Thorp Air Command - T18.net

Similar to my other post regarding ignition, I'd like some pros/cons of carb versus fuel injection.

Again weight, cost and reliability being the big three. with fuel consupmtion being a consieration.

I sure like the carb because it works with gravity. But I also like the idea of elimination of carb ice with injection and usually better ability to lean with ability to better balance fuel distribution to each cylinder of injection.

Thoughts people have would be appreciated.

Just for info I'm leaning to the following:

S-18 with wet wings
O-360
Fixed Catto prop, or ground adjustable Sensinich prop. something with metal/nickle leading edges to fly in rain w/o damage.

So is this such a controversial Chevy vs Ford argument that no one wants to enter the debate?

Or is this such an obvious answer that there is no need to discuss?

If it were an easy change I would put electronic fuel injection and ignition on my plane today. That said the sun is shining and the skys are clear in the PNW, I think I'll just go flying instead. That will be my winter time project this year. I currently have gravity feed fuel and Slick mags.

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

I would go FI, CS prop on a 360. I believe the price difference between the FI and carb setup is only a couple thousand dollars. I would have gone fuel injected at the time I put a new engine on mine, but I was concerned I would have to rework the lower cowling if I switched over to FI. I'm still not sure today whether that would have been an issue or not.

I don't think you will be disappointed with whatever setup you choose. The Thorp is such an amazing performer either way. Vans air force website has lots of threads about the pros and cons.

I would go with a carb'd O-320, and a ground adjustable carbon fiber prop with nickel leading edges.
I would put a VANs intake scoop on the bottom of the T-18 chipmunk cheek cowl.
I would use both an electric and an engine driven fuel pump.
I would use at least one electronic ignition.
I prefer cross over exhaust, it fits the carb heat well, and has only two little exhaust holes in the cowl bottom.
I am very interested in Tom Hunter "drop Tanks" that don't drop.
Install a Trusty Tail Wheel Spring, I like "Flyboy Accessories" Eagle Tail wheel, this is a matter of taste. The Trusty spring is a must.
Make sure you build the wings straight, and the leading edges are perfect, and the same from one tip to the other.
Install a big Carb Heat unit. this makes possible the use of carb heat at high altitude cruise, which evens fuel distribution and reduces fuel consumption.
Add some fittings to the fuel tank so you can add a fuel return line in case you upgrade to electronic fuel injection later, or add a ferry tank or wing tanks that transfer fuel to the main tank.
Build the fuel tank with a locking gas cap.
Do not make many changes to the plans, this delays building and adds unintended complexity down the line that adds time to the build.

Other than that, I don't have any strong opinions....
PS; I didn't build my T-18, but I did build an RV-8...

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Scott Emery
EAA Chapter 326
T-18 N18TE

Bringing this back from the dead.

What are opinions on a throttle body injection system like the rotec? It isn't a full fuel injection (direct injection) and still uses gravity feed. With my discontinued ma3spa carb for the 0290 this would be a cheaper option at 800ish $ instead of an overhaul on the carb at 900$ IF I can find someone that will do it.

The only downfall would be making a new airbox although I think it uses the same pattern that the ma3 carbs do. I just don't like the car type airbox on the bottom.

I like the simplicity of the Ellison or Rotec type injection. But I have heard of a lot of problems getting good or even fuel distribution to the cylinders with these. There are also different failure modes with this type as well.

Fortunately for the rest of us, Dave Read is the guinea pig on this one.

At Ky-Dam, I believe it was Gary Green who observed that Dave's exhaust seem to indicate a rich condition based upon the visible black exhaust it was putting out. Dave also has not seen any fuel savings that would otherwise be expected so there may be something yet to be tweaked.

Fortunately (or unfortunately) I am building at such a slow rate, I have no doubt that Dave, and maybe others, will have perfected the operation of the Rotec injection WAY before I need to make a decision about what type of engine fuel metering device I will choose.

