Prop Problems

[Mendlerr 4]

I posted this on TeamKitfox but I wanted some opinions here also.  It's a bit of a read.

 

I have a Rotax 582 with 3:1 Gearbox and a GSC 68" Tech III prop mounted on a Kitfox IV.

 

 

Before the tires left the pavement we ran the engine close to 3 hours (probably longer over a few weeks) and did a thorough inspection of everything, we were within CG and Weight limits and the density alititude was only 2,000ft at 66 degrees farenheight. Alot of precaution was taken. So we are trying to figure out why things almost went horribly wrong.

 

We lined up on runway 24 after warming the engine and performing a runup, we accelerated as normal and it felt like full power, we managed to climb at 50-55MPH from runway 24 at Johnson County Airport in Tennessee (elv. 2,240).  That worked well until about 200-300ft AGL.  The engine was at 6,500RPM's, EGT's were steady around 1,100 degrees and then, we stopped climbing, the rate of climb was around 50ft per minute.  Realizing this my instructor and I lowered the nose and attempted to accelerate, it would not.  The speed topped out at about 58mph.  As we turned crosswind we got a bit of a tailwind gust, 5-8kts at most and the aircraft began descending even at full power and holding 50mph indicated.  We immediately commenced a 180 degree turn into the wind and slowly climbed to 500ft AGL, we then did a 270 degree turn and landed midfield back on runway 24 with extreme haste.  We were both shaken up a bit at the total lack of climb power and ability to accelerate in very unforgiving terrain.

 

The first inclination was that the carbs were jetted wrong.  I checked and we had 170 main jets and 55 idle jets, the needle jet was on its lowest (richest) setting.  I backed the needle jet back to setting 3 to lean it out a bit.  I have since ordered a 160 main jet and 45 idle jets to give a try but they will not be here until friday.

 

The second inclination was to check prop pitch.  I checked it and it was at 18 degrees.  GSC recommends 14 degrees for my setup.  I just finished performing another static check and at full throttle the engine turns 6,425 RPM's which is a tad high according to GSC.  I reset the blade pitch to 19 degree's thinking it would reduce static RPM's to GSC's recommended 6,200 RPM, it did not, in fact we saw a small increase to around 6,500 RPM's static.  This is puzzling, so I called GSC and they told me to try 14 degrees.  It may be possible that we stalled the prop blades trying to turn them at such a high degree of pitch and trying to climb (although very unlikely).  Tomorrow I am going to reset the pitch angle to 14 degree's and see what happens but I feel our static RPM will want to overrev like crazy.

 

The third possibility is that our tach reading is way off, I'm attempting to get my hands on a prop tach to double check our tach readings.  Hopefully I can do this tomorrow.

 

I'm looking for suggestions, advice, experience or any helpful information regarding this issue.  The airplane runs awesome on the ground, makes power, enough so you can hold the aircraft level on the ramp at full power without much effort.  I just don't understand why it felt like we lost power on the takeoff with the RPM's around 6,500 and the EGT's normal.

Edited 27 May 2013 by RMendler

[birddog486 21]

Sounds to me If you had full power at takeoff 6500rpm give or take, and during the climb you stopped climbing, most likely you have a fuel delivery problem. It takes a couple minutes to suck down the header tank, thats why it doesnt happen until your a couple hundred feet off the ground.

 

Pull the gas line off at the fuel pump and see how fast it will gravity feed. Then I'd be looking at all the filters and finger strainers first before messing with the carbs to much.

[akflyer 1427]

1)  Did you loose RPM during the flight?

2)  What Tach do you have?

3)  If you were at 6500 static, then you would have or should have been over reving once you hit about 20-30 MPH.

4)  That do the plugs look like?  with 170s I am going to bet they are nice and black.  170 is what I run when it is -30 outside.  I use 165 in the summer temps about 20 degrees at sea level.

[birddog486 21]

I'm going to check the prop pitch but I don't feel like it's going to be a problem. It flew fine a few months ago when it was last flown, seemed to climb around 500-700FPM and cruised at 80MPH. I can't it's too far off.

 

I saw you posted this earlier on the other forum, thats why I'd start with the fuel delivery.

