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View Poll Results: Is a 15cm (6") aircraft with a 10g payload possible
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Old Nov 06, 2003, 04:15 PM
Registered User
jberg's Avatar
MSC Rödinghausen, Germany
Joined Feb 2001
954 Posts
Matt (Keenon this time),

Quote:
Originally posted by Keennon
You might find it has a natural rolling oscillation which is usual for very low aspect ratio wings. You might experiment with different size vertical fins, and maybe on the bottom instead.
I have experienced this with a very small delta. Is this the reason why the microbat has the fins on the lower side? I think it looks a bit oddly and have wondered about it.

Regards, Jochen
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Old Nov 06, 2003, 04:41 PM
Lithium Member #2
Electric Aircraft World
Joined Nov 2001
297 Posts
Quote:
Originally posted by Eco8gator
But there are far lighter servos, receivers and speed controllers out there now than what we used/had access to 2 years ago
Gator,

not quite correct.
The Jmp 0.7 g esc, the Westek Servos
at 2.4 g and the Skyhook rxs at 2.4 g
were all available two years ago.
As a matter of fact, only in recent
months have mass market servos
( Cirrus) and RXs in that weight
class been made available.

The biggest advance are
the Lipolys in itself.

www.homefly.com sells this super
micro stuff since years.


- Gigawatt
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Old Nov 06, 2003, 05:13 PM
Faroe Islands/Germany
epilot's Avatar
Joined Nov 2000
5,980 Posts
Quote:
Originally posted by gigawatt
Gator,

not quite correct.
The Jmp 0.7 g esc, the Westek Servos
at 2.4 g and the Skyhook rxs at 2.4 g
were all available two years ago.
I beg to differ. We now have Falcon servos (1.7grams), JMP RX (2.2 grams incl. ESC)
That is 5.6grams total. The equipment you mention is 7.9grams. So the new stuff is 30% lighter, not to mention cheaper.

Michael
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Old Nov 06, 2003, 10:04 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,438 Posts
I second Epilot and Eco8gator. We do have lighter equipment.

The pair of 1.3g Gasparin-Didel servos I have on my workbench right now were not available two years ago.

The 2.4g SHR receiver was and is very wide band (I have one). The newer receivers are narrow band and light and sometimes include a ESC at that weight.

Also, the Wes 2.4 servo weighs more than 2.4g with the JST Plug and wires. The Falcon 1.7g servo is a true 1.7g including the wires and plug.

Gordon
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Old Nov 06, 2003, 10:33 PM
Lithium Member #2
Electric Aircraft World
Joined Nov 2001
297 Posts
Gentlemen,
you are correct.

The new Didel and falcon servos
are, if I am not mistaken,
available since this year?

The question is though, how robust are they?
I have used westeks since about four years
and they survided rough handling
and many crashes.

- Gigawatt.
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Old Nov 06, 2003, 10:53 PM
Registered User
Gainesville, Fla
Joined Aug 2002
125 Posts
I was accidentally posting as gator anyways
The skyhooks receiver’s range over stated for some of our applications we needed well in excess of 500m range and we settled on a gws with a full wave hair thin antenna or a plantraco both are heavier(we still experiment with others). As far as durability we found that westek servos are not a good option for us long term every landing is a crash for us and ever flight is a crash and any medium sock to the main spur" gear would knock it off, or any force on the rod more than a typical flight load would jam the worm gear so we only used them in extreme circumstances also in a given season we can build dozens of aircraft and with 2 servos each we can’t really get that westeks to build new planes and replace the broken ones we generate.

We crashed so many times this year that the winning plane ended up with a gws and lighten hs50's. We went out to the competition with about 3-4 planes equipped westek but through the wind and repeated flights they were unflyable without at the field major surgery.

We haven’t had a chance to test the durability of microjoules falcons or didels (you can bet they are on order) or the new 2.4g penta receiver that the other members drooled over when I showed it to them. But you can bet they will see more than their fair share of crashes

Edit to add the motors draw a pretty hefty amperage from our batteries so every new battery tech that comes out helps us in someway (lighter, more C's,more capacity...etc).
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Old Nov 07, 2003, 11:12 PM
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
Matt,

Here are a few pictures of an MAV configuration that has worked well for me in sizes 8" to 3". It is based on a "trochoid" shape which has a fixed largest dimension between any 2 points, but is not circular or spherical. This shape has favorable aerodynamic properties for MAV's which are size constrained and works well at low Reynolds numbers. I have a paper on my web site describing some of the sizing issues affecting MAV's, but it was written in 1997, so the conclusions on propulsion choices no longer apply:

http://www.spyplanes.com/publications.html

The model in the photo is a 3" sheet balsa glider that is used to test stability and control factors. It glides nicely from a brisk hand launch and is very stable.

