Heat: How To

Proper temperature at 1'ight time can help you avoid and plug fouling, major causes of engine failures in light aircraft

What is carburetor ? And how of the mixture is reduced intention• You'repy, theflyingenginealong,just fatpurringand hap•on does it form when the outside air ally by the shape of the carburetor this cool fall day. The air is smooth temperature is nowhere near freez• barrel. The reduction of pressure and the weather strictly Victor Fox. ing? aids the efficient vaporization of the You glance over at your passenger The answer lies in the fact that fuel. But when a volatile fluid is and the thought passes through your most light aircraft flying today are mixed with air and the combination mind that this is the kind of day equipped with a float type carburetor is subjected to a sudden drop in pres• that sells airplanes. not yet surpassed by any other sys• sure, the temperature drops sharply. Just then your ear, so familiar tem for over-all economy and depend• This is the principle on which most with the exact accustomed pitch of ability. However, the Achilles heel mechanical refrigerators operate. Old Reliable up front, hears a little of the float carburetor is the fact Your carburetor is one of the pret• roughness. Probably you're over the that fuel is mixed with incoming air tiest little refrigerators you ever highest mountain or making that just at the point where the pressure saw. shortcut across a swamp or lake. The temperature drop can be as Quick reflex tells you "carburetor much as 40° F. Usually it is around heat." So you grab for the carburetor 25° to 30° F at cruise power. Just heat control and pull it full on. By the how much the drop depends upon time your heart has had a chance several factors: to skip only a couple of beats, Old by KENNETH RICHTER 1. The density of the air. Reliable is purring again. AOPA 113608 2. The temperature of the fuel.

and stars. In the end, as Ken puts An Iced-Up Carburetor leads Eventually, this trait was responsible for his making an intensive study of it, "I was like a friend of mine who To Development Of A New carburetor heat and what should be washed dishes to pay his way done about it. His article tells how through Harvard Law School. When Temperature-Measuring Device he developed a simple temperature he finished he got a fine job well probe, which is rapidly becoming suited to his talents-and as far as standard equipment in many light• I know he is still washing dishes. I planes. Success of the Richter Aero became a photographer." Kenneth Richter, author of "• Equipment's Type B-5 carburetor N ext, came five years in Holly• buretor Heat: How To Use It," is temperature probe and gauge has wood working on camera crews at a man with an inquiring mind. Never been phenomenal. The efforts of a major studios. While at Harvard, satisfied with what he sees before large segment of the population of Ken had been most interested in de• him, the Essex, N. Y., photographer• Essex, N. Y., have been put to work termining the problems of astrono• inventor-astronomer is the type of in order to supply the demand. mers in order to develop the techni• person who has to see "the other side Son of a chemist-inventor father cal means of solving them, and had of the hill"-or if there is a problem and an ex-school teacher mother, built equipment for the Harvard involved, he has to solve it. Ken got his formal academic training observatory. In Hollywood, he was This quest for knowledge led Ken in astronomy at Harvard, but photog• soon running a photographic special• Richter to take up astronomy and raphy always was in the background, ty equipment business, building high• photography while still in his teens helping to pay the bills. Photog• precision equipment to solve photo• at his home in Bridgewater, Mass. raphy finally won out over the planets graphic problems. enough gas to make your unlit home in no case was there an important ac• field, and just enough daylight left, cumulation of manifold ice without an extra fuel stop to replace fuel a hazardously large ice accumulation wasted by the application of full car• already in the carburetor itself. buretor heat may be the difference So the moral would seem to be: between getting home tonight ahead the crucial icing point in the whole of that front or being stuck in some fuel system is in the carburetor. If Use It en route town with nothing to do un• this is plugged with ice there is no til the weather blows past. alternate air source and you go Actually, there are five points in down. the fuel system where ice can give Studies with transparent carburet• trouble. They are: ors have shown that ice forms at the 1. The tanks or fuel line. If water point in the carburetor where the is present it can freeze on cold days pressure drop begins. The air has or at high altitudes where the stand• been squeezed all the way down the ard temperature lapse rate of about air scoop and then at the point where 3.50 F per 1,000 feet reduces the out• the fuel is mixed in, the carburetor side air temperature below freezing is enlarged. The expanding fuel• even when the field where you took air mixture goes into the manifold 3. And principally, the rate of off is comparatively warm. The rem• and thence to the cylinders. expansion which in turn is controlled edy for this is to use the This expansion in the carburetor by the power setting and also by the and wing tank drains so that no helps the volatilization of the fuel, configuration of the intake system. water remains in the fuel system to which will not burn readily as a liq• freeze. uid. But unfortunately (see your With all these variables, no won• 2. The intake air screen. This can physics textbook), this arrangement der the average pilot is instructed, become plugged with snow or slush, makes a very effective refrigerator. "When in doubt, pull full carburetor and thus cut off air to the engine. If the intake air is moist, the cooler heaL" But full carburetor heat You have an alternate air source air resulting from the refrigeration causes the same power loss that is through the carburetor heater, so effect can no longer sustain the load experienced on hot days. Hot air is the plane will at least continue to fly. of moisture and it condenses, usually less dense than cold air and thus a 3. Elbows or angles in the air harmlessly, on the coolest surface normal fuel mixture set for ordinary scoop. These can accumulate a depos• around, the carburetor wall and the temperatures will be wastefully rich it of freezing slush that has filtered valve, which have been when full carburetor heat is applied. through the intake screen. But most chilled by the refrigeration effect. If The same amount of fuel is being intake systems are designed so that the temperature of the intake air is fed in at the same rate, but the the carburetor heat duct enters after low enough, the temperature drop in engine is getting less oxygen to burn the last bend, so you are still flying the carburetor can result in the mois• it, so power plant efficiency is re• thanks to your alternate air source ture freezing on the walls of the car• duced, and plugs foul with unburned via the carburetor heater. buretor. The transparent carbon. The power loss can be as 4. The carburetor. Of this more revealed that ice occurs first as a rim much as 15%, meaning that it takes below. around the edge of the throttle or up to 15% more time and fuel to 5. The intake manifold. An exten• butterfly valve and a deposit begins cover a given distance. If you are sive set of experiments by a carbu• to develop on the carburetor wall at on that long trip home nonstop, with retor manufacturer has shown that (COli tillued on page 57)