[akflyer 1427]

I am confused.. if its fuel delivery, then there would have been a significant drop in RPM... Did the RPM hold at 6500 yet you suddenly stopped climbing and lost forward speed even with it turning 6500 still?

 

I had this issue once.. down drafts and micro bursts can be quite the bitch!  I took off from a 6000' long lake with my cousin in the plane, take off was normal, climb was around 500 FPM till I got over the far end of the lake.  We were at about 500' with the engine turning full RPM when we started dropping at 600 fpm hanging onto a 50-55 MPH airspeed.  I slipped it between the powerlines and the trees on about a 60 deg bank trying to get aligned with the highway.  within seconds we were over the highway at about 10' off the road looking at the headlights of a semi truck 300 yards off.  I got to the edge of the down draft / micro burst about 80 yards from the semi as smoke rolled off his tires, I climbed out and cleared the trailer by about 20'... It took us about 5 minutes before we even looked at eachother and started giggling like little school girls... you know, that nervous laughter when you know you were seconds from death but you cheated the grim reaper yet again...

 

Since that day, if the wind is blowing straight down that lake, I will turn out well before I hit the end of the lake.

[Av8r3400 1178]

First, foremost above all: answer Leni's tach question.

If you are running an analog, needle tach, assume it is not accurate. Get a tiny tach emediately for a cross check.

[lv2plyguitar 172]

If the engine is running normal at all levels it sounds to me like some characteristics with the airflow over the wing.  Like Leni indicated something with the air.  I found out the other day that even an AVID flying slightly above and in front of my AVID can be catastrophic to lift.

[Mendlerr 4]

So here is the update.  I did not read everything posted, just skimmed it, I will go back and read it later.

 

I have not changed anything except for the prop pitch.  I've been on the phone with GSC trying to understand why the Tach shows 6,400 RPM's static with 18 degrees of pitch.  We attempted to get a working prop tach, that was unsuccessful.  I have one but I cannot find batteries for it, it uses an odd watch battery no one seems to make anymore. 

 

So I have tried every pitch from 12-23 degrees over the past couple days just for a good self-taught schooling in prop pitch.  The prop seems to really like 19 degrees, it holds dead on 6,200 RPM static.  I have not had a chance to fly it though.  At full throttle on the ground the EGT's are holding at 1,000/1,075 respectively with the fuel pump off.  I'm not going to Rejet until I am positive my tach is correct, it is a Rotax OEM analog tach.  Then I am going to check the pressure coming from the fuel pump.  When you disconnect the line on the fuel pressure regulator the fuel ah flows like a river until you reattatch it or turn the fuel off.

 

Before the next flight I am going to put fresh fuel in the tanks and replace the spark plugs.

 

I did notice a small amount of trash in the fuel filter behind the seats, its a clear glass filter, but it was what I feel to be an insignificant amount.  If  I knew what size it was I would go ahead and order a replacement but I'll have to remove it and check the thread pitch.

 

There is also the fact that I do not like or trust this GSC prop.  It appears it may have been slightly overtorqued by the previous owner.  I cannot fit a 10 thousanths feeler gauge in between the hubs all the way around, a 12 thousanths fit okay though.  I do not like the adjustment or the fact that it doesn't seem to balance out well.  The plane will not idle below 3,000 unless I set the prop pitch to 12 degrees and at that pitch the engine immediately wants to overrev as soon as you add power

Edited 31 May 2013 by RMendler

[akflyer 1427]

#1 #1 #1  I would bet that your tach, just like every other rotax analog is atleast 400 RPM high.. So when you think your turning 6400 your really lucky to turn 6000.  TINY TACH.. Just about any motorsports / ATV place should have them or you can order online from a million places.  The LOW egts and black plugs are screaming that your over pitched and lugging the crapola out of the engine.

 

I would not suspect ANYTHING other than the tach at this point.  If the engine is not coughing, spitting or sputtering, the fuel flow is fine, other than the jets are a bit rich, but should not be enough to really make it blubber, just burn a little extra gas.

 

I would bet that you are running WAY low on the RPM (I have seen the rotax tach 4-800 RPM off) and it always is in favor of showing more RPM than your actually turning.  That is normally the dead givaway when guy say it takes 700' to get off the ground and it wont climb.. well, thats because your in the 45-50 HP range

 

[Av8r3400 1178]

+2 for Leni's comment.

