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  #1  
Old 08-22-2007, 01:35 PM
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Default baggage pods

ok - the baggage pods that you buy are, from a drag reduction standpoint, attached to the wing at the wrong point, the leading edge. The is the worst place that i know of for attaching to the wing, anyone seen anything different?
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  #2  
Old 08-22-2007, 01:37 PM
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Default Re: baggage pods

Make your own pylons and pods?
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  #3  
Old 08-22-2007, 01:47 PM
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Default Re: baggage pods

I believe from the structural standpoint, and the ability to retrofit existing aircraft, the current pylon system is just about perfect.

The four bottom hard points support the weight while on the ground. The cuff and top points hold the pylon in place while airborne. The cuff is transfering all the drag loads of the pylon and pod to the leading edge of the wing. I don't think the four bottom hardpoints would be able to support the shear loads while in flight.

Although the cuff does add a small amount of drag, I'll bet it accounts for less than one percent of the overall drag of the p[ylon/pod system.

I also wager that any alternative attachment system would be heavier and draggier (is that a word?) than the cuff system.

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Old 08-22-2007, 05:24 PM
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Default Re: baggage pods

From everything I have read pilots don't notice any reduction in speed with pods on. If they have its only 1 or 2 mph hardly anything worth worring about.
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  #5  
Old 08-22-2007, 05:56 PM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: baggage pods

Quote:
Originally Posted by Dust View Post
...The is the worst place that i know of for attaching to the wing...
Fascinating. Learn something new every day. Why do you say this?

I wonder why all commercial airliners with wing mounted engines attach their engine pylons to/near/at the leading edge of the wing? Why don't you inform Boeing and Airbus that they're doing it all wrong...
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  #6  
Old 08-22-2007, 06:48 PM
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Default Re: baggage pods

My pods cost me about 3 - 5 knots.

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  #7  
Old 08-22-2007, 07:38 PM
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Default Re: baggage pods

Quote:
Originally Posted by Dust View Post
ok - the baggage pods ..are attached to the wing at the wrong point, the leading edge. This is the worst place that i know of for attaching...
If you are transffering your stabilizer leading edge knowledge to this application, me thinks the two locations might not go exactly hand in hand.

The strake to wing junction begins the lifting surface pressure zone, while the vertical stabilizer is functioning with a tremendous amount of low pressure diagonal air coursing down the leading edge towards it. The staggering of that winglet leading edge back from the wingtip leading edge is not functioning as I see it in the same manner as the pods leading pylon to wing connection in its relation to the dead air/wingtip aerodynamics.
But maybe I'm wrong.

Also noted is that the pods are removable for different flights and the front cuff captures the load and spreads it.
I guess a guy could build a fin/pylon connection sticking out of the bottom of the outboard strake end, away from the leading edge, and bolt to that...but when not using the pods- you'd have that mounting tab sticking out into the airstream. Aero dynamaniacally Butt-ugly.

Since the pods hurt you only a few mph and are so easily and cleanly removable...I'm thinking that the present pod/pylon/attach config is a square wheel that I will live with.
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Old 08-22-2007, 08:38 PM
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Default Re: baggage pods

Hopefully this fall I will be able to report some numbers on the forum with and without the larger Gary Hunter pods on a MKIV. They are an easy on/off with the four screws and cuff. I am sure Thane will want to know the penalty of the pods however slight. I won't even comment on Dusts "factual" statements.
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  #9  
Old 08-22-2007, 10:41 PM
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Default Re: baggage pods

Quote:
Originally Posted by Marc Zeitlin View Post
Fascinating. Learn something new every day. Why do you say this?

I wonder why all commercial airliners with wing mounted engines attach their engine pylons to/near/at the leading edge of the wing? Why don't you inform Boeing and Airbus that they're doing it all wrong...
and to Dennis

Well, the ar5 video, both mike ?? the builder and the aerodynamicist go into great detail on how the leading edge of the bottom of the wing is far more draggy than if set inward

Seems to follow the "rule" to disturb the airflow as little as possible at a time. The leading edge is disturbing it, when you set the attach point, wether it be for a baggage pod or a landing gear back of that, you give the air flow time to stabilize before moving it again

I am probably making my own pods, love to make stuff, won't need them for the first year of flying, just need the hard points for em soon.

