4-place Builders with Continentals

[Mark Moyle]

I love that you've had a go at using a custom cowling. Good for you, the extra work will pay off with a great looking aircraft.

I note that the Mooney is a faster aircraft, and thus the cowl is designed with a lower cooling air inlet area. How will you tackle that difference?

The Acclaim had the turbo normalize 280 hp..more heat...then Mooney discovered the air inlets were to large and reduced the inlet...there is a formula to calculate the inlet out let. The other point is air density...the mooney flys at a much higher altitude...fewer molecules to vibrate...not to worried...good baffle fit should do the trick.....using the lancair 550 kit. Just have to make the baffles that fit around the cylinder cooling fins. 520 are the same diameter. 550 cylinder fins taper.


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[Glenn Patterson]

Mark maybe able to create a pressure cowl similar to those built by James Aircraft & LoPresti. He has the right cowl shape for a high performance cowl. James Aircraft make the eductor rings or they could be formed into the cowling. An eductor is easy to build and accelerates air or water through a necked opening to increase flow & pressure downstream. A pressure cowl improves engine cooling and reduces drag significantly where airplanes can pick up more speed with them. Schmidtbauers Mustang II uses a pressure cowl and through his constant streamlining has it flying over 250 mph. The big improvement was the induction cowl with a pressure plenum. A lot of air comes back out with regular nose bowls that create a lot of drag. There was an article on him in Kitplanes and my friends saw his presentation at Oskosh about 5 years ago. He said that it started at 190 mph and he cleaned it up so it goes around 260 with the same engine. He know can dial it way back and cruise at 200 burning far less fuel. Kent Paser's book Speed with Economy would a similar story. Here is some information that shows pressure plenums and induction cowls.

Here is some good information on engine cowls, plenums inlets, air filters etc..

http://www.n91cz.com/index.htm

[Battson]

I did a rough copy of the James aircraft cowl's features, including the ducts from the inlets for cooling and attempted ram air induction, modified for the Bearhawk. I didn't use a plenum, for maintenance reasons.

I would not want any less inlet area for my set-up, YMMV. My inlets are the BH standard. My outlet is a streamlined 100 square inches with cowl flaps closed, or 130 with cowl flaps wide open, which reduces temp by 25-30*F in summertime. It also costs me a several knots of airspeed with cowl flaps open, which I've noticed at lower altitudes only. They are always shut higher up, it's cooler up there.

[Glenn Patterson]

Your set up sounds good. I would like to have done a James style cowl as well. The prop location left no space to be creative. The inlets were ducted up to the baffles and sealed the baffling to the cowl and nose bowl. The upper baffles are sealed up tight all around. Our engine has everything on the top side so a closed plenum would not have worked either. It is amazing the effect of the cowl flaps & the lip around the air outlet opening. One thing about building a BH is that we all get a good education and learn to adapt.
Glenn

[Mark Moyle]

Great information. Building a pressure cowl is one direction I thought about taking... The plenum information seals the deal.... My cowl flap will be in the original Acclaim location. Will also be using one of the NACA inlets...and perhaps a KN filter.


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[Glenn Patterson]

The top of your engine looks suitable for a good plenum. I believe James Aircraft make cowls for RV10's with Lycoming 540's. I was a member of their forum for a couple years. They make the aluminum intake eductor rings that builders may use to create their own cowls. I was trying to find articles that I read on the rings being installed. The eductor rings is what makes the James cowl so efficient. An eductor is a short cone & a long cone with the small ends butted together. The air accelerates through the necked down short section and creates a vacuum on the back side that accelerates the air more to pack in more air in than would normally go through a plain opening of the same size. James aircraft rings for a 540 would work for a 520. There was an article in EAA or Kitplanes on installing the Jame rings. The key to the pressure cowl or any cowl is to make it as friendly for flow as possible and eliminate turbulence. Some duct the air out of oil coolers down to the cowl exit to make their coolers more efficient. We installed an aluminum flashing that is the shape of a half tear drop to make a soft corner over the sharp corner of the fire wall at the cowl air exit to reduce turbulence to promote laminar flow at the exit. There are lots of examples of that out there. The nice thing about a pressure cowl is that it really puts the air through the engine and it is sealed so no air or pressure is lost to the propeller opening. The next challenge is to get the air out without using drag to induce flow. The one advantage of the Continental IO360 is that there is nothing under the engine except the exhaust. I saw an article where they installed an inverted box in one model of airplane that is the width of the oil pan with the top plate an inch or 2 under the oil pan and the sides go down to the floor of the cowl. This creates essentially a left & right duct under the cylinder banks to clean up airflow to speed up the air to exit the cowl and it eliminates all the turbulence around under the engine. Once that mod was done then it eliminated the need for the cowl flaps. It is an interesting concept.

