Dukester

My Feedback: (31)

I've been following Japanman's Mig thread with interest as I like the idea of 1/2a ducted fan. However, I don't have the time or the skill to replicate his CF fan and I didn't want to spend the $ on a commercial unit to play with, so the idea moved to the bottom of my list.

Anyway, I was replacing the power supply in my daughter's PC yesterday and in my normal mode, I disassembled the old supply to see what's what. While looking around, I had removed the cooling fan when I got to thinking about how the cooling fan blade looked sort of like the fan Japanman made. The fan is a fairly stiff black plastic and while they are rated for 5K rpm I got to wondering how strong it really was. So I popped the fan out of the shroud and got out my trusty dremel.

Fully expecting to catastrophically demolish the fan, I prepared for the worse. I mounted the dremel in the soft vise, got out the safety glasses, and sent the kids inside. I mounted the fan on its original shaft into the dremel and fired her up. First attempt was disappointing as the stock shaft is just press fit into the fan and it immediately twisted loose and the fan was only wobbling along at a few thousand rpms while the shaft was happily buzzing along at full speed.

For the next attempt, I pulled the stock shaft off and drilled a small hole in the fan. To mount the fan, I used the dremel cut off wheel attachment and attached the fan to that. The next attempt was much more interesting as the fan was easily able to spin up to max speed with the dremel. I didn't tach it as I was staying well clear. but it ran for 4 or 5 minutes at full speed without any problems and examination after the run didn't reveal any adverse effects to the fan.

As I said, I didn't tach it but I'm estimating it was in the low 20s as my dremel is supposedly good to 30K, but is a little old and tired. It was getting a bit late last night so I put it away, but I'm going to try to tach it tonight and see how fast its really going. The fan moved quite a bit of air and properly shrouded might produce some significant thrust. If the fan holds together tonight after some more dremel time, then the next step is to put it on the 061 and see what happens.

Duke

SST

My Feedback: (2)

Hey, not to worry! I bought a set of plans on the bay a while back from a guy who shall remain nameless, for a F-86H. The plans are a POS, but the fan was made, get this, from a paint thinner can top, and what looks for all the world like a tomato can lid! All spun by ( I think ) an Arden .09.

Japanman

Hi Duke!,
Sounds like you are having fun!
I think the resin those fans are made from is pretty strong- but be carefull of course-the ones I have seen are really thin!
when you put it on the .061 it will be subjected to a little bit more stress than the dremel, as it has to act like a flywheel at keep the engine running. As such you will have to tighten it quite a lot to stop it spinning- this might make the area (which seems pretty thin in computer fans I have seen) a bit overstressed- If it is just a plain disk you might want to cut and glue in 1/8 inch or so of plywood to reinforce the area front and back- it will come under high 'twisting' loads if you use it in a plane when you pull up on the sticks, so it will need it anyway.

It sounds like you are being careful! If it helps you might like to imagine that any bits that come off at speed will be travelling as if they had been shot out of an air gun- I usually visualise this before I do any experimentation, just to keep a focus on what I am doing.

J.M

XJet

Yes, people often underestimate the amount of energy that is contained in a "fragment" of an exploding fan unit or turbine wheel.

I cringe every time I see fools standing in the rotational plane of a model turbine's compressor or turbine wheel. If only these people realised what would happen if the thing grenaded :-(

Andrew

Can you imagine -- such admonishment coming from someone who rides on a gokart with a bomb attached to the back.

the "other" andrew

Dukester

My Feedback: (31)

Well,

Didn't get to play with the fan tonight. Was putting the finishing touches on a new engine test stand to replace my older one. Then when the stand was done, I had to hook up my new (to me) OS 52 4 stroke and then of course the OS 26 4st. Then I went to the TT15 I hadn't run lately and then finally bolted up the 061 and was getting ready to mount the fan when the wife came out and gave me the evil eye. Something about running engines after dark when the baby next door was sleeping or some junk .

