Checking In!

[Av8r_Sed]

You ought to be able to idle much closer to 2000 RPM. A lot depends on the prop. Mine has a clutch so idle is a non-issue now, but once the prop engages around 2400 RPM, it's relatively smooth all the way to full throttle.

What prop, length and number of blades are you running?

[Rmendler]

68" 3-Blade GSC prop.

I must say I am learning a lot about MY Rotax, but not many people here fly them so I have not been able to listen to others engines but to me it sounds like a mechanical backlash in the gearbox..

I also need to rejet, I moved the airplane to high altitude and with the recent heat wave the egt's have been cool and the idle has risen 100rpm's. it's clearly running too rich

[Dave F]

Check your carb needles - s/b on the 2nd notch from bottom for summer.

Under 5000 ASL this should be a good starting point.
Prop pitch will change your EGT as well.

What is your EGT temps at cruise 5800 to 6000 rpm ?
- what colour are your plugs?
-what # plug is in the engine?

Cheers

[Av8r_Sed]

If you haven't done so, you should check/adjust the blade angles on the prop. There are other threads on the forums with advice and reference materials for the GSC prop.

Also, if the plane has been stored outdoors during its lifetime it's possible that one or more of the wooden blades have picked up some moisture, affecting the balance. This happened to a buddy of mine and his fix was to inset and epoxy in a coin on the back of one of the blades to restore balance.

[Rmendler]

I'm going to check the needle position and Jet #'s tomorrow. The plug color is normal, no abnormalities there with the exception it is running a tad rich with a small amount of fouling.

So I took off this afternoon at 3pm, first time she's been flown since moving her to the airport in Tennessee at 2,200ft MSL. The temperature was 66 degrees farenheight, density altitude was 2,000ft. Did a nice, long preflight while I was waiting on my instructor. Started the engine, let it warm up to 140 degree water temp, conducted a runup and back taxied down runway 24. As we were turning around we held on the brakes and throttled it up to 6,000RPM's and everything was great, seemed to run good. We rolled onto the runway and applied full throttle, immedietely the EGT's dropped into the 900's, then the 800's as we lifted off. They came back up to the upper 900's quickly but alas, we had a problem

The engine was making NO power and we were only 80lbs under gross. As we hit 200ft AGL the climb rate was only at 150-200ft per minute and as we turned crosswind we started losing alititude. After a fancy manuever we got ourselves back into the wind and made a midfield landing.

It's time to rejet. Looking back at the fuel totalizer, at 6,300 RPM's we were burning 6.5GPH! If we had not turned back there is no doubt in my mind that we would be in the tree's right now. Not many open landing spots in the high ridges of the Appalachain mountains. A minimum altitude of 4,500MSL must be achieved just to clear the first set of ridges.

I was shaken a bit so I came home, tomorrow I'm going to check the Jet sizes and Idle Jet sizes. I bet they are 165/55 respectively. I think a 155/45 change would be good for the engine. Not sure if I need to mess with the midrange Needle Jet or not, I have no experience with changing these. I suppose just changing its clip location may be enough to fix it?

If I had of flown 2 days ago with the temps in the mid to upper 80's and no wind I think we would have had to make an emergency landing immediately after takeoff. It may not have ended so well.

[Rmendler]

on a lighter note, has anyone tried making a radiator that will fit under the cowling? something that mounts to the gearbox similar to the ultralight radiatiors that Rotax sells? Radiator technology has improved vastly, I have a custom Griffing radiator I had made. It cools a 550HP Chevy LS1 with a 383 Stroker kit and 11:1 compression in a Mazda Miata and it does so very well. Enough that I have to cover it up if the temps get below 50 degrees. It's small too!

Also, I am absolutely sold on a clutch, saw one perform and wow. I can actually pull power back all the way at landing without worrying the propeller is pulling the engine and created a WAY lean situation.

[tommg13780]

From what I've read sofar it sounds like you are flirting with disaster. You stated that your ground runup only produced 6000 RPM's which was telling you that it ain't going to climb. At that point the airplane should have gone back to the hanger for corrections.
6.5 gal/hr is about what a 582 will consume at full throttle.
The most alarming thing going on is taking off with 2 people in an unproven setup that is not producing full power. You need a test pilot and test pilots fly solo.
Prop pitch as suggested by Av8r Sed can have a big influence on EGT temps and of course totally determines full power RPM's.
It almost sounds like the needles may be on top of the plastic slide in the carbs rather that under. That would give the symptoms described.

[tommg13780]

One more thing...... All the information you gathered while flying with your instructor could have and should have been done with that airplane tied to a tree, pickup truck or whatever.
I realize that this formum is intended for positive reinforcement, encouragement and all that sort of stuff but seriously you really need to be a lot more conscious of the risk management side of things.
Fortunately you have an opportunity to make the necessary corrections and get a successful flying program going.

[Rmendler]

Sorry I was unclear.

We ran the engine up to 6,000RPM's. It was running smooth, so we added that extra tad bit of throttle and let of the brakes. The airplane ran at 6,300-6,400RPMS no problem on takeoff and throughout the climb. The only discrepancy we noticed was the cool EGT's which were not apparent in ground testing and what felt like a 35hp J3 cub of an airplane. It has never done this before and has always flown just fine..

We have ran the engine on the ground for over 2 Hours taxiing and sitting still in different wind and weather conditions and found no problems. The engine always started and warmed easily, EGT's always held around 1,000 degrees and the runup always produced between 6,200 and 6,400 depending on the wind factors.

The airplane flew just fine in Virginia at 400ft MSL with 2 people and full fuel, in fact over 590 hours of flying there. We have only had problems since it was moved to a higher field elevation of 2,240FT.

It has been almost 3 months of preperation to make sure this thing would fly and it did, just not very well. I have had 2 mechanics go over everything and it has been given a clean bill of health, including the engine. I think the only change needed is a Jetting change for the altitude and cooler temperatures but I am also going to check prop pitch when I get to the airport later today.

[Dave S]

Richard,

I think checking the prop pitch and comparing it to specifications for the engine/prop combo is a best idea.

I have a hard time thinking that a change in elevation of the airport of use of 2000' would make the difference between a kitfox blasting off like a homesick angel and barely clearing the trees. If 2K of elevation change was that dramatic in terms of performance I think all of us who fly anything would be in deep pigeon pinchings.

Let us know what you find out on the prop pitch....I think that is a very logical next place to troubleshoot this deal.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp