Hello, I hope I'm not out of place but I coudln't think of anyone better to ask. I've been trying to do a lot of research and have some questions. I just bought a os .91/Dynamax/JMP Pipe is there a exhaust gasket that goes between the header and the cylinder. I'm building a ground model (boat) with this setup and I need some help on some things (who better to ask than you guys). Mainly mounting of the fan and engine and ducting "thrust tube" (single outlet) setups. Is there a tube that I can buy that goes in a jet kit or is it possible to make my own? I have no kit and designing everything myself, which I've made quite a bit of progress on. Some pictures of DF setups (mounting/tubes/etc) would be great! I've ran accross a few cause I've been searching like crazy. I just purchaced all the imporant stuff. Tanks, Tubing, Tee's, Wildcat 5% DF, Mc Coy 9's, etc. etc. If you can think of any information that might help me please let me know. Again I hope I didn't step on toes posting this here. If so delete. Thanks.

It would be helpful to see what you are trying to put this in. The Dynamax needs a pretty long thrust tube to work well. For a swamp boat type, you may want to go with a pusher prop to give you the torque to get going. If you really want a ducted fan, I would look into the Byron fan since you will have more thrust where you will need it and it isn't as critical when it comes to thrust tube design.

Good luck,

Mark

It's real close to the size of a 1/8th scale hydro. The fan in the picture is the dimentions of the dynamax fan. Should be plenty of room for any size thrust tube. If not I can make room. I have some more cad work of this with a lot more detail of the actuall construction of everything, but this gets the idea across I think. Anyone know about the exhaust gasket?

Go to JMPs website. There is a seal and a header that bolts to the engine.

I have the header and the orange seal, but i can't find anything on there site or OS site about a seal that goes between the cylinder and the JMP header. Does it just mate metal to metal?

just a question......wont it suck up an awefull lot of water ?

My Hydros dont seem very dry where your fan is

I'm going to have a few things to fix water spray. It won't be racing or catching water from other boats. I already have most the stuff to make it laying around so I'm going to build it and give it a shot. I won't be out much if it don't work. I can always take the hull and put in a prop drive.

LOL the batmobile. Thats exactly what one of my friends said after I drew it up.

Hi,
There is no seal between the JMP header(I'm assuming this is the hot seal type), the
best way is to degrease both surfaces then smear a tiny bit of 24hr epoxy onto one
them then bolt together lightly(very) coating the bolts with copper grease. A sharp tap with a block of wood parts them. As an aside did you get the longer retaining bolts(3.5mm thread)as the JMP header is thicker than the standar OS, using the OS ones doesnt give you much thread. Mike

Hi,
Me again, have been studying the boat drawing you posted, would I be right in thinking that the tube aft of the fan diverges or is constant diameter, if it does then you are going to need an inner than converges down to around 4", if you dont then the air doesnt accelerate aft of the fan, your current set up would give goodish static thrust but not much dynamic once it's moving.....mike

Yes, that is exactly why I was asking. I thought that the end diameter was quite smaller. The way i have it drawn is just like a fusalage, just a housing for everything. There will be a inner tube or duct for the fan. The size and setup of that tube I'm unsure of. I was hopping I could make my own tube that way I could make several and try different ones, or buy one thats made for a jet and build the hull formers around it.

Hi,
The only people I know who make a suitable area ruled duct that you can buy separate from a kit are Trim in Oz, suggest you give them a call(as they are not great with emails), hopefully they still do this, have used several myself with success, not expensive either.

http://www.trimair.com.au or Phone: +613 9743 7161

Mike

Hi,
Reference above, if you have no luck then drop me an email and I'll do some
measuring off one of mine and send you a drawing....mike

http://www.rcuniverse.com/forum/m_25...tm.htm#2528697

I found this post. Apparently i'm not the only one trying to make there own. Even someone saying they made theres from thin ply.

Hi,
One problem with making from ply is you cant apply the area rule (unless you're very clever?) essentially the duct tapers from 5"(fan diameter) to around 4-4 1/4" diameter at the rear, the best way I can explain the area rule is the shape changes from circular to a flattened pear shape and back to round, this takes into account the pipe, the pipe is supported at the top of the pear and this allows the cross sectional area through which the air flows to remain a constant taper or nearly so, this really does improve the thrust. You may also need to allow for clearance above the engine head just aft of the fan unit.

