Why did they do that

[chuck540z3]

Here's another curiosity of mine. The American F-15's with the Pratt and Whitney F100 engine have the "Turkey Feathers" left off, allegedly to speed up maintenance. The Israeli versions of the F-15 keep then on. Why then don't American F-16's, with the very same engine, have the turkey feathers off as well?

I do, however, have a guess: On the F-15, leaving the feathers off does not change the performance of the aircraft, but on the F-16 it does, so they leave them on?

[habu2]

I read somewhere the problem with the feathers on the F-15 was that aerodynamic flow around/between the engines led to vibrations that could cause the feathers to depart in flight, so they were removed. Obviously the airflow on an F-16 is different and they didn't experience this problem. However I have never heard an explanation as to why the Israelis left theirs on.

(edited for spelling typos...)

Edited August 14, 2014 by habu2

[habu2]

That fin actually fell off during one of the early testflights, after that the figured it flew just fine without it and hence it was never used since on either YF-12 or SR-71.

Can you cite a reference for this?

The fin folded to provide adequate ground clearance during takeoff and landing. During early YF-12 test flights there was an incident where the ventral fin would not fold/retract in flight. The Lockheed test pilot (Bill Weaver) was able to land the jet with the fin extended, he saved the aircraft but the fin was damaged during the landing.

All Lockheed test flights and USAF flights were made with the ventral fin installed and operational. The fin wasn't removed until NASA started flying the YF-12s. Since NASA wasn't launching missiles there was no concern about directional stability with open bay doors.

Again, if you can provide references for YF-12s losing a ventral in flight, I would be interested to learn about the incident.

edit: I found a reference (Paul Crickmore's book by Osprey) that states the radome mod and associated removal of the forward chines degraded directional stability. The fix was to add fixed strakes under each engine nacelle and the larger folding center strake. The book doesn't specifically mention the weapon bay doors so maybe I'm wrong on that. It did say the ventral folding was tied to the landing gear, so gear up extended the ventral, gear down retracted it. The fin couldn't be moved independent of the gear.

Edited August 14, 2014 by habu2

[habu2]

Again, if you can provide references for YF-12s losing a ventral in flight, I would be interested to learn about the incident.

I did some research and found the following information:

NASA acquired the two remaining YF-12s in 1969, after USAF and Lockheed concluded their own flight test program when they failed to get a production order.

In February of 1970 the folding ventral unexpectedly bent in-flight during a sideslip test. NASA then flew a number of flights with and without the ventral to determine handling characteristics and found they were not "substantially degraded" without the folding ventral. After the tests the folding ventral was reinstalled and remained so.

In February of 1975 the folding ventral fin separated in flight while conducting flight handling quality tests. The aircraft was at 15000 ft and M 0.9. The departed fin hit and damaged the right wing, resulting in a fuel leak. The aircraft immediately performed an emergency landing. The aircraft was flown six more times without the folding ventral fin, primarily to gather flow data around the ventral fin location as well as around the Coldwall experiment carried during that time.

Following the loss of the folding ventral, Lockheed designed a new ventral made of a different material (Lockalloy) and the new fin was first flown in January of 1976. The new ventrals remained installed until NASA stopped flying the YF-12 in 1979.

In summary, a ventral fin did depart during flight. However the incident occurred five years after NASA conducted flight handling tests with and without the fin and decided to keep it. In fact a stronger replacement fin was designed and used for the remainder of the aircraft's flying career.

[Marcel111]

In the case of the Lightning the top engine is effectively behind the same space occupied by the pilot in cross section, thus reducing the cross sectional area of the fuselage relative to the two large engines installed.

I have always wondered about this and never though of this very obvious reason... thx for the enlightenment

On the Phantom, there seem to be as many reason provided for the non-planar flying surfaces as there are non-planar flying surfaces on the Phantom. For the anhedral of the tail the most compelling reason I have come across is that the height of the vertical tail was reduced in order to comply with the carrier deck height specifications given at the time (hence also the very long chord of the tail). The "horizontal" tail was therefore given anhedral (i.e. a vertical component) so as to provide additional yaw stability.

I have read that the dihedral of the outer wings was introduced to provide overall wing dihedral, which in turn reduced transonic drag. Since I have no understanding of transonic flow, I have no idea if this makes sense.

