Yeah, there's a feedback loop there. An OEM makes profit and some of that goes to IRAD. The IRAD is used to make new products that align to BD goals and can continue existing product lines (new blades on H-60, rockets on V-22, VARS) or start new ones (XV-15, V-280, SB-1). Some of these OEM demos show potential or align to what the user wants and they go on to become real programs that go on to be implemented in the fleet.
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- Thread starter Randy Daytona
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I don't think there's any real "how it flies" differences. An advantage of a fan/fenestron is that it's harder to prang on stuff. And it looks cool. All the non-traditional tail rotors don't scale up well so that's why they only show up on little helos. I'd also imagine there's a maintainability difference in that stuff might be harder to get to. For NOTAR I'm guessing it drove up cost that's why people didn't buy it a lot.
Edit: also looks like NOTAR may be proprietary to MD helos. And Fenestron is proprietary to Airbus. Also fenestron is complex, more $, and uses more power in a hover.
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NOTAR requires a lot more power than a tail rotor or fenestron. So, a payload/performance hit. Its advantages are undeniable- a tree branch or a lamp post in a tight LZ won't bring down a NOTAR helicopter and nobody is going to get killed by wandering into the tail boom. (The second one is a big deal for things like a night EMS call to a highway crash scene... as you know.)
A good rule of thumb for helicopter horsepower is every 1% the horsepower changes (up or down) the useful load is affected by 2%. Part of the useful load is overhead (like crew, minimum fuel, mission equipment), so that 2% hit in useful load translates into an even bigger figure for payload.
I think the fenestron and Aerospatiale/Eurocopter/Airbus is getting to be that's the way they've always done it, since their aircraft have used them for so long. I notice that there don't seem to be any designs where the fenestron is tilted. The tilted tail rotor is a Sikorsky feature that they first started to compensate for the c.g. shift from when they put a third engine on the H-53. Long story short, they found tilting that tail rotor also improved total lift in a hover (good) but the improvement was more than how much additional power it required now that it wasn't built perfectly sideways (sideways lift vector isn't perfectly sideways, so tail rotor needs to blow harder to provide the same anti-torque). Who doesn't like "free" lift? They liked it so much they made it a feature on the then-new H-60. That begs the question why Eurocopter hasn't copied the idea. For that matter, why hasn't Bell? Go figure...
A good rule of thumb for helicopter horsepower is every 1% the horsepower changes (up or down) the useful load is affected by 2%. Part of the useful load is overhead (like crew, minimum fuel, mission equipment), so that 2% hit in useful load translates into an even bigger figure for payload.
I think the fenestron and Aerospatiale/Eurocopter/Airbus is getting to be that's the way they've always done it, since their aircraft have used them for so long. I notice that there don't seem to be any designs where the fenestron is tilted. The tilted tail rotor is a Sikorsky feature that they first started to compensate for the c.g. shift from when they put a third engine on the H-53. Long story short, they found tilting that tail rotor also improved total lift in a hover (good) but the improvement was more than how much additional power it required now that it wasn't built perfectly sideways (sideways lift vector isn't perfectly sideways, so tail rotor needs to blow harder to provide the same anti-torque). Who doesn't like "free" lift? They liked it so much they made it a feature on the then-new H-60. That begs the question why Eurocopter hasn't copied the idea. For that matter, why hasn't Bell? Go figure...
A fenstrom is heavier, more complex, and uses more power in a hover - but - in forward flight it is more efficient and substantially quieter.
Phoenix PD acquired seven MD 520N NOTARS in 1991. I think MD made them a sweet heart deal to promote the "other" home town helicopter manufacture. I heard the guys did liked them for the tail safety factor. They once landed in a neighborhood to deploy the TFO and an officer on a ride along when a shooter ran into an apartment building. Had a tail rotor strike on a tree in the process. They now fly five Eurocopter AS350B3s and an Augusta A109E they share with Phoenix Fire for rescues and fire fighting.
If by Eurocopter, you mean Airbus, no.I would imagine the Army and Eurocopter is staying with the fenstrom in place of a tail rotor. I am wondering how long it will be before mechanical tail rotors are replaced by electric tail rotors (see the article on Bell’s experiments) - less moving parts is a good thing.
Future Flight: Bell debuts electric tail rotor
Bell is flight testing a new system that it thinks has the potential to make helicopters safer, more efficient, and quieter.www.aopa.org
View attachment 32513
As for replacing the Kiowa, Bell and Eurocppter will have entries but I can’t imagine anything beating a derivative of Sikorsky’s high speed compound helicopter S-97 Raider.
View attachment 32514
The only remaining competitors for FARA are Bell and Sikorsky. The others, like MD were told “thanks but no thanks” based on deficiencies in their proposals and were not asked to make competitive prototypes.
Just because the sheet metal bears a similarity doesn’t make something a copy. The Comanche had a completely different rotor and tail rotor design, no supplemental power unit, and no wing.
Meeting the Army’s KPPs without resorting to exotic and unproven rotor designs is not an insignificant thing.
The Sikorsky design is not all upside, and I’ll leave it at that.
https://en.wikipedia.org/wiki/Fenestron :
Advantages[edit]
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Detail of the pitch control mechanism of an EC135 fenestron
- Increased safety for people on the ground because the enclosure provides peripheral protection;[5][17]
- Greatly reduced noise and vibration due to the enclosure of the blade tips and greater number of blades;[5][17]
- A decrease in power requirements during the cruise phase of flight.[18]
- Typically lighter and smaller than conventional counterparts.[19][9][N 2]
- A lower susceptibility to foreign object damage because the enclosure makes it less likely to suck in loose objects such as small rocks;[12]
- Enhanced anti-torque control efficiency and reduction in pilot workload.[21]
- Reduced chance for the tail rotor to cause accidents, because it could not strike the environment.
The Fenestron's disadvantages are those common to all ducted fans when compared to propellers. They include:
I have no idea what that actually means.
This is what I never quite understood on why the Fenestron was a plus...it requires more power in the phase of flight where I'm at my max power required. I get it's quieter, but where do the cost vs. benefit lines actually intersect to value? It's also interesting to see how the Fenestron gets sold as being quiet, but no one talks about how freakin' noisy the main rotor blades are on some Fenestron-equipped aircraft. The -135 spins at 394 RPM, and that sucker is loud at non-cruise speeds with those tiny blades. The -155 is definitely quieter, but then you also hear the Fenestron more (same with the -65).
Anyway, that star gear is freaky when you see it in person.
That’s pretty common in the army for skids…about my typical hover taxi altitude (maybe a foot or two lower) when I’m not barreling into cow pastures.
Several years ago there was a TH-57 mishap that, without getting too into details from the SIR, one of the endorsements really seized on the idea that the "cross country hover" and ran with it. That is a lower-than-normal hover, used to compensate for high gross weight (when you're loaded up with students, gas, and bags), and the associated IP technique may have been a contributing factor. (In the mishap the aircraft caught a skid on the ground and flipped onto its side, sort of a dynamic rollover thing but mostly touching down with too much lateral drift.)
Suffice to say that had a mostly negative reaction (putting it nicely) from the instructor cadre. Of course, there's a lot more to the story but it wouldn't be right to put all the details out on here.
Normal in the TH-57 is 5' (by the book) and the -60 was 10'. Coming from that background 3' seems a bit low for an aircraft of the Lakota's size being used in a primary training. So I agree with Chuck's "hmm, that seems low" reaction but then again I'm not involved in that program in any way (Army business is Army business).
Makes sense.