bmccarron

Hercules dihedral

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Can anyone advise me as to whether the new RCAF stretched c-130j shows any amount of dihedral or even anhedral while on the ground? I 'd like to know before gluing

Or hacking away at the kit. Many thanks, Brian

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Brain,

The C-130 has no Di/Anhedral, i.e the wing is flat.

Perhaps this should have been posted in the Props forum? This forum is for commenting on build articles on the ARC homepage.

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On 9/6/2016 at 6:51 PM, Trojan Thunder said:

Brain,

The C-130 has no Di/Anhedral, i.e the wing is flat.

Perhaps this should have been posted in the Props forum? This forum is for commenting on build articles on the ARC homepage.

 

Just saw your comment and have to correct it. Probably a bit too late for Brian though.

 

The C-130, all versions, have dihedral. The center wing, which extends from just outboard of the #2 engine, through the fuselage to just outboard of the #3 engine is totally flat. The outer wings, which attach just outboard of the inboard engines, have 2° 30' of dihedral on the lower wing surface.

 

Cheers,

 

John

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Is that truly dihedral or merely wing tapering due to change in air foil?

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11 hours ago, CF104 said:

 

Just saw your comment and have to correct it. Probably a bit too late for Brian though.

 

The C-130, all versions, have dihedral. The center wing, which extends from just outboard of the #2 engine, through the fuselage to just outboard of the #3 engine is totally flat. The outer wings, which attach just outboard of the inboard engines, have 2° 30' of dihedral on the lower wing surface.

 

Cheers,

 

John

 

Thanks for the clarification John,

 

Though I wonder if any kit offers this? I always think of dihedral from the wing root and that I why I answered as I did, I was unaware that there was any change further out.

 

From a kit assembly perspective when adding the wings I always make sure the top of the wing and fuselage area is flat, no angle.

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Ray, I am with you on this one.  R/ Dutch

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Posted (edited)

On 10/13/2016 at 10:16 AM, CF104 said:

 

Just saw your comment and have to correct it. Probably a bit too late for Brian though.

 

The C-130, all versions, have dihedral. The center wing, which extends from just outboard of the #2 engine, through the fuselage to just outboard of the #3 engine is totally flat. The outer wings, which attach just outboard of the inboard engines, have 2° 30' of dihedral on the lower wing surface.

 

Cheers,

 

John

Yes but,,, I'm pretty sure that the dihedral number was not for the lower wing surface because aerodynamicists, who use the number, define it as the midpoint between the upper and lower surfaces. This distinction is important in this case because the upper surface of the C-130 wing outboard of the inboard (originally and incorrectly stated outboard) engine is not flat, but angled slightly upward.

Edited by Tailspin Turtle
Error caught by CF104

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On 10/13/2016 at 9:14 AM, Slartibartfast said:

Is that truly dihedral or merely wing tapering due to change in air foil?

 

 

4 hours ago, Dutch said:

Ray, I am with you on this one.  R/ Dutch

 

 

I'll preface my answer by stating I have 10 years heavy maintenance and overhaul experience on the C-130/L-100.

 

img046.jpg

 

The wing thickness does indeed change from the inboard engines to the tips on the outer wings. A C-130 without any fuel on board will have a noticeable dihedral on the outer wings. The 2° 30' of dihedral is for a fully equipped but empty aircraft. When fully fueled there is a noticeable droop to the wings. 

 

The following photo illustrates an empty aircraft.

 

130110-F-UI543-002.JPG

 

 

Cheers,

 

John

 

 

 

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3 hours ago, Tailspin Turtle said:

Yes but,,, I'm pretty sure that the dihedral number was not for the lower wing surface because aerodynamicists, who use the number, define it as the midpoint between the upper and lower surfaces. This distinction is important in this case because the upper surface of the C-130 wing outboard of the outboard engine is not flat, but angled slightly upward.

 

The outer wing on the C-130 joins just outboard of the inboard engines and the dihedral angle from this point to the tip is constant in the case of a fully defueled aircraft. The outer wing is angled upward from this joint.

 

Cheers,

 

John

 

 

 

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Posted (edited)

28 minutes ago, CF104 said:

 

The outer wing on the C-130 joins just outboard of the inboard engines and the dihedral angle from this point to the tip is constant in the case of a fully defueled aircraft. The outer wing is angled upward from this joint.

 

Cheers,

 

John

 

 

 

I knew that but wrote outboard anyway. Thanks for the correction and the illustration. I also note that the dashed line showing the dihedral is lower at the inboard end than I would have expected but still above the lower surface. It is shown the same way on the three view in an early C-130 aerodynamic report, It may represent the location of the trailing edge of the wing.

Edited by Tailspin Turtle
Change trailing edge of the airfoil to trailing edge of the wing.

