth to change a valve housing to satisfy a “Fighter Pilot†on a herk?

(In some cases valve housing change improved or solved the lagging).

Season of Touch & Go training is coming; don’t have much valve housing in the stock.

Your inputs will be appreciated.

[tusker]

Hi!! Just for the heck of it!.....did you check the cables tension! I wonder if when you slam the throttles up, it could make enough difference to put you in trouble....Or else, a good Ground run and separate the mech control from the electronic control. Maybe the FCU doesn't like it! I suppose you don't have any throttle split.!.....Climb in the flight deck and get the feel of it!!Well!, there must be a few "hot" active guys on this forum. Keep us up to date on this one....................................John Boy

P.S. I forgot!.you're talking about more than one aircraft with that problem. Is it the same pilot!!!!! LOL!!!

[Steve1300]

Here is what our inspection cards say about this check:

________________________________

Transient Governing Response Check.

(l) Mechanical Governing - With the propeller governor switch in MECH GOV.

advance the throttle from FLIGHT IDLE to TAKE-OFF in four seconds.

RESULT: With steady winds of 10 knots or less, the over-speed

should not exceed 106 percent. The (accurate tachometer)

engine RPM should recover to within 100 (+1 percent)

within 30 seconds from the end of throttle movement.

NOTE: If it has previously been determined that a TAKE-OFF position,

the torque limit is exceeded, use 17,000 inch-pounds torque as

indicated on the tachometer for both governing checks.

(2) Normal Governing - With the propeller governor switch in NORMAL,

advance the throttle from FLIGHT IDLE to TAKE-OFF in four seconds.

With a steady winds of 10 knots or less, the over-speed should not

exceed 104 percent. The (accurate tachometer) engine RPM should

recover to 100 (+1 percent) within 15 seconds from the end of the

throttle movement.

________________________

[pjvr99]

Throttle anticipation. Sounds like valve housing is cr@pping out. Simple

enough ground check .....

Symmetrical engines

TD switches in auto

Prop governing switches in normal

Move throttles to 900°C TIT

Place finger across throttles to mark position

Retard throttles to 700°C

Rapidly move throttles back to 900°C

RPM should stabilize at 100% within 5 secs

You said rpm was going to 104%, so basically the fuel control governor is

coming into the game, too. I get one like that every couple of months

[Lkuest]

I agree with pjvr99 about fuel toppings. If you are hitting that, your power won't increase until the rpm drops. Here's the rub. The throttle anticipation check states that the RPM isn't supposed to increase more than 2% during the check, but another TO states that rpm spikes up to 6% are allowed during throttle movement as long as RPM corrects within the normal amount of time. I personally don't care about a little lag as long as the crew doesn't have directional control problems, but I also know the crew tends to move the throttles a little slower than I do, so they shouldn't have this problem. You may not be able to duplicate this problem as well during a maintenance run because the stagnant air slows the prop down quicker. You might ask if you can go up with the crew during the touch and go's to see exactly how quickly they are moving the throttles and exectly how much the engine is lagging. If everything is within limits and the crew isn't having problems keeping the plane straight, I'd say there isn't a problem. If they are having problems though, the problem is most likely with the prop.

If you are having a shortage of Valve Housings, you might swap them between props and see if the problem follows.

[Herc 308]

Sounds like the Throttle anticipation pot in the valve housing is on it's last leg.

[tusker]

the problem is:....Tenten is saying:....."for I am having some engines(T56-A-15) during fast open power ..." Think about it!! How many Hercs engines are you gonna play around with. Maybe the problem is on the seat behind the control whell!!

[tenten]

Appreciate all the inputs.

Quoting Tusker :

Did you check the cables tension!

Cable tension checked, within the limit, tension regulator including compression and expansion also checked within the range and limits (6 to 7),(0.25.)

The point is, the momentarily lagging appears clearly when slamming the throttle from Flt Idle to T/Off within let’s say 2 sec or less.

Quoting Tusker :

Maybe the FCU doesn't like it.

I agree, one of the Components- FCU, valve housing, tension regulator, ets. doesn't like to be slapped by this manner, - to me I don’t blame a component having a sense of honour -. But with no reference limit I cannot cash it; meanwhile changing costly components for a momentarily lagging hurts me.

Quoting Tusker :

Is it the same pilot!!!!! LOL!!!

No, more than one, but the rest of the more than one got cleared by the one. The…“Fighter Pilotâ€.

Hope you get it.

Quoting Steve1300:

Here is what our inspection cards say about this check:

Transient Governing Response Check.

(l) Mechanical Governing - With the propeller governor switch in MECH GOV.

advance the throttle from FLIGHT IDLE to TAKE-OFF in four seconds.

We haven’t got this type of check in our cards or books, But the statement of how to advance the throttle (from to) in four seconds , this is the one I am looking for, cause no book in our hand states how to push up the throttles in relation to time. (Appreciate if you send a copy of this check from your inspection card as attachment)

Regarding RPM stabilization time(30/15 sec)(mech/normal) our effected engines stabilizing within 3-4 sec.

Quoting pjvr99:

Throttle anticipation. Sounds like valve housing is cr@pping out. Simple enough ground check .....

Done, RPM stabilization time was less than 4 sec.

Quoting pjvr99:

You said rpm was going to 104%, so basically the fuel control governor is coming into the game, too. I get one like that every couple of months.

Yes, pj

Agree on that scenario in which actual RPM cross the threshold and enters the FCU topping range which might be over act or having an earlier setting and start cutting fuel to bring RPM back.

One time I tried to reduce the mechanical rpm to the minimum limit to check the behavior, doesn’t work.

Just a quick question, is there any adjustment in the FCU to delay the setting of fuel topping? only for the sake of isolating the defect.

Quoting Lkuest:

I personally don't care about a little lag as long as the crew doesn't have directional control problems.

That was the last deal with flying crew, but some keep writing in 781 with or without directional control problems.

Quoting Lkuest:

But I also know the crew tends to move the throttles a little slower than I do.

Which crew ground or flying crew?

IF you mean flying crew.

Not at all, for some pilots who loss 2/3 of the runway during the landing and transition to T/off condition, and feeling that the runway is diminishing.

I have been with the flying crew twice during T/Go, when pushing the throttle slowly all things looking good, but some claiming that their limit in pushing up throttles can go up to 1 second from F/I to T/off -which is unfortunately written on our throttle quadrant- .

Quoting Lkuest:

If you are having a shortage of Valve Housings, you might swap them between props and see if the problem follows.

Thanks lkuest. That is my intention for the first in coming defect.