Cowl Flaps

[corefile]

As I overthink everything while I'm waiting to pull the trigger on my 4place QB. After reading a few post about the challenges some are having with keeping their engine temps within range, and all the different option, better baffling, lip on the bottom cowl section where the air exits, louvers, and cowl flaps. I saw this (not trying to promote the product) was just wondering if anyone has looked at it or maybe even is using it, looks like a well made set of cowl flaps for the the RV's, but don't see any reason it could not be put on the bearhawk.

[whee]

Looks like a pretty nice setup. I'm pretty sure I'll be installing cowl flaps and this could be a good way to go. Wish they offered it with less joggle that 1/4".

I'm considering installing my cowl flaps on the sides of my cowl like the Carbon Cub. I guess they are more effective there than on the bottom.

[Mark Goldberg]

I do not have cowl flaps on my 540 powered BH and have not needed them. I know some have installed them and like them. But do not take it as a given that you have to do this to control engine temps. It does add weight and complexity. Mark

[EricP]

I am going to agree with Mark on this. If you really don't need cowl flaps it is just extra time, effort and money (as well as weight) to add them. Unless you are doing something that you know will make your engine run hot compared to the standard installation I would not plan on using them and only add them if it turns out you need them.

[JimParker256]

Yeah, I'm bookmarking that site, in case I wind up with a "hot" engine that cannot be solved otherwise. It's a really easy (and nice!) way to solve an otherwise very challenging problem.

But I really don't anticipate needing it, given the experience of other 180-HP Patrol builders...

[kestrel]

My O-540 powered 4-Place generally cruises with 300F on the CHT gauge. No cowl flaps.

[whee]

As shown the BH does not need cowl flaps in most situations. There are two reasons I plan to install cowl flaps:

1. I am installing a TCM IO360 which I'm told makes a fair amount of heat and requires good engine cooling control. I'd rather install the flaps and not need them then have to add them afterwards.

2. Looks. I'm not a fan of the large lips sometimes put on the lower cowl to help with cooling issues. I think they are ugly and yes I have seen them on BHs.

I don't want a lip like this (I purposefully chose a plane other than a BH so I didn't offend anyone here by calling their plane ugly):


Battson has a nice smooth looking cowl and I am going after the same look. Notice no lip on the lower cowl and he does have cowl flaps.

[Battson]

Corefile, interesting find. Making cowl flaps took some time, about 8 hours work without install.
For my money, I think the those ones from AntiSplat are a little on the small side.

I am always wishing my flaps closed up tighter. It's winter here, and I have to run richer than normal to keep my engine above 150*C (300*F). Anything colder than that for cruising, and you get problems with the engine long-term. In fact, Lycoming recommends CHTs average about 370*F for greatest engine longevity.

It costs me about an extra gallon per hour in winter, just to keep my CHTs above the yellow range (300*F), and in a cruise-descent from high altitude there is no way I can keep the CHT above 140*C (285*F). I am planning to modify my cowl flaps to make them close tighter, once I figure out an elegant way of retrofitting it. I wish I had made them close up smaller to start with.

[Bradrock]

Jono - you talk about struggling to keep your temps up. How often are you needing the cowl flaps open for cooling though?

[Battson]

Jono - you talk about struggling to keep your temps up. How often are you needing the cowl flaps open for cooling though?

Hey Brad,

I am using them with almost every change in flight regime. Here are some examples:

• Moments when I could be applying full power for more than a few seconds. e.g. take-off, manoeuvring in confined spaces.

• During any cruise climbing. e.g. In winter, I can climb at maybe 90kts with them closed, but any steeper and they need to open. In summer, I need to be over 100kts unless the cowl flaps are wide open, which is less than 500ft/minute. So most climbing in summer means wide open. But even with the flaps open, an extended Vx climb isn't possible in summer.

• When I am setting up for an approach, 5 minutes out I open the cowl flaps, habitually. By doing this, I arrive at the top of the base leg with the engine 25*F colder. Cold enough to close the throttle when required, without setting off my shock-cooling alarm. Otherwise, I would have to reduce power very gradually, about 2-3 inHg of MAP per minute, which means slower cruise speed as I near the airport. Of course, some will say shock cooling is really only a problem in TCM engines, but I would rather aim for 3500 hrs TBO than 2000 hrs.

• Prior to every landing, I always have them wide open in case a go-around is required. Especially in a backcountry situation.

Of course I have a bias - but I have to say, I am really happy I have them. Controlling >250hp requires proper cooling to make the engine last. If you look to GA, more installs of an engine that big will include cowl flaps, than will omit them.

People say they are heavier and more complicated, I don't really agree. Other (common) mods are heavier and more complex (more work for the builder) like an autopilot or a Kydex interior. All of the above are optional, and builder preference is what it comes down to. I am a mechanical engineer, so I like taking good care of my engine.

Jonathan

[EricP]

Years ago I used to fly both an A-55 Baron and a C-414A Chancellor for the same job. So I was flying both aircraft a lot. The Baron had normally aspirated engines at 260 hp each while the Cessna had turbo intercooled engines at 310 hp (later 325) per side. The Baron needed the big cowl flaps it has while the tiny cowl flaps on the Cessna 414 seemed like they were just there for show. So it really depends on what your engines turn out to need. I would have guessed the opposite of what happened in my case so I think each Bearhawk will have individual needs due to all the differences in our homebuilt planes.

[svyolo]

I am finishing up the last few details on the firewall, cabin heat and control cables, and two cables for the alt air door and cowl flap. The problem with the cowl flap being on the bottom is you have to disconnect the cable to remove the lower cowl. Any good ideas on how to put the B nut where you can access it? Even if I did an electric cowl flap you would need to disconnect the actuator to remove the cowl.

Not building the cowl yet, but want to figure out where to put the cable.

[jaredyates]

If I were to have made an electric actuator, I would have put those wires on a single weatherpack connector along with the nosebowl LED. That way a single plug would cover all cowling matters.

[svyolo]

Yeah, I have been thinking about what needs to get disconnected to drop the cowl. If I use a cable, I guess I can have the cable push straight down, and expose the B nut when it is open so I can remove/install the cable.

[Battson]

You just have two pins connecting the flaps, with spring clips holding them in place. Takes no time at all to disconnect.

[Gerhard Rieger]

I plan to install a single cowl flap like the Cessna Hawk xp use, it will align with the tunnel and when open will enlarge it more than the fixed standard cowl opening. I have installed a throttle vernier to regulate the movement and can lock it in whatever position makes the engin happy. The cowl flap will be open when the vernier is pushed in completely ensuring that takeoff is done with it open. When closed the vernier will be extended and in the way when you climb into the cockpit. In South Africa’s north west where I live we have summer temps in the 40 deg Celsius, it would in my opinion, be of necessity to install one.