Traditionally, airplane makers-at least spam can manufacturers-dont lavish much engineering on nose cowlings. If the engine cooling numbers are close enough and the front of the airplane looks like something marketing can sell, the engineers move on.
And the buyer pays the price in lower speed and higher fuel consumption caused by excess drag and, occasionally, poor cooling, which can shorten engine life. This lack of attention to detail has created a target of opportunity for the aftermarket, most recently tapped by famed speed guru Roy LoPresti, who has recently introduced a line of low-drag cowlings for Mooneys and Pipers.
During his days as an engineer at Grumman and Mooney, LoPresti developed a philosophy for coaxing more speed out of airframes through multiple subtle drag reduction efforts rather than the brute force of cranking up the horsepower. Through his Speed Merchants aftermarket skunk works in Vero Beach, LoPresti is still at it, at age 72. We recently flight tested his improved cowling for the Mooney M20 series and, frankly, were impressed as much by its construction as its performance.
This is not a cheap mod, topping out at about $13,000, depending on the model. Although the speed increase is measurable, this mod-at least on the Mooney-delivers less than the standard rule of thumb on cost versus speed: $1000 spent for every knot/MPH gained.
History of Speed
LoPrestis experience in speed tweaking Mooneys extends back three decades. As Mooneys chief engineer (and later company president), he lead the engineering team which developed the highly regarded Mooney 201 during the mid-1970s. It was the first production aircraft to turn in 1 MPH top speed per unit of horsepower.
Since those heady days, when GA was still enjoying brisk sales, LoPresti has bounced around on various assignments with other companies, including Grumman and Piper. He now has his own shop at Vero Beach, designing and building high-dollar speed mods for Mooney and Piper products.
He leads a capable engineering department equipped with state-of-the-art computerized engineering technology plus a complete tooling and machinery shop. We were impressed with LoPrestis molds and tooling for his cowlings and other products.
Given his background, the current Mooney cowl project was probably inevitable. By 1975, Mooney had produced the 180 HP M20C and 200 HP M20E which were fast for their day but growing ho-hum in the market, losing sales to Piper, Beech and Cessna high-performance singles. Something new was needed and that turned out to be a reworking of the 200 HP M20F into what eventually became the M20J or Mooney 201.
Without the sophisticated computer modeling available today, LoPresti recalls that we probably used intuition more than anything else to squeeze more speed out of what was already a relatively clean airframe. He says the mods were sketched, built, flown and tweaked until the engineering team found a respectable 6 MPH gain solely from an improved cowl, at which point they froze the cowl design, rather than fishing for more speed from that source.
Still, LoPresti realized that the Mooneys cowl wasnt the absolute best and that more drag could be eliminated. The J-models cowl had traditional air inlets totaling about 74 square inches compared to the pre-201 cowls guppy-mouth inlets of some 174 square inches.
Using todays sophisticated computer programs that proved a great help in defining low drag cowls, LoPresti began re-examining not just the Mooney 201 but the Piper Arrow, Seneca, Lance, Saratoga, Cherokee Six and the Comanche singles and twins.
Once some raw drag data was plugged into Speed Merchants computer models, it was obvious that yet more speed was lurking in the Mooney-and other-airframes solely by modifying the cowl, bringing LoPrestis Mooney speed mods full circle to the new cowling for the M20 series Mooney, which are called Super Mooney Cowls. In a nod to marketing sizzle. LoPresti calls the modified cowls for the PA-32 series Howl Cowls.
More Than Speed
Most speed mods are just that: They nip a little drag here and there but do nothing else other than tweak speed. LoPrestis new Mooney cowl, however, really re-engineers the front of the airplane. Its dramatically different in shape from the stock M20J cowl. LoPresti claims the cowl delivers better cooling and significantly more speed when typically these two concerns are at odds.
To a degree, thats where the speed comes from. J-model Mooneys dont generally have cooling problems and are probably overcooled, meaning too much air and drag is swirling around inside the stock cowling, sapping speed.
LoPrestis Super cowling sports more efficient circular inlets, completely redesigned low-drag cowl flaps and an innovative induction system that he claims provides an additional inch and a quarter of manifold pressure.
To accommodate the cowling, the top centerline of the airplanes firewall is raised nearly an inch into a small hill which continues rearward until it contacts the windshield. The surface of this hill is called the windshield wedge and it wraps around the entire area between the top of the firewall and back as far as the pilots side window and the cabin entry door. This fiberglass windshield wedge helps reduce cabin noise and provides less drag.
The M20Js stock ram air inlet with its manually controllable inlet valve was never very effective, although it did work better on the E-model. In LoPrestis cowl, this has been replaced with a new shuttle valve design that eliminates the need for the stock butterfly valve.
Never short of catchy names, LoPresti has one for the new ram air system, too: Its SCRAM for super clean ram air mod. A new composite smooth duct runs from the air filter to the engine injector body. When the SCRAM air control is pushed on, the SCRAM air slide valve moves laterally, positioning a clean cylindrical path (no butterfly valve) from the outside air stream directly to the injector body. This unobstructed passageway is free of any turbulence and seems to improve manifold pressure by 1.25 inches over the stock cowl.
