*** Posted by Kim Nielsen ***
Recently homecomed from a charter trip to south Spain, one Q about drag lies on my tounge:

During the actual 737's acceleration in air, airnoise around the fuselage appears quite sudden and keeps in the same sound level for the rest of acceleration and flight.
I've done the same observation in as well a 727, as an Airbus, however I can't estimate anything about the speed for the different planes when this happens.
Therefore do my question go like this: Is there, as for the sound barrier, some draglimits related to the speed, wich concerns all planes or is it highly related to the design of the plane/fuselage?

How experies You this phenomena in the F-16?

Kim

*** Posted by run ***
I've always experienced the noise as gradually increasing, but in a couple of weeks I'm going on a DC-10 to US & then I will try to listen for it.
I don't see any reason why this should happen, but I'm looking forward to listen myself. In the F-16 it's a gradual increase in noise.

run

[Recently homecomed from a charter trip to south Spain, one Q about drag lies on my tounge:

During the actual 737's acceleration in air, airnoise around the fuselage appears quite sudden and keeps in the same sound level for the rest of acceleration and flight.
I've done the same observation in as well a 727, as an Airbus, however I can't estimate anything about the speed for the different planes when this happens.
Therefore do my question go like this: Is there, as for the sound barrier, some draglimits related to the speed, wich concerns all planes or is it highly related to the design of the plane/fuselage?

How experies You this phenomena in the F-16?

Kim]

*** Posted by Rapier ***
Hello,

Firstly I would just like to ask Kim what is the facination with the sound of air on the outside of the fuselage? All planes are aerodynamic, some more than other's particularly regarding fighter's. When you go supersonic in an airliner (pretty rare apart from Concorde) you dont notice anything special from the inside of the aircraft itself. I have been on a DC-10 Run and they are terrible for noise pollution inside the jet. Because it is a medium sized airliner the engines on the DC-10 are quite close to the fuselage. It was anoying to get so much noise in the plane all the way to our destination and back. In the F-16 once the canopy is shut I doubt you could hear much. Also wearing a brain bucket silence's the noise a bit further because they are designed for a tight fit on the head but in a comfortable way. Most airliners dont go supersonic because they have to change course and deviate in altitude alot of the time.

Anyhow, good luck Run and hope you have a safe trip!

Regards

Rapier

[I've always experienced the noise as gradually increasing, but in a couple of weeks I'm going on a DC-10 to US & then I will try to listen for it.
I don't see any reason why this should happen, but I'm looking forward to listen myself. In the F-16 it's a gradual increase in noise.

run]

*** Posted by Kim Nielsen ***
Hi Rapier.

You must have misunderstood my letter.
I'm not facinated of the sound, but surprised, and interested in the technique around the background why it appears to its standing level such sudden (aproximately within a speed-difference of less than 50 km/t, due to the elapsed time of between 5 and 10 seconds during middle acceleration in climb!)
I realize that drag rises with the sq. of the speed, and did wonder about there was several levels in drag/speed like the one mentioned by me, wich konstructors as well as pilots do use/observe?

For my person, I have'nt been aboard the DC-10, but my misses have, and She can't remember any special anoring mecanical noise, though She was seated in middle/wing-section both ways to Florida.
But the DC-10 is wide-bodied and therefore I could imagine the noise caused of the drag must be as significant as for my own experiences in 737 and Airbus !

Regards, Kim

Firstly I would just like to ask Kim what is the facination with the sound of air on the outside of the fuselage?

I have been on a DC-10 Run and they are terrible for noise pollution inside the jet. Because it is a medium sized airliner the engines on the DC-10 are quite close to the fuselage. It was anoying to get so much noise in the plane all the way to our destination and back.

*** Posted by Rapier ***
Put it this way, the bigger the object the more drag there is through air space. You dont need all this mathematical shit it's just the way it is.

Regards

Rapier

*** Posted by run ***
Hi Rapier

Size is not always the most important. Shape is way more important. A little object can easily create more drag than a big object with the right shape.

run

[Put it this way, the bigger the object the more drag there is through air space. You dont need all this mathematical shit it's just the way it is.

