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May 26, 2006, 06:51 AM
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Build Log

Simple Jet


Hi

So far I have built and flown several parkjets including Steve's F-15, F-18.

All of them were very nice designs and they flew well. But I don't like flat wings also I wanted sth. simple so I decided to build this little jet.

Wingspan ~ 90cm
Length ~ 65 cm
Wing Area ~ 27dm2
Approximated ready to fly weight ~450-500grams

It will be an only Aileron setup which I will need 2 servos.

Power system:

BM 2408-21 (this is like one of those BP motors and has 1700rpm/v if I remember correctly)
1800mah, 3S lipo
GWS 8x6 slofly or 8x4 HD propellor.

I hope this cheap setup will give adequate performance(in theory it does!)


So far I have cut several parts and assambled the wing part. Here are the pictures:
Last edited by RedLabel; May 26, 2006 at 05:34 PM.
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May 26, 2006, 07:22 AM
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Hey like it so far looks a bit like mine...


Here are a few versions of mine and an IC version
May 26, 2006, 10:43 AM
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Quote:
Originally Posted by acr007
Here are a few versions of mine and an IC version

Beautiful planes Acr. And interestingly shape is very close to mine(But I did improvised mine ).

Well I am thinking of 1 tail instead of 2 in parallel. Also as you can see mine will be a low winged version. Do you have any suggestions?

Do you like yours? How do they perform?
May 26, 2006, 11:50 AM
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Now working on the fuse. It seems stronger then I thought which is a good thing. I am trying to use as few parts as possible.

Here are some more pictures:
May 26, 2006, 05:36 PM
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Some more updates:

Mounted the tail, added the right air intake.
The weight of the current state is about 85grams.

Here are the pictures to the ones who are interested (if any ).
May 26, 2006, 05:49 PM
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LBMiller5's Avatar
Looking good! Keep the photos coming!

Will you be posting plans once you are done?


One question? I did not notice any kind of wing spar in the construction. Are you going to imbed a carbon fiber spar in the wing somehwere, or are you relying on the strength of the foam by itself? If you don't plan on using a spar, you had better at least use some strapping tape on the outside of the wing for strength. I would hate to see the wing fold in half at the bottom of a loop!

Lucien
Last edited by LBMiller5; May 26, 2006 at 06:07 PM.
May 27, 2006, 06:55 AM
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Quote:
Originally Posted by LBMiller5
Looking good! Keep the photos coming!

Will you be posting plans once you are done?


One question? I did not notice any kind of wing spar in the construction. Are you going to imbed a carbon fiber spar in the wing somehwere, or are you relying on the strength of the foam by itself? If you don't plan on using a spar, you had better at least use some strapping tape on the outside of the wing for strength. I would hate to see the wing fold in half at the bottom of a loop!

Lucien
Thanks Lucien. If the maiden goes well I will clear the dxf files, put some comments in and release the plans.

Yes I did NOT use any spar in the model. Actually this is one of the reasons why I choose a profiled wing over a flat one.

So far I have build lots of depron wings and up to 90-100cm length two 3mm sheets and some 6mm reinforcements between make a strong wing. Here the blue one is 5mm and the green one is 2.5mm, and the result seems adequate.

But as you suggested I am planning tor reinforce it afterwards. If the result is fine I am going to glass it with 0.75oz cloth which I think give enough strength.
May 27, 2006, 06:58 AM
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Update:

The nose and the intakes are quite finished. I think I am going to install the equipment today, maybe there will be a maiden tomorrow .
May 27, 2006, 12:06 PM
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Now since the wing profile is not symmetric I am thinking of 1 degree of upthrust for the motor mount. Any suggestions?
May 27, 2006, 07:14 PM
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Yes Ladies and Gentelmen, I know that you've been waiting for updates so here it is( ). Mounted the motor(But still needs reinforcement) and ailerons. Tomorrow it will be completed I guess...
May 27, 2006, 08:50 PM
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LBMiller5's Avatar
Before you put on the top sheeting, you might want to cut some cooling holes through the fuselage sides into the intake tubes. This will allow some of the air going through the intakes to enter the inner fuselage and help cool the ESC and Motor. Without any airflow, the heat will stagnate inside the fuselage and the ESC will run warmer than normal, as will the motor.

