RC Bipe Under 2 inches - Page 2 - RC Groups
Thread Tools
Aug 21, 2014, 11:13 PM
No more nicotine for me!
micro_builder's Avatar
That is ridiculous! Quite impressed with its speed and maneuverability, you must have some good eyes to keep track of it buzzing around. The crash in the first take made me cringe, but no mass=no damage. The tweezers holder on the TX is a nice touch. Really nice work as always.

Nick
Sign up now
to remove ads between posts
Aug 22, 2014, 03:33 AM
Registered User
Quote:
Originally Posted by Martin SJ
- RobT on torque reaction. Yes, this is a significant problem on small planes but can be fixed with lots of right thrust and offsetting the whole fin to the right. Just don't try gliding.
Martin
Martin, thank you for the advice on side thrust and rudder offset. Do you know roughly how much of both you have used here ? I have looked at your pictures again and it is hard to see.

My [failed] attempts to date with really small stuff rely on lots of incidence and thrust so with the power off they plummet rather than glide!

Rob
Aug 22, 2014, 07:07 AM
Free foamie low waste plans
Airlight's Avatar
This is just beautiful, you are a master of the miniscule. I'm pretty sure if you could 'kitify' it, you would have a great many takers. I wouldn't know where to start with this. Just to clarify, did you make the Rx as well?

Stunning, well done.
Aug 23, 2014, 01:44 AM
Registered User
Martin SJ's Avatar
RobT on right thrust - Sorry, should have been more explicit. It's 6 degrees right thrust, 6 degrees downthrust and 6 degrees right vertical stab angle. I established these amounts on my 4.4" Spitfire, and they have worked well on the 4.6" P-51 and on Bipe-50. The vertical stab is attached to the fuselage only as far as half way back from the LE, and there is a vertical crease line at the half way point. The rear half of the vert stab carries the actuator and rudder. This lets me bend the vertical stab to adjust the right trim by relatively large amounts. The throws on the rudder are extremely small, nowhere near enough to use for trim.

Airlight on the Rx - Yes, I make my own receivers. I developed the Rabbit Rx back around 2007. It uses the 900 MHz band and frequency hopping technology, (hence the name - Rabbit, hopping ... never mind). A "normal" one weighs 115mg though I have made many variations. There's an old thread at
https://www.rcgroups.com/forums/showthread.php?t=754973
Nick Liechty makes them now and you can buy them from him at
http://microflierradio.com/Receivers900.html

Martin
Aug 23, 2014, 03:49 AM
Registered User
Martin, thank you for the numbers. It never occurred to me to leave part of the fin not stuck down in front of the rudder to use for trim, a genius idea.

Hs it ROGed yet ? I suppose a float version is bonkers!

Rob
Aug 23, 2014, 05:41 AM
Registered User
Chapeau!
Aug 23, 2014, 11:50 AM
Registered User
Martin SJ's Avatar
I finally came up with a name that I like - Thumbkin. I've edited the first post with the reasons.

RobT - I should have mentioned, wing-stab decalage is 6 degrees also. No ROG yet, but then, I haven't tried again.
Aug 24, 2014, 05:00 AM
Free foamie low waste plans
Airlight's Avatar
Good name choice Martin, Thumbkin would be a lot of fun to have on my desk at work. I have seen the Rabbit Rx before (I didn't realise you were the creator), but way out of my price range for now I'm afraid. Thank god they come with wires attached though, my soldering would destroy one of these in a heartbeat

Not quite the point I know, but is there any likelihood of plans for this, to make a bigger one? I've got a lot of quite thin eps sheet that weighs almost nothing, I think I could get a pretty light airframe if it was even 8-10" wingspan.
Aug 24, 2014, 03:44 PM
Only nerd in the village
There is a more moderately priced alternative in the DelTang Rx46 and it can be used with a proper transmitter:
http://www.deltang.co.uk/rx46.htm
Aug 30, 2014, 12:04 AM
Registered User
Nice work Martin.

Reminds me of the Amethyst Falcon.

Cheers
Dave
Sep 01, 2014, 08:03 AM
Registered User
Martin,

How long is 'Thumbkin' and do you have a rule-of-thumb (pun intended) for horizontal stab size versus main wing size ? From your photos the horizontal stab looks about half of the main span and about the same chord, is this by design, experience or just looks right ?

I find this really small stuff fascinating.

Thank you
Rob
Sep 01, 2014, 08:07 AM
Free foamie low waste plans
Airlight's Avatar
Quote:
Originally Posted by epilot
There is a more moderately priced alternative in the DelTang Rx46 and it can be used with a proper transmitter:
http://www.deltang.co.uk/rx46.htm
Thanks epilot, I've seen the DT stuff on Micron Radio Control, but I'm afraid it won't work with my Plantraco Tx, and I'm not able to shell out on anything new just yet. Sorry to be a bore, if I had more (any) budget, I think I'd go for something a bit bigger anyway. Much as I would love to be able to make this tiny stuff, mine always look like a wire grenade went off when I start adding RC kit, not yet refined my capability in this area.

Anyway, not to detract from Martin's great achievement, I will just say thanks for sharing, I wish I could make my own look this good, this small.
Sep 01, 2014, 06:45 PM
Registered User
Martin SJ's Avatar
Airlight on plans - I have attached a pdf of the plans

Dave - I had never seen the Amethyst Falcon , but you're right, it does look similar.

RobT on rule of thumb for size of horizontal stab - Smaller planes need proportionally bigger hstab and vstab areas, around 50% more than true scale. I have never heard a good layman's explanation for why this is. If anyone has an explanation I would like to hear it.

The relationships I developed for my own use some time back are:
Dh * Ah = 1/4 * Aw^1.5
Dv * Av = 1/8 * Aw^1.5
where
Aw = total wing area
Ah = area of the hstab
Av = area of the vstab
Dh = distance from the centroid of the total wing area to the centroid of the hstab
Dv = distance from the centroid of the total wing area to the centroid of the vstab
I know, I should be talking about the center of lift etc, but I don't know where that is. For Thumbkin:
Dh * Ah = 0.234 * Aw^1.5
Dv * Av = 0.124 * Aw^1.5
Sep 02, 2014, 04:50 AM
Registered User
Martin,

Thank you for the maths, I can see why your stuff always works so well. I am familar with the classic centre of lift / centre of gravity 'balance' diagram but it is very useful to see your practical numbers especially for the very small stuff.

Do you know if this still works well for nearly square wings (span = chord) ?

Thank you for sharing your hard work,
Rob
Sep 09, 2014, 08:32 AM
Free foamie low waste plans
Airlight's Avatar

Colourful Thumbkin...


Martin, I hope you won't mind these. I'm quite taken with little Thumbkin, and have started my first go at building an 8" WS version. I did some liveries, and got a bit carried away. If you'd rather they were'nt on here, let me know, I'll delete them.

All should have your moniker on them, as far as I'm concerned I just did some colouring in. Anyone wanting to play with them, I just use a program called Paint.NET for my graphics, it's really easy to use, so you could get these and recolour/shrink/expand them, and break up the image for printing at your prefered scale.

Hope you'll enjoy
Last edited by Airlight; Sep 10, 2014 at 07:50 AM. Reason: Just a couple more..


Thread Tools