Interesting Questions

[earl1937]

  I am told that from time to time, people in here like to read things and think about things other than whines and etc, so, here are a few questions to ponder!

#1- Why did Consolidated put 2 vertical stabs and 2 rudders on their B-24 aircraft?

#2- Why did the B-24 have "desk" top, roll up bomb day doors?

#3- On the B-17G, there is a glass dome just in front of the wind shield, what is it for and how is it used.

#4- What does the term: "just returned from IRAN" mean?

#5- All commercial aviation in the U.S. flies under 2 FAR's, part 121 and part 135. Which aircraft flies under which FAR?

#6- If you start a left turn in a B-29, B-17, JU-88, HElll, or a B-24, with ailerons only, which way will the aircraft's nose turn first and why?

#7- There is an antenna just in front of the glass dome on the B-17, shaped like a boomerang, what is it and how is it used?

#8- There is an antenna running from the top of  the dorsal area to the top of the vertical stabilizer, what is it and what is it for? (actually, 2 wires)

#9- Why did the P-47 jugs, in Italy, have a history of runway over runs due to brake failure and what was the cure?

#10- Just below the copilots window, along the lower side of the fuseledge of the B-17, there is a "bullet" shaped object. What is it and how is it used?

[Widewing]

I am told that from time to time, people in here like to read things and think about things other than whines and etc, so, here are a few questions to ponder!

Without touching a book....

#1- Why did Consolidated put 2 vertical stabs and 2 rudders on their B-24 aircraft?
Wasn't the tail simply borrowed from the Consolidated XP4Y?


#2- Why did the B-24 have "desk" top, roll up bomb day doors?
The obvious reduction in drag, as well as buffeting.

#3- On the B-17G, there is a glass dome just in front of the wind shield, what is it for and how is it used.
Celestial navigation... Shooting the stars.

#6- If you start a left turn in a B-29, B-17, JU-88, HElll, or a B-24, with ailerons only, which way will the aircraft's nose turn first and why?
Yaw right.

#7- There is an antenna just in front of the glass dome on the B-17, shaped like a boomerang, what is it and how is it used?
ILS antenna, I believe.

#8- There is an antenna running from the top of  the dorsal area to the top of the vertical stabilizer, what is it and what is it for? (actually, 2 wires)
HF antenna. VHF was on top of the fuselage, IIRC.

#10- Just below the copilots window, along the lower side of the fuseledge of the B-17, there is a "bullet" shaped object. What is it and how is it used?
Are you referring to the pitot tubes?

[earl1937]

Without touching a book....

#1- Why did Consolidated put 2 vertical stabs and 2 rudders on their B-24 aircraft?
Wasn't the tail simply borrowed from the Consolidated XP4Y?


#2- Why did the B-24 have "desk" top, roll up bomb day doors?
The obvious reduction in drag, as well as buffeting.

#3- On the B-17G, there is a glass dome just in front of the wind shield, what is it for and how is it used.
Celestial navigation... Shooting the stars.

#6- If you start a left turn in a B-29, B-17, JU-88, HElll, or a B-24, with ailerons only, which way will the aircraft's nose turn first and why?
Yaw right.

#7- There is an antenna just in front of the glass dome on the B-17, shaped like a boomerang, what is it and how is it used?
ILS antenna, I believe.

#8- There is an antenna running from the top of  the dorsal area to the top of the vertical stabilizer, what is it and what is it for? (actually, 2 wires)
HF antenna. VHF was on top of the fuselage, IIRC.

#10- Just below the copilots window, along the lower side of the fuseledge of the B-17, there is a "bullet" shaped object. What is it and how is it used?
Are you referring to the pitot tubes?

#1- 3 reasons, speed,(low profile of tail assy), better field of fire for top turret, and since this was first tricycle landing geared bomber, the height of the tail assy had to be taken into consideration, as during that period of design time, most a/c hangar doors were no more than 20 feet high, as most a/c had a tail wheel and the tail assy was no problem.
#2- The bomb bay doors were indeed designed with drag considerations in mind, but reason #1 was access to the bomb bay by ords dollys for loading of bombs and being an "over the shoulder" winged a/c, it naturally had little clearance between the ground and fuselage.
#3- Correct
#4- IRAN is short for "inspection and repair as necessary".
#5-FAR 121 concerns scheduled airlines such as Delta, United, etc. FAR 135 concerns unscheduled, on demand type of commercial flights.
#6- Correct, adverse yaw created by the "down" aileron.
#7- Very High Freq antenna.
#8- Low frequency antenna
#9- Runways on some bases in Italy had steel matted type runways. during takeoff, the tires would "grow" from heat and as gear was raised, sometimes hydraulic line was "rubbed" and a leak resulted. Fix was just simply touching brakes after takeoff, prior to raising gear.
#10- ADF antenna. Spawn out on runway, engage F3, use hat switch to move to right side of a/c  and it is in plain view.
Sorry for the post guys, was just trying to start a dialog about some of these questions.

