Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: earl1937 on October 28, 2014, 08:44:58 PM
-
:airplane: There are about as many different wing designs as there are aircraft flying today, but one thing is constant: The wing is either monocot or semi-monocot constructed! All aircraft which flew in WW2 were semi-monocot constructed wings. The following is a semi-monocot constructed wing and gives you some idea of the bracing which is enternal and covered by the aircraft "skin" on the outside of the wing structure;
(http://i1120.photobucket.com/albums/l488/05263739/wingconstrution.jpg)
The method of fasting used during that time frame is as follows:
(http://i1120.photobucket.com/albums/l488/05263739/rivetID2.jpg)
This is a cut-a-way of a P-38, showing the internal bracing and reinforcement spars and many other fittings, gussets and fillets:
(http://i1120.photobucket.com/albums/l488/05263739/P-38-Lightning-cutaway.jpg)
Following is a picture of the simplest of Monocot constructed items, which is where the skin of the object is the strength of the item, wing or what have you:
(http://i1120.photobucket.com/albums/l488/05263739/egg.png)
As you can see, it is a common egg!
Lets just see if anyone can list a aircraft which is being used to day, which has monocot constructed wings?
-
Monocoque :)
-
Monocoque :)
:airplane: An aircraft by that name?
-
And not all WWII aircraft were of monocoque or semi-monocoque design. The Hurricane for example was a steel-tube structure with aluminum cross-bracing, with wood and fabric covering.
(http://upload.wikimedia.org/wikipedia/commons/3/3c/Women_assembling_Hawker_Hurricanes_1942.jpg)
Another famous internally braced WWII aircraft was the Wellington bomber with its geodesic construction. It was very strong and resistant to damage.
(https://dl.dropboxusercontent.com/u/26232318/AH/Vickers-Wellington-undergoing-restoration.jpg)
-
:airplane: An aircraft by that name?
Monocoque, not "monocot". From the Greek for single "mono" and French for shell "coque".
-
Monocoque, not "monocot". From the Greek for single "mono" and French for shell "coque".
:airplane: Spelling has never been my strong point! Point of info: Any aircraft wing which has enternal bracing such as cross arms, ribs and other devices to strengthen the wing is consistered a semi-monocoque constructed wing. Even the tube type wings such as the one you show were also consistered this method!
-
Semi-monocoque construction is also known as stressed skin construction, where the skin carries some of the load. In the Hurricane and Wellington the skin was mostly doped fabric and carried no load. Wellingtons in particular were known for their ruggedness and regularly returned with large parts of the skin burned or blown away.
(http://ww2today.com/wp-content/uploads/2012/09/Wellington-bomber-fire-damage.jpg)
-
Looking at the props on the Wellington makes me wince.
-
Another Barnes Wallis creation.
-
Looking at the props on the Wellington makes me wince.
:airplane: Not sure the reference to the props, but what scares me is looking at that small "rudder". No wonder that they had so many accidents after losing one engine. I have often wondered at what time during the development of twin engine and or multi-engine aircraft, did someone say, "We have to been concerned with the minimum control airspeed when designing these aircraft"!
Generally speaking the larger the rudder and vertical stab, the lower the VMC of that aircraft. A good example of that is the B-24J, which had 2 rudders and 2 stabs, they were still relatively small for that size aircraft. The U.S. Navy had the "privateer", I think which was designated PBY4-1 and -2.
(http://i1120.photobucket.com/albums/l488/05263739/navyliberator.jpg)
(http://i1120.photobucket.com/albums/l488/05263739/b24navy-1.jpg)
I am unable to find the info needed to compare the VMC speeds with 2 engines out on one side, but I think it was a pretty good difference, which, as these aircraft were used as anti-submarine patrol aircraft and carried large loads of fuel, the margin of safety was wider with the single rudder as opposed to the twin rudder set up of the 24.
Don't ask me why Consoladated did not choose the single rudder and stab as opposed to the twin setup, because I have no idea! Again, this aircraft was designed during the development of aircraft and not sure if any wind tunnel tests of any kind were conducted.
-
Semi-monocoque construction is also known as stressed skin construction, where the skin carries some of the load. In the Hurricane and Wellington the skin was mostly doped fabric and carried no load. Wellingtons in particular were known for their ruggedness and regularly returned with large parts of the skin burned or blown away.
(http://ww2today.com/wp-content/uploads/2012/09/Wellington-bomber-fire-damage.jpg)
What made the Wellington so survivable was the inherent redundancy of the geodesic structure, with many alternative load paths. It wasn't a terribly lightweight structure though.
-
Don't ask me why Consoladated did not choose the single rudder and stab as opposed to the twin setup, because I have no idea!
In all likelihood Consolidated went with twin rudders on the B-24 to minimize hanger door height requirements and possibly to avoid the need for high torsional stiffness in the rear fuselage. The downside is that the twin rudder configuration can be more susceptible to the effects of prop wash and wingtip vortices, making for some weird stability issues.
-
What made the Wellington so survivable was the inherent redundancy of the geodesic structure, with many alternative load paths. It wasn't a terribly lightweight structure though.
No, "redundancy" and "ruggedness" is usually the enemy of "lightweight". It was also really complicated to manufacture and assemble.
-
No, "redundancy" and "ruggedness" is usually the enemy of "lightweight". It was also really complicated to manufacture and assemble.
Do you have any info on the manufacturing process? I'm curious what the tooling looked like, and if the parts count was really high.
-
The unique part count for the fuselage alone was over 1500 if I remember correctly. All those little struts and braces...
-
The unique part count for the fuselage alone was over 1500 if I remember correctly. All those little struts and braces...