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Posted (edited)

And to follow up, my examination of John's drawing using Illustrator strongly suggests that the C-130 wing is flat across the top from tip to tip as drawn, the outboard panel dihedral and taper (in thickness) canceling each other out. The side view in both John's drawing and the Lockheed report indicates that the top of the wing tip is slightly higher than the top of the wing at the fuselage center line but given the variability of the outboard wing position with respect to fuel load, flat across the top would be my choice.

 

C-130 Refueling.jpg

Edited by Tailspin Turtle

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Wing taper (airfoil thickness) is not dihedral/anhedral.  It is, as Tommy said, measured through the mid-section of the airfoil.

 

One could argue that the C-130 wing resembles the F-4 Phantom wing, where the wing structure has an obvious change in anhedral.  In the case of the C-130 the outer wing anhedral would be roughly half of the outer wing taper.

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All of this is very true and informative. Will it make a difference on what bmccarron wants to do the model?

Steve

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Hmm..., I have built several Airfix/MPC Herks over the years and never even noticed the wing outer panels' dihedral.  I assumed it was a matter of tapering wing thickness as molded in the kit.  However, one possible solution is to cut a thin "slice" running fore and aft in the lower wing at the appropriate spot and insert a "shim" of plasticard slightly thicker than the slice in order to induce dihedral in the lower outer wing. Wouldn't that work?  I think AVRO Lincolns and Shackletons also had a similar outer wing dihedral. 

 

I meant no offense in my previous comment about agreeing with Ray, I just never noticed it before.  It looked like a Herk to me.  Still does.

R/ Dutch

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Bottom Line I would say is to just make it straight on the top from Wing tip to wing tip. I say this because In all honesty you would never see a C-130 on THE RAMP with a completely zero fuel load, most aircraft will sit with a ramp load.  Of course if it is in a fuel barn then yes it could be drained.  I spent 20 years on C-130's as a mechanic and flight engineer and never noticed.  The only part I ever notice was the the tail is not the same on each site as far as angle.  This is done to eliminate the "P" factor caused by all four props trying to push the aircraft to the right.  Hope that makes sense....

 

 

https://theaviationist.com/wp-content/uploads/2013/03/C-130-Elephant-Walk.jpg

 

 

As you look at it you can see the angle difference.  Also the wings look level to me.... :)

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RCAF C130J Dimensions.jpg

 

My interpretation: The 2 degrees/30' of Dihedral is from the underside of the wing from the outboard engine #1 & 4. The top plane is straight and level. 

Edited by AlienFrogModeller

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3 hours ago, AlienFrogModeller said:

RCAF C130J Dimensions.jpg

 

My interpretation: The 2 degrees/30' of Dihedral is from the underside of the wing from the outboard engine #1 & 4. The top plane is straight and level. 

I think this is a sloppily defined drawing. See CF104's above and the illustrations in this LINK (Photobucket wasn't working for me today),which are from a Lockheed aero report on the C-130 (you can't read the dihedral on the drawing but it is given as 2.5 degrees). It may be that the later C-130s had a different wing (note the location of the external fuel tanks) but I'm inclined to doubt it. The dihedral is clearly not the bottom of the wing (my guess based on the side view is that it is defined at the trailing edge of the wing; note the twist between the inboard wing and the wing tip). Both views show the wing tip slightly higher than the root, although as pointed out above, fuel load may cause the outboard panels to droop.

 

 

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On 9/5/2016 at 2:19 AM, bmccarron said:

Can anyone advise me as to whether the new RCAF stretched c-130j shows any amount of dihedral or even anhedral while on the ground? I 'd like to know before gluing

Or hacking away at the kit. Many thanks, Brian

Here is a really nice pic in the link that may help you with you "on the ground" question. Also I googled Canadian C130J and found a few other good references. I have a few of my own detail shots while I was at 436 Sqn. But the pics I have to help you with you question wouldn't help much.

 

https://www.planespotters.net/photo/161953

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7 hours ago, Tailspin Turtle said:

I think this is a sloppily defined drawing.

 

Agree - or the illustrator doesn't understand dihedral either.