The Hollywood years have been followed by more than a decade of very successful specialization in for• eign film work on educational, docu• mentary and commercial motion pic• tures. Always interested in the equipment to make the hitherto im• possible shot possible, he set up in an unused former barn a machine shop to make the equipment he needed. It was in this barn that he developed his carburetor probe and gauge after that fateful day when he got carburetor ice while flying over the mountains and discovered that the equipment his plane carried was inadequate. Ken has been flying since 1946. He presently is flying a Cessna 180, and as he puts it, "lands on the front Ken Richter checks his camera with a reflex auto-collimator, a lens checking device he designed (Continued on page 57) and is now building at the Essex, N. Y_ plant where the 8-5 temperature probe is manufactured o fuel volatilization if power is required, but with the engine demanding a mini• '~~I:O 10 mum volume of air, the resulting pres• '\ sure drop or manifold pressure differ• °C ' / ,/ I ential is very small. Thus the refrigerat• / ~20 20 ing effect in the carburetor is also very ,-- _ '- CA~B TEMP'V much reduced: a temperature drop of MAINTAIN only two or three degrees below outside AT LEAST SOC OR 90F ABOVE air temperature at idle. FREEZING DURING POSSIBLE The place where carburetor heat is CARBURETOR ICING CONDITIONS often needed and not used is in climbout RICHt[R immediately after takeoff. For maxi• URO [QUIP I mum power at takeoff densest (hence coldest) air is required. But this air may be moist and of a temperature such -- that carburetor ice will form. Ideal con• ditions for carburetor ice are around 58°F with 60% or higher. Terrain permitting, proper technique Here is the B-5 carburetor temperature probe and gauge Richter developed, The recently developed would appear to be cold ail' for takeoff gauge has an expanded scale in the vicinity of the freezing point to permit more accurate reading run, and application of plus 5°C (9°F above freezing) of carburetor heat as measured by the B-5 probe immediately after becoming airborne. The mixture and told whether the carburetor heater to the fuel along with the tetraethyl can be leaned after the climb. was working, but only indirectly indi• lead. The combustion product is lead The limitation of any carburetor tem• cated the possibility of carburetor ice. bromide, a fine powder which is readily perature measuring system is that the Dependent as it is upon so many differ• blown out the exhaust system. But indication does not supply information ent factors, the temperature conducive gasoline has a lower vaporization tem• concerning the presence of sufficient to the formation of carburetor ice perature than ethylene dibromide, which moisture to form ice. indica• should, it seemed obvious, be measured in turn vaporizes more readily than tions given by air weather stations are at the point where the troublesome ice tetraethyl lead. So if the mixture is too a fair indicator of moisture in the air. occurs. cold in the carburetor to vaporize all The closer the dew point to the reported The project of evolving a suitable the fuel components properly, the tetra• temperature, the higher the humidity. 81 temperature probe and placing it prop• ethyl lead may be concentrated in only On the other hand it is quite possible to erly appeared easier than it turned out a part of the engine, in the form of fly ice-free with temperatures 30° to to be. It took three years and the price large, heavy droplets, and possibly sep• 50° below freezing. Ice formation in of a light twin to establish the facilities aJ'ated from its inhibiting ethylene di• carburetors seems to give its princi• and conduct the tests, which eventually bromide. During combustion, therefore, pal trouble at or near the actual freez• resulted in a Supplemental Type Cer• lead oxide may be formed. This lands ing point, where moisture, condensing tificate for the installation of the probe on the lowest point in the , the on cold metal, begins to build up a on licensed aircraft. New carburetors lower plugs, which then foul