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Thread: Jet engine intake in the nose

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    Jet engine intake in the nose

    The early jet aircraft (which had the engine mounted in the fuselage) used a nose intake with a long duct back to the engine. What are the pros and cons of this configuration? It must have been considered the best configuration by many great minds because it was used on both sides of the pond for a few generations of aircraft (although its use seems to have petered out by the mid-50s).

    I ask because I have long wondered if this configuration would be suitable for a very light jet. I remember reading about the issues Diamond had designing the two S ducts to get air back to the engine on the D-Jet (example from Plane & Pilot article: "One of the single greatest technical challenges Diamond has had to contend with, thus far, is its bifurcated engine duct design.")

    One obvious drawback is that the duct will detract from the cabin space, requiring a larger fuselage radius and the associated increase in drag. Anything else?

    Thanks,

    Michael

    Jet engine intake in the nose-snapshot1.jpg

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    Re: Jet engine intake in the nose

    More drag, maintenance is harder etc. That's why podded engines on the tails (smaller aircraft) and the wings are now the standard solution for civil aircraft. More weight in the back means a bigger tail (shorter tail arm), such that a more fwd placement like the Diamond or Hondajet might be favorable?
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    Re: Jet engine intake in the nose

    Having the intake in the nose (like the F-86, F-100, Mig-15, etc) is probably the best answer from an aerodynamic standpoint, but as you say it causes loss of cabin volume. I think the major reason we got away from it in fighters was the advent of radar: That big spot right in front of the fuselage and close to all the other systems is ideal real estate for a big radome, and so the intakes were moved somewhere else. Some aircraft mounted the radar antenna in a shock cone in the nose inlet, but it just proved easier in most cases to put the inlet in the wing roots, underneath the plane, or even on top.

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    Registered User cluttonfred's Avatar
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    Re: Jet engine intake in the nose

    If a small turbofan of appropriate power and reasonable cost ever becomes available, it's not unreasonable to see the nose intake come back for recreational light jets. A "chubby" Yak-23 with side-by-side seats, and the air intake running between the legs of the pilot and passenger seems like a very simple, compact configuration keeping the engine and both crew near the CG.

    Jet engine intake in the nose-yak23yak.jpg
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    Re: Jet engine intake in the nose versus pod or S duct.

    Quote Originally Posted by aviast View Post
    The early jet aircraft (which had the engine mounted in the fuselage) used a nose intake with a long duct back to the engine. What are the pros and cons of this configuration?
    .....

    Thanks,

    Michael
    The inlet in the nose has undisturbed air and therefore the inlet design is rather straight forward and has the least risk for the design to be predictable and efficient. As you said the S duct required a lot of engineering test and development. The down side is the longer duct for both the inlet and tailpipe and has more drag losses. Early jets, F 86 and Mig 17, were pure jet and therefore total airflow was relatively low. Later turbojet aircraft were bypass engines with a cold fan flow having much higher airflow (bypass ratios of 2.5 to 1). Not only would the duct need to be much larger but intake and exhaust losses with long ducts would be much greater.
    The longer tail pipe provides adequate room for the afterburner.
    Furthermore, the F 86 and Mig 17 only had one engine source. The pylons on modern airliners allow a choice of engines with little change to the structure.
    You may ask why the F 80 and T 33 had the dual inlets. The centrifugal compressor in the very first jets were more tolerant of inlet distortions in the airflow than more refined axial compressors of later generation engines.
    Conclusion, most designers chose the engine on a pod for aircraft like you are considering. Exception would be the BD 5J which was a piston engine replacement so there is no provision for a nose inlet and the engine chosen has a centrifugal compressor and it is not a fan jet.

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