Thorp Air Command - T18.net

Bill: I think you are correct in regard that the Marvel carb requires some type of "pressure " to the unit. My 1950 Ford 8-N tractor has the old reliable Marvel carb on it and gets it's fuel from a gravity fed tank above the carb... and there is some type of head pressure there ? Not sure how much , but has to be at least 1 psi ? My 1950 Ford tractor NEVER gets above ground level so I am not worried about fuel feed . My S-18 has a fuel pump for TO and landing . BOOM !

RB

The vent line that most of us use, when pointed into the wind, does create a measurable amount of pressure. At cruise speeds in a Thorp, it can amount to something like 1/2 psi. That may not sound like much, but it can also be looked at as an increase in head pressure that would be created by having your fuel level about a foot higher than it is. These are very rough estimates based on my memory (known to be faulty). Looked at another way, you will have about the same pressure feeding the carb while flying when your fuel level is low as you would have when sitting on the ground with a full tank. I'm too lazy, but those of you so inclined could look up Bernoulli's equation & do the math. Fluid mechanics never was my favorite subject. If you do, tell me how far off I am.

Gravity flow works perfectly with a T-18, and that has been proven for 50 years with all size engines, but you need to give yourself every advantage, in my humble opinion, if you're smart.

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

My advantage is a fuel pump

I had lunch with Tom Bernoulli yesterday and he said..."turn on your boost pump for take off and landing ." My advantage is also a boost pump .

RB

John is right as usual. My research once after an argument shows that it takes a little over 200 knots to make 1 psi. That has to at least improve airflow. You can also use a similar pressure chart to calibrate your airspeed indicator.

Don't look to me like your memory is lacking at all John, 1/2 psi is good. One of the attributes of the Thorp is simplicity, this attracted me from the start, not only that but it's down right good looking. Dan

Dan...you are simple and good looking , but I am NOT attracted to you !

RB

Thanks, David & Dan. To you fuel pump guys... when I say give yourselves every advantage, I'm mostly referring to a great advantage when using a gravity-flow system in a T-18. Everybody knows that fuel pumps never fail, and because of that you would never need or want any additional pressure to help push fuel through all those check valves & multiple pumps (or whatever you guys use), even if it is simple & free. I believe in K.I.S.S., as I know John Thorp did. Then there are those who wear a belt AND suspenders. All kidding aside, whatever gives you peace of mind is OK with me.

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

Aw Gee Rich, now ya hurt my feelins...................Ya onery Cuss....Dan

Here is the new vent scoop - will put a bug screen on it and test fly - will report any "mixture" changes.

That's interesting Frase...........Dan

Like Dan said...very interesting ! Looks like part of an air powered phone they used on WW II Battleships . It will certainly push some air ! I am sure it will work just fine ! If in doubt you could always use it as an ice cream scoop !

RB

That's a lot of air. You are carberated right?
Cubes

1. You may have to hook up ram air heat to the tube to prevent in flight icing .
2. Go the the County Clerks Office and give the Girl a name . Bertha ?
3. Make a "Kilt" Ram air tube cover .
4. Declare it as a dependant on your income tax .

BADA BING , BADA BOOM !

Just funnin with ya Bro !

RB

Lets see what that little scoop does I'm kinda curious.........Dan