Steve Morris
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Old Nov 07, 2003, 11:13 PM
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
Front view...
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Old Nov 07, 2003, 11:13 PM
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
Top view showing the trochoid shape.
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Old Nov 10, 2003, 06:53 PM
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
For what it's worth:

I installed an M-20 motor, a cut down GWS propeller, and a Kokam 145mah battery and tried to fly the 3" plane free-flight. It flies a slow circle (descending) for about 5 seconds before touching down at walking speed. It wants to trim at high angle of attack and really hangs on the prop. It needs more power to haul the 12.4 grams of weight.


Steve Morris
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Old Nov 10, 2003, 11:34 PM
Team 30 Micro EDF
Mike Taylor's Avatar
Camarillo, California
Joined Apr 2002
4,516 Posts
Is that prop on correctly? It looks backwards.
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Old Nov 11, 2003, 12:09 AM
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
Mike,

I don't think its on backwards, it rotates counterclockwise when viewed from the front. Maybe it just looks wrong in the photo.

Steve
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Old Nov 12, 2003, 02:43 PM
Registered User
Houston, Texas
Joined Nov 2001
112 Posts
Steve Morris,

I have a couple of questions on the MAV glider that you presented. What is the white tab on the rudder of the MAV? You used the term "trochoid" with reference to the shape of the MAV. I see a similariity in the shape of your MAV glider to the shape of a rotor for a Wankle engine. However, the trochoidal shape of the cavity of a Wankle engine within which the rotor rotates is the portion of the engine that has the trochoid shape and not the rotor. Thus your comment on the shape of the MAV being trochoid in shape has me confused. Is there some way that you can define or describe the shape of your MAV?

It is apparent that the two sectiions of the MAV glider differ in size, what are the relative dimensions of the two sections?

Thank you for your assistance.

Bryan Swinney
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Old Nov 12, 2003, 08:47 PM
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Palo Alto, California, United States
Joined Jan 2003
1,080 Posts
Bryan,

When I last looked this up the shape of the Wankel rotor was called a "trochoid". I think the shape of the volume it rotates in is an "epitrochoid", but I may have this wrong or backwards. To form a Trochoid draw an equilateral triangle whose side is the dimension of the trochoid you desire. Rotate each leg of the traingle about a vertex and the other end of the leg will trace the curved edge of the trochoid, which now contains the equilateral triangle.

The model I built is 3" in size and the wing's leading edge is cut back to make room for the prop. The wing chord is 1.65" and the tail chord is 1.3 ".


Steve Morris
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Old Nov 13, 2003, 08:03 AM
Registered User
Houston, Texas
Joined Nov 2001
112 Posts
MAV Project

Steve,

Apparently we are victims of a historical misapplication of technical terms as an internet search for the two terms, trochoid and epitrochoid, show that the definitions of the two shapes do not coinside with the terms used as applied to the Wankle engine components.

If you are curious as I am, you might take a look at the computed examples provided by the following URL:

< http://curvebank.calstatela.edu/cycl...ds/OidEG1.html>

With that put aside, your MAV glider design is intriguing. Why did you choose the Wankle engine rotor shaped instead of a standard right triangle? How did you develop this unique concept?

Just to be sure I have the correct concept, a right triangle (Equal sides and equal included angles) has its three sides reformed by striking an arc from each of the three corners that scribes an intersection of the opposing two corners - is that correct?

The photograph did not show the difference of the chords to the wing and tail, it appears that the two sections produce one complete "trochoid," when viewed from the top. From the photograph, the wing section chord appears to be two times as deep as the chord of the tail section. Is that accurate?

Is the small white rectangle piece on the tail a trim tab? What was its purpose as to flight control? Roll stability or turning control?

I gather from your comment on the powered version that the power train did not provide adequate speed for flight due to the high wing loading. Is that correct?

As I have a large supply of foam sheet, I would like to experiment with the shape myself. Your MAV glider is simply one of those things I have to try out myself.

If you do not already have a subscription to the publication, Radio Control MicroFlight, you might look into it as it has the latest information on equipment for ultra light construction. MLBCO projects are often featured in this publication.

Thank you for your time and patience,

Bryan Swinney
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