The net result of the new cowling on the J model is a 7 MPH in speed gain, according to LoPresti, at the same fuel flow for about 3 percent more range. (More on those claims in a moment.) LoPresti also claims better cooling, higher manifold pressure, improved safety via easier access to the engine and a quieter cabin.
Obviously, since older 200 HP pre-201 Mooneys have larger cooling openings, they should also enjoy more speed gains with this new cowl, up to 13 MPH and 7 percent more range.
However, the mod for the older airplanes isnt quite so simple to install. For one, youll have to bring the older Mooney up to stock M20J standards firewall-forward with a number of stock 201 parts such as metal baffles, oil cooler installation hardware, spinner, exhaust pipe and the 201 cowl flap mechanism, including its over-center locking linkage.
All of these items are used or needed by LoPrestis improved cowling and they arent included with the basic cowl kit. (Add about $4000.) In addition, the LoPresti crew has wisely lowered the split between the top and bottom portions of the cowling, thus making the circular inlets an integral part of the upper cowling only. We suspect mechanics and owners who do their own maintenance will like this, as it exposes a more of the under side of the engine for inspection and access.
Also, the larger access doors in the upper cowling lie directly across the rear baffle seals so a pilot doing pre-flight checks can see the accessory case aft of the seal, as well as the tops of the cylinders forward of the seal. We applaud this type of thinking and wish more manufacturers and STC shops would follow suit. We removed the LoPresti Mooney cowl and found this no harder to do than the stock 201 cowl.
The engine induction air filter is in the same location it is in the stock 201. Below the filter is a composite induction duct that ties the filter to the SCRAM valve box. The SCRAM air push/pull cable in the cockpit controls the ram air slide valve.
New Gear Doors
The cowl also includes re-designed nose gear doors that have smooth aerodynamic contours from front to back and overlap to reduce engine exhaust and propeller noise entering the nosewheel well. The doors are significantly longer, smoother and provide noticeably less drag than the stock doors.
The forward edge of the nosegear door shape is an integral part of the cowling. The aft end of the new nosegear doors is a fixed belly fairing that extends the nosegear shape 10 inches further aft.
We confirmed that the new nosegear doors block some noise from the exhaust and the propeller from entering the cabin via the wheel well, thus they help quiet the cabin noticeably.
Another nice touch is that the aforementioned windshield wedge can be removed easily by unfastening several screws. Removing the wedge allows the windshield to be removed and replaced and/or the pilot can gain access to the main gear brake hydraulic reservoir by removing the wedge.
Flight Trial, Owner Report
While LoPresti reports installing numerous modified cowls on M20Js, theyve done only one on a pre-201 model and we contacted the owner. Interestingly, hes a 25,000-hour former FAA designated check pilot who owns an M20F based in Colorado. He reported a 14 MPH speed increase on his 1976 Mooney Executive after LoPrestis cowl was installed.
In addition to contacting several M20J owners, we did an informal before-and-after flight test of the LoPresti cowl on a J-model. The owners we contacted reported seeing the claimed 7 MPH increase in speed and our observations based on a converted 1982 J-model seem to confirm the claim, within a MPH or two.
We collected our speed data via GPS runs on upwind and downwind legs. Although LoPresti insists the 7 MPH gain is a gimme, we tend to be skeptical that all airframes benefit equally from speed mods. We think actual performance is in line with LoPrestis claims but that a more realistic result is 5 to 7 MPH. We doubt if any owner would see no speed increase at all, which seems to be the case with other mods weve examined.
Frankly, we were as impressed with quality of construction of this product as with the actual performance improvement. We inspected the molds used to produce the fiberglass and carbon fiber cowl parts and examined each of the systems parts. Everything appeared to be well made, cleverly engineered and nicely finished.
Naturally, this comes up a price. The basic cowl sells for $9995 and, at minimum, plan on $3000 for installation. For a 201, then, the speed gain comes in at more than the standard rule of thumb for speed mods.
Which is to say that this is a pricey modification. As we noted, however, we see as much value in the cowlings improved engine access as in any speed enhancement. Further, as 201s begin to show their age, the original fiberglass cowls have incurred enough damage from weather, rain and vibration to be candidates for replacement. Given the cost of a factory-new cowl-if you can get one-we think LoPrestis new cowl for the Mooney is worth considering.
Keep a couple of things in mind, however: If youre upgrading an E- or F-model, make sure you get an accurate bottom line on all the additional parts youll need beyond the cowling itself. This will easily elevate the mod into the mid-teens or higher.
Second, well lapse into broken-record mode here for a moment. Although a modification in this price range will enhance the airplanes value, you wont recover all the costs, at least over the short term. Therefore, it makes sense to buy this mod if your stock cowl is worn out and/or youre planning to keep the airplane for a while and you can put that extra speed to use.Contact- LoPresti Speed Merchants, 2620 Airport North Drive, Vero Beach, FL 32960; 800-859-4757; www.SpeedMods.com.
-by Coy Jacob
Coy Jacob is an Aviation Consumer contributing editor. Hes also been in the Mooney modification business for 20 years and currently operates The Mod Squad in Venice, Florida.