I think the XF-85 could be redesigned with landing gears, by getting rid of the intake which IMO was a massive hazard and having vents at the back and sides. This could free up space and allow landing gears to be added, I already gave my ideas on where the cameras could go if it put into a reconnaissance plane role. But I find it quite hard to imagine it fitting into a fighter role.
Well, it was designed to be a fighter, and nothing else. It had practically zero endurance. The idea was that designing a traditional escort fighter for intercontinental ranges would be a nightmare wherein the "fighter" would be a huge whale of mostly flying fuel tank, no match for nimble enemy interceptors that did not require thousands of miles of range. So flip that around--make the fighter "escort" a parasite, deployed only for point defense of the bomber mother ship, and then it could have the advantage of speed and nimbleness by sacrificing every compromise a normal airplane requires in order to take off and land. Therefore half the horror someone like Archibald feels seeing the ridiculous thing is by design. These were early days of jet engine design after all; thrust tended to be anemic. So what we have is minimum airplane, just room for a pilot, some guns and ammo, wings and control surfaces wrapped around an engine for maximum thrust/weight ratio. I note from your statistics comparing to the later Thunderflash recon parasites that the Goblin had lighter weight/wing area ratio--which is probably mostly state of the art, the Republic plane being the later design following the trend of ever higher loadings corresponding to higher operational airspeeds. But in the role of defense fighter, the lower loading is good; it means it can lose airspeed maneuvering and still stay nimble, and it can be very maneuverable (if it doesn't fall apart structurally--but the compact form suggests it ought to have been pretty robust too). But it cannot have endurance! That violates the whole concept. The idea is, get dropped off, zoom over on your relatively powerful engine, kill the MiG bandits, then run home to mama for retrieval, refueling and presumably refilling the gun magazine. That, presuming it can do that, is all it can do. There is no point in putting landing gear on it; the radical cutback in parasite mass is due to it already being launched at full airspeed and altitude. There is no margin for takeoff and climb, it would run out of fuel before it got to intercept altitude. Recon also would require long range--if the parasite recon plane is not going far beyond the mother ship's line of sight, what is the point? Just put big telescopic cameras on the big plane; they've got to be lighter than a whole airplane and much less risky too! Clearly the Thunderflash had to go far out of the carrier bomber's line of sight, which given the really long distances one can see from a stratospheric altitude, means many many hundreds of miles.
Had the idea been to develop a parasite recon plane back in the 40s when Goblin was conceived of, the design would be radically different. You'd want moderate endurance then, so fuel tanks would be integral to the design; you are not aiming for combat maneuverability at high altitude, although some nimbleness would be desirable to evade interceptors. Speed is a virtue so the engine remains oversized, but so is stability to get good photos-I suspect flying Goblin was rather like piloting a bumblebee! Keeping it light overall is a virtue both due to the fact that you want to recover it to the mother plane, and to minimize overall size to make it harder to spot and track, but the recon mission suggests it would be good to have a second crewman to take the photos while the pilot concentrates on flying the plane. It would be wise to design optional landing gear, in case the mother ship gets shot down or disabled, but these could be simplified to be one-way drop-down gear (operated by compressed air or even a solid-fuel charge, or maybe just plain gravity perhaps with some springs to latch them tight) that are lighter, since we hope to avoid using them at all and we don't need them for takeoff, so no retraction mechanism. But we might omit them completely and write the plane off in such an emergency, with the crew bailing out (hopefully with the film canisters and any other recording media).
Overall it would wind up looking a whole lot more like a normal high-speed fighter/interceptor, which explains why just such an off the shelf design was adapted to the mission OTL.
