I'm into the RC car / truck side of the RC Nitro hobby. I don't know a whole lot about props, fans and mounting of such.

I wish what I was doing was written in a manual, I'd surely read it.

I'd like to mount a Ducted Fan (minus the duct) to a .21 size buggy engine that has a pilot shaft. Here is a picture of the host engine:


http://www2.towerhobbies.com/cgi-bin...?&I=LXFAC3&P=7

Here are the specs from a standard pilot shaft:

Crankshaft threading: 1/4-28
Pilot shaft diameter: 5mm (0.19")
Crankshaft diameter: 7mm (0.28") (flywheel position)

(also that brass tapered cone for the flywheel comes off)


This is the ducted fan blade I'd like to attach:


http://www2.towerhobbies.com/cgi-bin...?&I=LXALV3&P=7

specs:

Width: 15/16" (24mm)
Inner Diameter: 1/4" (6mm)
Outer Diameter: 3-1/2" (90mm)

The first thing I notice is that the engine's carb sits in exactly the wrong spot and would hit the fan if it were too close. I do know, however, that this can be done. People regularly use props to break in RC car engines. Here's is an example of that:



I need to know what kind of parts are needed to bring the engine and the prop together. Also, I haven't purchased the fan blade yet. I'm open to suggestions. I need to push as much air as possible with the above engine. The space that I can do this in should no exceed 4 inches in diameter.

I'm sorry if I have posted this I the wrong section. I'm hoping that the jet / ducted fan airplane hobbyists have some experience with this type of thing.

Thanks,
RobH

Hi !

The fan you are going to attach to your car engine has been designed for the O.S. Max .15CVX-DF.

I bet your engine is at least as powerful as the latter, so there is a potential hazard. If not, then it seems OK.

However, the large head in not exactly the right thing needed for a good airflow around the engine, especially if you mount a tractor fan.

Take care, be aware !

Thanks for the reply!

I understand the cooling head issue. Too much or too little airflow around the head will change the engine temps. I think the fan should be able to suck air around the engine and cool it effciently. That's something I'll just have to figure out later.

I also understand the RPM thing. If I spin the fan blade faster than it's designed for, it will explode. There is certainly a potential of that as my engine IS stronger than the O.S. Max .15CVX-DF.

That's why I've chosen to ask this question here. You guys know your ducted fan blades -- I don't. Is there another ducted fan blade made for nitro engines that is tough? Do they make them out of fiberglass or anything? The above one is plastic. The only requirement is that it's 3-4 inches in diameter.

I don't know where to start or where to search. Google turns up exactly squat on nitro ducted fan blades.

Thanks again for the help!

-RobH

RobH,

If you really want to get involved into small ducted fans, check RCJI mag, I remember they published an article about this a few years ago... The guy also used RC .21 car engines.

Just bear in mind this is not exactly easy to yield good results from such a setup. Great model manufacturers have tried this (Kyosho with the F86 for example) but did not succeed in making great performing models.

Have u ever flown any aircraft ?

Keep us posted about your results.

Strykaas,
Thank you again for the reply and the info about the mag.

This is not for an aircraft. I need to push air with a fan blade that won't explode when coupled to a .21 engine. Ducted fan blades from nitro aircraft seemed the most logical choice. If my project succeeds, RCU will be the first to hear.

Thanks again for the info on the mag!

Ok, I still need some help. I sent an email to the RCJI mag. I'm not holding my breath, however.

I did some more indepth searching on the forum, and I found places where talking about were using RC Car engines with ducted fan blades.

Here is one of them:

It sounds like the ducted fan blade will fit the application perfectly because I need high RPMs to push enough air to make this work... the only problem is running down the proper type of fan blade.

The Kyosho F-86 seems to be the DF airplane that used a smaller sized engine. Most the of DF aircraft use the huge .90 OS engine and the matching huge fan blades. I found an aircraft by Jet Hanger Hobbies that used a 5 inch ducted fan with an .46 OS DF engine. That's over kill!

