Glassair / Lancair Installation
The installation of the Ellison Throttle Body Injector ("TBI") on tightly
cowled sport aircraft, such as the Glassair or Lancair, requires careful attention to
induction system design. The air inlet, carburetor
heat system, carburetor and intake manifold are all aerodynamic devices; for maximum
performance these devices require the same careful design as other aerodynamic devices
such as wings, flaps or ailerons. Careful planning and testing will result in an
installation with maximum power, fuel economy and dependability.
The Lancair 235 cowl provides very little room for an efficient carburetor
inlet airbox and will not accommodate an adequate air filter. The
stock 1.5 inch high box induces a substantial pressure loses. In the Jan/Feb 1990
issue of the Lancair newsletter, John Bittner reports of a 50 static RPM increase (about
six horsepower) by simply enlarging the airbox and cowl a bit. Clearly, for maximum
performance, no matter what fuel metering device is installed, the stock airbox should be enlarged.
The sketch below shows an increase in airbox depth to about 4 inches. This will allow
the original flapper type valve arrangement for
heat and provide room for a proper size air filter such as a bracket filter.
Another possible inlet configuration would be to use a remote filter and airbox and a
NACA scoop for inlet air. If air is ducted to the TBI with 2 hoses in a symmetrical
arrangement, this should yield good fuel distribution even with a 2" deep air box at
To gain much needed cowl clearance, Ellison Fluid Systems, Inc. has designed a
plenum box which mounts to the standard
Lycoming updraft sump and allows the TBI to be mounted horizontally with it's inlet facing
forward. This plenum box gives excellent fuel
distribution resulting in maximum fuel economy. The use of the plenum box provides about 3
inches more cowl clearance than a standard Throttle Body/airbox combination. Also, airbox
design is now simplified because the induction air no longer has to make a 90 degree turn
before entering the TBI.
Glassair and Lancair builders with 0-320 engines can use an oil sump from a IO-320-B1A
which can be been modified to allow the TBI to be mounted to the front of the sump with
it's inlet facing forward.
Basic design suggestions relating to inlet airbox configuration are available
by clicking Inlet Airbox. Click
carburetor heat for an explanation of its
importance in a TBI installation.
TBI orientation that activates the throttle in a
spanwise direction will generally yield better performance than one in which the slide
moves fore and aft.
See comments related to vapor formation,
fuel filtration, and
suggestions when planning a TBI installation on a Lancair or Glassair aircraft.