Thorp Air Command - T18.net

Hello everyone.

I'm Jeff binder. I purchased a thorp t18, 78DW, last month. It's a basic vfr setup and ugly duckling but has plenty of hours left on the 0290. I'm in Terre haute Indiana with the plane located at k3i3 next to the large Khuf. It was a gpu properly converted to -D with crank upgrades etc as noted in the logs. It has a kx170b with the upgraded Mac 1700 faceplate.

Current things I need help with:
On full throttle I lose a few hundred rpm and get a sputter. Pulling back about .5 inch it clears up. It's about 800$ for a rebuilt ma3spa carb although it's difficult to find that specific one for the 0290. Because of that I've thought about throttle body injection like the rotec system. David read from olney Illinois uses is and suggests it. It's about 800$ and seems a better choice for new equipment than an old school carb.

68x68 demuth prop is only giving me 2150 rpm static which is giving me quite a long take off in the little 0290. Prop needs refinished so I've though about putting a better climb prop to help me get out of the smaller airport. Thoughts and opinions very welcome. I think wood would be the best option due to weight.

Passenger ptt is not hooked up. I'm not sure where to attach it.

Trusty tail wheel setup? Heard this will help keep it more stable on take off and roll out. Our airport is pretty bumpy which causes a lot of dancing. With my long take off distance it adds a degree of danger I would like to eliminate. I seem to do perfectly fine on the new smooth runways.

Nag/comm has some loose connections at the back so I need to take it out and make sure the wires are more secure. I have the owners manual but not installation manual telling me which pins go to which wires. That would be helpful.

I would like to add some safety by engine monitor since it currently has poorly operating cht and egt only on 1 cylinder. That being said I know I can get an all in 1 system with autopilot or I could go with a stand alone trutrak. Currently there is a trutrak vizion for sale at 1400$ with harness on vans site. I've also thought about the Gemini since it will replace some old heavy gauges that will most likely be needing service soon anyways.

Since avionics upgrades will not give me resale value I plan on keeping the old panel to put back in for future sale. This plane is most likely a throw away once hours are up as I want to build my own and make it perfect instead of fix all the little issues with someone else's build.

Since I spent a lot amount on the plane I'm enjoying the cheap flying and might not even do any of these upgrades until I start having issues with my current gauges or equipment. I am not he builder so I'll need to lean on you gentlemen to help me with information on taking things apart and how to find service points.

Pictures of the bird

Hi Jeff,
It sounds like we are in about the same boat. I just bought a T-18 to fly while I build.

My first thought on your high power issue is to ask if you are sure the mixture control lever on the carb is hitting both stops. I sometimes warm up engines by leaning them out but occasionally forget to enrich the mixture prior to take off. What I experience when that happens could be described the same way you described what you are seeing.

How do you know your static RPM if the engine will not run consistent at full power?

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

As far as I know it's hitting both stops. It is at the stops of the control arm although I haven't verified that it is at the stops on the carb. I just received my friction lock throttle that I will be installing to replace the horrible veneer throttle. Once I have that open and the air box off the carb I can verify many more things along with setting the stops if they need to be adjusted.

As for warm up, I keep carb heat on to help warm but as per the FBO mechanic out here I leave it full rich. I talked to him about leaning when only idling and he said don't mess with it for fear of safety in forgetting to richen it up. He said a good run up will burn off any fuel that loads when idling. He also says leaning the engine below 5k tends to wear cylinders out faster. He bases that on what he works on and what the owners tell him they do to the engines. So obviously that is not scientific evidence.

Here is one of the tricky parts of the carb issue. It seems to only start occurring after the engine is hot which is why the mechanic (without tearing it down) thinks it is over carb'ed. So on the ground just as it warms up we have performed multiple static checks. 2 people holding the brakes, full throttle. It seems to bounce right around 2150. That is of course with the aircraft tach as well. The last actual static check from an AP was shown 2200. That could either be some decline in performance or maybe the tach is slightly off. Since it's "close enough" I assume that's what the static RPM would be.

