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Topaz

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I've seen a couple of very nice discussions about the various "flying platform" concepts over at the Rotary Wing Forum. The TL;DR is that, without some form of "flapping hinge" freedom on the blades, even though these are shrouded, speed stability will suffer above about 15mph or so. Which, AFAIK, is exactly why these designs were rejected by the Army back in the day. Except for hovering and very low-speed flight, it took a lot of training to get them to fly straight and at a stead speed. And "a lot of training" was exactly what the Army didn't want.

The other issue is that they can't auto-rotate. Redundant engines helped, but if you got the wrong kind of damage or lost both engines (fuel starvation, anyone?) your flight path was pretty much like a falling stone - which is why you never see these things flying at any significant altitude.

I think the appeal of flying platforms is pretty much universal. The reality... well, not as great as the fantasy.
 
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BBerson

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The rotors on bottom are actually pretty stabile. Better than rotors on top according to the experts.
The danger then and now is if the engine loses power or a blade breaks..... well, military guys used to be expendable.
 

Topaz

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The rotors on bottom are actually pretty stabile. Better than rotors on top according to the experts.
The danger then and now is if the engine loses power or a blade breaks..... well, military guys used to be expendable.
I've heard the same with regards to attitude stability. What the guys over on the Rotary forum were talking about, however, is speed stability. The platforms are always fighting the pilot to return to a zero-speed hover. You'd think that there would be a stable cg position or control vane position to give a certain forward airspeed, but apparently the situation is unstable: any deviation (gust or pilot-induced) from the desired trim speed tends to magnify, especially in terms of slowing down. I didn't fully understand the reasons, but there seemed to be general agreement among their more-experienced members that this is a characteristic of truly rigid, propeller-like rotors.
 

BBerson

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Re: We need a low cost contra-rotating alternative!

What happens is the advancing blade gets more lift and 90° later it flaps up in front and therefor the rotor disc tilts back and returns to slow flight.
In a regular helicopter the pilot will correct for flap back by feeding in some more forward cyclic.
Without cyclic, forward flight is limited, I think.
 

Aviator2

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A Good Philosophization

I haven't been on the RotaryForum.com conference in a while, but I always posted there using my real name, Chuck Baltzer, as my username. I started the thread "A New Rotorcraft Concept" back in 2/2012, which is similar, but not exactly the same as this conference.

Risking the peril of criticism, I'd like to detail why a simplified, and much less expensive, version the Hiller style home-built flying platform is yet indeed a good idea.

It's been mentioned, correctly, that there's no viable way to make an emergency landing in a full engine-out situation. That's true, of course- ballistic chutes, extra engines, etc. are probably not very realistic on this type of a craft.

Also, mention has been made, again probably correctly, that forward speed must be very slow, due to the aircraft's design and aerodynamic qualities.

I also heard it mentioned, not necessarily on this conference, but by a knowledgeable person nonetheless, that: "As long as you're content to go only at walking speed- and just five feet above the ground- then you could be successful building such a simplified "aircraft".

So, let's stretch this flight envelope just a hair- let's say that our "simplified Hiller-type platform" could go up ten feet, and move at a speed of fifteen MPH (as has been previously mentioned as a reasonable speed expectation).

Then, do you realize what you have- you have a vehicle that very many people across the USA and around the globe would love to try out and utilize, for a novel and convenient means of hiking, exploring, sight seeing, and transporting themselves over previously impassable terrain.

For myself, the 10-up 15-ahead flying ability would be plenty enough to endlessly explore places that no other vehicle can, or ever will be, able to pass over (except high-up in an aircraft, but I'm referring to a ground-hugging vehicle here- too low to the ground even for helicopters to traverse).

It would leave conventional hovercrafts behind in the dust, and people could go only as high and as fast as they are comfortable with. It could feature a rugged "spring-strut" type of landing gear for hard landings, or some type of inflatable float-like landing gear if desired by the owner-builder.

With the reduced expectations in "altitude" and speed, the craft should be able to be built at a greatly reduced price. I can't hazard a very good guess as to what a person might expect to spend, but with a commercially produced, simplified, counter rotating mechanism available to homebuilders, as I have mentioned in a previous post, I would guess-ti-mate the cost to be much less than 10 grand. After all, a much wider selection of engines could be used, and lower priced, pre-owned propellers could also be considered.

A person could even start a business manufacturing inexpensive parts made uniquely for this type of a minimalist "aircraft".

I honestly believe that this vehicle, if affordably available to consumers, would begin much more of a transportation revolution than the Segway could ever have hoped to.

