On Jan 18, 10:40 am, T8 wrote:
There's an old rule of thumb that says that you need take off thrust
of about 1/4 your gross take off weight for satisfactory performance.
This holds true for a remarkably diverse range of aircraft, from J-3s
to jets. You can struggle off on less under favorable conditions, but
not a great deal less.

There's another rule of thumb that says that you get roughly 4.5 lbf
_static_ thrust for every hp in a typical propeller driven light
plane.

At 60 kts, a reasonable efficiency estimate for a light plane
propeller is 75%, yielding right around 4 lbf thrust per actual
developed hp at takeoff. That's about 800 lbf thrust for an L-19 or
any other 200 hp tow plane on a warm but not hot day. Plug in the
weight of your tow plane (fueled, with pilot) and various gliders it
could be towing and now you have some good semi-quantitative insight
into the relationship between thrust, weight and take off
performance.

-Evan Ludeman / T8

(some of you may see double post -- sorry about that: posted on wrong
account)

Evan .. some have missed a few of the parameters I stated up front.
The "model" EDF unit I am refering to advertises 38lbs Static
Thrust ... I can cluster and raise/retract this "cluster" into the
large bay of the Genesis 2 area that was designed to house a BRS
system. (though I would experiment with fixed mount first if I ever
actually tried this)

So 3 x 38 = 108 lbs Thrust .. but I stated and proposed 60lbs Thrust
(56%) because..
1 - I did not want to push the envelope of the EDFs
2 - I felt the mfg specs were probably optimistic and under ideal
conditions
3 - I felt there must be SOME loss of efficiency having the intake
ducts clusters so close together (ie touching).
(I am still hoping to hear comments on this subject ... I cannot find
ANYTHING on the web)

I had already considered Mike's technique of short auto-tow to get
airborne and would consider that as an acceptable requirement.
Working backwards from your numbers, could I assume 60lbs Static
Thrust translates to about 15HP in flight? That is the kind of
estimate I am looking for.

thx Evan and All

Curt -95