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[rathikrishna]

My veteran friends will some one help me in this matter..?..after my sucessful hover craft in 1998, my dream was a craft like that but not hover but must propelled with fans..so i turned to this project...it flies over the water with two RS 380 motors took from hand drillers..now my problem is this..it never travells in a straight line....it travells like a sidewinder snake...how can i overcome this..?..whts wrong with my design..? i tried with various power plants...turning is accomplished by rotating the two entire prop assy...help me..once..

[rathikrishna]

its on its belly...

[rathikrishna]

i tried it with more big prop took from an R/C helicopter...even then its like same...

[Tugwash]

i doubt you will stop that since its friction on the front that's making it go sideways. if you look at hover crafts in general you will find that the majority of them work in the same way, at least the smaller ones, im not entirely sure on how a hover craft works in regards to its direction control i can only imagine that one blade is slower then the other which will aid in its straight line speed.

have you considered fixing the fans in place and using rudders behind the fans to control its direction, if you set it up as a tank steering ( each motor controlled separably) perhaps you are able to control each motor individuality which may control the straight line direction better then the use of the rudders to turn it.

im not sure if i have understood your craft does this one hover at all? there's a air bag under it dose it work? if its not working then you really have just produced an AIR BOAT rather then a hovercraft in which case you will need to redesign the front end to 'skim' over the water rather then 'push' through it

if the bags working then i suggest you look at reducing the friction in the front maybe more lift is needed in that section, or its unbalanced and you need to make the rear slightly heaver to bring that nose up to reduce the drag its causing.

one option that springs to mid is something the power boat boys use is a set of trim tabs like fins off a surf board under the hull that are submerged in the water this may work to keep it straight but im not sure if its practical in your situation given its a hover craft

[sailorboy61]

From what I can make out from the picture you are using left and right handed propellors, I assume you have checked that they are wired correctly and both run ahead/astern together?

[Circlip]

Longitudinal stability is normally achieved by adding a keel, hovercraft, even full size, tend to skid. Go back to your aerodynamic theory, turning using rudder only causes the aircraft to slip, bank gives stability.

  Regards  Ian

[mattycoops43]

Hovercrafts use a rudder. i built a real one once! But, that is not hovering is it? it is acting as an airboat if I have understood you correctly. I would try some long thin strip runnnig along the bottom as mini keels, that hull looks to have a footprint which is very wide, with no directional stability built in. I reckon a couople thin strips of plastic or wood will sort it. i don't see any reason why turning the whole props would make it unstable, it should be MORE efficient!

Matt

[Circlip]

Yes Matt, two of us erroneously thought it to be a Hovercraft, but even an airboat has no longitudinal stability unless fitted with a keel or water rudder. Clarification with a pickky would show what the hull bottom is like. Instability in this case is todirectional control.

  Regards  Ian.

[rathikrishna]

Good morning all...and million thanks for the guidance..my this craft is based on my first hover craft, and this one yes indded not a hover craft.i decided to make this craft, wider ,because it is a NAVY's rescue craft. its bottom is fully expanded polystrene covered with tissue paper as usual. my hover craft is working well because i took the coaxial contra rotating rotor blades for it's lift that we can see in Kamov helicopters.so i can simply change the speed of each motor by a toy R/C. in this craft i use two props rotating in opposite directions.two of them are pumping correctly to the stearn, and it propels nicely...but after a bit long travel it starts to zig zag..uncontrollably...its sad..except that every thing is ok..naturely two motors drops 14 amps, at 9 volts.so i limits it with TIP 3055 control, within two amps.with two amps, i am getting more than enough thrust.i cant use rudder, under, because this craft is based to operate at shallow waters around my home.sad...i have tried independant motor control for each motors..but even then it behaves like same..so now i am in my work room, to make a infra red sensored direction controller , with a flip flop integrated circuit...for that i have to make a centrifugal pump, under its belly.but i am not sure it work or so...ohh..

[Sub driver]

hi. i have a few hovercraft and they are affected by wind / drag etc i think that in your case as it is not a try hovercraft but more an air propelled boat that it is drag that is affecting the directional stability. if the bow hits a wave or anything it will alter course just like a boat with no rudder. there are a couple of ways to sort this out the easiest would be to try and lift the bow by movement of ballast rearwords this will stop the bow digging in. the next is to fit a pair of air rudders directly behind the thrust fans. this wont stop it but will let you control it. the other method is to fit a gyro to the thrust motors this will sense the movement and compensate by reducing power to the motor that is giving more thrust..  hope this is of use
.. regards sub.

[rathikrishna]

Hey..Sub its great...GYROSCOPES...thanks for the BRIGHT IDEA.....oh god...i got it...A MILLION THANKS..............god may bless you...i will fix it today...sure...

[Sub driver]

Hi,
Glad you found the info of use, .
show us a video of it running when you get chance.

Regards Sub.

[rathikrishna]

Hai SUB, sure..and now its working well..i placed a micro GYRO, near to the bow, a ceramic one i made it for a R/C helicopter before..now i have rectified the problem, and its waiting a good finishing...a million thanks again...

[Sub driver]

More than a pleasure to be of service.

Regards
Sub.

[rathikrishna]

Great..i need more help from all...have a nice day...