Text Box: WARBIRD NOTES #20     6 Aug 97     (11)
FOAMED RUNWAY FOR BELLY LANDING?
  "Shot your wad, huh?"  Yeah, I know, a barnyard expression - but probably the exact feeling you're gonna have if the foam you desperately need from the fire/crash truck is uselessly sprayed over several thousand feet of runway, and all of it behind where the airplane finally came to rest after landing on its belly.  And now there's none left in the crash truck's tank to smother that little-bitty fuel fire that just ignited under the fuselage!  Yeah, that fire that's now going to destroy one perfectly good (albeit with its belly and flaps slightly bent from the landing) airplane!  Couldn't happen, you say?  Oh boy, been there and done that!  Let's discuss it a little bit here, OK?

                                                             

  If you ask a hundred experts, I'd bet that the preponderance of them will allow as to how any idiot knows that "we always foamed the runway for a belly landing!"  And, like many other WW II or postwar "old wives tales", that certainly was the conventional wisdom back then.  For sure!  Well, let me take you out beside the runway with a hand held communication radio, as I've had to do a few times.  Let's watch a belly or crippled landing, might be educational or edifying, you never know.

 

  Anyone ever try to flare out and land an airplane that has its landing gear retracted.  Nope, I haven't either!  But I've sure talked to a bunch of pilots that have that dubious distinction in their resume and their descriptions of the experience all share something in common.  The lack of drag!  With the gear up it's obvious that the drag is going to be less, just how much is anyone's guess but it's been described to me as very noticeable. 

 

  Let me share some observations of a landing I can recall with vivid clarity.  This involved monitoring and talking to (with a hand held transceiver), from the side of the concrete runway, a Convair 580 with Allison turbo-prop engines.  The 580 has steel propeller blades so it was considered best to E (emergency) handle the left engine several miles out on final.  This simultaneously shut down the engine and feathered that propeller.  From that point on it was a simple single engine landing.  Then we'd have the co-pilot (upon the captain's command) pull the E-handle for the right engine as they commenced the landing flareout.  As the big four bladed Aero-Products propeller "X"ed it provided what amounted to two steel sled runners on each side of the airplane for the airplane to rest upon during its skid to a stop along the runway. 

 

  What we need to stress here is the altering of the drag characteristics of the aircraft with feathered propellers, it is considerably less than the drag that propeller "disking" creates during a normal landing.  The pilot told me that it almost seemed to him as if he had added power to the engine when the E-handle was pulled.  So - keep this effect in mind if you're ever faced with this!  Also, added to this is a tendency on the part of the pilot to hold it off just a tad longer than normal in order to touchdown as lightly as possible in this stressful situation.  All of these things will very likely conspire to ensure an unintended result, it's very likely that the aircraft will float much further than normal down the runway prior to touchdown.  If you or someone has informed the crash crew how far from the runway's threshold the aircraft will touch down, it's very likely that this estimate may be substantially in error for those reasons.  If the crash crew opts to use your estimate, very likely the aircraft will partially or completely overfly the foam strip prior to touching down.  And, the aircraft will get only one chance, if the estimate proves wrong and the foam application on the runway is overflown, tough!

 

yet to write :

 

Lets discuss another problem, duration of the foam as a layer.  Estimates vary, but most would agree that the foam has a lifetime of x.  So, this means that you can't dawdle once the foam is spread out on the runway, if you decide to have them apply it.  The chemical breakdown and decomposition begins almost immediately, 

 

alleged spark suppressant          I hear all about the fact that people know it reduces the temperature of the grinding metal.  In actuality, I honestly don't think it really does.  The metal has to support a certain amount of weight, and this is the same if the surface of the runway is wet or dry.  The only thing that I can see it possibly doing is to retard or smother any sparks being thrown up.  However, in reviewing a good number of films taken of these incidents, I see what appears to be a "shower of sparks" thrown far behind the airplane as a "rooster tail", not into it.  Also, many of the pilots I've talked to mentioned another result or observation.  This is the strong tendency of the airplane to slide far out of the foam strip that was laid for it, ending up far beyond it.  They also mention that no difference was apparent to them in the sparks thrown behind it during the slide. 

 

slipperiness

 

Also, another down-side for you to consider in evaluating the situation and whether you really want to use the foamed runway.  If you do and are landing with only one gear retracted, therefore needing either or both the brakes and nosewheel steering during rollout, beware!  You may just have guaran-dang-teed yourself that you won't have the use of these directional controls after touchdown.  If any tire's in the foam strip, wouldn't you expect it to act just as it would if it were on glare ice?  Braking or nosewheel steering?  I think you can pretty well forget that!

 

I don't wanna be discussing effort of turning single engine prop with starter and glide maybe deal

 

Pervasive foreign OWTs

 

R. L. Sohn    1997  


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