 

Tiny Tach

 

Link #1

 

Link #2

[Mendlerr 4]

Okay guys I feel real F***** stupid.

 

I took another look at my engine and the panel and I noticed a red wire wrapped around one of the spark plug wires.  I immediately realized it was a digital tach.  So I started looking around and I found a freakin Tiny Tach already installed.  It's underneath my panel facing down, I will have to unscrew it and move it to actually be able to read it.  It's definitely not accessible but I do have it.  I can't believe I didn't find it earlier.  It looks like a relay or something and why they would face it upside down and behind the dash I do not know

Edited 31 May 2013 by RMendler

[akflyer 1427]

Make sure you wrap the lead around BOTH plug wires on the same cylinder so you can do a mag check.  Now that you know you have it, it will be easy to compare readings and see what your RPM actually is.  If the rotax tach is even close I will be AMAZED!

[Mendlerr 4]

So here are my results, 1 hour of engine running and the Rotax Tach and the Tiny Tach were only 50 RPM's off throughout the powerband except for 5,000 RPM's, there was about a 100RPM discrepancy at 5k.  At full throttle both tachs read around 6,200.  So it's not too horribly off, you can hardly read 50RPMs on the Rotax Tach anyway.

 

EGT's still hold at 1,050 and 1,075 at WOT and 6,200 RPM's.  I did notice that at certain RPM's in the power band the two EGT's temp difference gets a little large, close to 75 degrees off but it is only momentary, then they go back to being 25 degrees off or so.

 

I pulled the spark plugs and they look fine.  A little ashy light grey but from what I understand that is perfect.  1 of the plugs had a small amount of buildup but nothing to be concerned about.  FYI they are NGK part # BR8ES and they are gapped to about .018

 

I also replaced the fuel regulator, as I noticed a very small amount of fuel leaking from the regulator when the engine was warm.  The seal was expanding a little and allowing a small amount of fuel to escape from the adjustment knob, not enough to affect flight though.  Just good measure to replace it.

 

There is a an inline fuel filter behind the seats, it has some trash in it.  From what I can tell it is insignificant but I suppose there could be something plugging it up.  When I burn the fuel out of the wing tank I will replace the filter, they have them at the local O'Reilly's.

Edited 31 May 2013 by RMendler

[akflyer 1427]

gap the plugs at .016 max.  The ducati ignition does not like the larger gaps.  If you start at .018 and they wear a little bit, your asking for too much out of the ignition system.

 

I still never saw an answer to... did you loose power and RPM when it started sinking or did you just start sinking with the engine cranking out full RPM

 

You must have the ONE AND ONLY rotax tach that is that accurate.  Pull it out and send it to a museum to preserve.  Hell you may even be eligible for a guinness world record with that one

 

[Mendlerr 4]

gap the plugs at .016 max.  The ducati ignition does not like the larger gaps.  If you start at .018 and they wear a little bit, your asking for too much out of the ignition system.

 

I still never saw an answer to... did you loose power and RPM when it started sinking or did you just start sinking with the engine cranking out full RPM

 

You must have the ONE AND ONLY rotax tach that is that accurate.  Pull it out and send it to a museum to preserve.  Hell you may even be eligible for a guinness world record with that one

 

 

From what I hear this is extremely unusual but believe me, I started the engine and it took a second for the Tiny Tach to catch up but it was pretty accurate, I was expecting a huge difference.  I ran the engine at 3/4/5/6k RPM's then WOT.  I came back, shut down and let it cool down, went out and did it again.  Same results!

 

Then I got to watch a $20,000 RC Twin Turbine Jet smack the runway at about 200MPH.  That was fun, I feel bad for the fellow flying it, it was his first flight with a huge 2 year long project to build this thing but man, he had more pieces on the runway then when he bought the kit.  It came down vertical from 300ft or so at full throttle on a couple of $5,000 jet engines.  You could actually here the engines hit the nose cone on impact and you could hear them flying apart as they spooled down.

 

Oh and we maintained full 6,500-6,600RPM throughout the whole takeoff.  We just could not climb or accelerate.  There is no doubt that where my airplane is based is notorious for hard downdrafts and crazy ridge wind, but there were 5 people watching us on the ground and they did not note anything unusual.  About 13kt winds coming from the N and NW.