Anyway, I am being careful. Now that I know the fan will handle the rpms, the real worry is how the power pulses will affect it on the 061. The whole fan can't weigh more than 1 oz total (note to self, have to weigh it). The individual blades should be well under 1/2 oz. As long as I stay out of the plane of rotation, then I think that even if it sheds a blade (or all of them for that matter) the only real serious danger is one blade being ricocheted back or forwards. With their relatively large area and light mass, as long as I keep my safety glasses on the worst I'll probably get is a nick or small cut.

Anyway, will update tomorrow either with tach readings or pictures of some bloody part of my anatomy.
Duke

Bipe Flyer

I played with the same idea about 10 years ago with a computer power supply fan and a Mabuchi 540. It seemed to pull really well when I held the motor, but I never tried it in anything. Having spun a couple off I can tell you that there isn't a lot of mass there, but it does fly a lot further than a prop will. Just treat it with the same respect as you would for a prop and stay behind it while testing and you should be fine.

ZAGNUT

My Feedback: (1)

now i know what to do with all those muffin fans i've been hording all these years....time to put the old YS .45 back into service

i do agree that all this is really unsafe but then so is a TD spinning at 20K.... even if the prop stays together. why not use a few layers of kevlar for the fan shroud? would make a very good containment ring. hmmm, now i also have a use for the flak jackets i "saved" from my army stint


dave

Dukester

My Feedback: (31)

Bet you guys thought I went off and forgot about this. I've had a kind of busy few weeks with work AND I got Lasik eye correction yesterday. Its really amazing, I went from serious glasses to 20/25 day after surgery with nothign but improvement expected. Doc says I can expect 20/20 as a minimum and I'll likely end up with the same 20/15 I had with my glasses. Havign worn glasses since I was 8 yrs old, this is really a change for me.

But enough of that. I finally got around to firing up the 061 with the PC fan on it. Kind of hard to tach it due to the curve and spacing of the blades, but by angling the tach and using a flashlight instead of sunlight, I finally got a reading of 47K with the tach set for 4 blades. So working the math for my 9 bladed fan gives 47K * 4/9 = 20800 rpm. Fairly respectable for my old beat up Norvel 061. I was running 15% nitro and this engine is definitely not tight anymore.

Prop wash was pretty strong. I'll have to rig up a duct now and see how that affects the rpm and thrust. I think I threw the original fan shroud out. I kind of wish I has kept it now, but I'll figure something out.

Duke

Dukester

My Feedback: (31)

One more thought. Since Japanman is doing the Mig, if thsi fan works out, I might try my hand at the F-86 Sabrejet. Seems a fitting choice.

Duke

xanaphyst

My Feedback: (17)

If it works out I'm with ya on the Sabre.....and along with these piped rear exhaust norvels we've been working on they should be great....

SRA Foam Flyer

My Feedback: (11)

Be very careful with that cooling fan, I tried that several years ago with a strong looking fan and the it exploded about 1.5 seconds after the Cox .049 started. Luckily I was wearing goggles, but one of the blades imbedded in my hand. I also tried them on car motors and they quickly flew apart then too. It's not always the material that's the problem, it's also the length, pitch and shape of the blade(the design). Cooling fans are the "slowflyer" prop of the fan world, they were not designed for high RPM's and definitely not glow engines vibes.

Japanman

Well, if it really gets ugly I could mould you up one of my carbon fans- there is bound to be something you could trade with me.

J.M

Dukester

My Feedback: (31)

Well, I am being careful, but the fan got two approx 5 minute runs full blast. After each run I examined the fan and saw no color changes or lines of lighter color that might indicate stress areas. All the blades are still as solid as I started.

Also, I might add I'm a mechanical engineer by training so I'm plenty familiar with rotational forces and the like. I'm showing this fan plenty of respect, but so far I am impressed. I did some checks and saw that a lot of the cooling fans and the brushless motors they come with are rate for 5K to 8K rpms stock, so maybe its not so surprising if they use a 2 or 3x design safety factor.

