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Aero Nerdery Thread (rotary-curious welcome)
- Thread starter Gatordev
- Start date
I don't remember that. I was but a young ENS, griping that, "that's not what I learned in my BSAE..."
What's Vy of a Chinook long-lining an H-60 ? (why doesn't platform show full embedded previews of posts on X?)
How interesting. I wonder if VRS could be generalized into a rule-of-thumb for each helo based on disc loading, diameter, and Nr (or something along those lines). I’m amazed someone hasn’t tested that- or have they?
Up and ready! But rotary aero is… different. I understand a lot of the concepts, but a powered-lift V-speed buildup is definitely in the category or “ask an expert” for me.
VRS has a generalized/referred model. JJ taught it to us at TPS as an advanced topic at the end of helo perf. IIRC, it's just not quite as awesome at predictions as the rest of the perf models are.
For the academically inclined, here's a paper
Here's a diagram showing the general shape of the VRS region. Vz is vertical velocity, Vx is horizontal, and Vh is "velocity scale" and equals sqrt(T/2*rho*A), where T=thrust, rho=air density, and A=disc area.
Napkin math tells me Vh for a 50k-lb V-22 is roughly 40 knots, so the green line says VRS is only an issue < ~38 knots and descent rates > ~1,600 fpm
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No.
The Army is significantly more locked into institutional dogma than the Navy/Marines. If the book says so, it must be true. Whereas the Navy/Marines tends to breed a more questioning attitude.
This makes sense given how each service was designed to operate.
OMG Army IPs are for the most part dip shits! And I am/was one. The guys at HAATS in Eagle Colorado were the exception. Vx is straight up if you can. However, if you can't, it is usually just through translational lift. I used to demo this for rolling takeoffs.
First, the Vy and MaxEnd (Vbe) are definitely different airspeeds for the Black Hawk, but not necessarily the Seahawk. Why? Because the pitot tubes on the Black Hawk are mounted on top of the cabin and are greatly influenced by rotor downwash at low airspeeds. There is actually a correction chart in the -10 (Army NATOPS) for this when calculating Vy vs max endurance.
For you 60 guys, try this:
Restrict your Q to whatever setting you do to simulate rolling takeoff requirements. We use 10% below IGE hover power in the Army. Perform a rolling takeoff and accelerate to Vy once clear of the ground. Use whatever technique is required based on your desired profile. Note your altitude crossing the predesignated "obstacle". Repeat the maneuver from the same spot, but only accelerate to just above translational lift. Note the altitude this time crossing the "obstacle". You will feel slow and wallowing, and it will take longer, probably much longer, to get to the obstacle, but you will be higher when you get there.
Side note: If you can go to HAATS, DO IT!!!! It is fun, exciting and very educational. Plus, where else can you fly a stripped down 60A with T700-GE-401D engines? IGE hover at 6540' in those scalded dogs was less than 60% sometimes.
First, the Vy and MaxEnd (Vbe) are definitely different airspeeds for the Black Hawk, but not necessarily the Seahawk. Why? Because the pitot tubes on the Black Hawk are mounted on top of the cabin and are greatly influenced by rotor downwash at low airspeeds. There is actually a correction chart in the -10 (Army NATOPS) for this when calculating Vy vs max endurance.
For you 60 guys, try this:
Restrict your Q to whatever setting you do to simulate rolling takeoff requirements. We use 10% below IGE hover power in the Army. Perform a rolling takeoff and accelerate to Vy once clear of the ground. Use whatever technique is required based on your desired profile. Note your altitude crossing the predesignated "obstacle". Repeat the maneuver from the same spot, but only accelerate to just above translational lift. Note the altitude this time crossing the "obstacle". You will feel slow and wallowing, and it will take longer, probably much longer, to get to the obstacle, but you will be higher when you get there.
Side note: If you can go to HAATS, DO IT!!!! It is fun, exciting and very educational. Plus, where else can you fly a stripped down 60A with T700-GE-401D engines? IGE hover at 6540' in those scalded dogs was less than 60% sometimes.
Just ask any Chinook pilot. They ALL wear t-shirts or own car stickers that depict a Chinook long-lining a Black Hawk. It's a rivalry thing. My response was always, "That shirt is only accurate when your helo is out of the hangar and doesn't have a red X in the status block."
What is it about how it is designed to operate that makes the Army more by-the-book vs the others?
I think what he is getting at is that the army operates on doctrine. Pushed down from there everything from planning to TTPs (tactics, techniques, and procedures) reflect this. As individuals my experience (from the backseat perspective) is that army CWOs are very willing to flex the rules and try something difficult or different when needed, but typically they reflect their doctrine based training.
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This is essentially the Navy MDG for a max torque t/o or running t/o, except we don’t really test like you mentioned. However, if you have a student that doesn’t get you above 50 KIAS (maneuver completion standard), you feel the aircraft working harder than necessary.
And back to my chapter 11 rewrite I mentioned earlier. Feel like it was rewritten because the 46 to 60S transition types struggled with the autos. I don’t think that the rewrite (if technically correct), helped them learn to fly a good auto. If that rewrite was incorrect, bad on NAVAIR for allowing technically incorrect information to be put into a manual. In the end, you don’t need an intensive aero understanding to fly a maneuver in standards.
I didn't say that. I said there is an unwillingness from many (but not all) of the IPs I'm having to deal with that won't think beyond what their gouge is saying when teaching the training manual.
Also, you were not a straight-stick Army IP. Don't pretend you were....you had the benefit of getting exposure to both services. You've even made comments about how your Navy experience increased/improved your bag of tricks compared to a someone just exposed to the Army training (I still chuckle at your PTP story).
I was wondering if you were still around on the site and if you'd chime in (and welcome it). My intent isn't to degrade your experience, and in fact, it's clear you're understanding the very concept I initially brought up and are willing to discuss it based on actual performance data.
But some large percentage of Check Airmen that I have to fly with clearly don't, and will even refuse to debrief the discussion after the flight. Again, it's not all of them, but it's notable.