Welcome Aboard, Jeff. Sounds like you should have been at Kentucky Dam this weekend. Many of your questions would now be answered. Sounds like the enrichment circuit is cutting in on your carb. This is not a new issue. Static RPM on a fixed pitch prop on a high performance airplane is not going to match a Cherokee. RPM at 7-8 thousand feet should be about 2700 with full throttle. Lycoming says only use Full Rich mixture on Take Off. Lean for taxi and lean on the way up and lean in cruise whatever the altitude is. As for warming the engine with the carb heat on...Whatt! I would only do that if I wanted to be sure the plugs were fouled prior to take off! On warm up, you are warming the oil, not the engine. Trusty tail spring is springier than the leaf steel setup, so I don't think that will help on a rough field.

As an old fighter pilot, passengers do not need to talk on the radio, so skip the PTT.

Above all, have fun and fly safe!

_________________
Bob Highley
N711SH
SN 835
KLAL

lol, I agree on the PTT although the new grips have the button and the wiring is just flopping around. The other issue is I'm still training in it so it's a bother when I'm paying attention to flaring and the tower calls something out. That would be the only other issue. My gf is also finishing her private so it would be helpful on occasion if she grabs a radio call if I'm focusing on a larger busy airport. For that matter it's mostly about making it "complete".

I say using carb heat which sounds like a lot of extra fuel although my carb heat isn't exactly like a certified aircraft carb heat. It's just something that poorly closes off the ram air and pulls from the engine bay up by the manifold. I barely see a drop in rpm. I do this also when it first comes out of the hangar as I taxi it but well before my run up. Similar to how I warm up my race bikes and drag cars. It's minimal time with that on.

I wish I could have made Kentucky dam. David Read told me I needed to go although I'm not legal for another 1 hour in the plane for insurance and I'm not entirely comfortable in the plane. I'm doing good but still not sharp enough to feel comfortable. We went up Saturday morning and the winds changed. When I brought it down the winds were gusting 15 which was tough on a 50ft wide runway over 100ft trees and hangar turbulence. Later those turned to 27kt gusting. Until I get quite a few hours in this I'm playing on the safe side and didn't feel like renting a cessna to fly down to Kentucky dam. Next year there will be no doubt in my mind I'm going.

So is that enrichment circuit something I can adjust or repair or would it be wise to just put the Rotec throttle body on it?

If I can get a better climb prop then I can be off that runway faster and less dancing. Although a previous race mechanic for team kawasaki and 15 year pilot I'm new to purchasing and changing things on planes such as prop size and pitch. I appreciate all the help the community has to offer.

Jeff

Jeff,
I too bought my Thorp because my building project was going much too slow, it's going even slower now. My aircraft has an O290G with D2 cylinders (140HP), with a Great American 68 x 68 wood prop I see 2200 rpm static. I use 800 feet ground roll on take-off, if I use 1 notch of flaps my ground roll is about 600 feet. I always use 1 notch of flaps on a grass runway. I lean very aggressively for taxi, helps prevent fouling the plugs, and the engine will start to stumble with just 2-300 rpm increase, no chance to forget to enrichen for take-off. I also lean when I get to cruise altitude even 2000 feet, engine runs better and uses less fuel. The first upgrade I did was to install a Dynon EMS D-10 engine monitor to replace the 1 cht, 1 egt temp gauge. I would check the tach to see if it is reading correctly, see if your A&P has an optical tach you can use to verify the aircraft tach.

Enjoy

_________________
Bruce Finney
N18JF T-18C #262
Yelm, WA USA

The stops on the carb should always hit before you run out of travel in the cockpit. I set throttle, mixture and prop so there is a minimum 1/8 inch travel remaining in the cockpit after the stops on the components are hit. Although I am not overly familiar with experimental aircraft, the same generally holds true for cabled flight control systems. I set applicable flight controls up a bit tighter but there is always "cushion" between the stop at the surface and the stop in the cockpit.

