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RE: ARF Mig 21 Interceptor propjet - 3/31/2007 6:49 AM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		CRUMBS.

Talk about upping the anti--

Latest suggestion is NEU 1912/2Y on 12S 4900 Li Poly, 10 x 10 prop, for 16200 rpm and 2 KW. Speed 150 mph.

Given the drag of that thick wing, the above might be nearer the mark.

(any millionaires around).

OP.

< Message edited by oldpilot -- 3/31/2007 6:50 AM >

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RE: ARF Mig 21 Interceptor propjet - 4/1/2007 1:02 AM   
bob27s



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Status: offline 		from an aircraft drag / prop / speed point of view, a 12" diameter tends to work out about right. 10" will be spinning you wheels. An 11" is possible (one of those Vmars flying with a 90LX that I know of). From a physical point of view, it looks like 13" diameter is about the limit.


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RE: ARF Mig 21 Interceptor propjet - 4/1/2007 3:38 AM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		PROPS are as cheap as chips, (as compared to the cost of brushless, ESC, Li Polys etc

So for fifty bucks or so you can try a whole bunch of different props and play a game of "Suck it and See".

Judging from all the different experiences on these three threads, it would seem that 12" Dia is the most popular. Perhaps it's just a matter of experimenting with the pitch values to find a trade off between current draw and top speed.

A 10" prop may be a little less efficient at the higher RPM , but may also be more desirable in terms of ground clearance and less intrusive appearance. Don't forget we are talking about smooth electric power here, so the prop is not subject to the shocking accelerational vibrations produced by a single cylinder IC engine. An APC Pattern prop for instance is easily able to handle the 16K rpm suggested by the Neumotors motor performance program.

Cheers. paddy.

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       Post #: 128

RE: ARF Mig 21 Interceptor propjet - 4/1/2007 5:04 AM   
haze_b



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From: honolulu, HI, USA
Status: offline 		Aloha Paddy,

You can save a lot of time and money on your electric conversion by using "Motocalc" or a similar program. These programs detail performance info based on whatever power system options you enter. This allows you easily compare various setups. I've found Motocalc to be very accurate (if a bit consevative) and has saved me a lot of money. If it prevents you from wasting money on just a single bad setup, it pays for itself.

Just a my 2 cents........

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RE: ARF Mig 21 Interceptor propjet - 4/1/2007 12:18 PM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		Thanks Haze_b.

I do have Motorcalc but have found it to be a bit off when predicting brushless motor performance. This is particularly so in conjunction with ducted fans. Otherwise it is pretty good.

Cheers. paddy.

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RE: ARF Mig 21 Interceptor propjet - 4/13/2007 4:16 PM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		Well the ARF kit arrived.
Opened it up and pawed thru the contents. Horrified at size. Quickly put it away until after Easter. Filled the hole in the cowl with a backing of clear plastic sheet followed by a fitted piece. Looks OK, but needs to be painted. Like the Idea of turning the cowl so the patch is on the bottom.
Last Wed I started putting it together and six fractured hours later it sat all assembled on the glass dining room table. Had no problems at all with assembly, except I see what they mean about the rudder shaft binding.
Next morning I photographed it, and spent the rest of my free time trolling for information so I could get a handle on the motor/esc/battery/prop configuration. With the AUD at an all time high I thought I better buy something so ordered a Hyperion Z-4045-10 motor, a backmount and 12 x 10 APC Pattern prop. Thats all I could afford until payday, so the battery, RX, bec, retracts etc: are going to have to wait for a few days. Pics soon.

Cheers. Paddy.

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RE: ARF Mig 21 Interceptor propjet - 4/15/2007 4:22 AM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		Well. Just to give you an idea of how big this plane really is ---here is the basic airframe assembled.



That glass table is an eight seater dining table, just for size comparison.



Couldn't hang on the "Shockwave Cone"(AKA Spinner) as I havent got the motor to attach it to --yet.

While the Aus $ is so high I am going to order the new 25C batteries which Aircraft-World have in stock as of yesterday.

Cheers. paddy.