This should make my point, without letting the post get too long. Thanks for reading, and pondering! Aviator2 AKA Chuck Baltzer

 
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Topaz

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Re: A Good Philosophization

...So, let's stretch this flight envelope just a hair- let's say that our "simplified Hiller-type platform" could go up ten feet, and move at a speed of fifteen MPH (as has been previously mentioned as a reasonable speed expectation)....
As long as one is willing to accept those sorts of limitations, I don't see any reason to not "go there". I personally would like more capability, but that's me. If someone wants to float around, say, the deserts here in CA in something like this, why not? Sure beats walking, and you'd definitely "tread lighter" on the environment than the typical off-road vehicle.

As a commercial product, however, I'd be really curious to see the actual size of the market of people willing to part with at least several thousand dollars for that kind of capability. You'd have that much in engines, plus all the usual business overhead and margin, etc. I have no answer to that question.
 

BBerson

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Hello Chuck,
A few years ago, I started a project to design and build a "ground effect helicopter" for the reasons you mentioned.
A ground limited helicopter would have control lacking in the hovercraft. And a ten foot altitude would open up swamps and areas with short bushes, boulders, etc. I would go with helicopter, not platform, I think.
The project is on hold till my ultralight is developed.
 

Aviator2

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Hope you get it built someday!!

I hope you finish up on the "IGE helicopter" someday, that'd be very interesting to see (on video and in pictures)!

As Topaz alluded to above- sometimes people just aim too high, when a lesser machine might do the job, because after all- most types of flying is not for the masses. But maybe the minimalist platform might do the trick (not aerial tricks)!
Aviator2 AKA: Chuck Baltzer

 

bmcj

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Re: A Good Philosophization

What happens is the advancing blade gets more lift and 90° later it flaps up in front and therefor the rotor disc tilts back and returns to slow flight.
But does that effect go away when the prop is running inside of a shroud?


So, let's stretch this flight envelope just a hair- let's say that our "simplified Hiller-type platform" could go up ten feet, and move at a speed of fifteen MPH (as has been previously mentioned as a reasonable speed expectation).
Still holds the likelyhood of severe injury or death, and too low/slow for a parachute deployment. Perhaps an all encompassing airbag cluster that automatically deploys above a certain speed and altitude if the engine quits?
 

Himat

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Re: A Good Philosophization

Still holds the likelyhood of severe injury or death, and too low/slow for a parachute deployment. Perhaps an all encompassing airbag cluster that automatically deploys above a certain speed and altitude if the engine quits?
To catch a fall from ten feet a kind of airbag system sounds like a better solution than a parachute system.
One drawback, on s steep slope the pilot might be in for a tumble before he is at the bottom of he hill...
 

BBerson

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Re: A Good Philosophization

But does that effect go away when the prop is running inside of a shroud?
I never studied the platform in cruise. Seems the flow would be very mixed but still have similar effect.
The platform was designed for stationary hovering mostly. If they wanted cruise, I think they would call it cruiseform :gig:
 

Aviator2

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Safety Issues: SOLVED

I’d like to address the issue of safety/ emergency landings in this post.

On the Ten-Up/ 15-Forward Flying Platform (means it only goes about 10 feet up, and 15 MPH airspeed max) I would use the “Lawn Mower Principle”, that is- when was the last time your simple, good old dependable push lawn mower’s engine stalled while you were mowing your lawn? Never? Mine has never stalled after it was started and warmed up, save for when it ran outta gas.

Here’s what I’m saying: If you build your platform, and you obtain, maintain, and repair the platform’s engine to the absolute best of your ability (or have it done by a mechanic that you know you can trust), keep the air filter clean as a whistle, check and change the oil regularly, be sure its tank is full of gasoline that's free of contaminants and water at all times, and use new, properly gapped spark plugs- then you’ve done all that you can do to be sure that your machine is in its peak running order.

Always critique your machine’s engine sounds and vibrations before takeoff, just like you do in any other aircraft before you takeoff. If something doesn’t sound, or feel, right, then stop and find out why before you proceed to fly.

According to the book “The Great American Jet Pack” by Steve Lehto, at some point the engineers building the Rocket Belt for the US government realized that there was no known way for the Rocket Belt pilot to make an emergency landing- he can’t autorotate, can’t glide, parachute was incompatible and impractical etc.

So, what did the engineers conclude? They concluded that the Rocket Belt that they were building was at least hundreds of times more dependable than conventional aircraft, therefor the Rocket Belt’s ratio of pilot deaths would be far lower than military or civil aviation’s deaths caused by mechanical or structural failures.

And that was going to be their selling point for safety- it’s just too safe to worry about (I kid you not- that really was going to be their “plan” for emergency landings.)

Don’t get me wrong- I’m not implying that the home made platform is in any way immune to accidents or mechanical/ structural failures.