Ask yourself why factory builts all have Marvels, Schebler or Precision on them,

It's difficult & very expensive to change anything on a certified factory-built airplane, but your point is well taken Bill. I've seen quite a few builders who tried the Ellison throttle bodies, and a couple with the Rotec version. Honestly, without exception, everyone I can remember had difficulty with them & a large percentage ended up going back to a carburetor. That's just been my experience.

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

I asked this question in a different thread but I think it fits here better.... Has anyone tried an EFI system? There are automotive systems that could be adapted as well as pricey aviation systems now. My limited understanding of them is they can be programmed and tuned to the application which, in theory, would be leaps and bounds better than anything available to the average aviator.

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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

Jeff;
I have run an automotive based EFI system on my RV-8, when my Turbocharged Mazda Rotary was in it. I flew it 16 hours with Tracy Crooks EM-2 controller.
This was a very simple fuel injection & ignition controller with a complete back up controller built in.
Now Ross Farnham has the SDS controller, and others are available too. These are more advanced, but usually don't include a back up controller as the basic package.
Flying an EFI engine is the greatest. It starts like a modern car and runs evenly. you can tune the individual injectors on some systems.
You just have to 'trust' those computers and electrons...and the wiring harness you make.

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Scott Emery
EAA Chapter 326
T-18 N18TE

I would recommend either a carb or aircraft fuel injection. Like John, I have read about a lot of problems trying to get the TBI systems to work with people eventually giving up. Sounds like they are real critical on airflow and airbox design. As David has proven, they do work sometimes without tinkering. I do remember David's airplane at KY Dam looking real rich at low rpm though, with noticeable black smoke.

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Bernie Fried
N18XS

That is what I did when I removed the Mazda Rotary from my RV-8 (it ran fine, I just didn't like it).
I installed an O-360 with Airflow Performance fuel injection, which is an updated Bendix aviation type.
I prefer the Marvel Schebler MA-4 carb for my T-18, even tho- it's an O-290 and is supposed to have an MA-3. I intend to eventually bore the case to accept O-320 cylinders because it's an O-290G, and has O-320 crank, rods, sump, gear case etc. from the conversion.
I use carb heat when cruising at altitude and slightly reduce the throttle to get the EGTs running more evenly.
Furthermore, there was a period discussion about a bushing between the carb and the sump for O-320s to improve fuel distribution (same sump used on O-360 with MA4-5, hole too big for MA4 on O-320)
Also, the Mopar drag racing publication had an article on adding internal flow control in the intake manifold of their V8 engine to improve fuel distribution.
Grid type flow straighteners have been added before or after the carb...
There are many ways to get a carb system to work better.

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Scott Emery
EAA Chapter 326
T-18 N18TE

My interest is mostly academic. Looking at the advances in automotive systems that have given cars more power, better mileage and nearly non-existent tune up intervals, it would be nice to bring some of that to aircraft engines. I remember when a car engine was thought to be wore out at 100K miles, changing plugs and points every few thousand miles. Now they go 100K between plug changes and well beyond 200K is the expected lifespan. Some of that goes to better metallurgy and better lubrication but I think a lot of it has to do with better fuel and fire control too.

I looked at the SDS system on Aircraft Spruce. It might pay for itself in fuel savings over the course of a 2000hr TBO. I am not a fan of using adapters to fit spark plugs to engines nor am I a fan of slip-on ignition leads on aircraft.

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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

With direct injection I could see a possible fuel savings. I don't think a tbi will give much if any fuel savings based on the differences seen in automotive.

For myself the only difference would be a new product with access to parts. Seems to be an issue getting parts for the model carb I have.

People having issues and switching back to a professionally tuned carb is anecdotal evidence. How many of those people could properly tune a carburetor? If they aren't able to set up a carb from scratch then of course they will have issues with a tbi. I'd like to hear from someone with extensive carb tuning background that has tried a tbi. Tbi systems are very similar to carburetors so I can't see there being s huge difference in setup.