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Blue on Top

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11 minutes ago, Cargil48 said:

Except for one thing, my friend: The extra pressure you create which makes the excess water not going in and turning around the tin can translated to aviation is called one horrible word: drag...

But in the case of the airplane, all that air is going to flow around the cowling anyway. 

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5 minutes ago, PT20J said:

But in the case of the airplane, all that air is going to flow around the cowling anyway. 

But the spot at the cowl intake is stagnant, all.of the air trying to enter cannot, so it must find a way around the cowl. This is drag . . . .

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If you want the max air going through the cowl intake, open the cowl flaps all the way.    On my airplane this slows you down about 3-4kts.   If you close the cowl flaps completely, it goes faster.   This minimizes the air going into the cowl intakes.   There's enough that still goes through to keep the CHTs happy, but it's a lot less than if the cowl flaps are open.   The air that can't go through the intake due to the flow restriction goes around the outside of the cowl.   It's still faster to do that than to open the cowl flaps, at least on my airplane.

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17 minutes ago, Hank said:

But the spot at the cowl intake is stagnant, all.of the air trying to enter cannot, so it must find a way around the cowl. This is drag . . . .

Take an unopened tin can and hold it under the faucet. Looks pretty much like the opened one with a hole in the bottom. Most of the water flows around the can in both cases. The can is analogous to the airplane and the water is analogous to the air. In the airplane flying along at 160 kts, most of the air is going to go around the cowling either way.  

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its all about the effect of static pressure...take your can you speak about....put the can in your hand and let the air flow into the can as you spin in a circle to some degree it will act like a parachute...now take the can and cut out both ends, and you will find a lot less resistance doing the same exercise...

when the air flow gets backed up, it causes a high relative static pressure contributing to drag.  On the other hand, when you significantly open the cowl flaps, you change the surface airflow increasing aerodynamic drag.

my point is that completely closed or completely open will add to your total drag....optimum point is probably 1/2" open....my guess, not scientific

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4 minutes ago, larrynimmo said:

my point is that completely closed or completely open will add to your total drag....optimum point is probably 1/2" open....my guess, not scientific

My J is fastest with them in the closed position.   I have closed, half-open, and full-open positions selectable.   On most aircraft the "closed" position is there to minimize drag at cruise.

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1 hour ago, Hank said:

Regardless of how far the cowl flaps close, the open area needs to be slightly larger than the intake area on the cowl, else you won't have good flow. Bad flow creates drag . . . High power operations require more flow, so a larger exit. In low power cruise, the exit can be reduced but must still be larger than the intake. 

Exactly my point!...

PS: Unless the air pressure inside the engine compartment blocks the incoming air as PT20J says. But that "delta P" in my opinion results in drag since it is resistance to the airflow. It may be insignificant, maybe. Take that tin can with the small hole at the bottom he quoted, hold it firmly with your hand, step inside a car sitting on the right side, open the window and hold that tin can against the airflow at 60 mph. See what happens, what you feel in your hand and in the arm and tell us afterwards the outcome of the experience... :D 

Edited by Cargil48
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My point is simply that most of the airflow arriving at the cowling is going to go around the cowling (causing a certain skin friction drag) whether there are openings or not. When some of the air is diverted for cooling, there are losses involved which are highly dependent on the cowling design. Now, time to quit before someone brings up Meredith effect.

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5 hours ago, Austintatious said:

They aerodynamic questions I have are speed related.  When looking for efficiency, it all matters.

Does anyone KNOW how much extra speed the inner gear doors are worth?  My rocket does not have them and I am considering getting them and installing them...  but I would like to know if it is WORTH it or not. To me, worth it would be a 3+ knot gain

Is it really true that the elevator flying slightly TE up has no effect on speed?   I recently flew my aircraft with full aft CG and still my elevator was TE up in relation to the stab.  Seems to me they should be in line with one another in cruise for maximum speed, especially at aft CG.  However I have been told here that they all fly TE up and that it is of little penalty.

On a Rocket, should the cowl flaps be closing all the way?  I have seen 3 of them and on all of them the cowl flaps stay open about 1-2 inches when in the closed position... this seems like it would cause some extra drag.