 

I will definitely install new plugs and gap them to .016 if you feel that will help.  I can understand why it would.

Edited 31 May 2013 by RMendler

[Mendlerr 4]

I just called IVO to ask why I cannot use the Ultralight IFA on the 3:1 ratio gearbox.

 

They said I could, but there is not guarentee it will be safe.

 

The problem lies in the max torque value of the ultralight hub, when the 3:1 gearbox winds up it creates enough inertia to overcome the max torque on the bolts of the ultralight hub, this causes the blade roots to twist and flex.  It hasn't happened to all of them but it has happened to atleast one, so they cannot recommend the ultralight prop on the high ratio gearboxes, even the 3.47.  If the root twist too much then the blade will seperate (I'm assuming) just like the GSC props if they are overtorqued.  He did not get into details of actual failures but said they have happened.

 

He also told me that the Medium 2 Blade should produce the same climb, if not better, then the largest ultralight 3-blade prop but he could not give me exact numbers.  A 72-74" 2-Blade Medium would be my best match, according to IVO.  He actually recommended I switch to a 3.47 gearbox and a 66-68" 3-Blade Medium for best performance all around but we are talking big money then.  To turn the large medium smoothly requires an RK400 clutch which adds roughly $600 to the already high price.

Edited 31 May 2013 by RMendler

[akflyer 1427]

The original smooth flanged prop hubs from IVO had an issue with the 3:1 gears and what they thought was some sort or harmonics that caused some movement in the blade roots.  The new knerled flange faces bite into the blades and I do not know of any issues since then.  I run 3:1 gears and the ultralight 3 blade and have never seen the SS tape crack to show blade movement.  I even replaced the SS tape on the roots with aluminum tape and they never cracked.  almost 400 hrs now and I have not had any issues with blade movement on the ultralight prop at 3:1

 

I have done a few test flights on turbine RC jets.  Lots of fun, but it does get spendy in a hurry!  If I had the money right now that I had in RC planes, I could go buy a nice 180 on new floats   oh well, a guy can never have too many hobbies right?? 

 

I am going to now put money on the down draft theory.. if the engine never lost power, the chances of "stalling" a blade are damn near zero.  The chances of a down draft and weird weather phenomenon... alot higher!

 

 

[Mendlerr 4]

Weird, my dad got caught in a downdraft a few miles away near Grandfather Mountain (ELV 5,945FT) where I actually live.  This was about 15 years ago before he passed.  He was in a Piper Seneca II (light twin with 2 IO-550's) he almost did not make it out, it pushed the airplane down fast but fotunately he got away from it by shear luck. 

 

That would be very strange if we were in a downdraft but I suppose it's not unheard of.  Today was calm, dead calm, and hot, almost 93 degrees on the tarmac, at about 3pm the windsock started whipping around doing 180's at about 10-15kts.  It's been doing this for a few days now and it's kind of strange.  Severe wind changes and 10-25kts of wind out of nowhere

[akflyer 1427]

The incident I described on the micro burst was just like that.  Dead calm.. I mean DEAD calm, the sun pouring in through the skylight, damn near about to fall asleep.  I had not hit a bump or had to touch the stick in over an hour.. then it all broke loose with no indication from anything other than the bottom dropped out.  Scared the ever loving crud outta me!!!  there was not a cloud in sight, no dirt blowing off the mountain ridges, NOTHING.

 

un-predictable winds out of nowhere... me thinks we could be narrowing down the issues a bit here.  Not saying its the absolute 100% only thing that could have happened, but.. it is very highly plausible.  Had you come back saying that you lost, or gained a ton of RPM when this event happened it would have us (me) looking else where, however...

 

For the prop stall theory to work, the blades would have had to totaly unload, thus giving you a sudden increase in RPM.  The blades would have loaded back up when you lowered the nose, etc and things would ahve been just peachy then except for your tidy whities (or now un-tidy whities).

 

Fuel flow issue.. the engine would have surged, sputtered, etc..

 

Depature stall senario when / if the AOA got too high.. not even thinking thats what could have happened, HOWEVER, if it did, or if the onset to the stall was recognised and the nose lowered, then as soon as you lowered the AOA your wing was happy again and you would have flown out of it no problem.