You cannot hurt an engine at idle by leaning it out. It will either run or die. Leaning is only a potential problem at higher power settings. I have read articles on the subject that suggest that you can't hurt the engine by improper leaning at 75% power although I wouldn't want to experiment with that on my aircraft. I will instead use what Lycoming has to say on the subject: https://www.lycoming.com/sites/default/ ... edures.pdf

Checking the tach is also a very good idea. If your local mechanic doesn't have one you can borrow, you can go to the local radio control hobby store and buy one used on model airplanes and helicopters for about $20 that will get the job done.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

If other people are getting solid performance out of an O290 with a static RMP of about 2,200 I would NOT change the prop. It will only result in slow cruise flight.

Unless you really have a short runway issue that is.

I guess my opinion is that we are choosing and flying a high performance (fast) airplane. So you really want acceptable cruise speeds that allow you to operate safely from the runway of choice. So if the runway is not limiting you, you want to obtain the cruise speed that is "normal" for a Thorp.

And a 68x68 prop is extremely common. So again, I'd stay with the prop and look further into the engine stumble.

Also look for induction leaks.

I am a bit confused how enriching the fuel/air ratio by adding carb heat would help to "warm up" the engine.

Also if you don't get much drop when using carb heat on run up, you may want to look into enhancing the carb heat. You would hate to have carb ice and not have enough heat to get rid of it.

Just my novice rambling thoughts.

KY-Dam was great. Sure wish the winds were not as high on Saturday and as always more thorps would be great. I guess it served its purpose to kick me in the butt and go out and work on my wings!

Ugly Duck, I don't see an ugly Duck there Jeff, That's a Tiger that just needs a little Grooming, a little TLC so to speak, and we are all proud for the new Thorpers!!!!!! Every question you will have along the way to refinement and grooming, wiring, engine questions can be answered Right here, you my friend are in good hands.........Dan

The stumble is from too rich. I can almost guarantee it. Bob is right. The enrichment circuit is the last 1/4 inch or so of throttle. There is nothing you can do about it. It is built into the carb. I strongly suggest you lean aggressively. I lean for takeoff as well since we have density altitude issues out here. Lyc says you cannot hurt a naturally aspirated engine by leaning. The only issue you might run into is it dying due to fuel starvation.
With 1300 hours on my bird, my mechanic says he has never seen a better running engine.
Cubes

Cubes,
In the leaning procedures I linked above they recommend keeping an eye on the temps. In fact, the exact words are: "Careful observation of engine temperature instruments should be practiced to ensure limits specified in Textron Lycoming operator's manual are never exceeded." Additionally, as if saying it in Step 1 wasn't enough, they repeat in Step 6 using different words.

Why would they do that if you can't hurt the engine by leaning?

Jeff J

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

'Cause their lawyers told 'em to. I have operated my Lycoming O-360 with aggressive leaning for over 2800 hrs and have never even come close to the Lycoming operating temp limits. I live and fly in Florida.

_________________
Bob Highley
N711SH
SN 835
KLAL

I'm with Bob. I live where it's a mile high before you even leave the ground, so aggressive leaning is a way of life, but I lean my engine for proper operation no matter where I am. Spark plugs, cylinders/combustion chambers, your fuel bill - all are going to be better with proper leaning.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Lean and watch the temps and you will see. You can't get EGT anywhere near hurting the valves unless you are injected. But you don't have to trust the opinions on this page (you get what you pay for). Try leaning just a touch and see if it doesn't clear up the stumble. A Lycoming should not stumble, so there is an issue. More than likely it is a fuel delivery issue. So your choice is too much or too little. I can tell you that too little fuel (in my experience) does not stumble, it dies. Here's another way to check. Take your bird up to 10K feet without leaning. I bet it stumbles before you get there.
Cubes