| Interesting article
I have said many times that I would not fly an aircraft with ANY carb type without a good carb heat system. I came to that conclusion long ago but these comments by Ellison of Ellison Fluid Systems makes it clear in detail. Throttle Body InjectorsThe Ellison Throttle Body Injector (TBI), with no throttle plate downstream of the point of fuel injection, at first glance appears to be ice proof. Unfortunately, many of our customers have never gone beyond the first glance in spite of our warnings. A TBI, in any given application, may go years without accumulating any ice. Unfortunately, some of our customers feel that since the TBI ices up so infrequently, they won't be quite as dead as if it happened often. As with the Marvel-Schebler carburetor, the same two ice mechanisms are possible in the TBI. Here's how: 1. The same extreme temperature drop occurs in the TBI as with the M-S and for the same reason, namely fuel evaporation. With no throttle plate downstream of the fuel input there is little for the ice to adhere to. It is possible however, for ice to form on the sidewall of the TBI downstream of the throttle slide. TBI owners can convince themselves of this danger by running their engine at 1500 RPM for a while on a humid day with the cowl removed; the diffusion section of their TBI will look like a Popsicle due to atmospheric moisture condensing and freezing on the outside of the TBI. Deadly ice formation can also occur in the manifold of engines with long cold intake pipes such as VW conversions and Continental engines, to name a few. Updraft cooling can exacerbate the potential for manifold ice because there is no warm air from the engine cylinders flowing down over the induction tubes. 2. Idle circuits of most of our TBI models include an air bleed passage that makes the fuel behave as though it had much lower viscosity. On humid days, when operating at idle for extended periods of time, the bleed orifice (located in the bottom of the slide cavity) will ice over causing idle mixture to slowly enrich. Cycling the throttle a couple of times will sometimes clear the ice but the application of carb heat is the only sure cure. As the fuel contribution of the idle circuit diminishes as the throttle is opened, bleed circuit icing has negligible effect on power but can result in the engine quitting in a decent if the throttle is retarded far enough. This is a critical problem in Eze's because the driver, not being able to see the prop, has no good way of knowing that he's a glider pilot. SummaryFor certificated aircraft, FAR 23.1093 requires that the intake air heat system must provide a heat rise of 90°F at 75% power. It makes a great deal of sense to comply with this regulation when building an "Experimental" category aircraft. To prevent engine failure caused by carburetor or induction ice, this type of heat system must be installed on all aircraft (including experimental) which use the Ellison Throttle Body Injector.
-- Dr. Glen BradleyPensacola FL 850.454.9863
“The views and opinions expressed herein are those of the author in his personal capacity and do not necessarily reflect the views of Thatcher Aircraft, Inc. My comments should be taken only as those of a good friend of the company and the pilot of the first CX5.. Your aircraft may, for many reasons, fly and perform differently- especially due to differences in build and piloting technique."
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