The Hughes XH-17, a helicopter with the largest rotor system ever, powered by two GE J35 turbojets sending compressed air through hollow blades to tip jets where fuel was injected - 1952-1955

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CaptainCrowbar@reddit

So not only tip jets, which have never worked in the entire history of helicopters, but afterburning tip jets?

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Tutezaek@reddit

The Djinn was, for its time, fairly succesful

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Plump_Apparatus@reddit

which have never worked in the entire history of helicopters,

The Sud-Ouest SO.1221 Djinn was modestly successful with 178 examples produced. It was also a cold tip jet and quite quiet. The only tip jet rotor craft to see serial production.

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liberty4now@reddit

That one was new to me. https://en.wikipedia.org/wiki/SNCASO_SO.1221_Djinn

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The Fairey Rotodyne was technically fine, and there is no reason to believe it would not have worked well as a military transport aircraft. Noise issues prevented interest in civil applications, but there is no reason to believe it could have found a niche and worked well in it.

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SporesM0ldsandFungus@reddit

I can't think of any tip jet aircraft that did not have ear shatteringly loud noise issues...

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BobbyP27@reddit

Sure, but if your customer is the military that bought the Vulcan, they clearly have fewer concerns about loud noises.

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JL_MacConnor@reddit

"So you're saying that the sound itself is a weapon... I'm listening."

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Longjumping_Rule_560@reddit

You’ll love the NHI H-3 kolibri.

A tiny helicopter powered by two ramjets. Fuel consumption was massive so range was tiny. Noise levels were enough to cause complaints from people living over 5 km away from the test site.

While technically a success, if you can live with the range and noise, it was never a commercial success. Only about a dozen were build. In part because the USA were literally giving away OH-23s to the RNLAF.

Wikipedia

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Virtual_Area8230@reddit

Tip jets ARE afterburners. And they work just fine. They're just noisy and haven't been on a produced helicopter, but it's not because they don't work.

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Annual-Advisor-7916@reddit

Depends on the type of tip jets. There are hot and cold ones. Cold ones are essentially using the compressd air from the turbojet while the hot tip jets inject fuel too, making them, well hot.

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Virtual_Area8230@reddit

Cold uses compressor air. Hot uses air that's gone through the entire engine.

The tip jets we were going to use on the Heliplane used turbofan bypass air and injected fuel at the tip burners.

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Uranium-Sandwich657@reddit

Jets on the rotor wing tips?

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AnnualZealousideal27@reddit

What’s the worst that could happen? /s

*flies near anything flammable*

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fulltiltboogie1971@reddit

Excuse me sir there's no smoking on this flight

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dan_dares@reddit

This is very much a smoking flight.

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Either_Amoeba_5332@reddit

Where there's smoke,......well you know the rest....

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DukeBradford2@reddit

I read that in Ron Howard’s “Arrested Development” narration.

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FuturePastNow@reddit

So inefficient it had a 40 mile range.

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Virtual_Area8230@reddit

It was a test rig. The production version would have been the XH-28.

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CosmicPenguin@reddit

which have never worked in the entire history of helicopters

The history of helicopters hadn't been written yet, so they get a pass.

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beautifuljeff@reddit

Yes, but you forgot it was built from parts out of a pick and pull junkyard, basically

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kingtacticool@reddit

Fortunate Son intensifies

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Smooth_Imagination@reddit

The extreme diameter suggests it has exceptional lift per kw shaft power equivalent.

The losses in the tip jets however are probably pretty high compared to typical turbines.

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fullouterjoin@reddit

It would be interesting to do this electric motors on the tips

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Smooth_Imagination@reddit

Actually its been done, and the lift efficiency was reportedly great.

I saw this on a youtube video, if I find it again I will post a link.

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fullouterjoin@reddit

TIP JET Helicopter Mk1 (Will it fly?)

https://www.youtube.com/watch?v=6Rw3UTQpP7A

Related https://www.youtube.com/@NicholasRehm

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StormBlessed145@reddit

That looks terrifying.

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dienices@reddit

I'm surprised no one has mentioned the Fairy Rotodyne yet:

https://en.wikipedia.org/wiki/Fairey_Rotodyne?wprov=sfla1

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Beatleboy62@reddit

In flight, the main rotor spun at a sedate 88 revolutions per minute, less than half the speed of typical helicopter rotors.