Regards

Rapier]

*** Posted by run ***
[---snip---
Most airliners dont go supersonic because they have to change course and deviate in altitude alot of the time.
---snip---
Rapier
]
The reason airliners don't go supersonic is because they can't and not because they have to change course a lot. Transatlantic airliners don't turn a lot enroute.

The sounlevel in the f-16 is extremely high when you don't have the helmet on. I once had the engine started without any earprotection and that really hurt my ears. Even with the helmet on a lot of guys wear earplugs in order not to get too much noise. The noise though is mainly engine & ECS (Environmental Control System) related and not so much airnoise. With the helmet on the noise is a lot more pleasant than what you find in a small propaircraft.

run

*** Posted by Rapier ***
Of course, you make a good intuitive comment, but why would any aircraft designer design an aircraft with a high drag factor? Aircraft cannot be designed this way, it would be inpractical to do so. Everybody knows that military aircraft a the 1st in the field of aerodynamics.

Rapier

[Hi Rapier

Size is not always the most important. Shape is way more important. A little object can easily create more drag than a big object with the right shape.

run

Put it this way, the bigger the object the more drag there is through air space. You dont need all this mathematical shit it's just the way it is.

Regards

Rapier]

*** Posted by Rapier ***
Hello,

Airliners dont have to change course that much in a horizontal way, I meant they have to change altitude in order to avoid other flight's, they will sometimes deviate if there is on-comming traffic and also weather factors come into play when avoiding a thunderstorm for saftey reasons etc.

Many of todays pilot helmets are made to a high quality standard. They are also well insulated to prevent noise such as you mentioned and to stop damage occurring to the ears. Seeing the F-16 flying in real life when your not so far away from the plane is loud enough, much louder than from the cockpit. It is a bit strange that you mention it is loud inside the cockpit Run, not because I doubt you but because the engine is further back than where the pilot is sitting. I wonder if the shape of the canopy comes into play here with acoustics, this why it probably sounds loud in the pit. I am sure that when you were flying your F-16 Run, you get to know that aircraft well. You know all the strange sounds and knock's that make that aircraft. They should have designed the F-16 with more insulation, but being a military aircraft is no surprise, they are built like this.

Rapier

[---snip---
The sounlevel in the f-16 is extremely high when you don't have the helmet on. I once had the engine started without any earprotection and that really hurt my ears. Even with the helmet on a lot of guys wear earplugs in order not to get too much noise. The noise though is mainly engine & ECS (Environmental Control System) related and not so much airnoise. With the helmet on the noise is a lot more pleasant than what you find in a small propaircraft.

run---snip]

*** Posted by run ***
[
---snip---
1. Airliners dont have to change course that much in a horizontal way, I meant they have to change altitude in order to avoid other flight's, they will sometimes deviate if there is on-comming traffic and also weather factors come into play when avoiding a thunderstorm for saftey reasons etc.

---snip---
2. It is a bit strange that you mention it is loud inside the cockpit Run, not because I doubt you but because the engine is further back than where the pilot is sitting. ---snip]

add 1. Having to change altitude is not a big problem even when supersonic. The only reason they don't fly supersonic is because they can't. If they could they would ofcourse only be able to over water because of noise.

add 2. A little trick question for you: Where in relation to the engine do you think the noiselevel is highest on an f-16 ? Standing in front of the aircraft or behind ?

I'll go ahead and give you the answer. There is a lot more noise comming from the intake than the exhaust. So it is more noisy in front of the aircraft.

run

*** Posted by run ***
Sometimes you have to compromise, fx when it comes to stealth. The f-117 is not excactly gods gift to aerodynamics.

run

[Of course, you make a good intuitive comment, but why would any aircraft designer design an aircraft with a high drag factor? Aircraft cannot be designed this way, it would be inpractical to do so. Everybody knows that military aircraft a the 1st in the field of aerodynamics.

