Shameless update from Dale Kramer

On Sunday, March 20, 2016 at 7:41:42 AM UTC-4, Andy Blackburn wrote:
Dale - It's a pretty clever design. Thanks for sharing - gutsy move. ......

Thanks!

I am sure that a rotor disk loading of 18 lbs/ft^2 and thrust efficiency of about 5 lbs/hp is well within any theoretically feasible region for rotor design. At least it better be. I am basing my hover ability on motors and propellers that already exist. In fact on our Joby JM1 motors with 36x20 props at 4400 rpm we are getting about 110 lbs of static thrust at about 14 kw input to the motor controllers. That is about 5.9 lbs thrust/input hp (not motor shaft power!). This setup propels the eLazair in level flight at over 60 mph (the eLazair is pretty high drag at these speeds).
So, with about 500 lbs of static thrust from a WOT Rotax and 660 lbs from WOT electrics, the thrust to weight will be about 1.3/1. The electrics should only need about 1/2 power for hover.
The unknown is what amount of a zoom pullup versus a slow pullup and rotation thru a deep stall will be required. Rather than speculate on that I am just going to test it with model and full scale testing.
The transition is a very complex mixing of aerodynamic lift, aerodynamic drag, aerodynamic moments, thrust, thrust moments, mass and moments of inertia (probably other things too . I am sure I could spend a lot of time trying to model that mathematically but I choose not to at this point.

I think the broomstick analogy is not real good one for visualization because in my case the correction needed to bring the object into balance is not a sideways movement of the hand but simply an application of thrust moment about the center of gravity. During transition, the WOT signal sent to the multirotor controller should automatically result in WOT on the lower tail motors and 0 throttle on the upper tail motors and likely 1/2 power on the wing motors. Also there is still the elevator pitching moment that can be increased by design (at the risk of making high speed horizontal flight twitchy unless I use a separate, thrust vectoring horizontal plane or fly by trim tabs in high speed which I choose not to do right now). 3D RC modeling has shown what large area, high deflection surfaces can do. To start out I use the KISS principle and add from there.

Yes the electric nacelle 'tilt' method of countering the Rotax torque is expected to work for gross torque cancelling and the 'fine' adjustments will still be from the multirotor control of the electric motor counter rotations.

I am hoping to be able to handle at least one electric motor failure and possibly 2, depending on which 2. Model testing will determine this.

I am not saying the mechanical dynamics behind the broomstick analogy is different, just the visualization of it is a little different.

I don't think the dynamics of the mass moment being above the electric drives is necessarily a problem. The two necessities for electronic stabilization are that the drive moments are sufficient and that the electric drive dynamics are faster than possible plant disturbances. So the rate of spin up of the electric motor / prop system will need to be significantly faster than the rate that the broomstick can tip over or otherwise be perturbed by aero effects. The need for fast dynamics on the electric drives, in fact, argues for high disk loading.

The amazing effectiveness of electronic broomstick stabilization is routinely demonstrated by the various two wheel inventions that people zoom around on these days.

On Sunday, March 20, 2016 at 2:16:28 PM UTC-4, Steve Koerner wrote:
I don't think the dynamics of the mass moment being above the electric drives is necessarily a problem. The two necessities for electronic stabilization are that the drive moments are sufficient and that the electric drive dynamics are faster than possible plant disturbances. So the rate of spin up of the electric motor / prop system will need to be significantly faster than the rate that the broomstick can tip over or otherwise be perturbed by aero effects. The need for fast dynamics on the electric drives, in fact, argues for high disk loading.

The amazing effectiveness of electronic broomstick stabilization is routinely demonstrated by the various two wheel inventions that people zoom around on these days.

Agreed, but I have my doubts that these were all created by mathematically analyzing all of the Newtonian physics involved before they came into existence.

There is just a lot more involved in the transitions of the vLazair.

Keep thinking of more that I would need to calculate, derivatives of time, as you describe above.

On Sunday, March 20, 2016 at 9:53:48 AM UTC-7, DaleKramer wrote:
I am not saying the mechanical dynamics behind the broomstick analogy is different, just the visualization of it is a little different.

