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Old Sep 17, 2009, 11:57 PM
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Daren's Avatar
Los Alamos, NM, USofA
Joined Nov 2000
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Weird. I think having that many magnets is good, especially with the fan blast blowing right on the splitter plate.

One can get used to it looking like a Voodoo, that is until one sees a Phantom.

Daren

Quote:
Originally Posted by DanSavage
Thanks, Daren! Even though it looked right, I got so used to how it looked with out the splitter plate that when it and the hatch were mounted on the airplane, I thought the plane looked chunky in the back. Now, I've gotten used to it and it looks okay.

I had a weird experience while I was building the hatch. As I was sanding it to shape, I had to keep pushing it back into place and every time I did, it squeaked the sound of wood rubbing against wood.

I traced the sound to the front bulkhead of the hatch. So, I would sand the mating surfaces between the hatch and the fuselage bulkheads and it was still squeaking!

Then I realized the magnets were what was causing the two surfaces to be so tight, they squeaked. After this, I stopped sanding.

Dan
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Old Sep 18, 2009, 09:36 PM
It wasn't me...
DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,559 Posts
Quote:
Originally Posted by Daren
Weird. I think having that many magnets is good, especially with the fan blast blowing right on the splitter plate.

One can get used to it looking like a Voodoo, that is until one sees a Phantom.

Daren
We'll see when I run up the fan. The hatch/splitter plate comes off the model really easily. With the model upside-down, I just grab the front and pull up and it pops off. It goes back on easily, too. I just have to be careful when I put the front down because the four magnets really want to snap it into place. That's why I thought just one pair would be better.

And the Voodoo is a pretty cool looking airplane in its own right. It's got the coolest wing planform. It'd probably make a great-flying model.

Dan
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Old Sep 18, 2009, 11:30 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
20,647 Posts
it will act to pull the tail down and nose up ....the JHH F-4 has a very scale inverted cambered airfoil on there's but i think it may have some down thrust,too not sure i'll have to dig the plans out
Oh ..the build look great looking forward to how it all works out
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Old Sep 19, 2009, 12:20 AM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Thanks!

Yeah, the full-size designers use inverted airfoils on the stab to reduce trim drag. As an aside, the F-4's wing airfoil is a stab airfoil that I flipped over. I tried it on Daren's Beluga and it works great. Real smooth-flying, fast airfoil. I chose it because it had a deep enough belly way back with enough room for the retracts in the airliner wing planform. I liked how it flew so much, that it's now my favorite jet airfoil, which is why I used it on the F-4. I'll probably use it again, too.

When I was designing this model, I recalled reading from some source that models of the F-4 flew better with an inverted airfoil on the stab.

I do know that Daren's F-4, on which this one is based, used a flat-plate set to zero-degrees incidence and it was a great flying model.

So, I decided to try the inverted flat-bottom airfoil, but made the stab removable, just in case I need to replace it with a stab that has a symmetrical airfoil.
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Last edited by DanSavage; Sep 19, 2009 at 12:34 AM.
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Old Sep 19, 2009, 11:01 AM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Quote:
Originally Posted by AIR SALLY
it will act to pull the tail down and nose up ....the JHH F-4 has a very scale inverted cambered airfoil on there's but i think it may have some down thrust,too not sure i'll have to dig the plans out
Oh ..the build look great looking forward to how it all works out
Can you describe what you mean when you use the term, 'down thrust'?
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Old Oct 04, 2009, 11:42 PM
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Trabuco Canyon, CA
Joined Nov 2000
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Yay! It's on its feet!

Although I haven't posted anything recently, I have stayed busy. The work I've been doing is all assembly and internal fitting type work.

The wings are glued on. The retract holes have been cut into the bottom of the fuselage and wings. I built the nose gear strut and bent the main gear struts and mounted the wheels. I did a final rigging on the nose gear steering.

The horizontal stab is aligned to the wing. The vertical stab is aligned and glued into place.

I slathered on some light spackle to build up the aft engine fairing. This will be built into the production kit. I also filled all the little gaps here and there.

