Tony Bingelis •

Your aircraft will be quite comfortable, even on the hottest of days, provided you can get a good flow of air through the cabin. And, naturally, this circulation of air will be all the more effective if you can control the air flow entering - and its direction. Without this type of control over the cooling air, it probably wouldn't make much difference whether you have the cabin ventilation turned ON or OFF. Essentially you should be able to adjust your vents so that some of those gentle breezes waft past your face. It is the perceived effect of air flowing past you that helps make your ventilation system a good one.. . one you can brag about. In the interest of fairness, let's discuss a few ventilation system alternatives before I try to sell you on my installation.

blamed on the unpredictable corkscrewlike propeller slipstream pattern around the fuselage in the area where they happened to locate their NACA air inlet. A NACA flush inlet located on the right side of the fuselage often suffers from a much reduced mass flow of air through it compared to the amount of air that would have been ingested from an undisturbed slipstream. At any rate, the reason most cited is that the propeller disturbed slipstream tends to flow across the NACA inlet rather than enter parallel to it as it normally does in a free stream. Locating a NACA flush inlet in the side of the fuselage just ahead of the

instrument panel area and aft of the firewall area appears to make an effective installation - provided there is no internal structural interference there. In addition to obtaining a good volume of air from a properly located NACA inlet, the amount of ducting required to conduct that cooling air into the cabin would be minimal. However, you will have to design, fabricate and attach a plenum chamber inside the fuselage. This is so you will have a means for connecting a duct between it and the cockpit ventilator control. There is another consideration. NACA inlets can ingest a lot of rain water.

COMPLETED ALUMINUM FLANGE

RIVI

FOR INSTALLING 2" 1.0. DUCTING.

THE OPTIONS DRILL HOLES (2) FOR I/8" RIVETS.

Here are your choices. Cooling air for your ventilation system may be picked up from:

1. A NACA submerged (flush) air inlet built into the side(s) of the fuselage. 2. A NACA type inlet built into the top of the fuselage ahead of the windshield. 3. A NACA duct built into the tail fin area. 4. An external scoop (door or shutter) installed in the fuselage side, windshield or canopy. 5. An engine compartment ram air inlet located in the front deck baffle or

2"O.D. ALUMINUM TUBING IS BETTER

|.

FORM A TUBE

I TCB

IN DIAMETER

ALUMINUM STRIP (.032" OR .040") l" « 6

in the rear engine baffle. COMPARING THE OPTIONS

2, ) CUT OUT FLANGE

Quite obviously, each of the enumerated air sources has disadvantages, some of which may outweigh its advantages. However, any shortcoming attributed to a particular ventilation source should be weighed against the known advantages before jumping to conclusions. Option 1 - For example, a NACA air

BEND TABS 90*

SOFT ALUMINUM .040

inlet built into the side of the fuselage

(2024-0/50SH32, ETC).

makes a very good source for cooling

air . . . provided it is located in an area of positive pressure. Some builders are very disappointed when they learn that their super modern, low drag, NACA flush inlet doesn't bring in much cooling air. This is often

FLANGE DETAIL - FRONT VIEW

FIGURE I.

SIDE VIEW

FORMING ALUMINUM FLANGES (WITHOUT WELDING)

SPORT AVIATION 41

1/4" OIA. HOLES

"WHISPERFLO" VENTILATOR

INSTALLATION DATA

ADAPTER LAMINATES ARE 1/2" PLYWOOD

ADAPTER FOR ATTACHING AERODUCT 2" I.D. DUCTING. TO "WHISPERFLO" VENT.

ALUMINUM TUBE

2" OIA. > l" LONG (EPOXIED IN)

1/2" LAMINATES

,.*

FIGURE 2. "WHISPERFLO" VENTILATOR DETAILS

Option 2 - A NACA duct installed ahead of the windshield could inadvertently be located in a low pressure zone thus rendering it relatively ineffective. On the other hand, properly located it could blast air right into your face if no means of directional control is built into the vent. Incidentally, a single ventilator would probably be absolutely inadequate for side-by-side seating. Although a top of the fuselage location for a NACA inlet doesn't require much ducting to install, it may result in a noise level you might consider to be objectionable. This type of installation is difficult to weatherproof. That is, devising a way to keep rain water and water from washing the aircraft from entering could tax your patience and ingenuity. Option 3 - A flush NACA inlet built into the fin area is considered to be a 42 MARCH 1991

