BD-5 microjet attempt - Page 5 - RC Groups
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Sep 01, 2004, 12:05 PM
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Aaerogel, it's not 3 grams. The table didn't come out so well. The numbers for this fun are:

3.37gr @ 3v & 22000 rpm
4.25gr @ 3.6v & 25000 rpm
4.83gr @ 4v & 26500 rpm.

And if the battery could reach 4.2v then thrust is up to 5.17 gr, but for that to happen, some voltage booster is needed... it doesn't get hot at 4.2v so I'm going to check what's the volage limmit and thrust for this set up, even though it doesn't make any sence to check it. Just out of curiosity.
I've read yesturday the wholl post you've started with the 25m jewels in it. Facinating post !. You've done impressive job with duct funs.

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Sep 01, 2004, 01:57 PM
in persuit of low wing loading
Gordon Johnson's Avatar
In your post above, I put your numbers in a table in Excel and then copied and pasted that into MS Paint to save as a jpg file which can be uploaded. You can delete it if you think I got it wrong. I hope this helps you present your test values. I can add the rpm if you want, but wanted to make sure that is for the new version of your fan, not the old.

Anyway, delete what I've done if you don't like it. Keep up the good work.

Sep 01, 2004, 02:09 PM
Thanks for the Fish!
aerogel's Avatar
nachman Check out
Designed specifically for LiPolymer cells this converter can supply 5v and 300mA continously and 400mA+ for shorter periods. It works with input voltages from 2.5 to 5v and is ideal for driving pager motors or other electroncs such as video transmitters. At ~0.3g without the wires (SS30 supplied) it is pretty light.

That should do the trick...
Ill be posting some stuff soon...Im just geting back into it been out a while

Sep 05, 2004, 03:14 PM
Registered User
RNAF's Avatar
Don't want to steal your thread, Nachman but everyone is focused on a small, smaller, smallest fan. Why not make a somewhat larger fan to fit 50cm (19.7 inch) span jets?
I mean, you have those motors like aerogel gave us and they give, I think, relatively more thrust that the smaller ones.

Does any of you know how much a fan of 4 cm (1.6 ich) diameter with a N-20LV could produce of thrust?

Sep 05, 2004, 03:47 PM
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RNAF's Avatar
Oh yeah, I found out that the largest diameter may be 5cm or 2 inch.
The aiming point as AUW is around 40-50, say 45 grams.

Sep 06, 2004, 10:47 AM
Frequent Poster
Pete P.'s Avatar
I'll agree with Aerogel, that DC-DC booster would really make a difference. Even if you fry a motor every 10th flight, it's still worth it to make a really high performance jet :-) And how is it going over there anyhow? I had no idea they take you a whole weekend to make! I always thought a CNC was just you slide the block to be milled in, turn it on and go eat some food! Man, was I wrong!
Sep 06, 2004, 07:23 PM
Registered User
Pete, you thought right, but that will be the case with a machining center ( which I don't have ) after it's been set up for the job. There you have automatic tool changing system, full time cuting fluid flow, and a fifth axis for working on both sides of the part. For making one stator and impeller set, I need to go over this whole process: Perfactly align the raw materiall . Put an edge finder to get exact position of the part center so that I can get that same exact center when working on it's other side. Since the blades are so thin there is not much place for initiall position error. Then change all these tools manually: center drill, 0.8mm drill, 1.3mm drill, 6mm drill and 2mm flate end mill. Turn the part over, re-aligned it, find the center again, put back the 2mm end mill, and let it do it's job while purring some cuting fluid from time to time.
And it takes a lot of mchining time since all surfaces are curved now, and to get a resonable smooth surface, every cut the machine makes is of only 0.1mm. And the use of a small end mill doesn't let you go fast either, or it will brake.
And then there are the rest of the parts. The shroud is manually done on a lathe, and the spinner, the motor side end cup and heat sink are also cnc made, though much easier and faster. Here goes the weekend...

The DC-DC won't help here. I've tried to increase the voltage above 4.2, and the motor quickly got hot was ruined.
Sep 06, 2004, 07:36 PM
Registered User
I'm currently working on a new lighter frame. I hope to get it down to 2.5 grams. Did the main wing so far. This time it's better made (I'm learning...). It's one piece now, stronger and lighter ( came out 1.33 gr ). Has a closed D box through out. Also it's 8mm longer ( 245mm now).
Sep 06, 2004, 07:45 PM
Registered User
hehe... yes CNC machining is not quite as easy as it seems.... it can take an hour to get the raw material aligned properly ! then you have to go about changing end mills and what not because one kind can only do so much etc.. etc...
Sep 06, 2004, 07:56 PM
Registered User
I also really suggest an Intake ring.... for small fans even as big as the wemotec Microfan thrust losses can be up to like 30% if the ring is ommited!
Sep 07, 2004, 07:03 AM
Make something. Anything!
bgriggs's Avatar
Very nice job on the fan unit so far. One thing still concerns me. I notice you have a 4 bladed fan and a 4 bladed stator setup. Most ducted fans use one less stator blades than they have fan blades. Example: The Rojet fan has a 4 bladed rotor and a 3 bladed stator. The Minfan 480 had 5 blades (if memory serves) and 4 stators. Tom Hunt once mentioned this need to me, I no longer remember the aerodynamic reasoning behind it though.

Sep 07, 2004, 08:16 AM
Registered User
RNAF's Avatar
Nachman, about the wing.
Is the "cover" all .5mm?
How about the leading edge, how did you make that, it looks like a solid block?
The ribs, are those 1mm?

How about strenght? Is is more/less/equally strong?

Sep 07, 2004, 09:20 AM
Registered User
Dave: The "cover" is about 0.35-0.45 mm thick and the ribs are about 0.8mm. All is from the lightest weight balsa I could find. The leading edge is actually the "cover" rolled over the ribs. Was tricky to do, but the balsa wood was flexible enough to take the curve without any special method and without cracking ( didn.t have to soak it in water and stuff like that ). Then I added short stripps between the ribs to form a closed D shapped tube. That gave the wing very high tortional resist. It's probably all over due in strength, but I will probably crash a lot and want it to survive longer.
Bill: I wish I new that before. Now I've already started making some more funs for another flying craft and it's to late to change, but thanks for pointing it out. Will do it right next time.
Ssyed: I do have an intake ring now. Small one tough, but better then sharp edge. Didn't want to make it bigger then that.
Sep 07, 2004, 09:56 AM
Registered User
RNAF's Avatar
Nachman, could you make more pics?
I'm working on my own 24.5 cm span (about 10 inch) Hawker S** *a**... (don't tell anyone )

So far it doesn't need to be radio controlled, but flyable.

That's why I'm asking you for more detailed pics of your wing construction.

Did you sand your balsa yourself? Like 1mm balsa and you sanded off the half?

Sep 07, 2004, 01:56 PM
Registered User
RNAF's Avatar
Another lil' question: how thick (or thin ) is your wing?


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