DJLaPalme

On a propeller driven airboat the angle of the prop is important. As you said, if the prop(pusher setup) is angled down it will push the bow down. If up it will lift the bow. Most airboats run at/or close to 0 degrees angle. You may try the angle change or move anything you can towards the stern to lift the bow. Good luck and I hope you are better soon. Dennis

lawmaker140

Hi - new here, but have been reading about your project. Ive got two of the same D/F units from Ebay -I'm planning(well have bought all theparts ) for a D/F airboat. Hull is gonna be entirley from blue foam,IHave two 50a ESCs and a pair of 5000mah7.4V lipo'sthat will run in series to give 14.8v . I too was daft enough to run one of the fan units while holding it in my hand. At minimum throttle it wrenched free and sliced into the rudders of my hovercraft that was seving as a power scorce for the test....

Anyone interested in the pics when i start slicing the foam and not my fingers?

As far as thrust angle is concerned - I had the same thing with my hovercraft - the bottom 1/3 of the thrust goes down to give lift, the top 2/3 goes straight out of the back for forward thurst, so the thrust line is quite high. At full thrust the nose of the craft used to dip and it was actually slower than at 3/4 power. I added an elevator to dip the tail a little and so lift the nose, this has its own servo and only cuts in at above 3/4 power.

Anyway with the new airboat i plan to have the thrust as low to the water line as possible, intakes higher either side of a dummy cockpit.

Dont give up on the project, i took 4 years to get the hovercraft to run right......

jetpack

My Feedback: (1)

I've kinda stood back and thought about the thrust angle and such and wonder if that really isnt the whole reason it wont get on plane.

With it being a mono have anything to do with the abilty of it getting on plane?

There really shouldnt be too much difference if it is fan powered or not I would think unless I'm missing some finer points besides thrust angle which shouldnt be too sensitive.

All of the swamp boats I've seen are the everglades type you commonly see and what the Dumas boats are modeled after kinda with the wide, flat nose.

If that is the case, I'm still thinking how to avoid it.

That ski it forms in front I think could be making the difference.

I would try and go unconventional with the CG and put all the weight you can in back.

pinky_d_brain

Thrust angle has a bit to do with it but not much a conventional propped airboat will not react much different with an angle adjustment. One of the miss understood things about an airboat is that all the thrust is from the top of the boat forcing the bow down, meaning it is the reveres of a conventional propped boat. with this in mind if your CG is low and your thrust is high then you will have more down force on the bow from the thrust being farther away from the center of the CG. if you want to check the angel on the thrust get a light ribbon and connect it to the center at the back, fire the boat up and see where your thrust is going, the best is if it is going straight back. If it is your best bet would be somehow move your fan unit back or rays the CG. Try putting your battery on the top deck in a sealed bag or something to see what will happen. Chances are the battery is the heaviest component and is sitting on the bottom of the hull moving it up will move the CG more in line with your thrust reducing the down force on the bow. This will hinder your turning a bit but if you make your rudders only on the bottom half of the prop under the CG is best it will help lean your boat into a corner to compensate for the hire CG.
Anyway this is just my 2c don’t give up boat looks great [8D]

pinky_d_brain

looking back at your build the fan looks like it’s in a good spot try Velcroing your battery to the underside of your hatch at the back if you don’t have too much of a down force problem this may fix it right up. You could also try some ..... the lines on the bottom of a mono hull that help you plain off.... may help you as well

ISIRC10

Strakes they are called me thinks...?

srw1960

I thank you all for your input and thoughts on how to fix this.here are the changes I plan on making...I looked closley at the fan unit and it is in a down thrust angle right now so that def has to be changed..also I was told by the good folks in the electric jets forum that I HAVE to reduce the volume behind the fan by at least 10 percent..I will use some heavy card stock and make a funnell to downsize it to where it needs to be and then ill wrap it with a couple layers of glass and resin. the resin soaks into the cardstock and makes it nice and hard I have used that technique on some of my hot rod restorations to make new glove boxes and it works great...the new esc that is on its way has a bec circuit so I can loose some weight by loosing the receiver battery pack and have built a stand that allows me to test cg and also test thrust angle..ill snap some pics tomorrow and post them...
Also have talked with asmitnc and he made a very good point about how much drag my flat bottom hull has..I may need to add some STRAKES ( thanks ISIRC 10 ) or maybee build some sponsons and make it into a modified cat hull to get as much out of the water as possible...I checked the specs on my motor and battery and they apear to be matched up pretty good so I dont think its an issue of not enough starting current or not enough current flow to get it up and going...also I think im going to move the battery from the middle of the hull to the very back I think I have room in the radio box area for it...and I am going to make some new rudders with more surface area to help with the handling..

I think that covers it and I think it shows also that I am indeed listening to all of you good folks and again THANK YOU for the suport and dont be afraid to say something you might feel to be controversial I am very open minded..if you think I totaly screwed the pooch I need to know that as well..
Im hoping the new esc will be here end of next week..yes its coming from china cant be helped..

Well yall have funnnn and take care

Steve

johnnycat500

Well went to try out my DF boat...got 23 seconds of fun out of it....LOL Just like srw1960 this boat will not go on plane. The water rudders at full throttle work to good. It just did a barrel roll. It went better with the DF fan under water. I think a DF fan has to be in a wide hull so it won't tip over like it did. I have never build a boat from scratch, but I think a wide 3 point hull would work best with a DF fan.I have the nacelle which will go on anything I end up making.I had no one to run the camera so I put it of a tripod. Glad I did. If it is not going to work at least I got video of it. All in all I think the video is pretty cool. I almost put my flycamone on the boat,good thing I did not. The boat was upside down for about 5 mins till I could get to it. It had very little water in it. When I got home I hooked every thing up and it still works. Back to the drawing board. Check out the youtube vid and tell me what you guys think. I will not give upon this. Hey srw1960 you want to start a club...LOL

http://www.youtube.com/watch?v=Ky3jI1VQyp8

srw1960

LOL Why Not!!!!! call it the cool lookin boats that wont run club....I think you are right about the 3 point hull with the fan unit..I was worried with your nacelle up so high if it would cause a problem guess it did..
I found a much bigger fan unit that is cheap I may order it and set it in place and see what happens especialy after I make the hull mods..I have to keep reminding myself this was an experiement..