good ventilation air source. However, a major drawback is the very expensive long run of ducting that will be required to bring the air all the way up to the cabin area. It should be obvious, too, that the air flow to the cabin area would be slowed somewhat by friction. Nevertheless, because it would be free from engine and slipstream noises, it could well be the quietest of all ventilating air sources. Option 4 - Obtaining ventilation through a ram air scoop (of any type) installed in the windshield, canopy, or fuselage side is a poor choice and should be avoided. Although it does result in the simplest and lightest ventilation system, the raucous ram air noise will drive you nuts. Furthermore, the air flow entering through these scoops generally cannot

be directed effectively to where you want the air to go. Option 5 - The front entry baffle as well as the rear engine baffle are rather common ram air sources for the carburetor heat muff and cabin heat muff. Less frequently they are used as sources for cabin ventilation air - the

primary drawback being the rather long lengths of ducting required. Incidentally, contrary to what some builders believe, the ram air picked up at either of the engine baffle sources is not heated air. Certainly, the air picked up at the front deck baffle is just as cool as the outside air surrounding the airplane. There is some speculation, though, that a little teeny bit of warmth from the engine might be passed on through the vent opening located in the back engine baffle ... but, maybe not. After all,

A Whisperflo ventilator installed directly below the instrument panel. Notice how the builder cut away and rounded the lower right corner of the ventilator to enhance appearance. Appearance would also be improved by moving the vent up flush with the bottom of the instrument panel.

This Whisperflo vent, located on the right side of the fuselage, can also be easily reached and adjusted by the pilot.

Contrary to popular belief, ram air taken in through the rear engine baffle is not heated air ... certainly not to any noticeable degree. A protective aluminum screen should be riveted over the opening between the baffle and the aluminum flange.

Piper's Twin Comanche, for one, uses the back baffle as a source of "cold" air for its fuel injector. HERE'S MY PITCH The ventilation system I have in my RV-6 meets all essential parameters and is by far the best installation I have ever had. It is so effective that I plan to fabricate an identical installation for my RV-6A (currently under construction). Except for the impressive amount of air moved, the system is not unique . . . nor is it original with me. I attribute the success of my installation to the large amount of ram air delivered by the two large diameter "Whisperflo" ventilators located on each side of the cabin just below the instrument panel. I can swivel the vent openings in these large molded plastic units up to 40 degrees in any direction, thus allowing me to direct the cooling air where I want it. A thumb operated closure devise controls the degree of opening and the amount of air coming out. During cool weather, or any time I feel like it, I can completely shut off the airflow with a flick of my thumb. There is another thing I like about "Whisperflo" ventilators - their reasonable per unit price . . . about $13 in 1990 dollars. Compared with the high cost metal "Eyeball Air Vents" of the type used on most airliners, the larger, less expensive "Whisperflo" units effectively handle a greater volume of air. I must admit, though, the installation I have is not the simplest, lightest or least expensive way to do it ... but, man, is it cool! The vent on the left obtains its air from the front baffle deck while the vent on the right is served by the rear engine baffle. Incidentally, the ram air source installed in the aft baffle location requires far less ducting for the installation. Otherwise, both of these engine compartment ram air sources appear to be equally effective - and, I might add, I have not been able to detect a temperature difference in the air entering the cabin from either ventilator. Even if that had not been the case and the air coming out the right ventilator was not as cool (supposedly because of its rear engine baffle source), it wouldn't have bothered me much anyway .. . because that one is on the passenger's side. There are those who question the wisdom of using the engine compartment baffles as a source for ventilating air. Engine noise, they say. Well, I honestly cannot detect any inSPORT AVIATION 43

The screened opening in the front deck baffle provides the ram air source for a cabin vent. The big drawback is the long length of expensive SCAT ducting required for the installation.

This is the right side of a Glasair instrument panel frame. The airline type eyeball vent is connected by a short length of Aeroduct ducting to a fiberglass plenum epoxied directly over a NACA flush vent. This is a very light efficient installation . . . provided the NACA duct is located in a high pressure slipstream area.

