Shameless update from Dale Kramer

On Sunday, March 20, 2016 at 3:08:51 PM UTC-4, Andy Blackburn wrote:
+1, but I want a delivery position...if it works. Fingers crossed.

Andy

I will consider that a deposit on delivery position #1

On Sunday, March 20, 2016 at 2:22:53 PM UTC-7, DaleKramer wrote:
On Sunday, March 20, 2016 at 3:08:51 PM UTC-4, Andy Blackburn wrote:
+1, but I want a delivery position...if it works. Fingers crossed.

Andy

I will consider that a deposit on delivery position #1

#1? maybe I need a few brave should in front of me.

Yes - way back when I worked at NASA Ames on variable stability helicopters as part of grad school. They had the XV-15 tilt rotor there and well as the RSRA - talk about bad transitions to forward flight. It has a rotor that was an oval cross section with blowing slots on both leading and trailing edges. The idea was to stop the rotor in flight and swap the slots you were blowing out of on the blades that were facing aft (they were symmetric airfoils (fore and aft AND top/bottom) - so "aft" was more of a term of art as it depended entirely on the blowing setup. In forward flight it was an X-wing planform. I understand the transitions were "exciting".

You have an easy problem in comparison.

I agree with enough power and pitch authority you ought to be able to make the transition to forward flight (and back) without to much drama. The question I can't answer with simple math is exactly how much power you need. You've got a swept wing so it ought to be able to produce lift at pretty high AOA which is good. At some point the vertical component of the thrust vector will be insufficient to hold the aircraft in hover and as you continue to pitch over the wing better take up the slack or you will be in ballistic territory. If your total thrust to weight is 1.3:1 you will run out of thrust to hold hover at T*sin(Theta) = W, or Theta = arcsin(1/1.3) = arcsin(0.77) = 50.3 degrees nose up pitch. That might be a bit high, even for a highly swept wing. You'll need to get the elevator unstalled as well if you want to actually fly the thing through the transition with the stick. The hope is that the nose will want to pitch over anyway once you get started so you'd think you could sort of mush your way through the transition until the boundariy layer on the wing gets attached and the wing gets lifting - and hope that it doesn't get so draggy that it wants to mush and settle for very long.

My Dad was the project test pilot for a variation on this theme back in 1958:

https://www.youtube.com/watch?v=wDstVGAmI74

Like I said, with enough thrust you can do pretty much anything you want.

Andy

Andy, give up now on the hovercraft and RC drones, just launch one of those F-100D ZEL from you back yard.

On Sunday, March 20, 2016 at 4:30:23 PM UTC-7, Andy Blackburn wrote:
On Sunday, March 20, 2016 at 2:22:53 PM UTC-7, DaleKramer wrote:
On Sunday, March 20, 2016 at 3:08:51 PM UTC-4, Andy Blackburn wrote:
+1, but I want a delivery position...if it works. Fingers crossed.

Andy

I will consider that a deposit on delivery position #1

#1? maybe I need a few brave should in front of me.

Yes - way back when I worked at NASA Ames on variable stability helicopters as part of grad school. They had the XV-15 tilt rotor there and well as the RSRA - talk about bad transitions to forward flight. It has a rotor that was an oval cross section with blowing slots on both leading and trailing edges. The idea was to stop the rotor in flight and swap the slots you were blowing out of on the blades that were facing aft (they were symmetric airfoils (fore and aft AND top/bottom) - so "aft" was more of a term of art as it depended entirely on the blowing setup. In forward flight it was an X-wing planform. I understand the transitions were "exciting".

You have an easy problem in comparison.