Marcel

[Air-Craft]

Was the F-4's 23° downturned tailplane (that arrived between the AH-1 & F4H-1) not a compromise between stability & avoiding jet efflux?

The centre section / box, running from wingfold to wingfold was designed as a robust flat section for maximum strength / load, when it became apparent that more dihedral was required the wingtips went to 12° to give the required average dihedral (5°?) without having to redesign the costly / complex centre section. Slightly Heath Robinson, but it must have worked & certainly helped make the Phantom look the utterly awesome way that it does!

[Jennings]

Somebody must like it!

*Somebody* liked the Cadillac 8-6-4 engine too :)

[dryguy]

why did the spitfire really have elliptical wings? If have been told that the great RJ Mitchell actually misunderstood the aerodynamics, and that an elliptical lift distribution is not the same as an elliptical planform, and that in many ways the spitfire wings could be considered a wartime engineering failure! Crazy!

why was the turbocharged version of the allison engine not pursued more, or rather, why were the original p38s not equipped with turbos when sold to the UK?

Why did the allies not develop a counterto the tiger tank?

[Kevan Vogler]

Why did the US block export of the Volvo RM8 engine and thus hamstring any export success of the Saab Viggen.

Outside of having a Swedish developed afterburner married to it; the RM8 was just a license built P&W JT8D, a very common engine worldwide at the time thanks to the 727, 737 and DC-9.

There was nothing about that engine that warranted blocking its export.

[vince14]

Why did the US block export of the Volvo RM8 engine and thus hamstring any export success of the Saab Viggen.

Outside of having a Swedish developed afterburner married to it; the RM8 was just a license built P&W JT8D, a very common engine worldwide at the time thanks to the 727, 737 and DC-9.

There was nothing about that engine that warranted blocking its export.

One might suggest that the reason the US torpedoed export sales of the Viggen was due to them wanting NATO air arms to buy surplus F-4s instead...

Vince

[martin_sam_2000]

why did the spitfire really have elliptical wings?

From what I understand it was the most aerodynamic shape that would encompass the radiator housings, gear and 8 machine guns while keeping the wing as thin as possible. Draw all that stuff in and then find a shape fits it all effectively.

why was the turbocharged version of the allison engine not pursued more

it was. The P-38 DID have the turbo superchargre the Allison was originally designed with, but early on they were having problems so it wasn't installed on the P-40 as it was rushed into production when the war broke out. The RAF requested that the P-51 have the same engine as the P-40 so it got only the supercharged version, and it couldnt keep up with the Merlin (single speed/single stage in the Allison and a two speed/two stage in the Merlin)so instead of redesigning the P-51 with a turbo-surpercharged Allison they just fitted the Merlin

why were the original p38s not equipped with turbos when sold to the UK?

The RAF got the supercharged only P-38's since they piggy-backed on the French order(eventually taking the entire order over) and the French wanted the same engine as the P-40's they ordered(which also ended up with the RAF)to keep the number of spares low. After the RAF realised the poor performance and the need for higher altitudes and speeds, they changed the order to the standard USAAF P-38, but since the P-38 was having control issues at high speed(compresability)and the success of the P-51, they cancelled the entire order.

Sean

Edited August 16, 2014 by martin_sam_2000

[ChippyWho]

The F-14 was limited by that design (at least when it started doing air to ground stuff).

...which was not in the original brief, that of a Fleet Defence asset and platform for the Phoenix air-to-air weapon. But then, we now understand that no fighter aircraft is worth a light unless you can dangle a Buff-load of bombs under it! Of course, the F-111 and Tornado (IDS/GR series) were supposed to have this capabilty from the get-go and the solution clearly works. Just seems a bit Gerry Anderson to me is all...

The staggered engine arrangement on the Lightning was also not unique - the Sud-Est Grognard employed a 'stacked' engine arrangement - as did the Short Sperrin Bomber as well as some Soviet designs like the Sukhoi Su-15 of 1949 - although none were as neat as the Lightning.

As well as the reduced cros-section that Drewe points out, another slight advantage of the staggered engines on the Lightning is the lack of asymmetric thrust if one engine fails.