I just need to sand off a little bit of spackle and then the model will be ready for the covering/finishing phase. Yay!
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Last edited by DanSavage; Oct 04, 2009 at 11:50 PM.
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Old Oct 05, 2009, 09:08 AM
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eatond's Avatar
United States, MO, St Charles
Joined Nov 2002
1,744 Posts
Hi Dan,
It looks very nice. Hurry up and slap some paint on her, I want to see this fly.
What paint scheme you going with?

Dan Eaton
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Old Oct 05, 2009, 09:40 AM
I make bad look so good.
SteveC68's Avatar
League City, Texas
Joined Sep 2006
2,516 Posts
Quote:
Originally Posted by DanSavage
Can you describe what you mean when you use the term, 'down thrust'?
I think he means the exhaust nozzles are pointed down slightly. Since the engines were pretty much below the CG then the plane would tend to go nose up when you apply throttle. In the real deal the engines were tilted slightly down so that the thrust would counter the pitch up tendency.
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Old Oct 05, 2009, 11:07 AM
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Larry Dudeck's Avatar
Williamsville, NY, USA
Joined Sep 2000
4,483 Posts
"...But, yours and everyone else's kits will be correct..."

I've known for some time that I need to try a 90mm design.

I also knew I wanted an F4, even made some preliminary layouts.

I was thinking a decent kit would be nice for a change as opposed to rolling my own.

Then I started following this thread.

I think I've found the ideal solution to all three items with your excellent F4
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Old Oct 05, 2009, 10:10 PM
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Daren's Avatar
Los Alamos, NM, USofA
Joined Nov 2000
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Oh man, how did I miss this?!!

Looks very nice, Dan. The fillet really adds to the look of the F-4. From here on out, it will keep looking better and better (not that it doesn't look phabulous now! ).

Daren
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Old Oct 05, 2009, 10:17 PM
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Daren's Avatar
Los Alamos, NM, USofA
Joined Nov 2000
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Quote:
Originally Posted by SteveC68
I think he means the exhaust nozzles are pointed down slightly. Since the engines were pretty much below the CG then the plane would tend to go nose up when you apply throttle. In the real deal the engines were tilted slightly down so that the thrust would counter the pitch up tendency.
So is this up-thrust or down-thrust?



In reality, it's just the opposite from what you write. On my Beluga, the thrust line is well below the CG, but having the nacelles level or upwards would have introduced up-thrust.

Pointing the nacelles down gave the needed down-thrust to counter the natural tendency gain altitude under power. When the thrust is pointed through the CG as in the zero-length launch, or in this case, the F-4, it pushes the airplane whichever way the thrust is pointed.

I can't say for sure, but it may be that the up-thrust was introduced by pointing the nacelles down so that the full-sized F-4 behaved like a normal airplane; throttle controls altitude and pitch controls speed.

Daren
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Last edited by Daren; Oct 05, 2009 at 10:24 PM.
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Old Oct 05, 2009, 10:19 PM
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lavochkin's Avatar
Mokena,Illinois -United States
Joined Oct 2006
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Damn Dan!!!! That really looks nice!! No Joke. Cant wait to see her fly.
Brg, Joe
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Old Oct 05, 2009, 10:35 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,559 Posts
Quote:
Originally Posted by eatond
Hi Dan,
It looks very nice. Hurry up and slap some paint on her, I want to see this fly.
What paint scheme you going with?

Dan Eaton
Thanks, Dan.

Since I'm so close now, I'm going to start putting some time in on it during the evenings so I can get it finished.

How else would I finish it?
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Old Oct 05, 2009, 10:40 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Quote:
Originally Posted by SteveC68
I think he means the exhaust nozzles are pointed down slightly. Since the engines were pretty much below the CG then the plane would tend to go nose up when you apply throttle. In the real deal the engines were tilted slightly down so that the thrust would counter the pitch up tendency.
Yeah, it's pretty tricky when it comes to jets. With prop-driven airplanes, it's cut and dried. With jets, you're firing the thrust line through the length of the airplane and where the thrust line is in relation to the mass of components determines whether it's up or down thrust.
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Old Oct 05, 2009, 10:45 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Quote:
Originally Posted by Larry Dudeck
I think I've found the ideal solution to all three items with your excellent F4
Thanks, Larry.
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