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power loss on takeoff roll questions

C

csgj

Active Member
Ok
Here is my problem
I have a rv6a o-320 cs prop, 1000hr engine, regular mags. Had no problems for the last 30 hrs since I bought the plane
Flew 500nm last week no problems
Only use av gas
Practicing in the pattern yesterday at my airport. Did about 3 takeoffs and full stops. On the fourth takeoff (full rich,carb heat cold,CHT low 300's,oil temp 200) when I get bout 100 feet, there is this rpm engine drop for a good second and a return of the power but dont think it was back to normal so i aborted the takeoff.
When i taxied back sounded fine, run up with mag check at 2200rpm was fine, (brakes dont let me go full power at run up)
Tried it again and takeoff was the same so I aborted the take off
Sumped the tanks and pulled the gascolator, no debris, obstructions, or h2o.
No leaks in any of the lines that I can see.
Will check the plugs tomorrow
ANy other things to check? Pull the carb?
thanks!
Craig
 
Suspect mag

Sounds like a possible mag issue. I had the same thing happen to me on my instrument check ride in a rental 172. I had to fly 50 nm to pick up the examiner and on the way the engine change pitch a couple of times. During my run-up everything was fine and then on climb out I lost one mag completely.
 
Isolate the mags

I'd suggest on the ground run it up to high power and swap mags, see if one starts cutting out.
 
Mag check

Try a mag check at altitude, that's is where an ignition problem can be detected at the earliest time
Tim
 
How many hours on the mags? Bendix or Slick? Had a friend had power reduction at FT, he found a "B" nut loose just past his fuel selector, and at high demand it was sucking air. The weird thing is that it didn't leak, I would put a wrench on all of the nuts not just look for leaks.

TCM Bendix
Time between overhaul (TBO) is 500 hours or 4 years, whatever comes first. (Since the upcoming of SB643A TCM the ignition harness, The starter vibrator and the ignition switch are also included in these intervals)

Unision/Slick
for all engines with two ignition systems after a time of 500 hours;
for all single ingnition systems after a time of 2 years or 250 hours;
 
What's the life on the spark plugs?

I've seen them check fine on the runup but turn bad under full power. Can you see anything (ie., EGT instruments) that would shed some light on which cylinders - left versus right? That could narrow it down to the specific plug(s).

Dan
 
Make sure mud Daubers havn't clogged your vent lines. Almost brought my dads rv down on his first flight.
 
RPM Drop on Takeoff

Check the Spark Plug Gap--very carefully..!!
Excessive Gap can cause this exact problem at high power settings; and has caused more than one accident on takeoff. Check the NTSB accident database for RV's and you will see.
 
CS prop? As the others have said.... but you might also consider the prop governor and linkage. Had the same issue and a linkage adjustment fixed the issue for me.
 
I might also add.... that overhauling a mag is a not necessarily a prudent thing to do unless it is determined that a complete overhaul is truly needed. It is wise to consider an IRAN of the mags at 500 hrs. Inspect,Repair As Needed. You'll save a boatload of flying units most of the time.
 
Fuel starvation on acceleration??

What was the fuel level? did it do it on both tanks? If one your flop tubes is off you could get this issue. (If you have flop tubes for invert system.):)
 
here is a bunch of things to check.

1. Induction leaks, check the intake tube gasket and rubber hose clamps and hoses for leaks.

2. Spark plugs, all must be within 0.016 -0.018" and checked for resistance, must be below 5000 ohms.

3. If you have plug fouling, I would suggest you change your habbits on the ground and when pulling the power off on downwind and final, you do not need full rich until you go around or do the touch and go. But be disciplined when changing your normal method of operations.

4. Magneto's, when were these last at the Maggie shop?

5. Doing a Mag check at say 1700 r so RPM and leaned out not full rich is the only way to do it. I would suggest you idle at say 1100RPM, lean until the RPM peaks and just starts to drop. Then advance the throttle, to try for 1700RPM which it will most likely be a bit rough, then tweak the mixture just enough to restore power, this will be smooth running but as lean as you can get it. Then do a mag check. This is done by watching the EGT bars on your Engine monitor (which you do have!!!!) to see them all rise together. Go back to both letthem all drop again and then do the other mag. They should all rise together as well.

Suggest you take your iphone and someone to video you doing this just in case you miss something, or we can all tale a look at it if you put it on youtube.