Ken

Many thanks, Ken -you can't buy enlightenment like that! Well, I can't 'cause I'm skint. However, I would opine that the 'Le Grumbler' and the Sperrin (at least) are pretty good WDTDT fodder in themselves.

And now I'll pitch in with the F-107. (Let them all come! )

[Pete]

Why did the allies not develop a counterto the tiger tank?

They did.

The US developed the T29/T30, which wasn't complete when the war ended, and in a way, the M26 Pershing was also designed to counter the heavier types of German tanks.

The Soviet Union developed the IS series of tanks, introducing the IS-2 in 1944.

[hawkwrench]

Why is the sky blue????

He he he!!!!

Tim

[Kevan Vogler]

Why is the sky blue????

He he he!!!!

Tim

Because the blue dye was cheapest. :D

[vince14]

Why is the sky blue????

He he he!!!!

Tim

Because of Rayleigh Scattering.

Vince

[GreyGhost]

Why was the F-117 given an "F" designation and dubbed a Stealth "Fighter"?

-Gregg

[Exhausted]

At risk of sounding political, because the answer is, I will proceed.

In the late-1970s Congress was more willing to fund an advanced fighter instead of another bomber. 117 was chose as a continuum of Century Fighters.

In a way it is similar to the F-111, except that the F-111 was, at one point, a naval interceptor. The F-117 was promoted as having limited A2A capabilities, such as the ability to sneak in a shoot down enemy AWAC aircraft.

Edited August 18, 2014 by Exhausted

[scotthldr]

Why did GD decide to put the intake on the F16 under the fuselage, making it FOD hoover?

[Air-Craft]

Why did GD decide to put the intake on the F16 under the fuselage, making it FOD hoover?

To save weight & gain stability over a typical twin inlet arrangement & give good high AOA performance. It was also further back than previous intakes of the type to save further weight, reduce friction & reduce inlet pressure (weight).

[falcon20driver]

I think the question we all really want to know the answer to is, why aren't aviators trained in T-37s and flying F-14s anymore!? What has this crazy world come too?

[Falconxlvi]

At risk of sounding political, because the answer is, I will proceed.

In the late-1970s Congress was more willing to fund an advanced fighter instead of another bomber. 117 was chose as a continuum of Century Fighters.

In a way it is similar to the F-111, except that the F-111 was, at one point, a naval interceptor. The F-117 was promoted as having limited A2A capabilities, such as the ability to sneak in a shoot down enemy AWAC aircraft.

In the book "Skunkworks", Ben Rich talks about an actual AIM-9 live fire test that was done from a trapeze in the weapons bay in order to justify the "F" designation and appease the congressional folks funding a classified program they knew very little about.

Steve

[habu2]

Why did GD decide to put the intake on the F16 under the fuselage, making it FOD hoover?

[11bee]

At risk of sounding political, because the answer is, I will proceed.

In the late-1970s Congress was more willing to fund an advanced fighter instead of another bomber. 117 was chose as a continuum of Century Fighters.

In a way it is similar to the F-111, except that the F-111 was, at one point, a naval interceptor. The F-117 was promoted as having limited A2A capabilities, such as the ability to sneak in a shoot down enemy AWAC aircraft.

I thought the F-117 designation was selected as part of the subterfuge associated with this black program, since it was (kind of) in sequence with designations given to captured Soviet aircraft. Technically, it should have been a B-117 or more appropriately an A-117 but the AF brass are mostly all fighter jocks and anything cool like this jet was going to be designated with an "F". Also, I thought the term "Stealth Fighter" was something that originated with the press, not a term that was put into play by the AF?

As far as the F-117 having A2A capability, was this ever confirmed or was it just an urban myth, like the rumor that SR-71's could actually carry a nuke?

[pigsty]

Why did the allies not develop a counterto the tiger tank?

...

They did.

The US developed the T29/T30, which wasn't complete when the war ended, and in a way, the M26 Pershing was also designed to counter the heavier types of German tanks.

The Soviet Union developed the IS series of tanks, introducing the IS-2 in 1944.

Another way of looking at it is, they did, in the form of the air-to-ground rocket projectile.

Edited August 18, 2014 by pigsty