I did find a thread where someone put a CV-R (nitro car engine) into their Kyosho F-86:

http://www.rcuniverse.com/forum/m_13.../tm.htm#135876

You'll read that he removed some of the cooling fins. I think I will end up doing this too.

Ok... I think it's time I say what I'm doing. I have a plate of 6061 aluminum that is 7 inch wide and 19 inches long. Mounted under the plate is a rubber skirt that goes around the perimeter. I'd like to put a hole in this plate and mount my .21 engine so the shaft is vertical and pertendicular to the 6061 aluminum chassis. If I can find a fan blade strong enough, I want to use that .21 engine blow as much air as possible into the space under the chassis.

Yep, I'm making an RC Nitro Hovercraft. The weird dimensions are due to the fact that it will have a T-Maxx laxan body for a shell. The vehicle is going to weigh a lot. I need a lot of blowing power from and engine and a fan blade that does not exceed 3-4 inches in diamter. The hole that I create in the chassis of my hovercraft for the blower fan can't be very big because the larger the fan blade, the less support the chassis will have around the fan.

I'm hoping that the .21 Nitro engine is over kill. I want to have more hover-power than I need. This way, I can reduce the throttle on the blower engine and find my happy spot.

Anyway critical to this design is a fan blade that is no more than 3.5-4.5 ish inches in diameter and is strong enough to survive upwards of 35,000 RPMs.

I don't know how strong the Kyosho F-86 ducted fan blade is. I know that the OS .15 CV-R engine is rated at 31,000 RPMs. If the guy in the above thread can get his F-86 to 82 mph, he must be running at WOT and pretty close to 30K ish RPMs. Is he running the stock ducted fan setup? if so, that blade can take a lot. Can if take the added HP of my engine? Will I even need that extra power? I don't know.

Anyway, sorry for the long post. Any ideas on where I can get really really tough fan blades?

Thanks,
RobH

I think RCJI will give u the solution. I'll have a look at my issues, I think I have it.

However, I've seen LOTS of RC hovercraft working on std .25 aircraft engines (not as powerful as yours) with std props (sometimes cut) and they seemed to work great.

What is your maximum fan diameter ? If diameter is really an issue, then yes you are bound to use a little fan, which seems difficult to me, but feasible.

The thing that limits the diameter of the fan blade is the chassis. The hole for the fan will be in the center of the chassis and the narrowest spot is 7 inches total. So if I had to make a hole that's about 5 inch in diameter for a 5" inch fan blade, I'd only have 1 inch of material left on either side. That would make the chassis weak at that spot. I'd rather have a blade that is 3-4 inches in diameter and have 1.5-2 inches of material left on the sides.

Also, I picked a ducted fan blade instead of a prop because fans are better suited for moving air. I don't disagree that a prop can produce a lot of air, but I think the a fan blade can move more air per revolution. This also adds more resistance for the engine to turn against. RC Car engines are not designed to run screaming with little or no load. I'm looking for maximum air flow per revolution to get the heavy hovercraft aloft.

Thanks for taking the time to read about my silly project.

-Rob

RobH,

I've found the RCJI issues about .21 Car engines D/F aircraft. Danny Starkey is the man who has yield good results in this area.

These RCJI issues are : Dec-2001/Jan-2002 and Feb-2002/Mar-2002

He used a Novarossi .21 car engine + RK-20 and RK-720 Kress fans.

His website used to be ....

http://www.dannystarkey.freeserve.co.uk/

Strykaas, that's exactly what I wanted to know! thank you for all the help!

I have an OS .21 Buggy engine that has been converted for D/F use. I did away with the head and mounted the engine into a Kress RK-720 Ducted fan.

It produces approximately 3.6 - 3.8 Lbs of thrust which is ample for my 4Lb F-18

I'll include pics if you are interested