Yeah, I was wondering if that was the case, or if all those stringers were cut to shape at assembly time to match some master tool. Either way it sounds like a manufacturing nightmare.
-
They did manage to build them fairly quickly for an aircraft that size (less than 100 hours per unit IIRC), but my guess is they had to throw a lot of skilled labor at it.
-
In all likelihood Consolidated went with twin rudders on the B-24 to minimize hanger door height requirements and possibly to avoid the need for high torsional stiffness in the rear fuselage. The downside is that the twin rudder configuration can be more susceptible to the effects of prop wash and wingtip vortices, making for some weird stability issues.
:airplane: Now that you mention it, it was the height of hangar doors which dictated to Consolidated to design the B-24 as they did!
-
:airplane: Now that you mention it, it was the height of hangar doors which dictated to Consolidated to design the B-24 as they did!
Here's the solution for the B-36 (built here in Fort Worth)
(http://i1292.photobucket.com/albums/b570/happyfluffycthulhu/Mobile%20Uploads/B-36-nose-up-in-factory_zps7fdj5byn.jpg)
-
Here's the solution for the B-36 (built here in Fort Worth)
(http://i1292.photobucket.com/albums/b570/happyfluffycthulhu/Mobile%20Uploads/B-36-nose-up-in-factory_zps7fdj5byn.jpg)
:airplane: Your are correct, and for a short time, this was the way it was put into hangars, then they started modifying the hangar doors, cutting a "slot" in the middle, which would allow the B-36 into a hangar with using the hydraulic jacks to raise the nose and lower the tail. That had at Biggs AFB in El Paso in 57, a partial hangar which only enclosed the wing area's for maintance. They could have had them everyway, don't know, just happened to see those on a stop over.
-
:airplane: Now that you mention it, it was the height of hangar doors which dictated to Consolidated to design the B-24 as they did!
I was under the impression the twin-rudders were left over from the seaplane that the B-24 was adapted from. (Twin rudders have control surface in the prop blast, very handing when on water)
**Edit
The twin-fin empennage was that used on the Consolidated Model 31 flying boat (P4Y-1)
-
A good example of that is the B-24J, which had 2 rudders and 2 stabs, they were still relatively small for that size aircraft.
The B-24 has plenty of rudder authority with the twin rudder set up. I've had it down to 120IAS with #1 and #2 set to zero thrust and wasn't even close to needing full rudder. It is possible to do a missed with 2 engines out IF you're light and IF the density altitude isn't too high…just don't expect to climb very briskly….if at all. You will need some help getting out of the airplane since your right leg is going to be flubber. :x
-
I was under the impression the twin-rudders were left over from the seaplane that the B-24 was adapted from. (Twin rudders have control surface in the prop blast, very handing when on water)
**Edit
The twin-fin empennage was that used on the Consolidated Model 31 flying boat (P4Y-1)
:airplane: You may be right! I just don't know the real answer! I do know that most hangars at old U.S. Army airfields were all built the same way, with a "rounded" roof, offices on one side or other and I believe a 28 foot high hangar door...I can't find any specs on that! I just know that any hangars built in U.S. after about 1944 was high enough for the B-29 to enter with no problem.
-
Lets just see if anyone can list a aircraft which is being used to day, which has monocot constructed wings?
Hmmmm...Boeing 737 perhaps?
-
Hmmmm...Boeing 737 perhaps?
Afraid not. Airliners, with all their skin breaks needed for high lift devices, spoilers, access panels, windows, doors, etc. are terrible candidates for a pure monocoque structure. The only modern aircraft I'm aware of that come close are some smaller composite aircraft, like Rutan's creations, that use glass and/or graphite-epoxy.
-
Afraid not. Airliners, with all their skin breaks needed for high lift devices, spoilers, access panels, windows, doors, etc. are terrible candidates for a pure monocoque structure. The only modern aircraft I'm aware of that come close are some smaller composite aircraft, like Rutan's creations, that use glass and/or graphite-epoxy.
:airplane: I am pretty sure that there are some gliders which have the wings filled with foam, but the strength is in the skin over the foam! I wonder about the "Goodyear" blimp and if it has any internal bracing?
-
Hawker Hurricane had two kind of wings. The first version had canvas covering and the internal structure was different from the late one. The late version was internally lighter since the aluminum covering made the wing stiffer. I'm not sure what was the weight difference.
-C+
-
Hawker Hurricane had two kind of wings. The first version had canvas covering and the internal structure was different from the late one. The late version was internally lighter since the aluminum covering made the wing stiffer. I'm not sure what was the weight difference.
-C+
From what I'm reading, the stressed metal skins were introduced in 1939 on the mid-production MK1's. So apparently, practically all wartime Hurricanes had metal wing skins. Didn't know that.
-
:airplane: I am pretty sure that there are some gliders which have the wings filled with foam, but the strength is in the skin over the foam! I wonder about the "Goodyear" blimp and if it has any internal bracing?
The foam core is designed to carry the shear stresses and transfer them into the bonded skin (usually glass/polyester or graphite/epoxy). And because they're continuously bonded, the foam stabilizes the skins, so skin stability (compressive and/or shear buckling) is not an issue. In addition, bonded structures are typically very stiff, and don't suffer from the flexibility and high local stresses that mechanically fastened joints can have. So actually the skins AND the foam core are both crucial to the strength AND stiffness.
Blimps have a lightweight internal structure that is mainly there to transfer local loads (gondola attachments or say the mooring tower attachment at the nose) into the envelope. It's nothing like the far more substantial structure of a dirigible.