Thorp Air Command - T18.net

I lean the RED ROCKET very aggressively on the ground . Push the mixture up as I take the runway and start to lean about 1000 AGL . Since day one the CYL temps have not been above 275 and the EGT has not exceeded 1275 . CYL/EGT likes to rest around 250/1250 . I think these are the temps that Dan advertises also ?

RB
SHAZAM

Oh goodness! These responses are all great. I'm glad I have chosen to become part of this community. No multi quote so I'll try to get on each of these.

Bfinney: 800ft ground roll on your 68x68? I'm looking at about half runway length on a 3400ft runway with my 68x68 and 140mph@2500 rpm. I would love to have an 800ft ground roll. Maybe I need to clean up some things on the airplane first. I'm also new to the tail dragger and not real efficient on my take off roll. I'm slow to get the tail up and not as smooth going down the bumpy runway.

Jeff J: I just received my new friction lock throttle so when I install that I will double check the stops and set with stops hitting before the end in the cockpit. Thanks for the tip and the article!

Flyingfool: With how I've progressed in learning this plane I think I'm ok with the 68x68 now. It was just a little further than I was comfortable at first. I checked for intake leaks as the AP instructed me to do at first. As for the carb heat I guess it might not work as well as what we do with race bikes. Normally on start up we idle it slightly higher with a rich condition until the EGT starts to come up. Then it's removed and leaned back as normal. I guess I might have made it sound like I was letting it idle for a long time with carb heat but that's not the case. The builder did not do a great job at the carb heat and I will be fixing it this winter.

Dan: Great to know! I appreciate all the knowledge everyone worked hard to gather. It does need some TLC but myself and the mrs plan on taking care of it this winter when it gets too ugly to fly.

James: That's helpful to know. I'll probably still change some things up or at the throttle body injection so I can get the most out of the engine as I don't like the rich stumble on climb out. I'll try taking it up high and see what it does. I also have a handheld dual wideband that I was going to use in order to check what is going on. What EGT are you seeing? When I flew it home at 4500 feet I had it leaned back and saw 1400* F on the EGT. I'm not sure how accurate the EGT gauge on this plane is. I'm also not sure what proper EGT is for aviation. I'm used to turbo charged car engine egt numbers. What is a good egt temp to run?

As of this moment I have exactly zero time in a Thorp but I put in around 350 hours behind a normally aspirated aircraft engines THIS YEAR and it is easy to over temp them if you push them. Loaded at or above gross climbing about 25 ft or less a minute at 1,000' MSL will do it in pretty short order on an 80 degree day if you lean, gets pretty hot even if you don't. I doubt very few here actually push their airplanes at all...no reason to, even so, I don't think it is right to say you can't hurt an engine by leaning unless there is documentation that can be sourced. Someone posted they lean aggressively because they are at 5,000 ft. At 5,000 feet on a "standard day" the O-320 will only make about 85% power at full throttle (table on page 8-4 of the current operator's manual) so naturally it will be harder for them to actually damage an engine by leaning (the manual does not specify if the engine is leaned or not to get 85%).

I don't think I have ever read an article, an engine manual or a type certificate that specified an EGT number not to exceed. Other than finding peak, the numbers are useless according to most articles I have read published by AOPA, EAA, AvWeb and others. CHT is what matters.

From the O-320 operator's manual:
1. LEANING TO EXHAUST GAS TEMPERATURE GAGE.

a. Normally aspirated engines with uncompensated carburetors.

(1) Maximum Power Cruise (approximately 75% power) – Never lean beyond 150°F
on rich side peak EGT unless aircraft operator’s manual shows otherwise.
Monitor cylinder head temperatures.

This is about the closest thing to an EGT limit you will ever find. The airplanes I regularly fly don't even have EGT gauges.

_________________
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

I forgot to mention Cubes had a good recommendation for troubleshooting.

He also had another good point. The opinions in forums are worth what you pay for. That is why I try to back up a lot of what I claim with easy to research references and links so it can be verified.

_________________
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

First...... leaning the engine will NOT hurt anything on the ground. The sputter sounds like the carb is to rich. Also check and see that the butterfly and venture does not have anything obstructing it. When you go to full throttle does it puke black smoke? With your prop... that is a great prop. you can fine tune it. if you would like to get higher RPMs out of it you can mark and cut off equal amounts on each blade. Just remember once its gone its gone and to reseal and balanced it again. Welcome to the Thorp family....

