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Old Feb 05, 2011, 10:07 PM
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Doug I am working on it ... takes a while to upload the HD video to youtube ... one more hour or so.
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Old Feb 06, 2011, 04:08 AM
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I've been quietly following and admiring your work herb
You know I am a video-maniac myself, so my jaw was dropping when I fired up youtube and saw your baby as newest vid to my subscriptions.

Im am still sitting here, drooling...the video is great, and the flight and landing is just perfect!

Maximum respect!

I Hope you don't mind if I put your video into this thread for all the others to see this awesome piece of work
MiG-21 MF (Fishbed J) 100mm EDF (4 min 4 sec)
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Old Feb 07, 2011, 06:30 PM
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Hi Steffen,

Thanks for the comments, and for posting a link to the video

Here are a few more stills I extracted from the video,

.
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Old Feb 07, 2011, 06:39 PM
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... and a couple of pictures I took at the Prado field, before and after the two flights.

.
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Old Feb 08, 2011, 11:51 AM
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... the first flight required quite a bit of trimming, esp. on the ailerons. It was a bit touchy on the ailerons too. But I think it took off & landed with no issues.

Four of us were involved in the maiden, Doug A flying it, Gregg F working the trims & rates, Joe C spotting, and me focusing on taking the video

I did not want to use flaps on the first flight, this I will test in the next weeks to see if elevator compensation is needed - and how much.

It seems though that if you have enough elevator throw and the right CG (which seems to be the case ) you can pull up the nose quite a bit to slow it down on landing ...

Nevertheless, even with that long asphalt runway, it uses up most of it ! Maybe I need a parachute and brakes.

The original MiG-21 has a set of three huge airbrakes under the belly.

The speed is good, but I think I might get it to go a bit faster if I choke down the outlet a bit more. But then not bad for a $19 fan with a $110 motor and a $130 esc though.
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Old Feb 10, 2011, 12:28 PM
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... and here's the maiden flight video.

The video quality is a bit poor since my hd camera was still on the wrong settings (lcd display mode).
But on the whole I think the maiden went pretty well - given all the uncertainties of a scratch built.

MiG-21 EDF (100mm) maiden flight (2 min 48 sec)
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Old Feb 11, 2011, 10:37 PM
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Congrats Herb! Where's the drag chute?
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Old Feb 12, 2011, 12:37 PM
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I'm working on that ...

I also looked at the Kavan electromagnetic brakes, but they are way too big for the MiG-21's wheels:

http://www.hobby-lobby.com/wheels.htmBrake.htm

http://www.kavanrc.com/cgi-bin/dpsma...rch_02Index_01

With some patience I can probably make a similar, but smaller, set myself. The designs seems quite simple & lightweight.
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Old Feb 13, 2011, 08:43 PM
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Beautiful plane...I always liked the MIG-21 and never saw a model that I liked...until now. The intake is always too large and out of scale, but you solved it here very professionally. The MIG-21 has that same look as the ME-262/ME-109, you know, an indifferent cold predator stare saying 'I'd rather just kill you and leave you lying there'...IMO...and you darn near ran out of runway...

Joe
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Old Feb 14, 2011, 11:11 AM
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Thanks for the comments !

Yes indeed the MiG-21 does have that mean predator look ... The shock cone on mine is actually hollowed out at the bottom to allow more air to come in.
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Old Feb 16, 2011, 05:53 PM
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Hi Jonathan,

What airplane gyros do you use these days? I have some (3) older MPG-6 cirrus ones ($30 at the time at HP)

http://store.alshobbyshop.com/browse...iezo-Gyro.html

with a pot to adjust the gain, but they don't seem to like my futaba FASST FS617 receiver !!

The servos tend to go full right if I increase the gain past 50% or so , so there's a serious trim issue [They are NOT digital servos].

Did you have the GWS ones? If not, what type and where did you get them? Did you try the Hobbycity Ones

http://www.hobbycity.com/hobbyking/s...idproduct=9094

or

http://www.hobbycity.com/hobbycity/s...idproduct=9093

Mine look a bit like the first one (PG-03J).