You are correct - it was a crude analogy. The main point (which you clearly understand) is that whole thing in vertical flight is quite likely statically unstable and if it tips over beyond a certain angle of vertical it is likely to flop over nose down. Unless you have enough altitude when this happens to get flying speed and pull out...well it could be a problem. Ideally you want to keep it stable so you never get to that angle until you have flying speed, which entails tipping over with differential electric thrust enough to get flying speed through the deep stall where the wing and elevator can operate. Yes indeed adding big controls on the tail and big old Fowler flaps on the wing could help you get stable at a higher angle of attack and lower speed. Lots of the hybrid aircraft-helicopter designs I've seen resort to tilt-wing to facilitate the transition more easily but all of that adds weight and complexity.

A simple calculation would be (without benefit of the dimensions on your plans) 220 lbs of thrust from the bottom tail motors produces a nose-up moment of 880 lb-ft based on a 4-foot offset from the center of mass. If the center of mass is 5 feet in front of the lift of those two motors that are trying to hold the nose up and you have a TOW of say 500 lbs you'd end up with a nose-down moment of 2500 lb-ft which would overwhelm the ability of the lower motors to right the aircraft as you approach horizontal. Now calculating the nose-down moment for totally horizontal is not realistic as you'd be accelerating before you ever got to horizontal but a little trig would tell you roughly what kind of angle off vertical the voters have the juice to recover from. Obviously you also have the other motors pulling as well and the prop wash over the tail adds a bit of moment, but the motors on the vertical centerline mostly just reduce the effective mass feeding the nose-down moment for reasonably vertical orientations. They don't help you at all as you approach horizontal. I expect there is somewhere around 30-40 degrees off of vertical where things get interesting and you better have some forward velocity and altitude before you let the nose get that tipped over. Sounds like you have a computer program to figure it all out but my gut feel of is that the last half of the transition to forward flight could get pretty sporty - wing still stalled but the two bottom motors have run out of ability to add enough nose up moment. The reverse maneuver could be even more exciting - a zoom has been mentioned.

Of course with enough thrust almost anything is possible. :-)

Again, thanks for sharing. Interesting design. All in all I think I'd rather have one of these than those scaled-up quadcopter drones people are promoting for personal transportation. Yikes!

Andy

Andy, I see that you have excellent experience and obvious insight as to what hurdles I will have to overcome in order to transition at slow airspeeds..

Before I continue I just want to see if you agree with me that it is less critical to iron out these 'low' speed transitions IF #1 the transition to horizontal flight instructions are simply to accelerate vertically to, say 40 (or whatever testing dictates) knots, then slowly push over AND #2 the transition to hover instructions are, apply WOT electrics, do a zoom pull up to vertical from 100 knots and on the way up, when the airspeed is less than 40 knots apply WOT on the Rotax?

Sorry for run on there, I am just trying to present transitions where there is less need for calculations.

And, if we agree on that, the minutia of how slow of an airspeed before pushover and how little zoom altitude is needed can be determined in testing.

I think your simple calculation does not take into account enough variables, mainly airspeed before pushover.

I am hoping 1.3/1 thrust will be adequate but I have ideas to get more if needed.

On Sunday, March 20, 2016 at 11:52:47 AM UTC-7, Andy Blackburn wrote:
On Sunday, March 20, 2016 at 9:53:48 AM UTC-7, DaleKramer wrote:
I am not saying the mechanical dynamics behind the broomstick analogy is different, just the visualization of it is a little different.

You are correct - it was a crude analogy. The main point (which you clearly understand) is that whole thing in vertical flight is quite likely statically unstable and if it tips over beyond a certain angle of vertical it is likely to flop over nose down. Unless you have enough altitude when this happens to get flying speed and pull out...well it could be a problem. Ideally you want to keep it stable so you never get to that angle until you have flying speed, which entails tipping over with differential electric thrust enough to get flying speed through the deep stall where the wing and elevator can operate. Yes indeed adding big controls on the tail and big old Fowler flaps on the wing could help you get stable at a higher angle of attack and lower speed. Lots of the hybrid aircraft-helicopter designs I've seen resort to tilt-wing to facilitate the transition more easily but all of that adds weight and complexity.