Duke

jetpack

My Feedback: (1)

I have also been reading and watching the 1/2A ducted fan development projects, as a stick-and-tissue 1957 Berkeley Models Douglas "Skyray F4D-1" is sitting in it's box here, waiting for a suitable motor/impeller combination.

I currently have the original kit supplied stamped aluminum impeller - which I would consider too fragile for modern power (and would want to preserve), two Veron "Type C" nylon impeller units (now out of production) designed years ago for "Racing 1cc Racing Diesels - .061 - .074 cu/in" that look like they can be experimented with. Veron was also one of the first to produce ducted fan kits back then, but never seem to find too much on the web about them to do research. I am also considering the WeMoTec Mini-Fan 480 replacement blade kit, and possibly the Kyosho blade.

My engine of choice here is the Cox TD with a LH crankshaft, as the Skyray is a pusher motor arrangement, not a tractor setup. A left-handed blade would be nice to come across, so a standard TD would work. A reed motor would work also without making considerable design changes to the airframe, but only one choice there that I know of...and I'm not sure a Cox Babe-Bee would push things fast enough....I am trying to stay away from "Exotic" motors here, save maybe a special head and simple rework tuning of the TD - pressure tap, shims and exhaust throttle sleeve.

The Skyray is a fairly well designed kit, and as I have mentioned have a pretty well preserved original, and a nicely built copy with modern power and impeller I am sure would provide more than just an extended glide....

If anyone is curious about the specs of the plane, ask away...could be of some help.

futaba_pilot45

if you want more power out of your .049? shave your cylinder..... i did this to my 1/2A racer ... the engine was getting worn out so using a old ******* file (antique) shaved the sleve to the first cooling fin.....compression went back or past new condition, and 25% car fuel made it scream... befor it would just make head way. with a cox 6X4 or really hum with a 5X3 lol! worth a shot, ask if need help

~matt

Japanman

Do you mean shave off the cylinder fins? More info please!

J.M

xanaphyst

My Feedback: (17)

I think he means shaving as in raising the compression......seems like taking out the head gaskets would have the same effect (run like crap)
seems like a new engine would be a better choice..

xanaphyst

futaba_pilot45

xanaphyst, "run like crap"? maybe you should try before you comment or maybe you just havent been able to do it right

J. Man
if your not shure try on a old engine first. tho if not in fair condition it might not help at all mine was from a old c/l plane from when i was eight... now im almost twenty... and have reborn many engines that people give to me that are "tired and useless to me", by increasing the compression ratios also polishiing the piston and wall carefully, will help...

nope you cant just remove the gasket. let-me go get the rebuilt engine (i lost the sleve and head in a subterrainian flight when the crystal wiggled loose after a roll)... k.... looking at your cox engine with the glow plug/head removed. there is a ring (on the sleeve) that keeps the silver cooling fins from touching the black... grind this off flush to the first black fin using a file ( YOU HAVE TO ROTATE THE SLEEVE ABOUT A EIGHTH OF A TURN EACH PASS OR IT MIGHT NOT COME OUT RIGHT).. now the top is prefectly smooth... next remove the copper gasket if you havent already done so. now re-thread on the glowplug.. see the slight gap between the two parts? using the file, rubb the glow plug bottom down till it can go flush with the gasket on (USING THE SAME PROCESS AS ABOVE... e.g. black and silver touch WITH the gasket in now... but be careful! check fit after each pass! ... it took me maybe 30 mins to do this... DONT FORGET TO CLEAN THE PARTS AFTERWARDS!!! if your weary of this mod, try on a old one first.. maybe you'll have the same luck i did and get it right the first time you try this... and have a ball with it... it will bing new life to the tired engine, however run good amount of oil content... i was running power master 25% or wild cat eliminator car fuel (20% w/ 18% oil) another mod that you can try is open up the ports... i havent done this yet because i got to build another plane or fix the one i had...
also since were on the topic of ducted fans... i have a hot bodies A-7 .18 df... it is a pig... im in the process of redoing it and making it as light as i can... i havent flow it but the guy that gave it to me said to get rid of all weight possible... was he right ... the darn thing eats up runway.. and after 500 ft (of 600 ft) if i isnt up already i have to abort and redo the take off .... i havent yet got it airborne for more than 3 ft before it realizes it is flying and stalls... and i have rebuilt it twice...but i have talked to a few guy about it and they had the same problems with it and it staying on the pipe... i think that is why they dont sell it anymore.. but it is a toki .18 the fan and df is probally great once you fine the spot on the pipe... anther thing you should look at is the MRC DJ1 from O.K./ Pilot models again it uses the .18 but is really neat an is quick too i have the video ... also of the a-7 i wish you the best of luck and if you still need a diagram i could sketch it out and e-mail it .. let me know... e-mail is : [email protected] put the subject as engine or something....

