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Old Dec 23, 2010, 04:43 PM
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the fun of efficiency

Well, you both are right. A hydroski that is submerged is a hydrofoil even if it is not meant to be one.

As homo sapiens is also homo ludens it is fun to see people having fun. When the Shark guys like to mumbo jumbo the physics of their design, that is fine with me. But that will not get them government contracts.

I have fun coming up with designs that fit the right mission. I do not see many missions for the Shark except goofing off in the water. Which is fine if that is what you want to do.

I am interested in efficiency and efficacy and that the Shark is not. Compared to the lift from the hydroski the ground effect is almost negligible. As a matter of fact at its cruise speed, ground effect is at its lowest. Imagine using ground effect as take-off aid. This is topsy turvy. Second remark: when you settle on staying in touch with the water you might as well use the higher efficiency of a water prop instead of an air prop.

The shape of the Shark sure looks sexy. But also with boats that should ring a bell. Form follows function ;-)
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Old Dec 24, 2010, 02:45 AM
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Haha Luc, straight to the point, you're completely right. That the hydroski at first works like a hydrofoil is something I had also noted in my first post and I am still amazed about how calm the hydroski behaves.

You're right, the hydroski lift is probably massive compared to the groundeffct lift, and such a Shark boat doesn't have much use

But hey, the last part is something which goes for all my models haha Efficient or not, useless or not, I like the shark boat and i have to say it performs very well!

About the Aircat..Well I fixed the sponson but I didn't repaint it yet, there is still snow and ice everywhere and I loose paint after every run in this environment..so I'll just repaint it completely once the temperature gets above 0 again

I made a few runs on Ice today, full power straight against the wind..and it wouldn't lift off. Again, I am under the impression that it's noseheavy, because as the model passes at high speed, it seems to be well over lift off speed. It also..reacts like it's flying, but it isn't. I'll just move it backwards a bit, carefully, I don't want it to flip and crash on solid ice

And Yeah, I will try to make a video haha, till now I have been alone while testing it.

Marijn
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Old Dec 24, 2010, 04:26 PM
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Well no video yet(still alone), quite some progress though! I find the aircat to be very sensitive to tweaking, and a bit unforgiving. Also, due to it's Bixel design, high set wings and high speeds, it's not flying in very extreme ground effect, meaning that if you aren't carefull it easily flies out of GE Sounds cool? Well yeah, but with negative dihedral, no elevator and ailerons, you don't want this thing to fly out of GE!

So..lets start with the first runs.. very high speed, not even a single sign of Lift off. --> way too noseheavy, as predicted

Second run, Third and Fourth run...all still too noseheavy, but we are getting there, after every run I added more weight to the tail.

Fifth run.. now it's getting light, it doesn't quite lift off, but just scrapes along the ice with it's nose, at higher speeds it starts to roll during turns --> still just a bit too noseheavy

Sixth run...nervous...speeds up..skips a bit..comes loose, down again..skips up...and down again..skips sharper up..sharper down..now it makes quite an aggresive skip...nose bounces up about 10-20 degrees(by this time I had the power completely OFF), the nose goes back down again, impacts with the ice, bouncing the model sharply upwards, more than 60 degrees, it stalls at 2 meters height and plumets back to the ice, luckely ending upright...and with the necessary scratches and holes in it

So..back to a cup of coffee and rethinking what went wrong..

Hmm..either way it was still too noseheavy..yes definatly..but maybe also dynamically unstable in pitch(causing a sort of sinus movement in pitch)

So..I glued the stabiliser back to the craft(yes that also came off), but this time with 3 degrees less upwards AoA. This permits a more forward CG, increases the difference of Lift COeeficcient between the main wing and tail..improving static stability.

Without the dents repaired(will do that once I get it flying properly haha) Back onto the ice..

7th run..feels light..slightly skips along the ice, making flights of max. 2 meters --> juuuust a bit noseheavy

8th run.. full power..liftoff after about 50 meters..5 cm..10 cm..20 cm..(power OFF hahahaha s***)..30 cm.. 40..50..60..bank to the left, counter rudder, wings level again, now with a nose down attitude, a bit of power again, up with that nose!..again a flight up to about a meter, power off..bank left..counter rudder..nose down..* Bang* onto the ice, sponson and stabiliser off.

So.. that was interesting

Conclusion? I think the Stab Angle was now a bit too low, which decreases the tendency to pitch nose down once the GE weakens. Getting there!