Rapier]

*** Posted by Rapier ***
Hello Run,

Of course the F-117 is a stealth aircraft, so aerodynamics suffer with this plane. Designing a supersonic stealth aircraft would not be practical at all because supersonic aircraft send out an excellent heat signature, so it would not make it a steathy plane at all. Very advanced material's would have to be used for this, but I dont think the technology is quite there yet. Just like you said a compromise must be made in this situation. I found some info once that the SR-71 would sometimes expand by as much as 11 inches when the pilot pushed it to it's maximum speed and could'nt be held long because the cabin on the aircraft would get so hot that they found it difficult in these circumstances. As you can see the cockpit area of the SR-71 is not very aerodynamic and this was where the problem with heat build up was. I wonder if the same thing happens to the F-16, but on a much smaller scale.

Regards

Rapier.

[---snip
Sometimes you have to compromise, fx when it comes to stealth. The f-117 is not excactly gods gift to aerodynamics.

run]

*** Posted by Rapier ***
Hello,

I a modern day Airliner were to change direction if it were going at a supersonic speed the wing's would snap off in a second. It is much easier to change altitude and direction in a fighter because they are built in a compact and have a very strong structure to deal with the stresses of G as you well know Run, so they can make fast changes no problem. As you also know "Concorede" is the only supersonic passanger jet, capable of twice the speed of sound. Notice it is a delta wing aircraft to give good handling and lift, as well as stuctural integrity. You are corect though, although airliners of today cant go supersonic they also have their engines restricted in some way to stop noise pollution. Sometimes even fighter pilot's can get into trouble if they take of using the burner in a built up area when they have been told not to use it on take off.

With regards to the F-16 engine noise I realised that the engine intake is loud but did'nt realise it was that loud at the intake. Thinking about it logically this would be true because the air is being compressed at the early stage, the sound of the air being forced to the rear of the engine from the compression blades. So what's it like in the F-16 when you put the burner in, it must be louder at the rear then? The loudest aircraft I have ever heard was the Panavia Tornado's, they are so loud they make the ground shake when taking off and your insides literally rattle around. They should have called it the Panavia Earthquake. This was confirmed the other day when a airshow about 15 miles away from me was taking place, I had the pleasure of seeing 2 F-16's scream past at about 7000 ft followed by 2 Tornado's about 20 min's later. The Tornado's I could hear much earlier than the F-16's. It was a great site though!

Regards

Rapier

*** Posted by Kim Nielsen ***
Check "again,again": I'm writing about the SUDDEN aperance of the airnoise around the plane (caused by the drag)!

Kim

[Put it this way, the bigger the object the more drag there is through air space. You dont need all this mathematical shit it's just the way it is.

Regards

Rapier]

*** Posted by Rapier ***
I am well aware that you are talking about the SUDDEN appearence of the airnoise around the plane, it's quite common in all passanger planes! Please tell me why are you facinated by this phenomina?

The DC-10 is an OK aircraft but can easily be thrown around by turbulence. The noise inside the aircraft can be caused by many thing's.

One particular instance when I was on a DC-10 happened a couple of years ago now. I noticed this stange noise close to where I was sitting. I called the stuardess and whispered to her ear (not to make the other passagers frightened incase they heard me) about the strange noise. I told her to go and speak with the Captain and see if he noticed any strange values on his cabin pressure reading's. The stuardess came back and said it's probably nothing, so I thought ok. 20 mins later the noise got louder and some other passengers on the plane began noticing the noise like a high wisper at a high frequency. I called the stuardess again and told her to do the same thing as she had done before. She came back and passed a message on from the Captain saying thank you. Apparently the noise was cased to a faulty seal in the airframe and the noise of the engines was amplified. If the pilot stayed on at the same altitude there would have been trouble. He then decended to about 10000 feet and the noise lowered. That's the loudest plane I've been on but I did not remember any distinct noises around the plane caused by drag too much on take off. Infact I think the noise you are refering to may be caused by the flaps in the take off position, after a short while they are retracted.

Rapier

[Check "again,again": I'm writing about the SUDDEN aperance of the airnoise around the plane (caused by the drag)!

Kim]