A simple calculation would be (without benefit of the dimensions on your plans) 220 lbs of thrust from the bottom tail motors produces a nose-up moment of 880 lb-ft based on a 4-foot offset from the center of mass. If the center of mass is 5 feet in front of the lift of those two motors that are trying to hold the nose up and you have a TOW of say 500 lbs you'd end up with a nose-down moment of 2500 lb-ft which would overwhelm the ability of the lower motors to right the aircraft as you approach horizontal. Now calculating the nose-down moment for totally horizontal is not realistic as you'd be accelerating before you ever got to horizontal but a little trig would tell you roughly what kind of angle off vertical the voters have the juice to recover from. Obviously you also have the other motors pulling as well and the prop wash over the tail adds a bit of moment, but the motors on the vertical centerline mostly just reduce the effective mass feeding the nose-down moment for reasonably vertical orientations. They don't help you at all as you approach horizontal. I expect there is somewhere around 30-40 degrees off of vertical where things get interesting and you better have some forward velocity and altitude before you let the nose get that tipped over. Sounds like you have a computer program to figure it all out but my gut feel of is that the last half of the transition to forward flight could get pretty sporty - wing still stalled but the two bottom motors have run out of ability to add enough nose up moment. The reverse maneuver could be even more exciting - a zoom has been mentioned.

Of course with enough thrust almost anything is possible. :-)

Again, thanks for sharing. Interesting design. All in all I think I'd rather have one of these than those scaled-up quadcopter drones people are promoting for personal transportation. Yikes!

Andy

People have been known to climb aboard rockets. Rockets have the exact same requirement: you have to keep them pointed upward -- at least until you get airspeed for meaningful wing lift.

One could argue that relying upon motors to keep working is pretty routine for flying machines. A helicopter needs to have it's one motor keep working when it's taking off vertically to avoid a dire consequence.

Back to battery life... there must be enough for an aborted landing scenario. That means electrics on as you're screeching to a stop through deep stall deceleration, then maneuvering to the desired landing spot in vertical and letting down sufficiently gradually. If there is too much wind or if the landing site didn't end up in the right place or something is wrong at the site, there must be enough power reserve to blast back up vertically to flying speed and perhaps a horizontal landing elsewhere.

Agreed, right now I am sort of allocating 1 minute WOT electric time with about 3 minutes of reserve (even though hovering should require about 1/2 power in electrics). This is another fine tunable value when the full size vLazair is detail designed. I am hoping that I can make vertical landings that use around 30 seconds of electric time.

On Sunday, March 20, 2016 at 1:05:18 PM UTC-7, DaleKramer wrote:
Agreed, right now I am sort of allocating 1 minute WOT electric time with about 3 minutes of reserve (even though hovering should require about 1/2 power in electrics). This is another fine tunable value when the full size vLazair is detail designed. I am hoping that I can make vertical landings that use around 30 seconds of electric time.

I suppose if you can incorporate a very accurate indicator of remaining battery life with an alarm feature, or a separate reserve battery that is switched in when the main gets low, then that might work. I can't help but visualize myself spending several minutes trying to get her lined up to the helicopter pad on my future yacht. The seas are bumpy and the breeze variable -- I think the process might take a few minutes to get landed.

If Andy flies production unit number 1 and lives, and if there are positive reviews on Amazon, I will order unit number 7.

On Monday, March 21, 2016 at 5:41:25 PM UTC-4, Steve Koerner wrote:
On Sunday, March 20, 2016 at 1:05:18 PM UTC-7, DaleKramer wrote:
Agreed, right now I am sort of allocating 1 minute WOT electric time with about 3 minutes of reserve (even though hovering should require about 1/2 power in electrics). This is another fine tunable value when the full size vLazair is detail designed. I am hoping that I can make vertical landings that use around 30 seconds of electric time.

I suppose if you can incorporate a very accurate indicator of remaining battery life with an alarm feature, or a separate reserve battery that is switched in when the main gets low, then that might work. I can't help but visualize myself spending several minutes trying to get her lined up to the helicopter pad on my future yacht. The seas are bumpy and the breeze variable -- I think the process might take a few minutes to get landed.

If Andy flies production unit number 1 and lives, and if there are positive reviews on Amazon, I will order unit number 7.

I am with you but at this point I am trying to be realistic in my empty weight predictions. I will increase battery capacity, down the road, if I can. I am really trying to build with existing technology that is available. At this stage I have a perfect 25 lbish pack in mind, by the time I build the full scale we will likely have 300+ whr/kg packs available.

Lucky #7, but Amazon reviews, I really question