Has anyone quantified the speed gain from switching from the towel bar antenna on the vertical to the plate style?

Many of my access panels below the wing have somehow become concave... I have no idea how this has occurred, but I cant help but think they are causing extra drag.  Would it be worth replacing these panels with ones that are not concave OR removing and working the existing ones so that they are flush with the wing.?

 

I feel like all these things alone make little difference, but when you start to add them up, perhaps a 5-10 knot gain could be had?  I seem to be about 10 under book numbers and these items are the only things I see that might account for that ( well that or optimistic marketing)

My cowl flaps seem to close a lot - but not completely closed.  It seems as if it closing as designed.  I don't know.

Sometimes I think about cutting my step off...

Forget replacing your nav antenna - hide them in the wing tips.  I wonder how much speed that is worth?

Inner gear doors - and also smooth belly are then the only things left I could do.  I bet there is another 5 knots to squeeze out.

Well you could do the wing shaping that Byron did...

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55 minutes ago, PT20J said:

My point is simply that most of the airflow arriving at the cowling is going to go around the cowling (causing a certain skin friction drag) whether there are openings or not. When some of the air is diverted for cooling, there are losses involved which are highly dependent on the cowling design. Now, time to quit before someone brings up Meredith effect.

I referred already to it, citing the P-51...

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7 hours ago, EricJ said:

So a cool thing to have would be a plate antenna on a swivel axle mounted such that the antenna doubles as an angle of attack indicator.    It minimizes the drag of the antenna and provides an AOA estimate from relatively clear air (I'm always suspicious of the ones mounted near or under the wing).

I love your idea! (though I don't think it will work).

Trust the AOA vanes that are near the wing, they work well, but that is another topic entirely.

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Engine cooling is a really, really complicated problem and one that can't be modeled very well.

Bottom line is that the inlet openings and cowl exits are designed solely for cooling the engine/engine compartment/engine accessories during a maximum gross weight climb, maximum electrical draw, Vx climb on the hottest day the airplane is certificated for.  That's the reg.  Drag on the other hand is all the OEMs issue.

One can think of the engine cowling and cooling as a converging-diverging nozzle.  Air comes in the inlet(s), is slowed to near static (to gain the positive effects of dynamic air pressure, ~1psi at 200 knots), shoved down through the cylinder fins and reaccelerated to exit out the bottom of the cowling (down draft cooling … which is to keep the engine fire and smoke off the windshield in that event).  So, at speeds above Vx, more than enough air is available at the inlets and the excess air needs to go around the inlets.  This is why the lower drag inlets are round.  The slower we can push enough air through the cylinder fins, the more heat we can transfer to the air.  We want the exit air to leave the airplane at the airspeed of the airplane (lowest drag),  As mentioned previously, opening the cowling flaps all the way in cruise will cool the engine better (slightly), but because the cowl flaps form a low pressure area on an aft facing surface/area, it increases drag.  We all know Mooniacs and Draggiacs have been feuding like Hatfields and McCoys for decades.

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the following list is only private pilot logic... stuff I learned while hanging out on MS...


One of my favorite topics... Cool!   :)

Our engines have a few ways of dissipating heat...   throwing it overboard one way or another...

1) Most of it goes out the exhaust pipe...  we control this using the mixture knob...

2) a fair amount goes out the radiator... we call that the oil cooler.... where the oil cools a good part of the cylinders and a turbo if you have one... temp control provided by a temperature controlled valve... and a plate in front of the cooler on really cold days... essentially modulating the surface area of the oil cooler...

3) airflow around the cylinders, and engine parts seems to draw a lot of focus...  if we close the flaps completely... we haven’t really stemmed the tide...

4) My O got its cowl flaps screwed shut completely... it has no cowl flaps...

5) Air is compressible... but how this affects the air passing through the system would only change the openings a few mms... take a gander at the Acclaims air inlets where the less compressed air is available for cooling in the FLs... then compare them to the O’s air inlets for the same HP, down low...