Marijn

& Merry Christmas everyone!
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Old Dec 24, 2010, 11:03 PM
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Those guys didnot like my ekranoplan at first either
till I showed them the video lol

I love videos

my car with wings is a good one

the boat with wings is kinda cool as well, for me anyways

crazy design but nothing like the others people like hoverman design

cool videos BTW HOVERMAN

that engine or motor set up is different , looks like two jet engines or something

My favorite thing about this is the eficeincey of ekranoplans

and the speed of course
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That is a hydrofoil, not an ekranoplan.
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Old Dec 25, 2010, 07:54 AM
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Well, I did my best to make some nice footage, but it's not much

I managed to get it "stable" in pitch, and yes, it flies along the ice.. But it's how we call it in the Netherlands "onberekenbaar"

It rolls left and right with more than 30 degrees bank, without me giving any controll input haha

Ahwell, who cares, the model has got cracks and dents everywhere, and I managed to get some partial flight attempts on video haha, enjoy:







As you can see in the videos, I am struggling to keep it under controll. It does fly, buyt only the lights touch to the rudder stick makes it roll beyond controll.

Ow and I managed to crash it again hahahaha

It bounced and flew out of GE, stalling after reaching 3 meters or so haha









So... not to positive about it, but ahwell, at least it's not behaving as I expexted, that would have been boring right
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Old Dec 27, 2010, 04:29 PM
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presuure waves in pressure box?

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It rolls left and right with more than 30 degrees bank, without me giving any controll input
Could it be, Marijn, that the chopped off vortices coming off the prop blast play tricks on the craft underneath in the pressure box? The pressure wave rolls in but the box is symmetric. With the hoverwing, the blasts would come from behind ducted on each side from two props. The Rices did not mention this problem, but then again they rarely mentioned any problems.

Maybe you need to add a countertwisting element in the box like is done on vertical stabs when positioned in the prop blast but not exposed to the full prop diameter.
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Old Dec 29, 2010, 01:00 PM
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Luc, That's a great suggestion, maybe it's partially due to that. Based on my oberservation's I think there is more too it, let me explain:

As everybody can see on the videos, I am struggling to keep the model between the sideridges of the water I am flying on, as it's quite narrow. I am not going to proudly lie about it, clearly I am overcontrolling it all the time(pilot induced oscilations) , because it does behave more calm once I let go of the rudder stick.

But this isn't all, as can be seen on the videos on Youtube from the Rice brother's, it isn't very rock solid in roll either. As long as they don't really use the rudder it seems fine, but still it's not really...Well I wouldn't want to sit in it The design clearly has very high located Trailing edges..not something one would expect from a Ground effect vehicle. At the high speeds, low angles of attacks and the relatively high GE flight altitudes, I am under the impression that this model isn't really using strong Ram air lift to fly Ram air lift is great in keeping you're model solid along the roll axis, but as soon as you are flying without it, with anhedral on the outer wing panels..well you get the same thing as the aircat

Now you won't hear me say that the design is flawed, it works, as can be seen on the video's, but it's not the most efficient and safe flyer..more like a low flying airplane than a ship that's not touching the water

Marijn
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Old Jan 07, 2011, 01:28 PM
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Hey Guy's, time for the first post of this year

A lot has been going on, also in the WIG area. I fired up my scanner today, and scanned some drawings I made during the last couple of weeks. They may be full with errors(or not?) but I hope somebody finds them interesting anyway.

Also I managed to obtain several old plans of Designs Unlimited, an old Aircat, Bixel and Lippisch WIG design. I was quite dissapointed of how simple these designs and drawings are, but ahwell, still glad to finally have obtained them.
I am not going to post the plans online, I just don't want to mess with copyright

Anyway, the first thing I wanted to show are these threeviews I found. Don't bother asking where I got them, but they are actual threeview drawings of the 1:1 Bixel craft that we posted some photos of, some months ago. It's quite interesting to see that this craft uses a small lift fan in the nose, you can see it in the drawings if you look closely.


Cool right?
Further I made a threeview drawing of a simple rugged Bixel model, a few weeks ago:


And.. I was busy with the Hoverwing design from Fischer Flugmechanik, and thought about practical ways to build an RC model of it, here's a simple sketch of a possible layout. I made the drawing in the same period as when I was building the Aircat, which is quite visible in the design..I guess


And beeing inspired by the aircat designs, and having a spare evening with nothing to do, I sketched out this:


And.. a couple of weeks ago I osted some photos of the Hydroski/WIG combination, which also lead me to some simple sketches:



Marijn
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Old Jan 07, 2011, 02:18 PM
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Here's something else, I posted some photos of the front of an Orlyonok model which I build a month ago, just to trie how it looks, here is the drawing that I made to fit this model:


And, a bit dissapointed in the Aircat model, I concluded that a safer WIG vehicle is one which sticks more to..extreme GE. One which really needs RAM air effect to fly. The most stable vehicles for this purpose are ofcoursee..