Thanks HWH

EDIT: I see, you have these :

http://www.hobbycity.com/hobbycity/s...idproduct=6755

How did you get them to work with a Futaba FASST receiver ? Mine are perhaps too ancient ... but I thought they worked fine for me on good old 72 MHz

.
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Old Feb 16, 2011, 08:51 PM
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Hey Herb. I didn't do anything special to make them work with the FASST Rx. I just plugged them in. One thing I noticed though, was that you can't use the variable dial (CH6) as your gain channel. You need to plug the gain control into one of your two-way switches. I can't explain this as it makes no sense to me why it won't work on the variable dial. You can plug it into a two-way switch channel, and adjust the endpoints to get better control of the gain (like as if you were turning the CH6 knob) and it would work that way too. Weird.

If you are new to gyros, then all you really need to know is that if you send a low signal (1ms pulse) through the gyro's gain channel, the gyro interprets it as 0% gain, essentially "off". If you send a high signal from the Tx (2ms pulse), then that is 100% gain.

Things are different with a heading hold gyro. A low signal from the Tx is 100% gain in "rate" mode. A neutral signal (1.5ms pulse) is 0% gain. A high signal is 100% gain in "heading hold" mode.

On my Otter, I have rate gyros on the rudder and elevator, and a heading hold gyro on the ailerons. All gain wires from the gyros are tied together and plugged into a single channel that I can control. You can only imagine how tricky it was finding a proper setting for the gain since I'm using two types of gyros. For example, if I send a mid-low pulse of 1.25ms, the rate gyro is at 25% gain and the heading hold gyro is actually working like a rate gyro at 50%. If I send a neutral signal, the rate gyros are at 50% and the heading hold gyro is off. Make sense? Not being able to turn all the gyros off in flight is a little risky, especially during the initial setup. Good luck.

By the way, where are you going to use a gyro?
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Old Feb 17, 2011, 12:20 AM
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Jonathan, Thanks for the detailed reply !

So which gyro brands/types are you using ... one is the type I linked above, and the other?

I was indeed confused by the product description/discussion of the above $18 HK gyro which on the one hand has adjustable rate, yet does not work on a knob, only on a switch. Weird.

I am thinking of trying a small gyro on the aileron channel in the MiG-21 ... but I don't trust the Cirrus one I have.

Also, don't think I really even need to adjust the rate on a channel, a pot set on 40% or so should be fine. I have flown edfs with gyros on the ail and the sweet spot is usually around 40-50% rate, not more, above that they tend to overcorrect.

The Hobbico gyro below I had for a long time (since 2003) and have occasionally put in in jets (the JePe A-4 below), it is german made ("ACT wingo gyro", http://www.acteurope.de/Fuzzyenglisch.pdf ) and, besides adjustbale gain on the ch 6 knob on my Futaba 9c, also allows for flapperon mixing (2 ail connections).

This Hobbico/ACT one also seems to still work fine on 72MHz - but not on the fasst fs617 receiver !

http://www.rcgroups.com/forums/showp...&postcount=164

.
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Old Feb 17, 2011, 07:52 AM
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The gyro on my Otter's ailerons is the Assan 410 that I picked up from HK. It does drift often and usually requires at least one retrimming during flight. On my helis I use the Spartan Quark and the JR 770. Both of these are much more pricey, but they are rock solid and precise. I don't think you need gyros to be this precise for ailerons though.

Depending on the difference between your landing speed and your cruise speed, you may want to be able to toggle the gain of the gyro. DUring initial setup, I think it is very important to be able to toggle the gyro off. I've had setup flights where there was way too much gain, so it was nice to be able to just shut the gyro off until I landed.
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Old Feb 17, 2011, 11:17 AM
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Thanks again ... Yes high gain is not fun, that's why I start from zero and go gradually up, tx knob or gyro pot.... past 40-50% I never use.

Well somebody else seems to have the same problem I have, trim changes when the gain is increased:

http://hobbyking.com/hobbyking/forum...s.asp?TID=2513

Does not state what radio he has though. Seems a common malaise.

EDIT:

I think I now figured out part of my problem ... on the gyro I use (MPG-6) it does NOT like that you adjust the gain while the gyro is plugged IN, it wildly changes the trim.

The correct procedure is : to turn the gyro or receiver OFF, adjust the gyro gain (higher or lower), and THEN turn on the rx or gyro ON again. Now no trim changes after power up !

.
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