6) See how Ovation-like your air flow is with the cowl flaps closed.... If the front of your home let this much air flow through... you couldn’t afford the heat this way...

7) Anyone with a dog house around their cylinders knows how important small passages can be for maintaining cooling... apparently some small cracks in the wrong place allows lots of air to escape without passing over the cylinders cooling fins....

8) air cooling... Surface area and wind, is needed for heat transfer... more surface area exposed to the wind the better the heat transfer...

9) Drag... Surface area and wind again... more surface area exposed to the wind the stronger the drag...

10) We need some air-cooling... so we are going to get some drag with that... 

11) On those really cold days, when air cooling is really working well... we are stuck with more surface area and drag than we need...

12) Same challenge with the oil cooler size...

13) Big deal..? we learned it is all part of the compromise... :)

14) Drag not related to cooling... Austin’s topic of the week.... the apparent trim required to hold the tail down in flight... for stable flight our Cg is in front of our Cl... and our pull on the tail balances the forces at zero...

15) The tail continuously balances these forces through the entirety of the flight... the pilot does this by adjusting the trim...

16) On a different day with a different WnB... the tail feathers are again operated through a different range...

17) That single tail design, with variable negative lift... works through the entire range of flight... from T/O to landing... including cruise, and descent near Vne... from completely empty to filled to MGTW...

18) For anyone with a pic of tail trim in action in cruise... let’s get a few more pics of what things look like at the other trim extremes... my favorite trim position... flying solo with some weight tied down in the back... the balance is pretty close to the back of the envelope... speeding along in smooth air descending near Vne... the trim wheel is pressed into duty... minimizing any down force left on the tail...

19) Recognize there is still downforce on the tail... the whole in flight stability thing has to still be there...

20) It is possible that the engineers at the factory have not completely wrung all of the inverted lift available from the tail design and use elevator trim to get that last few pounds out of the system....

21) To determine if setting the trim to zero works... set the trim to zero on the ground... note the zero line on the indicator...

22) in flight... in all the various conditions... what condition of flight is nearest to having zero trim...

23) It’s only a PP guess... Austin doesn’t load the plane to the back of the envelope, fly at Vne, and take pictures.... while referencing the actual trim position and how close it is to the zero trim line....   :)

Still splitting hairs... we took the trim out but now are modulating the inverse lift to zero using our arm strength...

Ask Amelia how long that can last...? :)

24) Each speed mod listed on the Lasar website has a speed gain next to the price column... there are three that have enough value to gain interest by many people...

25) Paying for speed increases... pretty tough to do... they are horribly expensive for each knot...

26) The easiest way to justify the expense... If everyone in your family is comfortable flying for X minutes... and your usual trip is Y miles long... your plane needs to go fast enough to cover Y miles in X minutes...

27) Side note... the O was designed to get my family to my wife’s MIL’s house... before the traveling became the uncomfortable part... :)

28) Speed is of the essence...

 

Holy cow! There really is a lot of engineering involved in building the worlds fastest, factory built, four seat, airplane...

Go Mooney!

PP logic only, not an aero-engineer of any form...

Best regards,

-a-

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14 minutes ago, carusoam said:

5) Air is compressible... but how this affects the air passing through the system would only change the openings a few mms...

Holy cow! There really is a lot of engineering involved in building the worlds fastest, factory built, four seat, airplane...

-a-

Yes, air is compressible, but below M=0.3 even engineers ignore it.

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Holy cow, what a topic!!... 

Reading all what has been said here (and elsewhere too...), I ask one thing: We all speak of regulating the air OUT of the engine compartment and the cooling effect this change has on the engine. That's the norm. But the same way as the amount of air cooling the oil radiator is changed by an electrically operated baffle why does one not do the same on the INTAKE side of the cooling air, the way I designed on the pic below?

You want max cooling effect? Select OPEN and the (red pictured) baffle is horizontal letting all of the air reach the cylinder heads. You need less cooling? The adjustment has to be made through the proper selector on the panel. You want NO AIR cooling the cylinder heads? You choose the CLOSE position and the incoming air is fully diverted DOWN passing under the engine's oil sump and going out through the cowl flaps with a minimum of drag. This way, the air going in through the front cowl's openings get's out, cooling or not the engine, at your wish...

