Thorp Air Command - T18.net

Can you guys tell me the average cruise speed for a t-18 with the 0-290-g ? Also what is the fastest cruise for that engine?

I have done some mods to my cowl and I am looking at 173 mph indicated at 2600 rpm, just want to compare with others out there. Chuck

I'm certainly not an expert, but off the top of my head, I cant recall anyone going faster than that with an 0-290. I dont think i recall anyone in the old newsletters going faster with an 0-290 either. What prop maker and pitch you got on that thing? I want to copy you! I only get about 140mph at 2600rmp with my 0-290 powered T-18. My plane is heavy with climb prop.

John Shinn's 0290 powered Thorp won the Bowers Faulk Race back in the late 70s (perhaps 80s) at 198 mph. Bob Highley tells a great story of that airplane lapping the fly by pattern at osh numerous times. Look at the old newsletters for reference but remember, a light clean 0290 powered thorp can cruise with the big boys ... Just won't climb quite as well ( or sound as cool )

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Our ship "Feisty" has an O-290G.
It has an O-320E2 sump, carb and intake tubes, also it has O-290D2 cylinders and 7.5:1 pistons.
It has a crossover exhaust, and a Ted Hendrickson 68x68 wood 2 blade prop.
I get about the same speed, 172 MPH at about 4000 ft and 2600 RPM. Very close to your results.
Sofar, we have put 25 hours on it, I bought it in April, and flew it in June. Speed varies with weight and temperature. The wheel pants were good for about 12 MPH!
For general use, it burns about 4 gallons in a half hour trip, so 8 GPH which would be comperable to our old Cessna 172, which burned 8.5 GPH w/ 145 HP continental.
We use it to fly 50 miles to a residential airpark, which includes a climb to about 6,000 ft to clear some mountains. Right now, I'm cruising about 160 with the throttle part closed to improve the exhaust temp spread. I'm still learning how to operate it best, and making small changes to improve it, but NOT take it out of service...Too much fun!!
We have flown as high as 10,000ft, where the RPM runs higher, and cruise speed does too.
Can't beat it for economy and speed. Did I mention the fantastic view from this thing?

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Scott Emery
EAA Chapter 326
T-18 N18TE

My thorp was born in 72 with a o-290 and a cut down metal prop. she was on a weight gain plan until I got her in 08. I started with a new panel lost pounds without the loran and cassette player, then I went after the cowl. The whole thing looked out of alignment so I started over with the nose and belly pan from Spruce. I also made a pressure plenum to direct airflow. Vans carb scoop, sky-tech starter and a catto 68x68 prop. Directed the exhaust back too.

Next: Vans wheel pants and gear fairings. Hope to get 180 mph.

198mph, that is amazing! man, you guys are doing good. I need to clean my plane up.

I would love to see a write up on those cowl changes. Pictures too! Please.

N6cm has 1000tt on a o290gpu. Metal M76 that is a 68x73. Does 150mph at 2300rpm. 165-170 at 2450rpm. Burn about 6gph at low cruise and 8gpu high cruise.

O-290D for N38DT 175MPH @ 2600 RPM @ 2000 ft
Lance

Interesting experiment today. Took off the Vans carb inlet scoop and flew with bracket filter exposed to the airstream. Looks like the scoop is good for +5mph. Is this due to some ram air effect or the redirection of airflow? Chuck

What's your MP gauge say, before and after the change?

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http://www.dixiefriedfabrication.com/

No manifold pressure gauge. Would be interesting to see if it changes right?

Although "Feisty" has a fixed pitch prop, it does have a manifold pressure gauge.
I still rely on RPM in the pattern, but the manifold pressure is more useful at cruise speeds.
Big changes in manifold pressure make small changes in RPM when you are going faster than 130 MPH. Of course you use both RPM & Pressure together as well, Wer just don't have a propeller control lever
When making a "cruise arrival" into a valley airport at 160 MPH, the RPM can be above 2300 with the manifold pressure quite low, below 15" Hg.
A little 2-1/4" Manifold pressure gauge is not expensive, and does not take much panel space, but you will be glad to have it.
Also, you will realize what a joke the "running Oversquare" arguement is. Engines with fixed pitch props run oversquare much of the time and easily make TBO.

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Scott Emery
EAA Chapter 326
T-18 N18TE

I have a O290G with D2 cylinders. I cruise 150 MPH at 2350 RPM at 2000'. WOT at 2000' is around 180ish with rpms between 2600 and 2700. I have a Great American 68x68 wood prop which seems to be a good compromise between climb and cruise for my airplane.

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

Bruce: Did you put hydraulic lifters in your 290? If so who did the work I would like to copy. Chuck