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RE: ARF Mig 21 Interceptor propjet - 4/15/2007 6:17 AM   
JEFFHINES73



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From: sheppartonVIC, AUSTRALIA
Status: offline 		Old pilot

Where did you get yours from i have been looking for one for wahile and cant seem to find one ?

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RE: ARF Mig 21 Interceptor propjet - 4/15/2007 8:07 AM   
oldpilot


 

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Status: offline 		JEFF.

I got it from Don at The Australian Model Arodrome. Nth Fitzroy. Melb. He had two in stock, and I took one of them.

His Ph # is (03) 9489 8383. Tell him I sent you and he will probably give you a good deal. I think he is keen to move stock.

I paid $495.00 plus shipping to Sydney---two big boxes. My kit was flawless and everything fitted together perfectly.

Cheers. Patrick.



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RE: ARF Mig 21 Interceptor propjet - 4/16/2007 4:56 AM   
Blockbuster


 

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From: Jacksonville, FL, USA
Status: offline 		I'm glad to see at last someone will do an extreme speed prop jet electric conversion. Pat, I hope you will finish this project soon and have a camera crew on stand by. Keep me posted how it will come out. Did you deside on the motor/prop combo yet? Will you use a retracts?

< Message edited by Blockbuster -- 4/16/2007 4:58 AM >

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RE: ARF Mig 21 Interceptor propjet - 4/16/2007 10:16 AM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		Yes Blockbuster. I have already ordered some of my stuff while the AUS doller is still high.

Hyperion Z-4045/10, CCP 85 opto ESC, 2 x HP-LVX 25C 5S 5000mah Li Pos in series, 12 or 13 x 10 APC Pattern prop; (subject to experiment). Will need a switch BEC or auxillary battery for the 8 channel RX. I have already sourced/ordered the Robart air retracts.

So far I am up to the tedious bits --like threading all the servo linkages etc: I am using all standard servos.

Did not find the rudder the problem I expected from the experiences of some on this and other threads. Just needed to burnish the rudder axle wire, take the pressure off the plastic tube by sanding the nose of the fin, and relieving the bottom of the fin at the forward end so that the fin sat down firmly on the interior structure, but didn't show above the fuselage spine. Rudder works real easy now.

BACK TO THE COAL FACE.

Cheers. Paddy.

< Message edited by oldpilot -- 5/4/2007 4:51 PM >

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RE: ARF Mig 21 Interceptor propjet - 5/4/2007 1:31 PM   
Robert Groves


 

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From: Johannesburg, SOUTH AFRICA
Status: offline 		Anyone got any info on the Tiger? F5E
This ARF looks good and I'm thinking of making it a new project.

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RE: ARF Mig 21 Interceptor propjet - 7/31/2007 7:23 AM   
Blockbuster


 

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From: Jacksonville, FL, USA
Status: offline 		Paddy, did you fly your MIG 21 yet?

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RE: ARF Mig 21 Interceptor propjet - 8/11/2009 4:50 AM   
Dieselman1220



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From: Mcallen, TX, USA
Status: offline 		I know im bringing up a really old thread but I have been after this ARF for 6 months now Richmond RC just keeps telling me its backordered and now they are saying November. GRRRR anyone know what the hold up is?

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RE: ARF Mig 21 Interceptor propjet - 8/11/2009 10:06 AM   
oldpilot


 

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From: Church Point, AUSTRALIA
Status: offline 		I still haven't finished mine yet.
I have had a problem with a mismatch between the threads on the prop adaptor and the hexagonal extension.
Also I am not familiar with air operated retracts and am finding it a little bit difficult to sort out where to put everything, (given the 2 massive 5S 5000mah batteries and the air tank.) CG is going to be a headache.
Am beginning to wish I had used the very nice fixed undercarriage, but then it is so unscale to fly around with dangley bits hanging down.

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RE: ARF Mig 21 Interceptor propjet - 8/11/2009 11:23 PM   
JS615


 

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From: Old Hickory, TN, USA
Status: offline 		I was told a few months back that there is a balsa shortage in vietnam,,, something about all the balsa is going to make the huge wind mill blades for power generation.,,, could just be BS.

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