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Couple of quick TW-5 questions
- Thread starter Gatordev
- Start date
WinterMute
New Member
First off, all that follows is SWAG based off a half-remembered Aerospace degree.
As other posters have implied, there a couple of possible reasons for this. Higher Np means more stress on the blades since the tips are spinning faster, but is better for the RGB since the planetary gear experience fewer stresses when operating near their designed constant speed of 2000 RPM (100% Np).
At lower altitudes, the speed of sound is lower due to temperature, you get more thrust at lower Np because of increased density, and the relative winds change faster .
The possibility of the tips of the propeller breaking the sound barrier is a real concern. The problem gets even more complicated when you consider that the propeller is not fixed pitch. So, it is probably just easier to use a courser pitch and lower Np at low altitudes and avoid turbulence or whatever causing enough change in relative wind to put the very tips of the blades in transonic regions, which completely ruins your efficiency and causes vibrations which in turn cause prop-sleeve touchdowns.
Also, even at flat pitch, 80% Np will result in non-negligable amounts of thrust if the density of the air is high enough. IE, you would still be producing significant thrust at Idle if you keep the prop spinning really fast.
So, to reduce wear-and-tear and make the RGB and engine more efficient, higher Np good. To prevent Prop-Sleeve touchdowns and losses in efficiency due to trans-sonic turbulance, higher Np bad.
So it is about trade-offs, wear and tear on the RGB, resulting in Chip Lights, or prop-sleeve touchdowns...Resulting in Chip Lights.... Above 10K, transonic tips are not such an issue at 2000RPM (Higher speed of sound), so you might as well increase the Np and save the RGB the stress and get fewer losses due to gearing.
WinterMute
New Member
What he said.
More SWAG from me.
Basically, the PMU does not update and change the oil pressure and prop pitch fast enough to deal with the rapidly changing density and prevent excess torque on the prop when you are screaming out of the sky at 10K per minute under 10K. Above 10K, it does not matter, it is just keeping the prop at 80% Np anyway, and the prop can deal with that at lower air densities. In a fully developed steady state spin in a T-6, a good recovery is about 3-3.5K lower than entry. It takes about 3 turns (1200-1500ft) to even get in one. It is not unusual for people to spin through 4-5K before recovery (6 Turns). I have heard of students gaffing it up and instructors pulling out of the spin at 8-9K below entry.
Uncontrolled ejection altitude is 6K...Well, you get the point.
So yeah, what I said.
It spins both ways fine, but I remember something being said in VT-10 ground school about right hand spins being rougher. I did spins both left and right, but supposedly spins to the right are "slightly rougher". I can't say they felt any different.
Nothing in the NATOPS (IIRC), so I'd say the oil pressure thing is bad gouge.
WinterMute
New Member
Well....I...Well....Its just your insight...... It's stunning....I hadn't comprehended until now......
*Wipes tear off cheek*
Suppose there is only one thing to do now sir!
*Sighs, stands strait, whips out best salute*
My days of troubling people of your caliber are OVER!
*Proceeds to cut out own tongue*
WTF...
Please no more: *pointless descriptive narrative text*
Please no more: *pointless descriptive narrative text*
WinterMute
New Member
Normally I would reply with a retort about how people don't appreciate absurdist humor these days, but since I have no tongue, there is really no point. Back to lurking.
Just because you can post doesn't mean you should.
Sure about that Sparky? Last time I checked, temperature went down with increasing altitude and so did the speed of sound.
WinterMute
New Member
Correct, my SWAG is wrong. Hence the wild guess. Speed of sound is proportional to square root of temperature, not inversely. I'm gonna stop talking now. Nice graph:
