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F-105 Thunderchief #439 | Ducts Gone Wrong

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8 Responses to “F-105 Thunderchief #439 | Ducts Gone Wrong”

  1. rye says:

    hey bob

    wouldnt the painting inside the duct hide a lot of it?

  2. Brad says:


    Just an idea, cut the wing ducts 1″ FWD of the wing root, glue them together and incert them into the other internal duct going to the turbine. The only other thing you would have to do is create a flang so the new wing duct will incert into the fuselage duct. Just an idea what do you think?


  3. John Mardock says:

    Hi Bob,

    Do you really need the internal ducting? For example in the Flash everybody’s removed the inner duct and the turbine shroud. More power and they seem to run a little cooler. In other words the wing/wing duct will get the air to the inside of the fuse and that is all thats really needed, the suckn’blow will have plenty of air don’t you think?

    All the best

  4. With out being a Jet expert, I tend to agree with John Mardock`s reasoning.

  5. Gary Baugh says:

    John, it would seem to my limited knowlege of jet intakes that allowing that much pressure unchecked within the fuselage would invite all sorts of potential problems in the way of FODDING (Foreign Object Damage) the engine as well as stress on other components such as wiring, servos, tankage, etc. Perhaps I am too naive in regard to all the air velocity that will be rammed in when flying and its potential for displacing things within the confines of the aircraft’s skin. Bob’s ducting will channel (isolate) all that pressure to only the engine’s intake nozzle.

  6. catman says:

    High speed air does some pretty weird things when you let it do whatever it wants to. It is not unheard of for full-sized airplanes to come apart when high velocity air got into places it wasn’t supposed to. P-51, B-1 and the space shuttle have all suffered from this issue. I think Bob is on the right track with his intake ducting solution. His ducts will not only look good when the model is finished, but will smooth out the airflow as well and channel it more efficiently to where it needs go.

  7. John Mardock says:

    Gary, Catman remember these are models. Will not be doing 400mph+ In fact we have a speed limit of 200mph right? Few models have complete duct systems. Many are just scoops on the outside of the fuse dumping air into the fuse. The entire and very popular Boomerang jet line has no ducting internally. They are, as you are probably aware, plastic film covered wood structures. No where near the strength of the F105 Fuse Bob has constructed. No ducting failures I am aware of in the Boomerang lineup even though many are pushed to the 200mph limit. Also I am sure you guys are aware that turbines do not require air be fed to them. Many designs have no scoops or inlet ducting like the Shockjet and the MachJet 60. They just have holes in the fuse side, right. Bob has tubes through the turbine area so no exposed wires in a slip stream. Even if they were in the breeze I am sure he would tye wrap them. Also probably being redundant but I am sure you are aware also that these do not behave like the ducted fans. Ducted fans require careful duct planning and construction for air volume as well as flow turbulence this to achieve maximum thrust.

  8. catman says:

    Hmmm. I see your point, John. I sometimes get caught up in the moment and want to take things to the extreme. Bob’s intake duct work may not be absolutely necessary for his Thud to fly — after all, RC jets must do all their flying in the equivalent of an airport traffic pattern and do not have to exhibit the range, speed, sophistication, etc of a 1:1 airplane — but I think Bob has moved from stick and monokote construction to a higher plane, if you will forgive the pun. He has the skills and abilities and all our support and is raising the bar. You can see that in each of the models he has built for us so far. Whether the duct work is needed or not, it kicks things up a notch. That’s how the hobby has grown from Boomerangs painted like a circus wagon to high fidelity representations like Bob’s Thud. Besides, whether they work or not, the finished intakes look cool. I’d want ’em my Thud were I to build one.

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