Bonanza cowl flaps

[Caldemeyn]

Hey all.

A question, even though its written to close them for cruise, in the plane i see that full down they only cost me 2 knots but CHT's fall somewhere to about 20-25° C less, i would call that a bargain as far as engine longevity is concerned . Or am i introducing something bad here and not know it yet ?

[Scav]

Cruising with them deployed can be hard on the linkages in the real thing. This is coming from a few years back when a Bonanza owner took me up in his aircraft; I remember clearly him reeling the flaps in as soon as we were up and explaining that to me.

[Caldemeyn]

Hmm that may be true, still its a bit strange, they should be rated for such speeds on the other hand its written to close them, so maybe thats why ?

[Scav]

Hmm that may be true, still its a bit strange, they should be rated for such speeds

True, true. If I remember correctly the rationale also was that this was a 40+ year old aircraft and the owner was a) very proud of it, and b) not wanting to stress moving components unnecessarily, and c) a Bonanza owner doing Bonanza things.

[Caldemeyn]

Yup, wouldn't want to get into someone's head with my heresies especially bonanza guy.

[Scav]

Yup, wouldn't want to get into someone's head with my heresies especially bonanza guy.

But . . . but . . . heresy is such a strong word! I prefer to think of them as dynamically applicable hypotheses.

[Caldemeyn]

"...You confuse me with your cowl flaps babblin, cessna peasant, now off with you before i send hounds after you"

[Scav]

And now for a more lucid, concise reason given some further digging:

The cowl flaps don't close off airflow in the closed position; at cruise there is still enough of a flow that under normal, proven circumstances, temperature stability is predominantly assured. As long as you're operating per the POH and environmental considerations (OAT, density altitude, humidity, etc.) are taken into account and everything under the fiberglass is in good condition, you shouldn't need to cruise with cowl flaps opened once you're in cruise configuration.

That being said, they are there as part of your complex training as a piece of the equation of engine temperature management (along with throttle, propeller and mixture) and your CHT gauge (or snazzy engine management panel you spent many AMU's to get) should be the queue you should take when deciding whether to run with flaps open or not while you're 'up there.'

That also being said, given the above conditions (CHT's within normal range, etc.) open cowl flaps do have a measurable detrimental effect on airspeed so it behooves the person riding left front to keep 'em closed when they're not needed.

Bottom line to the OP question: You're trading airspeed for cooling, but you may be invoking a mechanical issue in a real aircraft (bent control arms / snapped cotter pins, etc.) if you're bumbling along at 140+ knots IAS and you have the flaps wide open.

I think I've regurgitated this information accurately and correctly. Please correct me if I'm wrong.

[AKar]

So far with A2A Bonanza, I've had no difficulties in maintaining comfortable cylinder head temperatures with closed cowl flaps in cruise flight.

-Esa

[Caldemeyn]

Thanks guys for your opinions

Personally i don't have a problem with keeping the temps low at cruise, its just that most of the time lower chts are better and such a small decrease in airspeed for quite a nice gain with cht's seemed very lucrative from the perspective of elongating engine life.

But if this could end up with something broken then perhaps i'll revise my ways

[ClipperLuna]

I tend to take a middle-of-the road approach and leave them cracked open just a notch or two (unless I'm descending, then they're fully shut). I haven't had any problems yet keeping the engine CHT below 177C, and AFAIK that's cool enough to keep the engine happy and long-lived.

[Oracle427]

Parts for certified aircraft are terribly expensive. Take for example a piece of small piece of stamped aluminum, or aluminium for those who prefer to say it that way ;p~. The dimensions are roughly 2" by 3" with two rivets holding the two pieces together.

A picture for reference https://www.picclickimg.com/d/l400/pict ... racket.jpg

What would be a reasonable price for this with some margin? $50, $70?

How about $600? I had to buy a few of these recently on a restoration project. I found out that they are made from a rare alloy heretofore referred to as Textronium.

A cowl flap hinge alone may run over a thousand, but a cowl flap assembly will definetely be several thousand. These machines require a lot of babying to make all the parts last a long time.

[ClipperLuna]

I like that the file name on that part ends in "racket". At those prices, it is indeed . . .

[DHenriques_]

Generally speaking the way I've always used cowl flaps has been to mentally tie them to the CHT gauge in flight.
I use the POH recommendation for ground ops and takeoff and landing. I do watch their use closely on descent. Regardless of the arguments concerning over kill about shock cooling, I always treated my engines carefully by close monitoring of the engine temps. Many times I'd "crack" the cowls to stabilize a temperature.
Just consider the cowl flaps as a tool to help you maintain a good stable engine temp and you'll never go wrong.
Dudley Henriques