Asmithnc suggested an elevator across the back a very good idea I think im going to try.and like I said if it just wont go with the fan Ill make a pod and hang that enya .10 on it and I bet it goes then...Ill try to build a 3 point hydro and see if the fan will move it maybee a canard type..anyway im getting ahead of myself..the new esc should be here mid week next week so as soon as it arrives ill reset the thrust angle and add some strakes to the hull and see what happens

johnnycat500

This hull is real narrow so it tips real easy. That is the fun of it seeing what works in the real world. Why do you think they won't go on plane not a big enough DF?. I think I should put the nacelle on the bottom and see how that works. I would really like to build a hydrofoil. I built a hydrofoil kneeboad years ago that did work quite good. Maybe that is the way I will end up going

srw1960

Well after talking with a couple good folks I am concerned that there is just to much drag from so much hull in the water...the fan isnt designed for alot of grunt to get something on plane its built for airspeed...I am begining to think it would probably work better in a hydro type hull

ISIRC10

well, I think that calls for a test then!

make a simple outrigger out of foam and mount the DF plus electronics (in a tupperware container, nothing fancy) and let her rip!
at least thats what I would do... then I would make a hull from that and make it fancy and all...
BTW, this may be a bit off topic, but your paintin skills have got me envious.... so I took a major risk yesterday. I risked messing up a perfect flat black paintjob on my jetboat in order to acheive a three color scheme... this was the first time I used more than two colors on a project...
I am still stuck with spray cans, but this is how it turned out - blue painters tape and some careful spraying can come a long way. I am very proud of my first "true" paint job! BTW, this is also the first time I tried to do a fade. Not too bad me thinks, it could have been better but I like it anyways.

Thanks for the inspiration, thats what pushed me to experiment!

srw1960

I was not feeling at all well today and you just put a big smile on my face..THANKS Im glad I was able to help and I think you did an OUTSTANDING job..not a thing wrong with using the rattle cans and I think your fade job is fine...

Also if after these few tweaks on the ducted fan Im going to do exactly that build a simple and cheap test hull and see what happens..if the tweaks dont work..should have the new esc mid week im hoping

DONS BOAT WORKS

My Feedback: (3)

For a test hull I would recommend a small boogie board.
It should be light enough to get on plane easy.

johnnycat500

I just got back from testing the DF boat with hydrofoils. The hydrofoils work pretty good. The front one lifts the hull out of the water real good. The back one lifts about an inch, so I need to increase the area of the wing.The DF fan just does not have enough thrust to get it going fast.I am going to modify the back foil to get it to lift out of the water more. Then I might do away with the fan and put a prop on it. There are some neat rc hydrofoil boats on youtube that work really nice. here's some pics.

Video

http://www.youtube.com/watch?v=tyF7PeI35U4

srw1960

I am still waiting on the new esc but I am loosing hope this will get up and go so i have started designing a stand for an engine and prop and convert it to regular prop driven I bet itll work just fine then

mike walker

Ive been watching you guys hoping you would come up with somthing. I took a huge outriger I got somwhere 59 in long and stuck a K&B 82 byrojet fan on it. It will run about 50 mph on grass and maybe 15 in water before it noses over I think it was the angle of the fan. I gave up, your stuff is to pretty, got figure it out
Good luck

jasperrc

Question about your foil, is there any wing shape to it or does it work just by the angle of the foil?

I had thought of trying this years ago but other ideas got in the way. You've got me thinking again.

srw1960

Thanks for the nice coment..it may not run good yet but at least it looks like it should...
I am still waiting on the new esc..the company I bought it from said they test everything before they send it out and the one they were sending me failed..they tested the others and they failed as well so They placed an order for a new batch and had to wait for them to come in...sooo it is on its way at least and it should arrive in good working order at least they didnt go ahead and send a bad unit...

I am going to remove the water pick up. the new esc is rated way higher than I need so no way should it overheat...and it has a bec circuit so I can do away with the receiver battery pack thatll save a bunch of weight...and im adding strakes to the bottom of the hull welll see if the added lift helps any

johnnycat500

Yes the foil is flat.I did away with the ducted fan and used it's motor for a prop. Hope to try it out sunday. i have rc helicopters so I have alot of broken blades so that is what i want to try next to make the hydrofoils with an airfoil. If you are interested in hydrofoils go to youtube and search hydrofoils. There are alot of video's

srw1960

Im gonna give this thing one last good attempt and if it doesnt perform then it gets abrand new os la .15 on it with a 8x9 prop and well see what it does then

pinky_d_brain

I think your fan is too high and is too far forward. The rake of your boat is almost under your fan meaning there is nothing to resist the down force on the bow. Lower and move back is my recommendation a prop is going to have a hire thrust line meaning more done force on the bow. You want to get your thrust line as close to the water as you can and as far back as you can.

evader512

you should put a out board motor on it

srw1960

naw got plenty of outboard powered boats around here..

OK FINALY the new esc is here..sheez last time I order from them literaly on a slow boat from china....

Ok Ill try to get the new esc in it and finish the mods and try this again

mike walker

Cant wait let us know