 

Accelerated stall.. You would have been in one hell of a bank and the problem would not be a mystery to you..

 

I dont know about yours, but in the avids and kitfoxes I have flown, a stall is NOT a surprise event.  The plane tells you 100 times it does not like where you have put it and you should lower the nose LONG before the actual break that you have to FORCE the plane into a full stall.  also the AOA at full power is so stupid that again, it would not be a mystery to you as to why you were falling out of the sky..

 

I know I am rambling on here, but I am working out possible senarios out loud and not really coming up with a smoking gun other than a possible down draft / micro burst.

 

Anyone else with any bright ideas to monday morning quarter back this event??

 

[Mendlerr 4]

Well we have mechanically eliminated many issues now.

 

The prop pitch was INCORRECT, but not by much and it has been corrected.  Fuel flow is just fine, checked it today.  I don't think the blades stalled after talking with GSC and testing the prop up to 23 degrees, it pulled HARD but would not go over 4,800RPM WOT.

 

Do any of you 582 guys run the fuel pump on takeoff?  I notice with the fuel pump on, the RPM doesn't really dip but I notice a slight audible change and the fuel burn goes from between 1.2-1.4GPH to 1.6-1.7GPH sitting still.  Should I use the fuel pump on every takeoff?  The takeoff checklist I have does not include the fuel pump being turned on, only for starting and when the wing tanks run out but this is common on other aircraft..

Edited 31 May 2013 by RMendler

[akflyer 1427]

I have an electric boost / back up pump on mine.   I will turn on the master, hit the pump till it pressures up, shut it off, give it a few squirts of primer, then hit the key.  I never run the boost pump inflight or on take off.  I dont see any RPM difference with it on or off, and a slight increase from 6.9 GPH on take off to 7.1 with the boost pump on. 

 

A buddy had a MK IV extended speed wing that handled great, but take off and climb pretty much sucked.  I put my old ground adjust IVO ultralight 3 blade on it and it woke it up nicely!  it took it from 152 at gross performance to off the ground in 100-150' and climbing hard.  I loved the way that plane flew!  And that was just a ground adjustable.  The engine ran and idles MUCH smoother also!

 

[Mendlerr 4]

Good information, very informative.  My instructor insisted we use the fuel pump to be safe on the first takeoff, I'm thinking this may have been a bad idea and led to the unusally low EGT's if the fuel pressure regulator was not functioning properly.

[Av8r_Sed 82]

Ditto what Leni said on the use of the electric fuel pump.

You've mentioned you've got a fuel pressure regulator installed. I'm not sure why this is needed in your fuel system unless the boost pump pressure is too high. My boost pump pressure is 3-5 psi if I recall correctly. In any case, the regulator may be playing a role in your fuel flow fluctuations.

[Mendlerr 4]

I took the fuel pressure regulator off and installed a piece of 1/4 fuel hose.  I started the engine and then turned on the fuel pump without the regulator.  I got an immediate change in noise from the engine and a drop in RPM and an increase of about .8 GPH fuel burn.  No apparent change in EGT's or CHT's.

 

I then re-intalled the new FPR and did the same test, no change in noise or drop in RPM, a slight increase in fuel burn of .1-.2 GPH and the engine ran smoother.

 

I think the pump is moving too much fuel, but I cannot get in to read the part numbers off the pump, it is encapsolated in a custom aluminum heat shield on the firewall

[Av8r_Sed 82]

What are you using to measure fuel flow? The common meters are notoriously unreliable and subject to installation errors especially in our ~5 gal/hour flow rates. Pressure pulses from a different type fuel pump could easily upset the measurements. These meters are great for measuring relative differences when playing with small throttle changes or mixture changes (if you have controllable mixture) but I wouldn't believe the absolute numbers without a good calibration and lots of flight experience with the particular installation.

Any fuel pressure between 3 and 6 psi delivered to the carb should keep the float bowl full and allow the float needle valve to regulate the fuel level. If the pressure gets too high, fuel can lift the float valve and cause rich running plus spilling fuel from the overflow. To low a pressure would allow the float bowl levels to drop and show signs of fuel starvation.

You want to be sure the fuel system can deliver more than sufficient fuel in any flight attitude. Have you done a gravity feed fuel test on this plane yet?