totm october 2020 Airplane Design Q&A

[wumpus]

55 minutes ago, mikegarrison said:

Since I was tossing the term around -- "balanced field length" refers to the length required to reach takeoff speed, then reject the takeoff and come to a full stop again before running out of concrete.

I'd have to wonder if this would lead to the use of parachutes.  Not  so much to rescue the passengers during a disaster (although it might be sold as such), but to act similar to the parachutes used by drag racers to extend the runway and hopefully use a smaller airport.

[mikegarrison]

3 minutes ago, wumpus said:

I'd have to wonder if this would lead to the use of parachutes.  Not  so much to rescue the passengers during a disaster (although it might be sold as such), but to act similar to the parachutes used by drag racers to extend the runway and hopefully use a smaller airport.

Drag (drogue) chutes have certainly been used, particularly on military airplanes.

 

Edited January 13, 2021 by mikegarrison

[JoeSchmuckatelli]

1 hour ago, mikegarrison said:

By going fast. (And probably by having some high lift flaps and or slats you don't see in the picture.)

I will also note that last year Aerion started showing a different render:

One of the problems with the F-104 was its high landing speed, required because of its high wing loading.

According to Wikipedia, Aerion is aiming for a balanced field length of 7500 feet. That's pretty long for a business jet. Many business jets try for shorter field lengths so that their operators can fly into smaller airports.

That render looks like something that can fly.  The image in the article I linked looked like something that can only fall with style 

[mrfox]

The layout bears some semblance to the final proposed design of the (cancelled) Boeings 2707 SST from the 1960s. 

The initial version had variable sweep wings too - which would’ve been great for field performance. Its a shame variable geometry fell out of vogue - it really made for some good looking airplanes.

[JoeSchmuckatelli]

5 hours ago, mrfox said:

Its a shame variable geometry fell out of vogue - it really made for some good looking airplanes.

Was that because Fly-by-Wire took over predominance?  I love planes like the F-14, and its performance was legendary.  B-1B is certainly a performer... why did it's frame not get converted to a passenger version?

[magnemoe]

57 minutes ago, JoeSchmuckatelli said:

Was that because Fly-by-Wire took over predominance?  I love planes like the F-14, and its performance was legendary.  B-1B is certainly a performer... why did it's frame not get converted to a passenger version?

Only really needed for large supersonic jets who few new has been build as in any after the B1?
Fighter jets probably has enough TWR to not need them. 
You also has the option to take off with less fuel and top up in the air. 

[mrfox]

 I think it’s a combination of better aero fluid modelling during the design phase, coupled with digital fly-by-wire that allows for more complex permutations of control surface positioning in flight. In a nutshell - computers.

There are some pretty big downsides to swing wings too... weight and mechanical complexity being the major one. Another is poor distribution of the center of pressure of the wing, resulting in high trim drag during supersonic flight.

A similar thing has happened in recent years that has seen the demise of triple and double slotted flaps and the elimination of active CG control - both replaced by better designed and actively positioned flaps brought about by better computers.

 

 

Another variation on the variable geometry theme  is the XB70, another elegant design with downward folding wingtips that better optimised wing area, longitudinal trim, increased vertical tail area for lateral stability and provided compression lift for Mach 3 cruise.

Edited January 14, 2021 by mrfox

[mikegarrison]

Swing wings turned out to be not really worth the weight and cost.

43 minutes ago, mrfox said:

A similar thing has happened in recent years that has seen the demise of triple and double slotted flaps and the elimination of active CG control - both replaced by better designed and actively positioned flaps brought about by better computers.

This is mainly for noise reasons. The more slots in the flaps, the more aero noise during landing.

[mrfox]

2 hours ago, mikegarrison said:

Edited January 14, 2021 by mrfox
Deleted

[Meecrob]

46 minutes ago, mrfox said:

 

Careful, you are comparing an A320 to an A321.  You can tell by the cargo door position and over wing exit. The 321 is the only one of the family to have double slotted flaps whether CEO or NEO and has to do with it using 320 wings on a plane that is much heavier than a 320.

[mrfox]

On 1/14/2021 at 3:06 PM, Meecrob said:

Careful, you are comparing an A320 to an A321.  You can tell by the cargo door position and over wing exit. The 321 is the only one of the family to have double slotted flaps whether CEO or NEO and has to do with it using 320 wings on a plane that is much heavier than a 320.