If you cut out a rectangular opening, and angle the cuts slightly, it will form somewhat of a scoop to help pull the air into the central fuselage. It does not take much air to get rid of the heat generated.

Just a thought!

Lucien
May 28, 2006, 06:57 AM
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Quote:
Originally Posted by LBMiller5
Before you put on the top sheeting, you might want to cut some cooling holes through the fuselage sides into the intake tubes. This will allow some of the air going through the intakes to enter the inner fuselage and help cool the ESC and Motor. Without any airflow, the heat will stagnate inside the fuselage and the ESC will run warmer than normal, as will the motor.

If you cut out a rectangular opening, and angle the cuts slightly, it will form somewhat of a scoop to help pull the air into the central fuselage. It does not take much air to get rid of the heat generated.

Just a thought!

Lucien
Thanks again Lucien, you are the only one who is interested in this.

I was thinking just the same thing. Will put some holes between before covering it.

Actually another idea I was thinking was to use 2 bp motors driving 6x5 or so giving good thrust and high pitch speed at about 20A max. Again cheap setup but can give nice results.
May 28, 2006, 08:24 AM
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I've had 2 BP-21s. One was in Steve's F-18 and I have one in a King/Alley/HouseCat clone I'm flying now. They are decent motors for what they are though quality can be hit or miss. First motor was way out of balance and the second one ran fine. In my F-18 I ran a 2220 3cell with a 8x4 prop. Plane flew OK on this motor. About the same performance as the GWS 350 on 3cell. The sweet spot for this motor is a 8x4 and a 3cell. I don't think with a 6x5 prop you will get that much from this motor and at 20amps you'll burn it up! - Unless you are talking about a different motor? If you are looking at a cheap motor combo, take a look at the 2409-18. Little bigger an more powerful. I have one in Steve's Super Bandit, 2220 3cell and 9x6 prop, and it flew nicely (only one flight so far). By the way, I built the Bandit with a symmetrical airfoil and think it fly's better than the F-18 did, especially in turns. Probably comparing apples to oranges but I'm sold on symmetrical airfoil over the flat plate.flys better than the F-18 did, especailly in turns. Probably comparing apples to oranges
May 28, 2006, 09:29 AM
TGK
TGK
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Redlabel,

Very nice job so far. I am anxious to see how it flies.

Tim
May 28, 2006, 01:45 PM
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Quote:
Originally Posted by WDuck
I've had 2 BP-21s. One was in Steve's F-18 and I have one in a King/Alley/HouseCat clone I'm flying now. They are decent motors for what they are though quality can be hit or miss. First motor was way out of balance and the second one ran fine. In my F-18 I ran a 2220 3cell with a 8x4 prop. Plane flew OK on this motor. About the same performance as the GWS 350 on 3cell. The sweet spot for this motor is a 8x4 and a 3cell. I don't think with a 6x5 prop you will get that much from this motor and at 20amps you'll burn it up! - Unless you are talking about a different motor? If you are looking at a cheap motor combo, take a look at the 2409-18. Little bigger an more powerful. I have one in Steve's Super Bandit, 2220 3cell and 9x6 prop, and it flew nicely (only one flight so far). By the way, I built the Bandit with a symmetrical airfoil and think it fly's better than the F-18 did, especially in turns. Probably comparing apples to oranges but I'm sold on symmetrical airfoil over the flat plate.flys better than the F-18 did, especailly in turns. Probably comparing apples to oranges
Thanks for the advice. Actually I'm not thinking to use those cheap brushless motors until the plane flies stable.

But I think there is a misunderstanding here. I was talking about 2 BP21 in parallel. I guess with 6x5 or 7x5 props I can get or exceed the thrust I am getting from one bp 21 with 8x4 while having better pitch speed. Of course by 20A I am referring to the sum of the current flow from both motors.

Also I am thinking of using the two motors in opposite directions so I can eliminate the torque roll and hence have more stable flights at a wide range of speeds.


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