Here is a sample of a LOP in flight mag check at FL130, this is the result you want to see. If you see anything else, there is your sign of trouble.

http://www.youtube.com/watch?v=s155lSZxsKQ&list=UU-KheOmXOz79f5wrOVPOADg&index=1&feature=plcp

Make sure your fuel flow to the carby is free flowing as per spec and that your boost pump works.

Finally again with your EMS being video recorded, do a takeoff run and then reject the takeoff when the problem occurs, upload this so we can all have a look.

If you do not have an EMS, now you are about to go here http://www.dynonavionics.com/docs/D10_intro.html and buy one plus the probe pack. Best investment you can make!

All the best and be careful.
 
Thanks for all of the replies!

Ok, just checked the engine logs, mag points were changed in June '08 at 723 hrs ( not sure if slick or bendix)and spark plugs changed in '09 with 800 hrs
Fuel pump was on at all times
Will check plugs this week
I have a jpi engine monitor and will check egt's this weekend and try to video the results
Will bring these posts to the hangar and make sure all your ideas are checked
Fuel was close to full both tanks, and I don't have any inverted systems
Thanks!
Craig
 
My advice: elicit the help of an experienced mechanic to work through this issue with you.

NTSB reports are full of "lost power immediately after take-off" accidents.
 
Walt said:
My advice: elicit the help of an experienced mechanic to work through this issue with you.

NTSB reports are full of "lost power immediately after take-off" accidents.
Click to expand...

Good advice, as usual, from Walt. Dust off your cheque book and get some professional assistance. The engine is your life support system.
 
fuel pressure (going into the carb) constant on takeoff.if it drops suddenly then it has to be fuel..either starvation or vapour lock.

Frank
 
Could it be the spark plugs after all ?

Pulled the spark plugs which were 200 hrs and 3 yrs old
Lots of carbon deposits and the bottom plugs wet and oily
Changed them with new (put 38 hrs on the plane since I bought it but thought I was leaning the plugs out)
Did mag checks as instructed from u guys, egt rises uniformly and normal,fast taxi to 70 knots normal, sounds strong

Did not take off cause of ifr weather but 2400 rpm with the brakes, leaned it out, mags check fine
So unless some fuel problem just cleared on it's own, the carbon deposits on the plugs could do it?
 
I'm amazed that so many owners will let more than 100 hours go by without checking the spark plugs. My AP and I rotate a set of cleaned and gapped plugs at every oil change. (50 hours) We ALWAYS find at least one plug that has lead deposits, and we lean pretty aggressively. Takes about 15 more minutes in the oil change time and saves much anxiety for 50 hours.
 
woodmanrog said:
I'm amazed that so many owners will let more than 100 hours go by without checking the spark plugs. My AP and I rotate a set of cleaned and gapped plugs at every oil change. (50 hours) We ALWAYS find at least one plug that has lead deposits, and we lean pretty aggressively. Takes about 15 more minutes in the oil change time and saves much anxiety for 50 hours.
Click to expand...

I do the same and also test them with an ohm meter.
 
woodmanrog said:
I'm amazed that so many owners will let more than 100 hours go by without checking the spark plugs. My AP and I rotate a set of cleaned and gapped plugs at every oil change. (50 hours) We ALWAYS find at least one plug that has lead deposits, and we lean pretty aggressively. Takes about 15 more minutes in the oil change time and saves much anxiety for 50 hours.
Click to expand...

Partly why I never run 100LL if I can help it. I still take a peek at the (perfectly clean) automotive sparkplugs every other oil change or so.

Frank
 
Check your carb floats. I have seen this exact problem before caused by leaky floats. There is an ad on the marvel carbs for floats and for casting
 
woodmanrog said:
I'm amazed that so many owners will let more than 100 hours go by without checking the spark plugs. My AP and I rotate a set of cleaned and gapped plugs at every oil change. (50 hours) We ALWAYS find at least one plug that has lead deposits, and we lean pretty aggressively. Takes about 15 more minutes in the oil change time and saves much anxiety for 50 hours.
Click to expand...

And 9GT

EXCELLENT POSTS

You MUST keep your plugs between 0.016 - 0.018" and not beyond 0.020" if you want them working right!

And the Champion plugs are seeming to drift past 5K ohms after a couple of hundred hours.

Here is a high level LOP mag check.....if you do not know EXACTLY what I am doing and why, ask, but this is what a good result looks like :)

This is FL130 and LOP.......RV10 and 36 LPH or 9.53GPH :) ......you can't beat an RV:)

http://www.youtube.com/watch?v=s155lSZxsKQ&list=UU-KheOmXOz79f5wrOVPOADg&index=2&feature=plcp

DB
 
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