Good catch with the picture and a poor misleading example on my part. you are correct on the 321 ceo and the initial 321 neo. It is on the latest 321 neo XLR that had the flap design change.

 

Same thing for the 747 for its -8 update - triple slotted to double and single slotted.

Edited January 17, 2021 by mrfox

[JoeSchmuckatelli]

I'm probably late to this party - but I ran across this plane for the first time today. 

Super Guppy: The original supertransporter airplane | CNN Travel

https://www.foxnews.com/science/what-is-nasas-super-guppy

Pretty crazy, and very cool that something like this is possible.  The story of how some guy was laughed at, built it anyway and then succeeded is good.

 

It's being replaced by the AB Beluga  Airbus Beluga XL - Biggest Planes in the World - Beluga XL Specs (popularmechanics.com)

 

Sidenote: I've seen the AB Beluga in person - they're fun

Edited March 7, 2021 by JoeSchmuckatelli

[mikegarrison]

The Superguppy was an enhanced version of the original "pregnant guppy". Anyway, for years people were giving Airbus some jokes about using a Boeing product to build their airplanes with, so it was a no-brainer that they would build the "Beluga" into an Airbus airframe.

I used to (pre-COVID) see the LCFs ("Dreamlifter") fly in and out of Paine Field.

They all are slightly different. The Guppy design swings out at the nose. The LCF design swings out at the tail. And the Beluga design has that drop cockpit.

I don't know about the Beluga, but the LCF actually has an interesting restriction on its type certification. It is only allowed to be flown in support of Boeing manufacturing.

Quote

These airplanes are not approved for commercial freight hauling operations of material other than that approved per Exemptions 8769, 8769A and 8769B. Only cargo that supports Boeing corporate lines of business is allowed for carriage

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/880e62e05df2f52f862585fa00368b83/$FILE/A20WE_Rev61.pdf

Edited March 8, 2021 by mikegarrison

[magnemoe]

2 hours ago, mikegarrison said:

The Superguppy was an enhanced version of the original "pregnant guppy". Anyway, for years people were giving Airbus some jokes about using a Boeing product to build their airplanes with, so it was a no-brainer that they would build the "Beluga" into an Airbus airframe.

I used to (pre-COVID) see the LCFs ("Dreamlifter") fly in and out of Paine Field.

They all are slightly different. The Guppy design swings out at the nose. The LCF design swings out at the tail. And the Beluga design has that drop cockpit.

I don't know about the Beluga, but the LCF actually has an interesting restriction on its type certification. It is only allowed to be flown in support of Boeing manufacturing.

https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/880e62e05df2f52f862585fa00368b83/$FILE/A20WE_Rev61.pdf

Now that is super weird, an plane who is only legal for internal use. Is it still some sort of experimental build? 
However as its an freight plane it makes more sense to limit the airports and routes it can fly as its more dangerous than other planes and not allow extra crew. Lots of cargo planes has some passenger seats for replacement crew or people who handle the cargo, probably also used to move crew around. 

[mikegarrison]

Just now, magnemoe said:

Now that is super weird, an plane who is only legal for internal use. Is it still some sort of experimental build? 
However as its an freight plane it makes more sense to limit the airports and routes it can fly as its more dangerous than other planes and not allow extra crew. Lots of cargo planes has some passenger seats for replacement crew or people who handle the cargo, probably also used to move crew around. 

Freighter planes are not more dangerous than passenger planes.

As for the restriction, I don't know why. All I know is that's what it says in the TCDS (that I gave the link to).

In case you didn't know, you can look up the FAA or EASA Type Certificate Data Sheets on line and find all sorts of information about airplanes, engines, etc. Probably other regulatory agencies too, but usually I only need to look up the FAA TCDS or sometimes the EASA (European equivalent) TCDS.

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

plane who is only legal for internal use

Sounds like a Contractor getting a pretty sweet Government approved monopoly.

[magnemoe]

43 minutes ago, JoeSchmuckatelli said:

Sounds like a Contractor getting a pretty sweet Government approved monopoly.

If so its not Boeing who benefit as Dreamlifter can not be used for other stuff than moving Boeing parts. 

[wumpus]

12 hours ago, mikegarrison said:

Freighter planes are not more dangerous than passenger planes.

As for the restriction, I don't know why. All I know is that's what it says in the TCDS (that I gave the link to).