~matt

gcb

Jetpack,
If I remember correctly, the Skyray was a FF model using a Space Bug, Jr. or a Ok Cub type engine. The fan will not hold up for high RPM engines. It's a NICE plane though...always wanted to build one. Are RK fan units (Kress Engineering) still available? Perhaps the fan only, although the shroud does afford some protection.
Modelers were experimenting with plywood hubs and thin plywood blades back in the 1950's when good fans were not available. Ducts were often created from doping silkspan on a sheet of glass, then removing and forming the cone. Just make sure the exit is a little larger than at the fan so the air will flow well. I read the articles but don't remember all the particulars.

George

gcb

~matt,

What kind of plugs are you using? If you are using a "product" reed valve engine, you may gain some RPM by switching to a high compression head or even the Tee Dee head which has a squish band and a fluted combustion chamber for more power.
It would appear that you are creating a high compression head (perhaps with a squish band) the hard way.

Lapping the plug bottom surface lightly will ensure seal with the gasket. Some have even lapped the gasket seat on the cylinder for better seal. Most still use a plug gasket. You might also consider trying a Galbraith head with a Nelson plug.

All of these changes will work with your modified cylinder or a stock one.

I'm guessing that you already know about the different cylinder porting available from Cox for their various engine types.

BTW, if you are really going to hop-up a reed, you might consider getting a hardened crankshaft. Also have your piston reset tool handy and use it often. Good luck with your hop-ups.

George

futaba_pilot45

thanks, ill have to look into all that! i know some of the avalable parts to modify the engine... i would love to have the tee..dee.. but i have many of the "product" engines, with remote tank... infact i haf one in a sailplane with a 2 oz tank.... never again!!! it flew for a hr!! lucky for me i had low drain micro servos... lol

oh guys ... im always looking for cheap stuff in this hobby, today i went to the store and found duracell 2050 m. amp NiMH batteries ( AA size) for 9 bucks for 4 cells... but the best part is the 5$ mail in rebate... got some today and already made up a pack... infact its on charge right now... just thought yall might like to know..!!!!

~matt

hcker2000

Hi guys new to the forums but I'v been working with computer for about 7 years now. I'm suprised the type of fan your talking about would stand up to 20k rpms. If you have a bit of spare cash ($16 usd or so) then I would recomend picking up a Delta case fan for a computer. The come in various sizes from 60mm (these fans run at 6k rpms so the blades are at least good to that) up to 120mm. They are about 40mm thick depending on which size you get and generaly have a metal center in them.

Japanman

Hi H2000- That sounds promising- do you have a photo or a link to a place that sells them?

Stefan

BMatthews

Dukster, you're not missing out on much by loosing the original shroud. From what I've red the shroud needs to be quite long to avoid lots of turbulent flow.

The mouth should be belled out to a nice venturi shape and should extend forward about 1/2 the diameter of the fan. The rear should be about 1 fan diameter long and can benifit from being tapered slightly. My guess tells me the outlet area should match the donut shaped area at the fan. Donut shaped due to the central pod and hub of the fan.

A very interesting project so far. I'd love to see pics of the fan you're using.