BD-5 microjet attempt - Page 4 - RC Groups
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Aug 29, 2004, 08:48 AM
Make something. Anything!
bgriggs's Avatar
Much of the fans inefficiency is due to the lack of a bell shaped inlet lip. The aair hits the flat front edge of the duct and scatters and creates all sorts of vortices. He might get a 5% increase by adding a properly formed inlet.

BTW I used to make a BD-10 kit and they do fly well. I never did get around to the BD-5. Perhaps someday.

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Aug 29, 2004, 12:25 PM
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RNAF's Avatar
did you make a model kit or the real life one?

Kind regards,
Aug 29, 2004, 07:02 PM
Registered User
Flight test with two duct funs fail. I had to add so much weight to keep it balanced that it was just to way much wing loading (18.7 grams on 84 sq cm). I then made a simple test plane from a Bob Selman foam wing panels I had. With half the wing loading ( and probably a much better wing profile), it had enough power to fly, but still far from a good flyer. I figured out that the problem is not static thrust but poor dynamic thrust. With the fixed rotor blade angle, not much of the blade area was doing anything as the speed went up. So I decided it's time to make a real duct fun for this plane. This time taking into account all the remarks and suggestions that were made pluse some common sence and some luck. The new duct fun, when doen, will have cambered stators, twisted ( for a constant pitch ) and cambered impeller and inlet lip. And one more thing, it will be a tractor not a pusher. Alfredo you were right about it. I've just found a picture of a pusher duct fun, and saw that even with the engine mounted in front of the impeller, the stators are still behind it. The pictures are of the unfinished new fun. So far the weight of the unit went up from 2 to 2.17 grams. Blade thickness is now only 0.3 mm. Pitch of impeller is 1" . Will update when I'll have some data from this fun.
Last edited by nachman; Aug 29, 2004 at 07:29 PM.
Aug 29, 2004, 07:56 PM
Cheapskate freeloader!
Zeroaltitude's Avatar
Nachman, very nice project you have going here!

Ive got a question regarding the actuators. Im a total newbie at this micro-stuff, and have just bought a RTF Peanut-scale Nieuport 11 from Gasparin, so youll have to forgive me if what Im about to ask is stupid. If I understood correctly, youre planning on using magnetic actuators in the BD5, correct? Unless Im totally mistaken, this plane will need to fly pretty fast for the fans to be efficient. Wont you experience problems with the actuators having difficulty overcoming the airflow at "high" speeds?
The reason Im asking is because of something Ive noticed about my Nieuport 11. It has excellent controlauthority in normal flight, but If I try to dive it to build up speed (for a loop or similar) it will not enter a dive steeper than 15-20 degrees with full down elevator. There seems to be a maximum speed that this plane will not go beyond in a dive. The only reason I can see for this is that the actuators are unable to deflect the elevator at that speed, so the plane stabilises itself in a shallow dive.

For my Nieuport this is not a problem, actually it might even be a good thing. I just thought it might be a problem with a plane like yours, because I suspect that it will need to fly at a much higher speed.

For a faster model of more normal dimensions with normal servos, you would just get stronger servos. But how strong can you make a magnetic actuator without sacrificing wheight?

Please dont take this as "advice" or anything of that sort. Its a just question from someone with very little knowledge in this area of R/C flight.

Anders O
Aug 29, 2004, 08:36 PM
Thanks for the Fish!
aerogel's Avatar
Kewl There it is the Twist...That look like it will grab some air!

Aug 29, 2004, 08:59 PM
Make something. Anything!
bgriggs's Avatar
Originally Posted by RNAF
did you make a model kit or the real life one?

Kind regards,
I made a model kit. It used a Wemotec minifan 480 and 10 800 AR cells on a plettenberg HP 220 series motor. Top speed close to 100 mph.
Aug 29, 2004, 09:05 PM
Frequent Poster
Pete P.'s Avatar
OMG! NAch- That fan unit kicks butt!!! I cant wait to see what you do with the 7mm motors! Oh, and BTW I'm buying those tomorrow! :-)
Aug 30, 2004, 12:15 AM
Registered User
Propjob81's Avatar
Awesome stuff!! I have had many thought about the LRF F-16 or F-18 being made someday, maybe it will sooner than I thought.

Aug 30, 2004, 12:40 AM
Nickel what?
Phreakish's Avatar
I didn't see it in any of the posts... How in the world do you make these fans!??

Are these cnc'd from something, or what? I'd really like to know.
Aug 30, 2004, 03:18 AM
devilscries's Avatar
Oooooooowwwwwwwwww!!!!!!!!!!!! Ooooooooohhhhhhhh!!!!!!!!!!!!!!
Aug 31, 2004, 08:18 PM
Registered User
I've finished the new duct fun. Big improvment over the original one.

original fun new fun
weight: 2gr 2.4gr
motor: Didel 6mm 4.5 ohms same
ID : 23mm same
OD : 24mm 23.6mm , 25mm at front lip
shrood length 9.7mm 16.2mm
pitch: varies with diameter 1" constant

I'm not sure it can get much better then that with this motor on this fun size. One fun should be enough now to fly this plane.
Last edited by nachman; Sep 01, 2004 at 04:26 PM.
Aug 31, 2004, 08:46 PM
Registered User
Anders, it's pager motor powered after all. I'm not expecting it to be a rocket. Bigger and havier duct fun powered aircraft in previews posts seems to do ok with actuators. I personaly don't have any experience with actuators, so I'll just have to try.
Zlatko, I have checked the EDF-30. Although sounds not much bigger, it is. 9W input power vs. 1.5w is one thing for example. I couldn't find the weight of that unit in their specifications to compaire.
Sep 01, 2004, 10:51 AM
Registered User
RNAF's Avatar
Yeah, I've seen the EDF-30 too. It isn't updated for a long while so I suppose it weighs 15 grammes with 10 grammes of thrust (hahahahahaha )

Looks sweet Nachman.
Sep 01, 2004, 10:53 AM
Thanks for the Fish!
aerogel's Avatar
nachman your work is excellent.!!!! love the heat sink : ) 3 grams is great for that size of motor.. I check out the edf 30 around the same Trust numbers I was geting On My 25mm jewls a year ago...

excellent workman ship keep it up..

Sep 01, 2004, 11:45 AM
Registered User
bmutlugil's Avatar

As much as I understand, 3 grams thrust was for the older fan at 4V. The thrust for the new one must be 4.8 grams at that voltage..

I don't know much about fans and thrust, but this looks very good to me - the thrust to weight ratio is greater than 2..

We must not forget the incredible craftsmanship..



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