Shameless update from Dale Kramer

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

Looks like this is the kind of project that gets funded nowadays on Kickstarter, the world will be such a better place

https://www.kickstarter.com/projects...?ref=discovery

On Tuesday, March 22, 2016 at 4:02:40 AM UTC-7, DaleKramer wrote:
Looks like this is the kind of project that gets funded nowadays on Kickstarter, the world will be such a better place

https://www.kickstarter.com/projects...?ref=discovery

I will apologize for using the word "stinking" - I will let your attitude speak for itself.

That said, this design is problematic. For example, you list the battery weight at 25 lb. I calculate that you will need about 100 lbs of battery (batteries cannot be discharged 100% and expect any decent lifetime). And that ONLY allows by your statement, 3-4 min of hovering. This is totally inadequate for any landing I would dare attempt. This means you will need MUCH more battery capacity than you allowed for, but I will stick to this time for the rest of the analysis.

Using freely available references, I calculated the ideal power to hover at sea level (not climb, mind you) at 131 hp with a MTOW of 1175 lb. Using a 0.75 FOM this increases to 175 hp. At a 10,000 ft density altitude this becomes 158 and 211 hp, respectively. Clearly your design is severely under powered. It gets worse when you want to climb and be able to transition from hovering to forward flight, when some of the electric motors will have to be shut down. These same references state that VTOL aircraft have a horsepower loading of less than 2: you are more than double this.

I am not confused about fore and aft. The pilot is faced forward in forward flight; his position must change to an aft facing position AND rotate 90 degrees. That amounts to 2 rotations on 2 axes of 90 and 180 degrees. When, exactly does this occur, while travelling forward in level flight or while hovering? I would assume hovering because of the extreme air blast and speed brake effect. While hovering the pilot WILL be exposed to the full thrust of the main motor. The thought of attempting such a maneuver scares the hell out of me! The potential of vertigo is not just huge - it is virtually certain. Another point that went unanswered.

Andy makes excellent points about the counter-rotation and stability issues.. As currently envisioned, the main motor cannot be operated at full power because the electric motors would not stabilize its torque. This problem is exacerbated when the aircraft tries to transition to horizontal flight when half the electric motors would have to be shut down. Combine an electric motor failure and you have a real problem. Notice that Dale never answered my question about thrust vectoring.

Fly by wire? You have just become a million dollar aircraft! This is completely unrealistic. You REALLY need to consult with engineers who have ACTUALLY designed fly by wire aircraft.

Qualifications are not important? Since the hell when? Building conventional aircraft from who knows what designs is NOT a representation of qualifications. I am approaching this whole project from the viewpoint of an unsophisticated investor; I don't particularly care what Dale does with his own money. BTW, there WERE NO aeronautical engineering schools at the time of the Wright Brothers; they invented it (they also used their OWN money!)

So 2G,

Does this mean that if Dale builds a model and successfully flies off vertically, transitions to horizontal and lands it vertical, then you will eat the molds that the plane was made from?

Or are you saying that you will only eat the molds if he changes nothing from concept to completion?