question about flames of Saturn V

[ckikilwai]

I've seen some of the launch pictures of the Saturn like these: <br />http://www.space.com/images/ig204_09_02.jpg<br />http://www.apolloexplorer.co.uk/photo/img/AS6/10074832.jpg<br />and you can see the flames climbing up half the first stage.<br />My question: Why? and Wasn't it dangerous, because a small flame burning through the external tank was already catastrophic for Challenger?<br />

 

[vogon13]

IIRC, a EELV-4 (probably got that wrong) was massively scorched in a recent KSC launch.<br /><br />It still worked just fine. <br /><br />(Instantaneous flame contact on the aluminum Saturn V 'hide' isn't the risk that physically punching a hole in a shuttle TPS component is)<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[tomnackid]

Its a boundary layer effect caused by the changes in air pressure as the rocket moves through the atmosphere at high speeds. Its sort of like a floating piece of debris being carried along in the wake of a boat. I don't think it did more than scorch the paint and insulation.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>IIRC, a EELV-4 (probably got that wrong) was massively scorched in a recent KSC launch. <p><hr /></p></p></blockquote><br /><br />That would be the Delta IV Heavy. Quite a sight! <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[trailrider]

During lift-off, there can indeed be flames circulated up around the booster, though what often looks like flame is really the steam caused by the suppression system water vaporized by the heat of the engine exhaust. The effect is of short enough duration not to cause any significant damage.<br /><br />At altitude, the reduced atmospheric pressure allows the exhaust plume to expand and sometime flow forward along the skin of the vehicle. As long as the flow is within the design parameters of the skin of the vehicle, there won't be a problem.<br /><br />Where problems can arise is if there is recirculation into the base of the vehicle. This is usually handled by having sufficient insulation around the structure, tank bottom, hydraulics packages, etc. This WAS a problem back in the early days of the Polaris missile. "Hot bottom" burnthroughs on the hydraulics packages was handled by adding more insulation in the form of phenolic panels and "E-pon" epoxy.<br /><br />Another thing to keep in mind about the appearance that the exhaust is climbing high up the vehicle's side is the angle from which a lot of the cameras view the climbing rocket. The exhaust expands quite a bit, and may appear to engulph the whole vehicle when actually it doesn't.

 

[drwayne]

One of the big issues that the Saturn 5 had to deal with was that the first stage fuel being kerosene, meant that the exhaust was fairly sooty.<br /><br />If care was not taken, significant soot deposits could get on the viewports of the command module - so timing of uncovering these ports had to take this into account.<br /><br />I have done simulations that look at the detachment of the aft shock layer and its propation up the vehicle. <br /><br />Some of the launch camera videos that you can look at show this from the missile perspective...<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[propforce]

<font color="yellow">and you can see the flames climbing up half the first stage. <br />My question: Why? and Wasn't it dangerous.... ?</font><br /><br /><br />Late reply here, but these are interesting photographs.<br /><br /><font color="yellow">WHY?</font><br />What you're seeing is a combination of interesting aerodynamics and combustion phenomena that makes it unique on the Saturn vehicle. <br /><br />First the aerodynamic effect, the relatively high engine exit pressure from the 5 F-1 engines created a large enough plume that forced "oblique shocks" from the air flowing down the first stage. This creates a "flow separated" region where the higher pressure from the plume creates a "back-flow" into this separation zone and recirculates.<br /><br />Second, the above flow separation coupled with the fuel-rich exhaust from the F-1, which is fuel rich (left with unburned fuel) that "back flow" into this zone rich with oxygen and with a pressure high enough to encourage combustion, it then burns and flows out along the "oblique shock" line.<br /><br />This is interesting and unique because a single engine vehicle usually does not produce a strong enough "back-pressure" to cause this phenomena. But multiple engines, esp. a combination of 5 engines, creates a strong "jet pump" effects in between the engines. When it "entrains" air, the air accelerates thus further lower its static pressure which further encourages the engine plume to "back flow" foward.<br /><br /><font color="yellow">Wasn't it dangerous.... ?</font><br />It could be if you have a easily flammable materials in that zone. But fortunately for the Saturn, as well as most launch vehicles, that there are usually insulations in that area and they are not easily burn. So it is mostly safe.<br /> <div class="Discussion_UserSignature"> </div>