Tandem Wings

We have ofcourse thoroughly tested Tandem wings in this Topic, but I figured I wasn't quite finished with the concept yet, and I still hadn't been able to make one fly stable in AND out of GE without significantly changing the CG.

But, we all have seen that even if they aren't longitudinally stable when flying too high or pitching up more than 10 degrees, they are Very stable as long as they are kept low and fly on an even surface.

This initial very good stability in very extreme GE is ofcourse caused by the two wing Pairs, which damp out every pitch movement, as long as they are close too the surface and RAM air lift is Strong. This works so well, that managed to get the same results on models with same profiles fore and aft, with thick profiles aft only, with thick profiles forward only, with a higher angle of attack on the front wing, with a higher angle of attack on the rear wing etc etc, and all for wide ranges of CG.

I don't consider this to be enough for a safe WIG though, as we have seen Tandem wings tend to drastically loose stability when pitching up more than..10 degrees, or when flying juuust a bit too high. Günther Jörg partly tackeled this problem by using specific profiles and angles, creating a pitch down moment as soon as the craft flies too high. I have tried to reproduce this system earlier in the Topic and only got some partial good results.

So.. Now I wanted to take it to a higher level. What is more stable, a Tandem with simple high angle of attack wing pairs, both at the same angle, and a small stabiliser on the tail(cheating)..

Or a Tandem with the stability system invented by G. Jörg, which I have 'overtaken' a bit.

First the first concept:

Both wings at 10 degrees alpha, model is stable with and without Stabiliser, in GE.

Out of GE, without stabiliser it flips and stalls, with stabiliser it..well it doesn't quite flip, it's more a sort of pitchup to 15 degrees..till its slow enough and drops back.

Some ideas resulting from this concept:



And..the other concept. I have overtaken the stability system by not only reducing the effect of Ground Effect on the rear wing, but by trying to get rid of RAM air lift on the rear wing entirely. Like this the front wing has maximum GE dependancy, the rear wing minimum.



Testing reveals? Well a very far forward lying CG ofcourse! And.. well it's flying stabily in GE beyond 5 cm's height, which..for a Tandem Wing is incredibly much! I havened tested it further yet, but it seems to be quite interesting.

Some brainstorming with this concept :





And it's just brainstorming, I am not going to build something just yet

Something else, for the WIG fans, I took some time to make a threeview drawing of the Two seater Tandem Flairboat from Günther Jörg. I had a simple threeview of this craft but it was highly inaccurate and the more I worked on my own drawing the more I noticed that this other drawing is probably just a sketch made from a photograph. I tried to detail it as accurately as possible, forgive me for possible mistakes but it should be right for more than 95%

Enjoy:
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Old Jan 09, 2011, 05:55 PM
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fun

Marijn, it shows you are having fun. Just a couple of remarks:
- I have looked over the hoverwing design for a long time and I have not found one jota that is not there on purpose and is just perfect the way it is. Your model may be inspired on the hoverwing but it does not jive as the hoverwing. For example, how are you going to blow back the prop wash into the body box? Look also at the thrustlines of the original two props - just perfect. A one prop hoverwing is going to be very difficult to design with similar balances.
- I had not seen the front lift fan in the bixels before. Good find. This indicates to me that the prototype he built did not get on GE as well as he wished for. This may also suggest that your departure from the T shape wings to a more square wing may have merit for flat wing designs.
- Joerg would not have appreciated a ram prop in front. I wonder what that does to the carefully calculated balance between the two wings?
You'll have fun finding out, I am sure. Luc
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Old Jan 10, 2011, 12:30 PM
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Hey Luc, you're probably right about the Hoverwing and about my design, but as said, it was just a sketch I made when I was busy with the aircat etc, just an idea I expect it to be a faulty anyway, because to my guessing the movable flap won't be necessary at all. If the prop blows into the cavity in such a horizontal direct manner, I guess there is going to be more of a low pressure than a high pressure area under the nose, before the part where the prop wash enters the cavity..

This is also why I think that the extremely rugged front step on the aircat isn't necessary at all, I think that the model behaves just as fine(or even better) if it's left away and the cavity is just open below the nose.

Ow btw, you made the suggestion that maybe the prop wash is playing tricks on my Aircat model, in the air cavity. Well, I recieved a copy of the older Aircat 1/2 plans today, which has got two more walls inside the cavity, so it's effectively devided up in three cavities! Maybe this has got something to do with your suggestion..


Further..the progress on the Tandem wing.. well Luc, I know that Jörg created a very carefully calculated balance, and as you know I nearly never calculate anything on my models, so my tandem wing models are just..what looks right flies right, and if not I just rip the wings off and reglue them differently. Well I ripped the wings of ágain, several times today, and finally found a very well working balance. As I told, I was going to 'overdo' the stability system invented by G.Jörg, and after several changes I managed to get these results:

I now have a tandem wing model which in GE flight shows a..slightly noseheavy attitude..juuust slightly, very stable! I tried it with gusty winds, crosswinds, and collided it with small rocks etc, nothing seems to bother it. But, this is something we have seen before, in GE Tandems are very stable, so this is nothing new.