Engine-Cooling-System.gif

Engine-Cooling-System-2.png

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... Many of my access panels below the wing have somehow become concave... I have no idea how this has occurred, but I cant help but think they are causing extra drag.  Would it be worth replacing these panels with ones that are not concave OR removing and working the existing ones so that they are flush with the wing.?

i brought this up a few months back and made a slight change to my ugly paint 65C. I purchased some 4" wide 3M 471 and taped up all the forward inspection covers, doing away with those gaps. I haven't put in a doubler yet to get rid of the concave feature, but found that the plane flew noticeably smoother after the unsightly addition. I have some ideas on how to proceed with a more permanent solution, but all require time, which is in short supply in my life at the moment. I also wonder whether modifying the larger, rear panels would be as effective due to their position on the wing, aft of the spar. 

Open to criticism or improvements of my idea.

Patrick

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4 hours ago, Cargil48 said:

Holy cow, what a topic!!... 

Reading all what has been said here (and elsewhere too...), I ask one thing: We all speak of regulating the air OUT of the engine compartment and the cooling effect this change has on the engine. That's the norm. But the same way as the amount of air cooling the oil radiator is changed by an electrically operated baffle why does one not do the same on the INTAKE side of the cooling air, the way I designed on the pic below?

You want max cooling effect? Select OPEN and the (red pictured) baffle is horizontal letting all of the air reach the cylinder heads. You need less cooling? The adjustment has to be made through the proper selector on the panel. You want NO AIR cooling the cylinder heads? You choose the CLOSE position and the incoming air is fully diverted DOWN passing under the engine's oil sump and going out through the cowl flaps with a minimum of drag. This way, the air going in through the front cowl's openings get's out, cooling or not the engine, at your wish...

Engine-Cooling-System.gif

Engine-Cooling-System-2.png

The Yak-52 has that setup. Not sure it makes much difference where you put the throttle to control the airflow.

Skip

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Cargil48: Flow around the airplane is more efficient than flow through the engine compartment.  As Skip mentioned, you can throttle at the inlet or exit.  OEMs look at failure modes (either way hurts the same here), complexity and part count.  Exit openings are the easiest.  In fact, the Ovations don't have those because people complained that they were too complicated, maintenance was high, cowling removal was difficult and cost too much … for 3-4 knots.  I like the innovative idea!

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7 hours ago, Johnnybgoode said:

... Many of my access panels below the wing have somehow become concave... I have no idea how this has occurred, but I cant help but think they are causing extra drag.  Would it be worth replacing these panels with ones that are not concave OR removing and working the existing ones so that they are flush with the wing.?

Patrick

All clean up of steps and gaps will decrease drag.  As the airplane gets smaller (like Mooneys), what we call crud drag becomes a larger percentage.  For example, 20-25% of the drag on a business jet is crud drag (antennas, steps, gaps, etc.).  On a Mooney, that value goes up to ~30%.  Smooth is good.

You are also correct in that the further aft on an airplane the less it matters (the boundary layer is thicker), but it all matters.  You're an inspiration!

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6 hours ago, PT20J said:

The Yak-52 has that setup. Not sure it makes much difference where you put the throttle to control the airflow.

Skip

If you put flaps on the output, or even a little lip like a Gurney flap (like on a Cherokee/Arrow or a C172, etc.), it helps to create low pressure on the back side which can help increase flow.   A throttle on the input won't do that.   We do this for cooling air and such on race cars all the time.

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12 hours ago, EricJ said:

If you put flaps on the output, or even a little lip like a Gurney flap (like on a Cherokee/Arrow or a C172, etc.), it helps to create low pressure on the back side which can help increase flow.   A throttle on the input won't do that.   We do this for cooling air and such on race cars all the time.