I have always been a lot more charmed with the concept than say Archibald is; it is too goofy not to love IMHO! I'm also a big fan of airship-based hook-on airplane operations too, and my thoughts on and knowledge of the latter subject suggest to me that the basic problem of the OTL test operations was that the "trapeze" mechanism was too close to the airplane. The plane was going much faster than an airship, which eliminates the obvious problem of a high-speed plane trying to "land" on a 60 knot airship, but the solution is similar. Here, the problem is the airplane (mother ship I mean, meant to be B-36 in operations) relies on dynamic lift and is going much faster, 300-400 knots or so, 150-200 meters/sec, and so tremendous turbulence vortices are coming off it. The solution is distance--get the trapeze itself a good 50 meters or so away from the airplane, and the approaching parasite plane has pretty clear air to approach in. When hook on speeds match, as with the Naval ZRS rigid airships of the early 30s and their biplane Sparrowhawk fighter/scouts, then in clear air operations are a breeze compared to the daunting yet routine task Naval carrier plane pilots have landing at (nowadays) approach speeds over 100 knots on a pitching effectively stationary deck.
I believe carriers generally steam as fast as they can straight into the headwind, which can take some 25-60 knots off the effective approach speed, but the high speeds depend on strong surface winds which introduce new complications of turbulence, whereas modern heavy fighters probably need a lot more than 100 knots airspeed at landing, and of course little can be done to eliminate pitching. By the way one might imagine hydrofoils, honking heavy ones to be sure, combined with 20-30 knot water speeds, could dramatically help with the aid of very responsive foil pitch control, but I've never heard of such a stabilization project.
Anyway everything I've read about the ZRS experience with hook on operations says that after a few early glitches (in one case, the trapeze mechanism was bent by a hard landing and the pilot of the test plane, maybe not a Sparrowhawk yet, had to climb up and hit it to unjam it!) the pilots had quite an easy time, with no losses due to failures in that phase of operations. On the other hand the German aviation mandarin Udet once attempted to try it out in person, with a rig attached to Hindenburg, and reported it was quite difficult for him. Maybe the Germans placed the rig badly--it was off center of the airship hull for one thing, and perhaps in at a much more turbulent, more rearward station. But I also suspect Udet might have "thrown" the test, perhaps one reason he did it himself--neither Goering nor Hitler had any fondness for Zeppelins, and I suspect he knew what his bosses wanted to hear. Anyway the Americans had no trouble with it, and I think it has got to be less dangerous than conventional landings on seaborne flattops.
I am not sure just how far out of the main slipstream of the airplane a high-speed trapeze would have to go. In addition to going much slower, airships operate close to static equilibrium, meaning little to none of their lift comes from dynamically diverting the slipstream. (I know, dynamic lift can be significant, and a lot of people think hybridizing to rely on more of it is the way to revive semi-LTA, and a lot of current designs rely on it heavily. I happen to think it is a mistake to neglect the advantages of pure static lift myself, so I ignore that factor. To be sure, precisely during hook-on operations is when an airship mother ship would be most out of static balance, since to be in it after retrieving the planes, it would need to be light before doing so, or vice versa if in balance before hook on it will be heavy afterward. My point here is, any dynamic component of lift is relatively small on a traditional airship and the bigger the airship the more true this is--absolute lift goes up, but more slowly than the static component). So the turbulent layer around an airship is large mainly just because of its size, but just a few meters off has clear air. With a dynamically lifted airplane of a couple hundred tons, flying at say 350 knots, the turbulence is much worse despite its relatively compact dimensions. But anyway, at some radius below the fuselage, air should be pretty clear. An approaching airplane at the same airspeed should be able to hook on as easily as the Sparrowhawks did. Doing it much closer to the big plane is a recipe for disaster of course.
The hanging trapeze and cable would be a turbulence generator itself of course. And at high airspeeds, drag would be considerable and trail the trapeze far behind at a wide angle to vertical, also drawing it back into the turbulence cone of the big airplane. I would propose streamlining the heck out of the trapeze itself, the cable (giving a cable a thick airfoil like section can lower its drag dramatically, see "RAF wire") and also adding a propulsive unit just above the trapeze itself--a pair of well-controlled propellers flanking the bottom of the cable, powered by electricity from the big airplane or a light engine in the hanging assembly, with variable pitch that responds rapidly, to provide counter-thrust pulling the cable back forward and damping out any crosswinds or turbulence. Once hooked on, the assembly and parasite plane can be winched in, perhaps the thruster props will need to fight turbulence that might otherwise toss the little plane around until firmer, shorter lines or cranes can be attached to mount it rigidly and pull it in tight for refueling and rearming, perhaps swapping out the pilot with a relief.