So, what if I throw it as hard as I can at about 5 cm's height? This used to be well outside the stability envelope of Tandems of this size, but in this case the model shows no sign of pitching at all. It does roll left and right though, clearly showing reduced roll stability due to weak GE.

If I throw it out of GE completely it will at best continue in a straight flight, gently rolling on it's side, at worst it slightly pitches up to about 20 degrees, slows down and stalls. No flipping here aswell!

So, this configuration seems stable and reliable enough for an RC model, here are some photos..



And no I just couldn't resist, and started another rush of rapid prototyping, starting on an RC model. Just 1,5 hours of hot wire cutting and hot glueing:




The large Hull step is located before the planned CG, but still I am thinking of adding an extra step.

Greets,

Marijn
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Old Jan 10, 2011, 03:23 PM
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Quote:
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This is also why I think that the extremely rugged front step on the aircat isn't necessary at all, I think that the model behaves just as fine(or even better) if it's left away and the cavity is just open below the nose.
You are right. My guess is that the front step helps in the very beginning of the acceleration and is a hindrance as soon as there is significant air flowing over the wing. The hoverwing solves that dilemma elegantly.

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And no I just couldn't resist, and started another rush of rapid prototyping, starting on an RC model. Just 1,5 hours of hot wire cutting and hot glueing:
I guess you won't be putting the prop in the back ...

I guess at that speed it would take you minutes to build a quick model with a simple central freewing pivoting at 20% of chord, like in http://ntrs.nasa.gov/archive/nasa/ca...1970014919.pdf (skip the math ) You would be the first to try this in GE. Eternal fame and glory will be yours
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Old Jan 12, 2011, 10:27 AM
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Nope, I won't be putting the prop in the back, Jörg tried to run the thrust line of the prop through the CG, causing the prop to create a downforce on the craft. Surely it's not very safe to mount a prop on the front, but as it's just an RC model, i can mount the prop on the nose, point it upwards, run the thrust line through the CG and instead of a downforce, it's now uplifting. If mounted correctly, one can even guide a small amount of prop wash below the wing pairs..well it convinced me to give it a try

BTW, frontal props on Tandem wings & PAR on Tandem wings isn't new:
http://www.universalhovercraft.com/
--> Scroll down and select UH-TW-1 - Tandem Wing Development from the Information Menu.

My craft is strikinly similar to this craft, which really is just a coincidence, what's interesting is that they used flat plates as wings(very much unlike Jörg) sort of Bixel Tandem Wing combo?

Luc, About the freewing, I have been thinking about it, but I do think that it would have to be totally different from the normal freewing planes. Why? Well one could say that a freewing is a vehicle which has got two independant 'flying wings' attached to its side, two..refelexed airfoiled wings(they aren't reflexed but use a flap to create the same effect and to make it able to change the reflex during flight for flight controll and speed changes), but on a WIG vehicle you have a moving CP, which brings in the need of a stabiliser. I haven't been able to build a Flying wing which is fully stable in GE, without having a Stab(even Alekseyev didn't manage to do this), which would mean that if I have 'freewings' on my WIG, both wing's would need a stabiliser to cover for the CP movement. Otherwise, if I would fly in GE and suddenly fly too high, both freewings would pitchup dramatically..causing a stall.

So I guess freewing is possible in GE, but than maybe not with a direct flap on the wing, but with a small vertical fin and variable out of GE Horizontal Stabiliser on each wing.. right?

Hard to describe, but I have a messy vision of a very strange looking craft in my head haha

Marijn
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Old Jan 12, 2011, 10:33 AM
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Now that I think of it, I believe I have seen a simple drawing in a patent script a while ago, actually describing the vehicle that I meant


Found it, it's not much but it shows the general idea:



Marijn
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Old Jan 12, 2011, 02:59 PM
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Quote:
My craft is strikinly similar to this craft, which really is just a coincidence, what's interesting is that they used flat plates as wings(very much unlike Jörg) sort of Bixel Tandem Wing combo?
Yes, that is amazing. It looks like fun. I wonder how much power/weight is necessary

Quote:
I haven't been able to build a Flying wing which is fully stable in GE, without having a Stab(even Alekseyev didn't manage to do this), which would mean that if I have 'freewings' on my WIG, both wing's would need a stabiliser to cover for the CP movement.
Of course. A freewing wig would need an independence in pitch from the float(s) and at least one stabilised GE wing. What about this one?
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