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Old Dec 08, 2009, 10:44 AM
It only takes one good idea
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Fishers, Indiana
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Build Log
A-7D Project

This is my A-7 Design Log, that will become my Build Log

Here is some of my design development 3D's and CAD. As I said I will not be doing anything with this design (maybe when I am traveling) until the B-36 is in the air. This will be a duel design, My 101" span A7-D, and a 36" span A7-D.

If I had to guess I would say this design will be done around December. And that depends on the B-36.
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Old Mar 04, 2011, 06:49 PM
It only takes one good idea
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Fishers, Indiana
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I will update this as I get more of the design done.

Thanks, Dag
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Old Mar 04, 2011, 07:00 PM
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Old Mar 04, 2011, 07:38 PM
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OK Dag,

Found the video on Jack's site, the link is here:

http://www.flylowandfast.com/Files/V...20(High_L).wmv

The file is a little large but worth the download. You will notice that Rob does not use partial throttle very much during the flight, it's nearly like he has it on a two way toggle

Regards,

- Birger
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Old Mar 04, 2011, 08:14 PM
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Old Mar 04, 2011, 08:49 PM
It only takes one good idea
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Fishers, Indiana
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Quote:
Originally Posted by bdelapen View Post
OK Dag,

Found the video on Jack's site, the link is here:

http://www.flylowandfast.com/Files/V...20(High_L).wmv

The file is a little large but worth the download. You will notice that Rob does not use partial throttle very much during the flight, it's nearly like he has it on a two way toggle

Regards,

- Birger
Is the way he uses the throttle because he wants speed, and not to burn up the ESC/motor? When I flew DF I was always between 50-70% power except on take off.

Also I found out with DF that once you had the plane clean and in the air it did not take a lot of power to fly the plane scale. If you wanted to go fast you just screamed around at full power. And I understand that most EDF's can't run at 100% for long with out getting hot.

If I take on this project I will do a ton of testing, but what I want to find out is if you have a plane with a huge wing (this would have 2,049 square inches) and have a very clean airframe, and has extremely efficient systems what would it take to really fly it. I have learned long ago that to fly scale takes much less power than most put into planes now days.

Thanks Buddy,
Damon
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Old Mar 04, 2011, 08:58 PM
It only takes one good idea
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And another thing.

After watching that video 3-5 times, that plane is so clean that it most likely hits max speed very efficiently, and fast. There is no drag on that plane and there for would not need a mid throttle setting to hold speed. I bet the EDF set up would fly twice the weight of that aircraft if it had twice the wing.

That is a great jet, but no way is it a scale flight. He seems to only use the power to hit a speed he is aiming for, then uses energy management to glide, until he hits the turbo-boost to hit his speed.

Very cool jet, but for what I am looking for way over powered.

Also keep in mind, the DF of the 80's were very under powered, we flew the wing, and had to stay a mile ahead of our jets. , kind of funny, that's the way the real ones were.

Thanks, D
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Old Mar 04, 2011, 09:31 PM
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Quote:
Originally Posted by dag214 View Post
Is the way he uses the throttle because he wants speed, and not to burn up the ESC/motor? When I flew DF I was always between 50-70% power except on take off.

Also I found out with DF that once you had the plane clean and in the air it did not take a lot of power to fly the plane scale. If you wanted to go fast you just screamed around at full power. And I understand that most EDF's can't run at 100% for long with out getting hot.

If I take on this project I will do a ton of testing, but what I want to find out is if you have a plane with a huge wing (this would have 2,049 square inches) and have a very clean airframe, and has extremely efficient systems what would it take to really fly it. I have learned long ago that to fly scale takes much less power than most put into planes now days.

Thanks Buddy,
Damon
So the main issue is currently the ESC's. There are not a lot of ESC's that can take that kind of power for long periods of time. The second thing is how ESC's generate heat, there are two components to how ESC generate heat:
  1. One is dissipation from the current passing through the transistors, higher current = higher heat (this is many times not the most critical component).
  2. The second is the heat generated from the actual switching, transistors only consume power when changing state (switching) thus generating heat during all these transitons.
This basically means that the worst heat generation in the ESC is typically between 60% and 99% throttle position when the ESC is in PWM. Now most of this problem will go away once ESC's have the ability to better take the power but right now 8000W is about where the technology has gotten.