[colmbo]

I expected you to mention the trailing wire antenna the -17 and -24 had.

[earl1937]

 

I expected you to mention the trailing wire antenna the -17 and -24 had.

I did not include the HF antenna question for a reason, more on that later!

[DurrD]

To fully close the loop on question 6, it is adverse yaw, as noted in several of the replies.  Common to many aircraft, it is caused by the aileron that is going down (and thus lifting that particular wing) causing more drag than the aileron that is going up (on the descending wing).  This drag causes acts like an airbrake on that side, and causes the aircraft to yaw away from the desired direction of turn.  Leading the turn with the rudder is the fix, and there are some design fixes as well, built into most modern airplanes.  Fly by wire can remove this effect entirely for all intents and purposes by having the flight computer compensate for it.

[pembquist]

Also early ailerons were simple hinged flaps. An improvement is the frise aileron which dips the nose of the down aileron below the wing to add drag to balance the adverse drag of the up aileron.

[earl1937]

Also early ailerons were simple hinged flaps. An improvement is the frise aileron which dips the nose of the down aileron below the wing to add drag to balance the adverse drag of the up aileron.

The adverse "yaw" is created by the down aileron, not the up aileron. The up aileron does not have as much effect because it is usually behind the separation point of lift on that wing, which means it is not getting clean air like the down aileron.

[pembquist]

By up and down I mean what the effect on lift is. Left stick means the right aileron is the up one and the left aileron is the down one in my post which is approximately the reverse of how DurrD put it, sorry for the shorthand.

[DaveBB]

One documentary I watched said that the B24 had roll up bomb-bay doors so that enemy fighters wouldn't know when the bomb-bay was open (and thusly the aircraft was more succeptable to attack).

The B-24 had twin tails for a better field of fire for the top turret gunner and also to reduce vertical stabilizer height (Good grief, ever see how tall the vertical stab on the Navy PB4Y is?).

The longer the antenna, the lower the frequency.  Even with HF frequencies, you can talk thousands of miles (especially in an aircraft).

The plexiglass dome on the front of the B17 was like Widewing said, celestial navigation.

[earl1937]

One documentary I watched said that the B24 had roll up bomb-bay doors so that enemy fighters wouldn't know when the bomb-bay was open (and thusly the aircraft was more succeptable to attack).

The B-24 had twin tails for a better field of fire for the top turret gunner and also to reduce vertical stabilizer height (Good grief, ever see how tall the vertical stab on the Navy PB4Y is?).

The longer the antenna, the lower the frequency.  Even with HF frequencies, you can talk thousands of miles (especially in an aircraft).

The plexiglass dome on the front of the B17 was like Widewing said, celestial navigation.

What u say about fighters attacking bombers with doors open first might be true, but take a look at the following picture and see why they have roll up doors!

As you can see, very little clearance below bomber for hinged doors!

[earl1937]

One documentary I watched said that the B24 had roll up bomb-bay doors so that enemy fighters wouldn't know when the bomb-bay was open (and thusly the aircraft was more succeptable to attack).

The B-24 had twin tails for a better field of fire for the top turret gunner and also to reduce vertical stabilizer height (Good grief, ever see how tall the vertical stab on the Navy PB4Y is?).

The longer the antenna, the lower the frequency.  Even with HF frequencies, you can talk thousands of miles (especially in an aircraft).

The plexiglass dome on the front of the B17 was like Widewing said, celestial navigation.

Pretty good answers, but on the HF answer, there are some limitations, especially if one wants to talk to someone in the U.S. from Britain for example! Following is a link from radio school in the USAF, which was taught at Keesler AFB, Biloxi, Mississippi during WW2:  HF part of the spectrum can transmit signals by ground-wave or sky-wave propagation. Ground-wave propagation is effective from 30 to 300 miles. Sky-wave propagation can span the world depending on atmospheric conditions and the frequency used. HF is widely used for long-distance communications, short-wave broadcasting, over-the-horizon (OTH) radar, and amateur radio. HF transmitter power can range from as low as 2 watts to above 100kW, depending on the intended use.