I had a conversation with some AME's at our airport facility about air in and out. They said the air in is easy but the key is to exit the air efficiently.

Glenn

[Mark Moyle]

Thanks Glenn. I like eductors, they work well. Incoming air is the motive force, once through the narrowed section the gradual taper creates kinetic energy. Acts like a pump. Built a 12" eductor dredge in VZ. And a 4" eductor dredge in Spokane for use in Cambodia.


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[Mark Moyle]

I wonder if I could do something on the Pacer cowl inlets? They're not round. The nose bowl inlets looks very similar to the Bearhawk's bowl. I have to make a new lower cowl....I ground off aluminum at the right bottom section rendering the thing junk. I'd like to not install the exit lip like the Bearhawk uses. Maybe a cowl flap like Jim Yonkin's pacer. Today I should be finished with paint prep. Sandblast/paint is booth now clean...Hanging all small and large steel parts. Using Superflight system 7.


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[whee]

I'm planing to use cowl flaps like Battson did.

[Glenn Patterson]

[QUOTE=Mark Moyle;n10270]I wonder if I could do something on the Pacer cowl inlets? They're not round. The nose bowl inlets looks very similar to the Bearhawk's bowl. I have to make a new lower cowl....I ground off aluminum at the right bottom section rendering the thing junk. I'd like to not install the exit lip like the Bearhawk uses. Maybe a cowl flap like Jim Yonkin's pacer. Today I should be finished with paint prep. Sandblast/paint is booth now clean...Hanging all small and large steel parts. Using Superflight system 7.

The cowl limits options somewhat. We were faced with a similar situation using the std, BH nosebowl. Seal up & make the baffling as air tight as possible to eliminate all the air leaks. A big clean up is to seal around the prop opening so that air cannot exit. About 15% of the cooling air can exit back out the prop opening. If you have a Lycoming with updraft them you could build a plenum ducted to the air inlets. I ducted the air inlets back as tight to the engine as possible. The air runners and the need to easy access the fuel system on top of our engine frustrated building a proper pressure cowls. The old baffles were used as a pattern to build new ones that fit the engine to our cowl and nose bowl. Would louvers placed towards the back of the cowl underside not assist cooling? My partner wants to use louvers if there is not enough air flow as he insists that they create no drag, I have not looked into louvers much. Our AME friends are telling us to wait until we have it running before using louvers and to be careful where they are installed so the air does not short out and the engine does not cool evenly. We will paint a set in case.
Glenn

[Battson]

It is easy to use ducted inlets with the standard BH nose bowl, and I would highly recommend it.

Just don't make your outlet too big, if you do use an efficient cooling system. 100 sq-in is too much during winter, LOP means the engine runs too cold. I wish my cowl flaps closed down the outlet area a little more, when shut.

[Mark Moyle]

On the Pacer I'm using Airforms Inc baffles..heck of a lot better than the stock baffles, Vans oil cooler plate to shut off the air flow through the cooler. For the Bearhawk's 520 Lancair uses a box and lid around the oil cooler to shutter air flow. The Lancair baffle kit has plates to seal tight around the prop/crank flange... I'm using prop heat off a 2006 cessna...will need to see if the brush ring will clear the baffles? Will probably need to fabricate a couple plates to partially block the cowl inlets for winter operation. This winter NOT. Haven't seen anything colder than 20 degrees...last fall was grounded until the temps got to -25 degrees.


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[whee]

I've been looking into this a little more. I made calls to Lycoming and Continental last week to get explanations of the weights listed in the TCDS. TCM weights include everything but oil. Lyc weights include everything but oil, starter and alternator. Add 30lbs to the Lyc numbers to compare to TCM numbers. Also the Lyc tech said angle valve cylinders weigh 5lbs more each than parallel valve so that is 30lbs for the 540.

I ran some numbers based on the weight and balance I have for a 180hp Bearhawk to see how the CG worked out for each. The Lyc O360 BH weighs 1270lbs CG 12.61". Based on my rough numbers a O540 in that airframe would come out at 1320lbs CG 11.03". Does that seem close? A IO520B BH would be 1343lbs CG 10.34". That moves the CG further forward than I'd like. If we move the engine back to 52.25" like Mark M. did then we get 1343lbs CG 11.32". That seems pretty good to me. And just for kicks, a IO550B placed at 52.25 would be 1341.6lbs at 11.36".

These numbers are rough and include some assumptions that diminish the accuracy.

[Mark Moyle]

52-1/4"......datum to prop flange.


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[whee]

Thanks Mark. I must have been smoking something good tonight because I ran the numbers 10" short. Will redo tomorrow Sorry guys.