As far as boeing and airbus, you'll have to talk to them to find out why the engines are put out into the airstream, the video i watched did not goint the trade off of air to wing mounted engine versus drag of pylon placement.
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Last edited by Dust : 08-22-2007 at 10:57 PM.
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  #10  
Old 08-23-2007, 07:47 AM
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Default Re: baggage pods

Quote:
Originally Posted by Dust View Post
...just need the hard points for em soon.
What's an "em"?
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  #11  
Old 08-23-2007, 09:20 AM
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Default Re: baggage pods

The reason why Boeing and Airbus place their engines so far forward of the wings is due to a thing called "area rule". It helps especially at transonic speeds.

Google "area rule" and you'll see. Also see http://en.wikipedia.org/wiki/Area_rule

If done right, the baggage pods and the pylons that support it should actually reduce drag and improve top speed, as well as reduce fuel consumption at cruising speed. Well, at least it would if the top speed is about 500 knots, or Mach .80 or so.

Part of this is due to taking advantage of the supersonic shock-waves as the air flow go faster than the speed of sound over the upper airfoil (even though the aircraft is flying below the speed of sound), to improve lift and reduce drag while at the same time providing a bit of thrust.

I don't know yet how effective the area rules are at the ~200 knots speed most canards cruise at, but it seems that there is some potentials for improvement there.

An interesting way to see how the aeronautical industry understanding of area rule is improving, is to see the changes in the Boeing 737 airfoils over the years (from NASA reports).

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  #12  
Old 08-23-2007, 09:32 AM
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Default Re: baggage pods

Quote:
Mach .80
OH YAH

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  #13  
Old 08-23-2007, 09:53 AM
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Default Re: baggage pods

Quote:
when you set the attach point, wether it be for a baggage pod or a landing gear back of that, you give the air flow time to stabilize before moving it again
Can you clarify? I'm thinking you're talking about the attachment at the "leading edge" which disturbes the airflow at the leading edge, correct? I don't think Boeing engines are mounted this way. Not sure where the landing gear has a relationship to this airflow disturbance.

Another point to remember is the placement of the pods. I believe they're far inboard enough to not disturb the airflow over/under the wings. In the OSH Cozy forum of 2005 Nat speaks of how the wash from the canard goes over/under the strakes. This is why Burt designed the wings lifting characteristics and length beyond the strakes. I think it's an excellent place to mount the pods. Hope this helps.
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  #14  
Old 08-23-2007, 11:06 AM
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Default Re: baggage pods

Quote:
Originally Posted by neverquit View Post
Can you clarify? I'm thinking you're talking about the attachment at the "leading edge" which disturbs the airflow at the leading edge, correct?
Well, at the leading edge attach point you are already asking the air to go around the wing. If you attach the pod to the leading edge, you are also asking it to move side to side. increases interference drag.

Been lookin at the boeing engines and where they used to be round years ago, they are now sort of flat on top, would make for a roomier baggage pod.

Also the slope of the pod seems excessive to the rear, looks to me like they could be bigger for a longer length with no increase in drag penalty.

Gotta review the AR5 video again and get out pencil and paper.

oh Waiter - your 3 to 5 knots sounds realistic, the 1 or 2 MPH that i have heard for years did knot
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Last edited by Dust : 08-23-2007 at 11:16 AM.
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  #15  
Old 08-23-2007, 11:32 AM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: baggage pods

Quote:
Originally Posted by WileEZ View Post
The reason why Boeing and Airbus place their engines so far forward of the wings is due to a thing called "area rule"....
While the position of the engine may or may not be dictated by the area rule, the issue was the attachment point position, not the engine/pod position.

If the leading edge was, for some reason, a crappy place to attach things, the engine pylons could easily be attached somewhere else - just on the bottom surface, just on the top surface, 1/2 way back on the chordline, etc. But they're not.

The speed loss (due to drag increase) from the pods is attributable to the increased wetted area of the pods and pylons, and the accuracy with which the installer aligned them with the local flow field, not to their attachment scheme to the wing.
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