A ram air scoop or clam shell door is a poor choice for cabin ventilation. The raucous air noise can drive you nuts. 44 MARCH 1991

crease in cockpit engine noise when the vent is opened . . . nor a reduction when the ventilator is closed. Apparently, the fairly long run of the installed rubberized SCAT and CAT ducting muffles whatever engine noise may be present way up front at the source. When you are trying to pick the best source for cooling air, you find that the design of your aircraft plays an important role. The larger the aircraft, the more complex the installation is likely to become. And, certainly, an aircraft with side-by-side seating does not have the same complex air distribution problems confronting the builder of a tandem seat airplane. Anyway, after weighing the pros and cons for the various options, you, too, may conclude, as I did, that a source capable of providing a good volume of air is really the most important single consideration . . . especially for someone who flys the Texas territory more often than he does the Alaska bush country. For this reason, I selected the engine compartment as the ram air source for my ventilation system. This in spite of the longer, more expensive ducting required. However, I must confess that even if I were absolutely sure of locating a pair of NACA ducts in areas of positive pressure, I still would balk at having to fabricate a couple of fiberglass plenums. Fiberglass work is not my favorite sport. Of course, maybe I should have bought a couple of prefabricated NACA inlets and plenums and fitted them to a pair of "Whisperflo" vents . . . but I didn't. DUCTING THE COOLING AIR

I routed the cooling air from its engine compartment sources to the cabin ventilators through both SCAT and CAT AERODUCT FLEXIBLE DUCTING. Inside the cabin, between the firewall and the "Whisperflo" outlets, I switched to the less expensive CAT ducting. Even so, the CAT ducting can also withstand fairly high temperatures . . . up to 300 degrees F. The ducting is connected at each end with stainless steel clamps fitted over separate 2 inch aluminum flanges riveted to the engine baffles and to the firewall. A total of 6 aluminum flanges were needed to complete my particular dual ventilator installation. To cut costs, you could make your own flanges by rolling a short tube out of .032" aluminum sheet. (Soft aluminum like 5052 H32, 6061 T6, etc., are easy to form and bend.) If you cannot weld aluminum, try attaching a flange to the 2" diameter stub tube by preparing it as shown and rivet it on (see Figure 1).

Of course, substituting a short length of 2" thin wall aluminum tubing would be an easier and quicker way to do it. Because the "Whisperflo" ventilator units are relatively inexpensive, it did not surprise me to learn there was no provision for attaching the ducting to them. This was not a big problem because I was able to fabricate a means of attachment by using a short section of 2" aluminum tubing inserted into a wood adapter. The adapter was then bolted to the "Whisperflo" ventilator unit. Some builders might prefer making the adapters from soft wood laminates or from fiberglass. Simple aluminum brackets were used to attach the ventilators to each end of the instrument panel against the sides of the fuselage. From its location just under the instrument panel, I can direct the cooling air from my vent in almost any direction I want. In addition, I find it just as easy to reach over to the passenger's side and similarly adjust that ventilator to obtain the maximum benefit from the criss-

If you wish to contact the author of this column for additional information, please send a SASE to Tony Bingelis, 8509 Greenflint Ln., Austin, TX 78759. BOOKS BY TONY Trie following books by Tony Bingelis are available from the EAA Aviation Foundation, EAA Aviation Center, Box 3086, Oshkosh, Wl 54903-3086, 1-800/843-3612, in Wl

1-800/236-4800, in Canada 414/426-

4800. Major credit cards accepted.

- Sportplane Builders (Aircraft Construction Methods, 320 pages) - $17.95. - Firewall Forward (Engine Installation Methods, 304 pages) - $19.95.

-Sportplane Construction Techniques

(A Builder's Handbook, 350 pages) - $20.95. Add $2.40 postage and handling for each publication ordered . . . or order all three for

crossing breezes. With fall and winter coming on, it is very nice to be able to effectively shut off the cooling air. SOURCES "Whisperflo" Ventilators - ACD Corporation, PO Box 2081, Wichita, KS 67201, 316/264-1462.

"Whisperflo" Ventilators and Flanges

$52.97 plus $6.95 postage and handling. Wisconsin residents add 5% sales tax.

- Aircraft Spruce & Specialty Co., PO Box 424, Fullerton, CA 92632, 800/8241930 (order hotline); Wicks Aircraft Supply, 410 Pine St., Highland, IL 62249, 800/221-9425 (order hotline); Van's Aircraft, Inc., PO Box 160, North Plains, OR 97133, 503/647-5117.

YOU'LL SMILE, TOO!! When you find that

WICKS has your parts in stock ready for immediate shipment! Call us today 800-221-9425 EUROPEAN CONNECTIONS

COSY Ahornstr 10 D-8901 RIED

W. Germany

Tel: (49) 8233 60594 FAX: (49) 8233 20150 German/English

WICKS AIRCRAFT SUPPLY 410 Pine Street Highland. IL 62249 FAX: 618-654-6253

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SPORT AVIATION 45