Horsham Aviation Services

Home of Quality Light Aircraft Maintenance
& Supplier of Aircraft Accessories

ABN 65 007 339 451
Horsham Aviation Services Aircraft at Sunset

Airugo Mods & Pro

Importers of Light Sport Aircraft &
Suppliers of Aircraft Modifications & STC's

ABN 60 120 285 887

Ph: +613 5381 1727    Fax: +613 5381 1626    Email: info@horshamaviation.com.au

Cessna 182 Series (Continental powered) Cowl Flap

Downloadable Order Form AUSTRALIAN (File Size 30Kb)STC Order Form AUSTRALIAN
Downloadable Order Form INTERNATIONAL (File Size 31Kb)STC Order Form INTERNATIONAL

Download STC Order Form and email or fax to us. Note that we need the information in our STC Order Form for our STC records

To buy please fill out the purchase details in the form or purchase online

Removal modification H.A.S.   S.T.C. AU No. ASA027ML and USA FAA No. SA01570WI approved for Cessna 182B (1959 year of manufacture) SN51557 through to 182R (1982 year of manufacture) SN 68160.

Cowl Parts
Cessna 182 Cowl Flap Mod kit includes S.T.C., Engineering Order (paper work package) and mod kit. Australian customers $AU700 + $25 Post & Packaging, plus GST. International customers $US700 + $AU70 Post & Packaging. (USD/AUD exchange rate used is the rate advertised by Westpac Bank)

Ever since I have known and worked on the continental O-470 powered Cessna 182 series of aircraft, premature cylinder problems along the lines of burnt⁄leaking exhaust valves due to worn guides and wasted valve stems and in some cases annealed piston rings have been all too common.

It has not been an isolated problem with continued reports from all around Australia and throughout the world as read in articles in the C.P.A. magazine. In a lot of cases engines with less than one or two hundred hours total time since new or overhaul have needed to have cylinders removed. One engine shop in Australia had overhauled 11 continental O-470 engines in a period stretching over two years. Since then 9 of these engines which have had a mixture of factory new and second run overhauled cylinders have all needed to have some cylinders removed for rectification.

Initially, we all pointed the finger at Teledyne Continental Motors (TCM), who tried 3 different types of exhaust valve guide materials and incorporated some other minor modifications. Unfortunately all TCM's efforts made no real improvement and the cylinder problems continued.

After 18 years of putting up with valve and softened piston ring problems in the TCM O-470 powered 182 installations, with my experiences as a licenced Aircraft Mechanical Engineer and interest as a commercial pilot, I have learnt that engine cooling and the condition of engine baffling and sealing rubbers is extremely critical to the T.B.O. of any air cooled engine.

Cowl Flap Fitted

Engine baffles and rubbers must provide a perfect seal so the cooling air is all forced down through the cylinders to provide adequate and even cooling. I have seen brand new TCM powered 182Q aircraft with perfect engine baffles run right into cylinder problems (all six cylinders were removed 76 hours after new due to leaking exhaust valves and annealed piston rings).

Cowl Flaps fitted to a C182P

It's also very important for the ignition timing to be correct. Even a slight advance will increase the CHT's notably

After 18 years of experience, I realised it was cowl flap control that determined the T.B.O. of the cylinders and the fact that they are not foolproof and in some cases inadequate to provide sufficient cooling to enable engines to reach their T.B.O. without cylinder removal, especially in warmer climates.

If you do not believe me just go to your 182 and close the cowl flaps, then have a look at the total air outlet area. In my opinion and experience it is not anywhere near enough for the two hundred and thirty horse power engine.

From observing other engine installations that have their engines repeatedly run through to T.B.O. without any cylinder problems, we came up with a target operating CHT of 300° F (about mid green on an accurate standard Cessna CHT gauge).

We acknowledge that these engines will certainly run fine with CHT's all the way up to the 460°F red line but have concluded that any operations with CHT's above 350°F will come at a cost and that is premature cylinder related problems. We now advise T.C.M. powered 182 owners to give their engines plenty of cooling air using cowl flaps and to try not to exceed our target CHT reading of 300°F (mid green on the standard Cessna CHT gauge with a Bayonet type probe). Note - add 50°F to our noted temperatures if a spark plug type CHT probe is being used. With our target temperatures in mind, we were now starting to see vast improvements in cylinder T.B.O.

We also found that our customers had to fly with their cowl flaps wide open to achieve CHT readings of 300°F when the ambient temperature reaches 30°C. Above 30°C ambient temperatures, CHT readings of 300°F and below could not be maintained, and when the ambient temperature is around 40°C the CHT's rise to approximately 450°F just short of the 460°F red line.

As we could not achieve our desired objective, which was to maintain the CHT readings around 300°F + or - 50°F and to make the cooling system fool proof we removed the cowl flaps and fitted fixed shortened type flaps with a trailing edge augmentor strip.

This made the cooling of the engine foolproof and lowered each cylinders CHT reading by 50 to 65°F with a medium amount of cooling drag.

The larger air outlet areas also make it a lot easier to carry out engine oil changes and remove the lower engine cowl induction air snorkel from the carby air box to facilitate lower engine cowl removal. It also eliminates the continued maintenance of the cowl flap hinges and control cables.

This modification without a doubt has certainly improved cylinder T.B.O. and has reduced the labour involved in engine oil changes and lower engine cowl removal. It is also easily reversible if the aircraft is relocated to an operating area where the ambient operating temperatures are very low (10°C and below).