Thats right Rich, 250 CHT idling, push in the throttle and it will run 200-225 CHT all day. I think you will agree that Plenum is just a portable refrigerator. I do watch the EGT, but I always lean up to rpm drop and then go in with it back to smooth running, usually ends up at about 1300-1350 EGT and thats about average. I too will start leaning as soon as wheels are up, and I lean aggressively on the Ground. Dan

I have an O-290 powered T-18, and my wife has an RV-4 with an O-320. Both of us lean for max power before take off. Then we richen the mixture a bit, but not enough to lose top static RPM, then we Take Off.
I think you should find out if your full throttle stumble is from running too rich or too lean. Tie down the tail so you don't nose over (standard precautionary legal mumbo jumbo) in a safe place before running the engine at full throttle, then while doing so, slowly lean the mixture. If it is too rich, then leaning will allow the engine to speed up a bit before additional leaning causes the engine to slow and sputter. If it's initially too lean, then when you lean it out, it will immediately lose power, slow and then sputter out.
Taking off with a 'too rich' carb mixture can cause black smoke, rough running and low power, but seldom quits. Leaning to full power for take of is acceptable and commonly done. Do it on the rich side of full RPM power.
Taking off with an engine that runs too lean at full power is bad, and should be addressed before the next flight.
PS; Rich mixture has more than one cause. A low float setting or sinking float can cause it. A carb calibrated for another engine displacement or airframe application (different emulsion tube) could be the cause.
My T-18 has an O-290, but the intake and carb are from an O-320, so a mixture mis-match may occur. Also, the intake scoop on the nose & the air filter/plenum can effect this. My air filter housing is too small, so I have to use a very thin filter media or suffer low power. I'm addressing now while my T-18 is down for repair.

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Scott Emery
EAA Chapter 326
T-18 N18TE

N78DW looks like it used to be N6937 which was owned by Frank Baldwin of Troy, Missouri until a few years ago. You could try to catch up with him, he might be able to give you info from his many years of flying N6937 which you might find helpful.

That is interesting, Frank was my DAR for N718DR and that same day gave me the dual in that plane to meet my insurance requirements back in 2007. David

I'll check out that source for more info. I've been watching AP videos and texts about the situation.



When I put my new throttle on next week I'll have everything apart to examine. My other concern was stops being improperly set and if the butterfly was properly open. Both will be examined. As for smoke I don't notice any but I'll check. I'll tie it down and have a friend run it up and watch. Since I have a decent amount of smoke residue on the underside of the plane I would say it's rich.

I'm having the prop re-finished and after reading I don't think I will be changing the prop. Now that I'm getting used to take off I'm getting it off the ground much sooner than before. I think it was my inefficiency with take off due to my inexperience with tail wheel.

I have also thought about installing bungs in the exhaust to use my handheld wideband for diagnostics like I do on my drag cars. I've noticed in aviation very few use widebands o2 sensors. I like using wideband sensors and data logging.



Ok, I'll watch CHT. That sounds about right on my plane. In cessna I was trained to lean until RPM drop then add about 3 full turns (or until the rpms peak again) with the veneer. We don't have cht or egt in the rentals so that was my only method before. I was trying to use the other methods people use but when someone says "lean of peak" I get confused as I don't know exactly where "peak" for my engine is yet.



I'll try out those methods and see what it does. Since it has improved as the weather dropped 20*F I am assuming rich condition. It's burning 8gph at 2500rpm in cruise flight so that seems like a high burn for this engine and rpm setting.



Small world david! No you will get to see your old friend once again when I bring it down to visit you. I would say in the next week or 2 I'll be comfortable for solo flight. I mentioned to you it came from that area and I remember you saying you flew with someone over there. How crazy is it that it's the same person?


On that note, if this carb needs adjustments and things the overhaul cost is actually more than putting throttle body injection so upgrading might be my best option since it sounds like overhaul might not even change things.

I appreciate all the help everyone has given me! I purchased a cherokee 140 last night and will get delivery next week. It will be my simple certified plane while I tinker with the thorp.

I flew mine for the first time today. What a treat! I should have gotten one a long time ago. I had a C-172 for a chase plane and to stay in formation I had to fly at 1700-1800 rpm. Kind of gusty and rough so I didn't play much in the unfamiliar airframe. Between the 172 and the headwind it took 3.3 hours to go 239 miles but I only used half a tank of fuel

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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

Well done Jeff!!! Welcome to the family! Those who get bit with the Thorp bug rarely get rehabbed!

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

You must have a quick one! Is it an 0320 or 0360? Mine was cruising around 140mph 2500rpm on a hot day. It is a little faster now that the weather has dropped off but still slower with the 290. It also has some parasitic drag that I'm going to clean up which should give me a good 5-10mph.

I have a 160 hp O-320-B3B with a 68x74 Sterba propeller. I think Chuck did a great job with the build. I am seeing some teething issues with the Ford to Lycoming conversion but nothing serious or unexpected. For instance, Chuck had a sliding gate baffle bolted on the oil cooler the first time I looked at it but the oil was getting hot in phase 1 testing so he removed it and installed a scoop to draw more air. I was the first one to fly the new configuration but I only saw oil temps up to 130°. I will either simply remove the new scoop and try it or make some minor modifications of his baffle and re-install. I also think the right mag is always hot (no drop) but I didn't do anything to confirm it yet.

The engine "feels" a little rough. More vibe than miss so I am going to try balancing the prop but I am also wondering if I am experiencing what others have corrected by installing an inertia ring.

_________________
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

Whew, that engine combo and prop is a hot one! What are you seeing for take off distance? I'd like to get a prop like that for good cruise but my little 0290 would take a mile to get off the ground. I have too much life left in my engine (under 300 hours smoh) so swapping engines would be silly at this point.


Lee, I messed up my quote in the above message. I quoted my comment to you.