I agree with enough power and pitch authority you ought to be able to make the transition to forward flight (and back) without to much drama. The question I can't answer with simple math is exactly how much power you need. You've got a swept wing so it ought to be able to produce lift at pretty high AOA which is good. At some point the vertical component of the thrust vector will be insufficient to hold the aircraft in hover and as you continue to pitch over the wing better take up the slack or you will be in ballistic territory. If your total thrust to weight is 1.3:1 you will run out of thrust to hold hover at T*sin(Theta) = W, or Theta = arcsin(1/1.3) = arcsin(0.77) = 50.3 degrees nose up pitch. That might be a bit high, even for a highly swept wing. You'll need to get the elevator unstalled as well if you want to actually fly the thing through the transition with the stick. The hope is that the nose will want to pitch over anyway once you get started so you'd think you could sort of mush your way through the transition until the boundariy layer on the wing gets attached and the wing gets lifting - and hope that it doesn't get so draggy that it wants to mush and settle for very long.

My Dad was the project test pilot for a variation on this theme back in 1958:

https://www.youtube.com/watch?v=wDstVGAmI74

Like I said, with enough thrust you can do pretty much anything you want.

Andy

Andy,

Sounds like the RSRA had a reaction rotor powered by air, but I don't see that in the specs I found? And are you saying that after the RSRA rotor was stopped, they continued to blow out the 'horizontal flight' trailing edges for some reason?

I was assuming that there may be some loss of altitude during the vLazair 'push' to forward flight. Part of the 'push' transition procedure could not only be 'only push when you get to a certain vertical speed' but also a minimum height above ground to make allowance for a slight height loss. Or worst case it might be 'climb straight to X altitude and then push over, it will dive some but you'll pull out of it In the early 3D flight RC model days I had a model with not much over 1/1 thrust. I have never been able to hover very long but I don't remember ever having much altitude loss or control problems coming out of a hover attempt. I know Mr Reynolds and a lot of other things likely skew that example but I can't wait to see what my 1/4 scale will do on these transitions (btw I am planning a tether system for 1/4 scale testing).

Fortunately I believe the stability through transitions will be augmented by the multirotor controller which is closed loop on heading and pitch until the throttle command is shut down to it when horizontal flight is achieved..

I also think it is possible that the aerodynamic controls are not needed at all below their un-stalled AOAs.

Wow, that video clip is awesome! I think of my electrics on the vLazair as a sort of re-chargable JATO system

Ah, maybe the blown rotors was just for changing rotor speed during transitions?

Andy,

Since we are doing napkin calcs (I have this on a spreadsheet somewhere): Mass (M) = 850 lbs, Average Unbalanced upward force for 0 to 40 knts (electric props still gives about 80% of static thrust at 40 knts and assume linear decay)(F) = (250 lbs * 0.9 * 32 ft/sec^2) = 7200 lbf, Acceleration upwards = F/M = 8.5 ft/sec^2, Distance to go from 0 to 40 knts (67.5 ft/sec) using v^2=u^2+2as is 270 ft and the time to get there from s=ut+.5at^2 is about 8 seconds.

I hope I did that right, I even have those equations in memory after nearly 40 years

So, at 1.3 thrust to weight and a vertical acceleration to 40 knts, this puts us 270 feet high in 8 seconds after liftoff (accounting for some thrust loss at 40 knts on electrics, Rotax variable pitch should pretty well hold its static thrust at 40 knts, aircraft drag at 0 AOA and 40 knts not considered). Wow, rocket calcs

Knowing this, my gut felt good about being able to go straight up and pushover fairly easily and quickly so I went on to other things. Should I reconsider, I think 50 or 60 knts may work as well at which point I will add some airframe drag estimates.

The blowing was to use the blown air to create the trailing edge if the airfoil so you could have a rotor where the clockwise edge was trailing when the rotor was spinning and then when you stop the rotor to fly the blades as wings half the blades blow out if the counter-clockwise newly trailing edge. Without this, you'd have half the rotor ballades trying to fly backwards when you convert them to fixed wings. It's a crazy idea that blowing through a slot on the lower aft edge of a blunt shape creates a trailing edge streamlined effective shape.

Interesting, could they make it like a down flap shape if they blew harder?

On Sunday, March 20, 2016 at 8:24:39 PM UTC-7, DaleKramer wrote:
Interesting, could they make it like a down flap shape if they blew harder?

There's a joke in there somewhere...