When setting up the duct on a d/f model you need to have the duct 1-2deg positive ie high at the tail end with respect to the model centre line or you get rotation problems, I suspect given you want the boat to get on the plane(right term?) then you will need to do the same, suggest you design in some allowance for adjustment of the thrust angle.

The easiest way to make your own tailpipe is make a male plug with a smooth surface. Gel coat it, then wrap with cloth, it doesnt need a great deal of strength so 200gm is sufficient. When cured cut along the top middle, remove, tack with cyano then 1" bandage. This obviously depends on your skills with glass but its not difficult. You can use anything to hand, white foam, blue foam, balsa, whatever to make the plug, doesnt really matter as long as you get the shape and achieve a smooth finish(necessary for good airflow). Mike

You can build the thrust tube out of 1/64 ply but you have to seal the inside of it with epoxy paint or something to fuel proof it. I've never tried it, but you can also lay up some fiberglass cloth and epoxy on a sheet of glass. You can then roll it into the shape you want for your thrust tube.

If you are going for all out speed, I would taper your thrust tube down to about 3 1/2 - 3 3/8" outlet. The JMP Starfire used a 3 3/8" outlet.

In fact, I have a complete Starfire II thrust tube with the engine cover that you can cut down to match the length you need, if your interested. If so, PM me your address.

grbaker, I might be interested in your thrust tube.

Can someone explain to me static and dynamic thrust. I think I kinda know, but its shady. I'm affraid I might need some umphff to get the boat on plane... but not so much once its there... And the thrust tube is going to be the determining facter in "umphff" and speed? I'm thinking I want both ... Or at least a way to try both.

From what I've seen of thrust tubes is there just a tube tapered from start to end. Correct?

Hi,
The best way I can explain static/dynamic is static thrust is what you need to get going, basically how much air your fan
can shift at full power when the model is stationary , dynamic is the thrust change when the model is moving through the air, this is the result of inlet/fan/tailpipe combination.
Essentially if you are looking for static thrust then go for a Byron type pusher fan, if you're looking for the best
dynamic then go for Dynamax/Ramtec tractor type fan, looking at your drawing then I suggest you move the fan rearwards, you
need more inlet than you have, also do you want the weight forward ??
Regarding the tailpipe then if you were using a pusher fan then a straightforward taper is fine, but using the Dynamax then
you need to apply area rule (as per my previous entry) to maximise performance. Hope the makes sense.
Anyone got a picture of just the tailpipe assembly they can post, I dont unless I strip out a model, this would help getting the
point across....Mike

The CG will be between the back of the front sponson to be back of the rear sponson. I can adjust the wieght and move the fan pretty much anywhere by moving the the engine, tanks and electrics. So far figuring out this inlet and tailpipe stuff is the last of the stuff I need to work out also the hardest... Looks like I'm going to have to find something premade. The way I'm builind the first model is on a very expandable and movable platform. I can change the angle of the sponsons, engine location, and almost anything, without to much effort. Cause its going to take a lot of experimentation to find the sweet spot for the boat.

Sounds like a cool project. You can buy the engine covers and tail pipe from Yellow Aircraft. They have several different ones that would probably work.

Looking at Yellow Aircrafts website I wonder if I could mix and match there inlets and tailpipes? Like use the starfire thrust tube and another planes intake? Unless they are matched to preform together. Most all the intakes are split. Which is fine, might actually be better. Less likely to suck water and would be less batmobilish lol. I can't think of any reason I couldnt' work with that. This would make construction a lot easier for me. I might email them and ask them. I think the F-14 style intake would be nice looking turned upside down hehe... Help if they had pictures of the parts maybe they could send them to me.

You should have no problem mixing and matching inlets and tailpipes as long as you use thier engine covers. Good luck on the F-14 parts, they haven't been available for quite awhile.

I emailed and PM'd YA the other day about the parts, not got back to me yet. I might have to call. When people switch from DF to turbine do they change all the ducting (Intake to exhaust). I just got all the rest of the parts i've ordered. Fuel is crazy... had to order 4 gallons cause my LHS didn't have any :-( Plus 20 bucks extra for shipping. Jet guys are neglected, at least where I live.