out. To deposit, usually starting adjacent to are being supplied already drilled and avoid this, it has been found that warm• the throttle valve exactly where the tapped to accept the probe. Older car• ing the fuel-air mixture in ,the car• Type B-5 probe is located. Laboratory buretors have an existing hole, which buretor will aid the volatilization of all experiments have shown that under needs only slight modification, in ex• the fuel elements together. Experiments conditions of 1001- humidity, ice will actly the right place. have shown that an indicated tempera• accumulate in the carburetor at tem• The sensing unit is wound and assem• ture of about 5°C (9°F) above freezing peratures from freezing down to 18° F bled in a pressurized, dust-free room measured at the throttle valve will (-8°C), possibly lower, as measured entered through an air lock. A filter assure proper volatilization, preparing at the throttle valve. At lower tempera• system removes all airborne dirt over the fuel for maximum efficiency. This tures moisture will be precipitated out 1/75,000 of an inch in diameter. Special results in incl'eased plug life and en• of the air in the form of harmless crys• machinery and an assembly line oper• gine reliability. tals by the refrigerating effect of the ated under microscopes, together with Max Conrad (AOP A 95611), that expansion of the gas-air mixture into sophisticated electrical and vibration grand fellow of trans-Atlantic light• the manifold. With this expansion• test equipment, qualified the small plant plane commuting, uses this mixture• refrigeration effect manufacturing car• recently for its Federal Aviation warming gimmick in a very foxy way bUt'etor ice from moist air - the pilot Agency Parts Manufacturers Author• on his long hauls. He takes off the oil must be alert to keep the carburetor ization. The product, the Richter Aero radiator, eliminating its weight and heat level above freezing during condi• Equipment B-5 Carburetor Tempera• drag (and also his fast climbout capa• tions of high humidity. If allowed ture Probe, has been adopted as fac• bilities). In his engine, the intake mani• through oversight to drop a degree or tory equipment by leading aircraft fold, passing through the hot oil sump, two below freezing, the partial use of manufacturers. runs warmer than usual: 210°F as carburetor heat could bring about icing A collateral benefit derived from the against 175° normal. This improves his trouble. use of information provided by the Type fuel preparation and distribution, he Since more than half of the engine B-5 probe has recently come to light as leans a little to compensate for the failures in light aircraft are attributed a result of complaints about plug foul• warmer mixture, and arrives in Paris, to carburetor icing and plug fouling, ing in higher compression engines. A San Francisco, or Timbuktu with clean proper management of carburetor heat major manufacturer has plugs and gas to spare. The average is essential. The Richter Aero Equip• found that lead deposits on the plugs pilot can get the same effect with meas• ment True Carburetor Temperature B-5 in engines using higher octane gasoline ured carburetor heat, and keep his oil Probe, the final element making 'Possi• are usually the result of inadequate radiator functional for that hot day ble this proper management, has al• volatilization of the anti-knock com• climbout. ready been installed on over 1,500 light• planes, single-engine and twins, all over pounds used to raise the octane rating No pilot trained in recent years is L of the fuel. Most such fuels contain likely to forget how his instructor the world. Statistically, a single-engine ~ tetraethyl lead, which if allowed to harped on "carb heat before throttling plane equipped with this system is less C burn without an inhibitor, would form back just before turning base leg." likely to have a forced landing due to o metallic lead oxide. Therefore another This may be of value in keeping the engine failure than a twin without it. S substance, ethylene dibromide, is added carburetor parts warm enough to assist END 4

THE AOPA PilOT DECEMBER, 1959