Here’s what I’m saying- If I do everything in my power to make my flying platform safe, and use a huge dose of common sense, and stick to the platform’s flight envelope of 10-Up/ 15 Ahead, then I would feel safe enough to fly my platform without worrying too too much about the engine stopping in flight.

There you have it- there’s your emergency plan: a perfectly built and tuned machine with fresh, clean gasoline- no parachutes or airbags necessary. I would be comfortable flying it- would you?

Aviator2 AKA Chuck Baltzer


“If you are looking for perfect safety, you will do well to sit on a fence and watch the birds...”
— Wilbur Wright, 18 September, 1901

BBlakebrough.jpg
 
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BBerson

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Re: A little Bit of Update

I wouldn't use airbags. I would use extended collapsing struts. I think the standing position helps as your body and legs are designed to leap from ten feet but a drop from ten feet while seated can cause lift threatening spinal injury.
Rotating blades and machinery can cause injury after the impact.
 

SkyClimber

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Re: We need a low cost contra-rotating alternative!

Regarding the need for a simple CR Gearbox, I Whole Heartedly Agree. I have been searching for just such a unit for some time now to no avail.
I have approached at least two manufacturers who produce similar devices but neither was interested in expanding their product line to include a simple CR gearbox for a tractor configuration.
How many tractor aircraft are there out there? How many Ultralights and LightSport types are there that already use speed reduction?
I hope this thread continues. It is a bit old but the subject is at the leading edge. I have been "into" CR props for quite a while so I could go on and on, but I wont. Suffice it to say for now that the benifits of CR props are well known, but there is a great deal of inertia in aviation. In order to convince people to put more weight and complexity on their aircraft would not be easy, but I believe that CR props will be the next "quantum leap" needed in aircraft performance.
 

Victor Bravo

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Admittedly I'm coming in late to this conversation, but it seems to me that most all the previous flying platform ideas are laid out upside down. I am well aware that many highly qualified engineers (with much better resume's than mine) were involved in some of them, but having the engine/rotor/meat slicer underneath the pilot is clearly still much more risky and unstable and inefficient.

WHATEVER type of rotor, propeller, thruster, fan, or lift device you use is much more likely to have a better air flow path, and be more efficient... if there is clean, undisturbed air coming in from the top. Same as 100% of the production helicopters, for the same reason.

Protecting the pilot from being chopped up by a rotor/fan underneath always means more structure, and more guards, and more grill-work under the pilot. With the pilot him/herself also above the fan, this causes even more disturbance to the air flowing into the lifting device, which means there will be more thrust losses.

Not to mention the proximity to dirt, dust, rocks, and FOD problems caused by a low mounted fan.

IMHO, a standing or seated platform under the rotor has a much higher chance of success. The Japanese Gen-4 is not perfect and does not have enough power/performance, but the general layout has been shown to work. A larger version of this layout, with better pilot protection and a better powerplant system, would be a much better starting point than a bottom-fan layout.
 

Dana

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Admittedly I'm coming in late to this conversation, but it seems to me that most all the previous flying platform ideas are laid out upside down. I am well aware that many highly qualified engineers (with much better resume's than mine) were involved in some of them, but having the engine/rotor/meat slicer underneath the pilot is clearly still much more risky and unstable...
No, actually, putting the rotor on the bottom makes it stable; putting it on top is unstable, which is why conventional helicopters are so difficult to learn to fly. The bottom rotor's inherently stable configuration makes the intuitive "lean in the direction you want to go" control possible without the complexity of cyclic pitch controls.

But yes, there are certainly other compromises involved. Stability is the only reason to put the rotor on the bottom, but the simplicity makes it attractive.

Dana
 

BBerson

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No, actually, putting the rotor on the bottom makes it stable; putting it on top is unstable, which is why conventional helicopters are so difficult to learn to fly. The bottom rotor's inherently stable configuration makes the intuitive "lean in the direction you want to go" control possible without the complexity of cyclic pitch controls.

But yes, there are certainly other compromises involved. Stability is the only reason to put the rotor on the bottom, but the simplicity makes it attractive.

Dana
A typical hinged rotor is more stable when on the bottom. A rigid rotor (like the Hiller Platform) would be very stable above or below. In fact, the Hiller platform was so stable the pilot could let go of the handle and fire a rifle.*


*the Army soon figured out that standing on a platform is not the safest place to shoot from :gig:
 

Dana

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I can't wait to hear how a pendulum is more stable with the weight above the suspension point.
But it's not a pendulum. Non scientific explanation, picture it: Say it tilts in one direction. It starts to move laterally in that direction, and both the inertia of the mass above the support and the air drag tend to right it.

Also picture a toy gyroscope: You can stand it on a table and it'll stay straight up, but if you hang it from a string on top it'll start to tilt up and spin around.

Dana
 
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