In the HF range, two-way voice and data (record) communications can be supported in various ways. This includes point-to-point broadcast and air/ground/air operating modes using upper or lower sidebands. Besides long-range communications, HF is also widely used in tactical environments to supplement communications when LOS radio isn't possible or feasible.

Another HF mode is short-range near-vertical-incidence sky wave (NVIS) used with the NVIS antenna. The NVIS is useful when stations are separated by obstacles (such as mountains). When direct communication isn't possible, a NVIS antenna can radiate an HF signal almost straight up for reflection down (over a mountain peak) to another station only a few miles away. NVIS operations are most effective when using the lower HF frequencies (2 to 6MHz).

HF can accommodate IMC, voice, and teletypewriter operating modes and can operate in secure modes using a variety of available COMSEC devices. HF radios can be mounted in vehicles, ships, or aircraft and can be fixed, portable, or man pack configured. Transmissions are normally in either the single sideband (SSB) or independent sideband (ISB) mode.

HF sky-wave propagation is extremely vulnerable to intercept, particularly the high-powered, long-haul systems. The HF part of the spectrum is currently the frequency band most susceptible to jamming. Electronic countermeasure (ECM) jammers far from the receiver can jam or disrupt HF sky-wave communications. Proper use of COMSEC devices and burst transmission techniques can reduce this vulnerability however. Without some form of anti-jam protection, HF communications aren't considered suitable for critical C2 systems.

[FLS]

To fully close the loop on question 6, it is adverse yaw, as noted in several of the replies.  Common to many aircraft, it is caused by the aileron that is going down (and thus lifting that particular wing) causing more drag than the aileron that is going up (on the descending wing).  This drag causes acts like an airbrake on that side, and causes the aircraft to yaw away from the desired direction of turn.  Leading the turn with the rudder is the fix, and there are some design fixes as well, built into most modern airplanes.  Fly by wire can remove this effect entirely for all intents and purposes by having the flight computer compensate for it.

Adverse yaw is greatest when you roll to set your bank angle. The roll creates more lift on the rising wing. The wing with more lift has more induced drag. Once the roll is stopped the lift is more equal between the wings and the yaw is greatly reduced until it's reversed by rolling out of the bank.

[earl1937]

Adverse yaw is greatest when you roll to set your bank angle. The roll creates more lift on the rising wing. The wing with more lift has more induced drag. Once the roll is stopped the lift is more equal between the wings and the yaw is greatly reduced until it's reversed by rolling out of the bank.

Well, not sure how to answer this reply, but: the wing produces, (in lay terms), relative lift, which holds the aircraft in flight, and resultant lift, which turns the aircraft! Lift is what turns the aircraft, not the controls, all the controls do is put the aircraft in the desired attitude to produce the performance that the pilot wants from that attitude. Relative lift always works vertically from the top of the wing. Example: if a wing is 60 feet long, in a 45 degree bank, you have effectively reduces the lifting area by 30 feet, hence the reason for back pressure on the elevator to compensate for the loss of relative lift, you have to increase the angle of attack of the 30 foot wing, to hold the aircraft in the air that was designed for a 60 foot lifting area.  The resultant lift always acts 90 degrees to the wing. Again, as in a turn, the reason for the back pressure on the elevator is to compensate for loss of relative lift by changing the angle of attack of the wing to maintain constant altitude. The resultant lift will remain the same though out the turn unless some outside force acts on the wing to disturb the bank angle, turbulence for example can and does change the bank angle with out the pilot making any control inputs.
The main thing that any pilot should understand is the wing's lift is what turns the aircraft, not the flight controls. Now, in the case of 90 degree bank and applying back pressure to create and maintain the turn, you are talking about an all together different set of aerodynamics which affect the aircraft. What we are discussing here are prop driven aircraft! I don't think we need to get into wing "spoilers" and their effect on the aircraft, but they to, have an effect on aircraft yaw when starting a turn, but as I understand it, it actually has the opposite affect of the aileron controlled aircraft. Example: when starting a left turn with a spoiler controlled wing, the spoilers on the left wing come up to decay the lift on the left wing, and the pilot, because of the drag of the up spoiler, now has to apply a small amount of right rudder to compensate so as to stay coordinated during the turn. Maybe some these jet jockeys which are playing the game can weight in on that and explain it for us all.
I don't think, and wind tunnel tests have proved this: starting, during and recovering from a banked turn in aircraft, one wing does not produce more lift than the other!

[FLS]

http://en.wikipedia.org/wiki/Adverse_yaw

Here you go Earl.