I think had it been deemed worthwhile to proceed, the hook-on problems of the Goblin could have been solved in this fashion. With that fixed, my impression is that Goblin would have been able to serve its intended purpose, point defense of a bomber with a nimble, effective and fast short-endurance fighter, reasonably well as designed. We may not be sure of that since the test program gave up without solving the essential hook-on problem first, but it seems likely enough it would be doable to me, especially in view of later success with the Republic airframes.
The trouble was, the doctrine that bombers would need to be accompanied by fighter cover was abandoned, first of all, in favor of the hope that bombers could be made to fly fast enough, at high enough altitudes, that enemy interceptors would not be able to down them. Or at any rate, that enough bombers would get though to make the inevitable losses to interception acceptably low. Secondly, the variation on the hook-on theme of in-flight refueling was developed instead, which did enable fighter cover to go a lot more forward without compromising either by designing in hook-on operations (which clearly compromise both the fighter and the bomber, the latter being the bigger concern I believe) or by making them into mostly fuel tank. (That too was proposed, I believe an early postwar Douglas design, or it might have been the last Curtiss, was meant to have the endurance--and it was indeed a heavy whale, if not a blue whale than anyway an Orca!) It also greatly extended the range of the bombers themselves of course. B-47 and B-52 were indeed remarkably fast and very high-flying turbojet designs. The Soviet "Bear" although powered with turboprops flew in the same envelope, and with greater fuel efficiency (maybe somewhat slower, though by far the fastest prop plane ever flown, and with a much worse radar cross-section and identifiability thanks to those contra props--noisy too if that matters) and also eschewed fighter escort in favor of nimble maneuvering and high speed and altitude. Then of course ground-based SAMs were developed capable of reaching even the highest attainable altitudes, with rocket projectiles far exceeding any sustainable airplane speed, even of a plane designed at great cost to fly at high supersonic speeds like the B-70; at this point bombers could only hope to get through by a combination of stealth/deception and sheer saturation of enemy air defenses--which by the way a couple of early 1960s operations in the USA demonstrated were not nearly as good as was hoped. Or by going over to treetop skimming below-radar approaches, which some airframes designed for high-and-fast could adapt to and others could not.
Obviously against ground gun fire or SAMs, or on low-altitude below-radar missions, parasite fighters are quite useless. Wherever fighter escort might be most useful and practical, airborne refueling at the edge of the combat zone enabled standard designs to do the job without compromises in the design.
And of course the whole vexed (from a traditionalist like LeMay's POV anyway) subject of missiles on all scales was critical as well. It is not clear to me that nuclear strike bombers should have been retained at all in that role, once ICBMs were developed and deployed. Thank God the matter has never been put to the practical test. We have used both big bombers and fighter-bomber designs extensively since WWII, armed with conventional bombs or cruise missiles or other stand-off air-to-surface missiles, and missiles have taken over much of the role of air-to-air combat, Experience teaches it is foolish to design a fighter/interceptor with no machine guns/cannon, but the air to air missiles they must also carry are intended to be the first recourse, with guns coming into play only later in a dogfight. (Lack of guns cost Air Force, Naval and Marine pilots a lot of kill opportunities in Vietnam, but it would have been bad to have no missiles at all too). If we have a bomber today that fears it might need to run an interceptor gauntlet, it is clearly better to upgrade the same (conceptually anyway) air-to-air missile a hypothetical parasite fighter would need to carry anyhow, to give it more range and sophistication, and fire that, and forget about recovering it, than to carry a defensive parasite fighter. Hence schemes like Pye Wacket.
It would be cool to somehow game or freeze the advances of technology that closed the window on parasite fighters so firmly, but I have no clue how to plausibly do it. If it were done, I do think Goblin could have performed well enough in its generation to have the mission it was meant for.
It certainly is
not adaptable to other missions such as strike or recon!