In case you didn't know, you can look up the FAA or EASA Type Certificate Data Sheets on line and find all sorts of information about airplanes, engines, etc. Probably other regulatory agencies too, but usually I only need to look up the FAA TCDS or sometimes the EASA (European equivalent) TCDS.

Odd.  The only reason I'd expect freighter planes to be as safe as passenger planes is that it wouldn't make any sense to use different designs to manufacture multiple models of the same aircraft.  If the FAA didn't require the same level of safety (because the news isn't as hard in air traffic when FedEx loses a jet, similar for general aviation) then I'd expect freight planes to often be "retired" passenger planes, and have a reduced maintenance schedule (well, reduced from what it would be for passengers, it was likely retired because of increasing work).

[mikegarrison]

16 minutes ago, wumpus said:

Odd.  The only reason I'd expect freighter planes to be as safe as passenger planes is that it wouldn't make any sense to use different designs to manufacture multiple models of the same aircraft.  If the FAA didn't require the same level of safety (because the news isn't as hard in air traffic when FedEx loses a jet, similar for general aviation) then I'd expect freight planes to often be "retired" passenger planes, and have a reduced maintenance schedule (well, reduced from what it would be for passengers, it was likely retired because of increasing work).

Freighters can either be purpose-built or converted from passenger airplanes. However, they have to meet the same airworthiness standards as passenger airplanes (except for obvious things like not needing emergency oxygen or escape slides for the non-existent passengers).

There are also planes known as "combis" that have half the main deck for freight and half for passengers. And there are planes known as "convertibles" that have a freighter door and deck but have palletized seating that can be loaded in, making them quickly converted to passenger service.

[JoeSchmuckatelli]

1 hour ago, mikegarrison said:

there are planes known as "convertibles" that have a freighter door and deck but have palletized seating that can be loaded in, making them quickly converted to passenger service.

I've rode on those - they're loud. 

[mikegarrison]

2 minutes ago, JoeSchmuckatelli said:

I've rode on those - they're loud. 

What did you ride on?

I've actually done noise tests on an airplane like this (noise is what I did before I did emissions), and at least in that case it was the same as a regular passenger airplane.

[StrandedonEarth]

1 hour ago, mikegarrison said:

There are also planes known as "combis" that have half the main deck for freight and half for passengers

Especially popular in remote communities which tend to have fewer passengers and more freight flown in. 

[JoeSchmuckatelli]

25 minutes ago, mikegarrison said:

What did you ride on?

I've actually done noise tests on an airplane like this (noise is what I did before I did emissions), and at least in that case it was the same as a regular passenger airplane.

I'm using a little liberty in the use of convertable: C-5 Galaxy and C-141 both have the palletized / bolt in seating.  Military planes are known for lacking in amenities.

I did get a coke during my MAC flight to Honolulu, though.  That was nice.

[mikegarrison]

10 minutes ago, JoeSchmuckatelli said:

I'm using a little liberty in the use of convertable: C-5 Galaxy and C-141 both have the palletized / bolt in seating.  Military planes are known for lacking in amenities.

I did get a coke during my MAC flight to Honolulu, though.  That was nice.

Yeah, I wondered if you meant that.

Convertibles are something pretty different than a C-5 with seats. They have a full passenger interior, with all the doors and galleys and lavs and insulation and such, but they have a cargo deck and a cargo door. So an operator can slide in seat pallets and have a passenger plane. Or they can slide the seat pallets out and have a cargo plane. Or they can have two sets of seat pallets, such as one set that is all VIP First Class seating and another that is all economy seating, and can quickly switch between one or the other.

27 minutes ago, StrandedonEarth said:

Especially popular in remote communities which tend to have fewer passengers and more freight flown in. 

Yes, Alaska Air used to have a combi 737 that would for instance fly to Seattle with a load of frozen salmon in the front and passengers in the back.

Edited March 8, 2021 by mikegarrison

[JoeSchmuckatelli]

3 minutes ago, mikegarrison said:

Yeah, I wondered if you meant that.

Convertibles are something pretty different than a C-5 with seats. They have a full passenger interior, with all the doors and galleys and lavs and insulation and such, but they have a cargo deck and a cargo door. So an operator can slide in seat pallets and have a passenger plane. Or they can slide the seat pallets out and have a cargo plane. Or they can have two sets of seat pallets, such as one set that is all VIP First Class seating and another that is all economy seating, and can quickly switch between one or the other.

I realized as soon as you asked the question that I had goofed; I've actually seen the 'interior insert' modules