Anyway, we can have a long discussion about this at SEFF

Regards,

- Birger
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Old Mar 05, 2011, 05:45 PM
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Old Mar 06, 2011, 07:18 AM
It only takes one good idea
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Fishers, Indiana
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Hey all,
I have gotten a ton of e-mails this weekend from guys sharing info on this project.

A guy that flys a system shared some numbers with me. He stated that if I want a targeted thrust I also need to know what tail pipe speed I need. He stated that the efficiency of the system will rely on the fan used, and all my ducting. He also shared some thoughts about in coming/out going are volume. I already have some of the formulas used on full scale, but because most of those can go super sonic it doesn't really work at this scale. Also a real jet only needs a small percentage of incoming air as the out going is expanded hundreds of times from combustion. EDF are just suck and blows. He also stated that there are not that many EDF guys that fly in a scale manner. He stated that the EPX system on 12C will pull under 120 amps and have at least 16 pounds of thrust, and that there are plenty of controllers out there that can handle that. He said the castle I used on my A-100 would work.

My design is going to be very aggressive as in the starting stage of the fuse it will be built in 2 halves to allow for as perfect at possible ducting system to be placed in side.

DAG
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Old Mar 06, 2011, 10:23 PM
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Very good. Happy. OH yeah... Excited to see this one.
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Old Mar 06, 2011, 11:01 PM
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Been following the B-36, definately following along with this one.
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Old Mar 07, 2011, 09:48 AM
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I'll follow this one too! I was on the USS Midway yesterday, which has an A-7 on the flight deck. I'm actually embarrassed to admit I am not really familiar with the A-7, but it is a nice looking plane. BTW, if you're ever in the San Diego area, the Midway is a must see. We didn't get there until around lunch time, and half a day really is not enough time for even a "fast" visit. I probably missed the audio tour for 75% of the planes, didn't read a lot of the displays, and didn't get to hear any docent talks. I think I could easily spend 2 full days there.

Here's a pic of the A-7 - I thought I had more, but I guess not. If I'd known about this thread before I left I would have taken a lot more to post.
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Old Mar 07, 2011, 06:26 PM
It only takes one good idea
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Fishers, Indiana
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Quote:
Originally Posted by bdshort View Post
I'll follow this one too! I was on the USS Midway yesterday, which has an A-7 on the flight deck. I'm actually embarrassed to admit I am not really familiar with the A-7, but it is a nice looking plane. BTW, if you're ever in the San Diego area, the Midway is a must see. We didn't get there until around lunch time, and half a day really is not enough time for even a "fast" visit. I probably missed the audio tour for 75% of the planes, didn't read a lot of the displays, and didn't get to hear any docent talks. I think I could easily spend 2 full days there.

Here's a pic of the A-7 - I thought I had more, but I guess not. If I'd known about this thread before I left I would have taken a lot more to post.
Very cool picture, Thanks!

I travel out there about 4 times a year, but never seem to have time to see anything cool. I will have to see the carrier though.

Thanks, DAG
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Old Mar 07, 2011, 06:40 PM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
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I have had some wonderful e-mails about this project, just wanted to say thanks for the info and support to all that like the A-7.

One e-mail I got was about how I go about my designs.

First I do the rough math of the airframe, then I size it to a power system that will give me a .25-1 to .5-1 power ration. My Emmaselle had a .3-1 on takeoff, and a .16-1 at cruise. She was a draggy pig and flew on the wing. So what I look at (and has worked for me all except once) is what will the plane need to fly in a envelop that will allow a good climb at takeoff with 100% power, but also cruise at level flight and make shallow turns at about 45-65% power. I have always pushed my designs to be light. Using bargain contest grade balsa, and CF I can build really light. Using CF tube on main gear struts also saves weight. When I am laying out a design, and I look at all the data on its size and weight, it is then at this point I look for the power system, then take the data of that system and scale the size of the airframe to that data.

It kind sounds like I am saying two things at once, and I kind of am. Knowing the material of what will make up the aircraft will give you a weight target, then when I find a close power system I then tweak the size for that power system, do I sound crazy yet. Or.... once I find a power system I know is cool and has some good data to support it, I size the airframe to that power system

I am going to try to share all of my design steps in this thread with this aircraft. I hope it does not get to boring, but I hope some will find it helpful.

Rock On!

DAG
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