Eric, you start pointing at the essence of the whole thing. My experience comes also from the racing car aerodynamics, especially on high speed circuits. One difference, a vital difference, is however that in car racing you need always air to cool down the engine, in aviation using recip engines not. And this is what we are debating here in detail. Let's analyze the formula cars because it's easier: On the side of the car and in front of the radiator opening there are the so-called "bargeboards" which start very close to the chassis, but soon begin to expand and connect to the edge of the floor in front of the sidepod intakes. These "bargeboards" are curved and are the part number 1 in the pics I show here. Now, the important part is: According to the circuits and the weather and correlated temperature, they change the bargeboards before the race for letting more or less air going into the air intake for the radiators. Why? Because the more air one lets in, the more drag it produces, and in high-tech racing this is vital. What I showed in the design I made above was exactly the same: A movable "flap" (either mechanically driven by a lever on the dashboard or automatically driven by a thermostat) and this movable flap (I draw in red) directs the incoming air either to fully hit the cylinder heads, or partially or even not at all, in this case directing the incoming air DOWN directly to the exit, to the "fixed cowl opening" the author of the original pic shows very well. The pic is not mine, I only draw that red flap, so the original author opted for a fixed cowl opening for a reason... and the reason is the INCOMING air flow, for aerodynamic reasons. If one needs it or not for cooling, that is regulated by those bargeboards (in racing cars) or with a movable flap just after the air intake to direct the air to where one wants it to go (in airplanes). In airplanes, this may be a detail, costing maybe 3 or 4 knots, in car racing this difference is vital... And y'all can believe me: the rules of aerodynamics are the same...

area-behind-front-wheels-side.jpg

area-behind-front-wheels-top.jpg

Edited by Cargil48
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On 12/6/2019 at 10:37 PM, Blue on Top said:

 

One can think of the engine cowling and cooling as a converging-diverging nozzle.  Air comes in the inlet(s), is slowed to near static (to gain the positive effects of dynamic air pressure, ~1psi at 200 knots), shoved down through the cylinder fins and reaccelerated to exit out the bottom of the cowling (down draft cooling … which is to keep the engine fire and smoke off the windshield in that event).  So, at speeds above Vx, more than enough air is available at the inlets and the excess air needs to go around the inlets.  This is why the lower drag inlets are round.  The slower we can push enough air through the cylinder fins, the more heat we can transfer to the air.  We want the exit air to leave the airplane at the airspeed of the airplane (lowest drag),  As mentioned previously, opening the cowling flaps all the way in cruise will cool the engine better (slightly), but because the cowl flaps form a low pressure area on an aft facing surface/area, it increases drag.  We all know Mooniacs and Draggiacs have been feuding like Hatfields and McCoys for decades.

Yup. its about the higher pressure, slower air.

Also,  few realize that 737s have no wheel doors. 

 

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If you really want to get into the details of airplane cooling design, check out resources at EAA. There’s lots of good information there. Homebuilders have two great advantages: engineering time is “free”, and they can optimize a design without worrying about production cost.

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"Speed with Economy" by Kent Pacer is a great real world drag clean-up book!  It is for Experimental aircraft, but as got noted above, airflow is well airflow.

For those that are thinking of experimenting, I'll give a couple words of caution.  Modifications that affect type design data are not legal unless the airplane has been put in an experimental category (R&D, show compliance, market survey, etc.).  One is often surprised by a little change that makes a large difference.  Oh, and that insurance thing, when they find out, modified airplanes are not covered by insurance.  With that said, let's do some really cool stuff!

PS. Once air goes into an enclosure (the inlet on an airplane), a price will be paid for any changes before it exits.

 

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40 minutes ago, Blue on Top said:

"Speed with Economy" by Kent Pacer is a great real world drag clean-up book!  It is for Experimental aircraft, but as got noted above, airflow is well airflow.

For those that are thinking of experimenting, I'll give a couple words of caution.  Modifications that affect type design data are not legal unless the airplane has been put in an experimental category (R&D, show compliance, market survey, etc.).  One is often surprised by a little change that makes a large difference.  Oh, and that insurance thing, when they find out, modified airplanes are not covered by insurance.  With that said, let's do some really cool stuff!

PS. Once air goes into an enclosure (the inlet on an airplane), a price will be paid for any changes before it exits.

 

Mooneyspace message to you please.  Thank you Ron.

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