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I hope this makes sense.  The dihedral is the upward slope from the wing root to the wing tip.  A C-130 is a little different because the wing root is actually below the wing.  Most times when we think of dihedral the wing is a low wing, with the root above, such as a P-51 or BF-109 or a plane of that sorts.  The slope is positive, but it throws us a curve because of the C-130 design. The only time I had to walk up a slope on top of the wings was when the whole plane sloped to one side.  I hope that helps to clear the mud. :)

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12 hours ago, shadoweng said:

I hope this makes sense.  The dihedral is the upward slope from the wing root to the wing tip.  A C-130 is a little different because the wing root is actually below the wing.  Most times when we think of dihedral the wing is a low wing, with the root above, such as a P-51 or BF-109 or a plane of that sorts.  The slope is positive, but it throws us a curve because of the C-130 design. The only time I had to walk up a slope on top of the wings was when the whole plane sloped to one side.  I hope that helps to clear the mud. :)

Dihedral is not necessarily measured from the wing root to the wing tip, certainly not in the case of the F4U Corsair, F4H Phantom, or C-130 Hercules. Each segment that has a different angle will have a dihedral number associated with it. It's rarely defined by aerodynamicists as the angle of the lower surface of the wing (i.e. I've never seen an example), although that's a convenient measurement, particularly during construction of model airplanes. I can't find a commonly accepted definition of the measurement. It's usually depicted as being along the midpoint of the upper and lower surface of the wing when viewed from the front. However, in the case of the A4D Skyhawk as apparently here, it is defined as the angle of the trailing edge of the wing with respect to horizontal. Note that in this case, the three-degree twist of the wing results in the dihedral line going from low on the front view of the wing at the break between the inboard section of the wing and the outboard panel that has dihedral to somewhat proportionall higher at the tip.

 

With respect to low and high wings, an airplane with a wing located at the bottom of the fuselage needs notably more dihedral than one mounted at the top of the fuselage to achieve the same dihedral effect. An airplane with a swept wing needs less dihedral than one with an unswept wing (note that the F8U Crusader that has a high-mounted wing is has anhedral). After that, the discussion gets very complicated.

 

 

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32 minutes ago, Tailspin Turtle said:

Dihedral is not necessarily measured from the wing root to the wing tip, certainly not in the case of the F4U Corsair, F4H Phantom, or C-130 Hercules. Each segment that has a different angle will have a dihedral number associated with it. It's rarely defined by aerodynamicists as the angle of the lower surface of the wing (i.e. I've never seen an example), although that's a convenient measurement, particularly during construction of model airplanes. I can't find a commonly accepted definition of the measurement. It's usually depicted as being along the midpoint of the upper and lower surface of the wing when viewed from the front. However, in the case of the A4D Skyhawk as apparently here, it is defined as the angle of the trailing edge of the wing with respect to horizontal. Note that in this case, the three-degree twist of the wing results in the dihedral line going from low on the front view of the wing at the break between the inboard section of the wing and the outboard panel that has dihedral to somewhat proportionall higher at the tip.

 

 

With 25 years as an aerospace engineer, I would say the dihedral angle is whatever the airplane designer says it is.

 

It's virtually impossible to measure on a real aircraft with anything but the simplest wing shape. Once you factor in wing sweep, taper, twist and incidence angles just isolating the dihedral angle becomes a challenge. For a straight tapered wing with no twist or incidence it's going to be the angle between the aerodynamic root chord and tip chord in the front view, but the aerodynamic root chord is on the aircraft centerline for the projected wing planform.  

 

For a C-130 model kit it may be easiest to measure the seam between upper and lower wing halves. If the kit captures the dihedral correctly there should be a kink to the seam outboard of the inboard engine to represent the change in dihedral.

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Correct me if I'm wrong, I really curious now...

2.5 degrees , the number in the drawings

576 inches the length of the ref point zero of wing joint to the tip.

 

If the slope is 2.5 degrees over 576 inches, would the rise not be .5/foot?

 

if so wouldn't the rise be equal to 24 inches approx?

 

I think I would expect a significant visual rise difference at the wing tip, which i am still not convinced it's there. However I do see the approx 24" rise on the underside of the wing.

 

Take the nose tire measurement of 1 foot 10 inches, compare to the wing tip rise, the scale may not be exact but it does seem plausible.

 

Even on a "sloppy" drawing there would have been a significant change on the drawing to reflect the dihedral on top of the wing. I suspect in my interpretation the dihedral is under the wing, supported by many pics of the Herc wing as being flat on top (not including the shape of the wing from the chord perspective).

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39 minutes ago, AlienFrogModeller said:

if so wouldn't the rise be equal to 24 inches approx?

 

 

25.12476712" (if length; 25.14870312" if span)

 

That doesn't mean that the *top* of the wing is 2' higher, just that wherever they measure the chord will be.

 

As a *really* rough example...  The black lines in this drawing are 576" @ 2.5`  The 'thick' end is 50"; the 'then' end is 20" (numbers pulled from my fool, because they look vaguely in the ballpark).  The "upper wing surface" is still angled at about 1` (1.00922337°), while the "lower surface" is about 4` (3.98515049°).

 

In other words, the dihedral raises about 2', but the upper surface *visually* looks pretty flat.

 

Part1_zpsgrvd4mlr.jpg

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