Thorp Air Command - T18.net

The checkout took longer than I expected, and that;s on me. Finally got the hang of the landing site picture and got them to acceptable levels. 1.75 hrs home, best landing of the day. A couple of things from the xc: #1 I think the prop is over pitched. It's a nearly new 70CM7S16-0-77 that appears to be an RV6 prop. Previous prop was M76 74-68. 9 inches of additional pitch on the same engine has me turning about 1900 static and barely 2100 at cruise. O-320 E2D, no mods. Looking for suggestions. 150mph xc is much lower than I expected. #2 The radios are junk, knew that going in. $$$ will fix that. I need an MX-11 if anyone has one they will part with. Finally, the stab trim cannot be adjusted at cruise, I have to slow to about 110mph to get it to move. I'll dig into the build sheets to figure that one out. Otherwise, it's a tight ship with some upgrades and cosmetics for the winter project.

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Base: KALX
N8786
SN 929

Treat yourself to the Grainger electric trim motor for elevator trim. That and electric aeileron trim were two huge improvements on my plane.

Thanks for the quick response, and apologies from a newbie but can you expand on both? I don't see anything about either in my box of documents. It appears that my left flap is manually adjustable for the equivalent of aileron trim. Is there a forum thread about mods and improvements?

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Base: KALX
N8786
SN 929

I need to know the density altitude where you were getting your RPM numbers but, you are correct, they should be higher. You only get 150 HP if it is turning 2700 rpm. The tach could be off too but that would be an awful big tach error. I would expect a static rpm somewhere around 2500. Do you know what the rpm was during takeoff or straight and level with the throttle wide open?

added: 2 other possibilities, 1) not getting full travel on the throttle linkage and 2) same for the mixture.

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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

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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

I should have posted, I did all the basic checks. Throttle is opening and closing to the stops, 1900 rpm static. DA was about 7k ft, WOT 2100 rpm. The old prop was 68" the new one 77", thats alot of twist for a 150 lyc. I preach to my guys at BAC.org about 2700rpm all the time.

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Base: KALX
N8786
SN 929

See this thread for the elevator trim motor: viewtopic.php?f=4&t=6201

Aileron trim thread here: viewtopic.php?f=4&t=6463&hilit=AILERON+TRIM&start=15

Yep. Too much pitch.
Cubes

I have one of the original Sensenich 66LM76 wooden props on my T18, apparently designed by Sensenich for the Thorp. I have an O-320 A2A (150 hp). Static is usually 2000/2050 but WOT at 5000' it will get 2800 rpm. Cruise at 8 or 9000' will see a TAS 155 kts @ 33 litres/hr.

Tony Schischka
T18C
ZK-VMS

By way of comparison, I have 160 hp O-320 and this is the info I sent to Catto last year but I am still running the Sterba 68x74. Density altitude for everything except the static rpm was 7400 feet:


Airframe: Thorp T-18

Engine: Lycoming O-320-B3B (160 HP)

Prop: Sterba 68x74

WOT RPM: 2690 (verified/digital)

MAP: ~23.3 inches (analog)

TAS: 164 mph (wheel pants removed)

Static RPM: ~2550


I can't remember my specific cruise numbers but I generally cruise 2300-2400 rpm and 150-155 mph indicated well below 7,000'.

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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

If you elect to change props, consider the Sensenich and Whirlwind Ground Adjustable Carbon Fiber props.
Several T-18 owners have them now.
You can dial them in to your airframe and engine, and if you go with high compression pistons later, easily re-pitch yourself.

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Scott Emery
EAA Chapter 326
T-18 N18TE

Perfect, just what I need, I'm on it during July, KALX is repaving.

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Base: KALX
N8786
SN 929