Jeez, that is downright wacky. It makes it feel like a minature someone made for a children's show.

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whywouldthisnotbea@reddit

134 foot diameter rotor system.

2pi*r = 420.97 foot circumference

Circumference * 88 rpms = 37,045.65 feet per minute traveled by a single blade tip

Feet per minute / 5280 feet = 7.02 miles per minute

Miles per minute * 60 minutes = 420.97 miles per hour

TLDR the tips are so freaking massive that they make 420 mph at the tips look that slow.

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Beatleboy62@reddit

Good LORD

Thank you for doing the math to put it all into perspective.

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flounderflound@reddit

So this is quite literally the speed the rotors were spinning at in the video then, as opposed to the weird way cameras often capture helicopter rotors. Unsettling.

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Beatleboy62@reddit

It looked too slow like it was framerate matching, but so consistently slow I had to look if that's how it was actually moving.

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LongjumpingSurprise0@reddit

This was essentially just a hodgepodge of parts from different aircraft. The Cockpit was made from a Waco Glider. The Landing Gear came from a B-25 and a C-54.

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fullouterjoin@reddit

This is how it should be done for prototype aircraft. Or prototype anything if you can wing it.

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AskYourDoctor@reddit

I was about to post this from the wiki:

To speed construction, parts of the XH-17 were scavenged from other aircraft. The front wheels came from a North American B-25 Mitchell and the rear wheels from a Douglas C-54 Skymaster. The fuel tank was a bomb bay-mounted unit from a Boeing B-29 Superfortress. The cockpit was from a Waco CG-15 military glider and the tail rotor from a Sikorsky H-19 Chickasaw was used for yaw control.

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cat_prophecy@reddit

Did Hughes ever make anything that wasn't totally insane?

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Federal_Cobbler6647@reddit

AIM-120 is pretty sensible. So was the AIM-54 Phoenix as soon as they removed nuclear warhead.

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pedrolucan@reddit

Wait the Phoenix was supposed to be a nuclear Air-to-Air missile?

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Federal_Cobbler6647@reddit

Its direct predecessor. Designation changed during project, but it really was one development.

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Pynchon_A_Loaff@reddit

We also made radars/fire control systems for the F-106, YF-12, F-14, F-15, F/A-18, etc. But yeah, we were insane.

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AskYourDoctor@reddit

I know it didn't end up working out (and between the crash and senate investigation is actually kind of infamous) but the XF-11 wasn't a crazy design on its face was it?

That said, I totally agree with you in spirit

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liberty4now@reddit

OH-6 Cayuse/Hughes 500 is iconic. So is the AH-64 Apache.

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cat_prophecy@reddit

I guess I didn't realize that Hughes made the AH-64.

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FletcherCommaIrwin@reddit

This always gets my upvote. What a thing, what an insane, beastly looking thing that is.

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TheManWhoClicks@reddit

I assume this isn’t a low inertia rotor system?

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ThatHellacopterGuy@reddit

Considering how heavy those blades almost-certainly were, I think there would be plenty of inertia.

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pesca_22@reddit

looks like those blades have to weight twice the rest of the copter

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CocoSavege@reddit

I'm still boggled this didn't catch on. It's plainly obvious it didn't catch on so I'm left to wonder why.

Tail rotors are expensive. So much so that irl dual rotors are a thing, duplicating all the parts for dual rotors, the maintenence fir dual rotors, the complexity of dual rotors. That's how much tail rotors are expensive.

And "big but slow" rotors, the pattern of tip push helis, is actually a fairly attractive meta in some regard. Efficient along some axes.

Thinking out loud here, the join from the air pump to the rotor is probably a bitch though. Rotor is spinning, pump is not. Rotor is getting collective, pump is not. Sliding seals are an engineering nightmare.

"Big but slow", thicc rotors, they have a lot of momentum. Can't change speed easily at all. Hard to add and remove power.

There's gunna be some friction loss running all that air through the rotor blade. Probably the least of the problems.

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Xeelee1123@reddit (OP)

Source: https://youtu.be/obNlc-3NxEE

Source: https://en.wikipedia.org/wiki/Hughes_XH-17