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Old Sep 30, 2012, 10:45 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,372 Posts
Quote:
drag goes up as the square of the speed, ie drag at 30 = 1, at 60 = 4, pretty severe penality for increasing speed!
Yup, cutting the speed to 35mph would mean their power system only needs to produce a quarter as much thrust... And that means they need to use just a bare fraction of the power because prop drag follows the same squared relationship.

One thing I notice about this project, and about many long-distance FPV flyers in general, is that the preferred airframes are often very inefficient for their purposes. If I had to come up with a plane for maximum flight distance, I would do a few specific things.

- Airframe would be a deeply swept, high aspect ratio flying wing with a thin airfoil. Balsa construction would keep it light. The motor and prop would be mounted in a pusher configuration for FPV purposes, but the sweep allows them to be placed very far back from the wing's trailing edge so I could run a big prop in relatively clean air. There's an F5B competition wing that someone built in this format and it appears to perform extremely well, and in my opinion this is one of the most aerodynamically efficient designs possible.

- I'd use a high-Kv inrunner motor with a light gearbox to drop the effective shaft Kv down to useful levels. Doing this allows the use of a smaller, lighter motor than would be possible if I were to go with an outrunner of similar performance abilities.

- I would base the power system on voltage rather than current to reduce the weight of the wiring and ESC needed. I would go with low-discharge lipos (~15-20C packs) since they're usually lighter and I would have zero need for sustained high current. The power system would be designed to cruise at full throttle to minimize ESC heating and losses; this ain't a sport ship so flying at half throttle and having a bunch of extra power on tap would only hurt efficiency.

If these guys are serious about this project, I suspect they'll have to think a little bit outside the "usual" stuff.
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Old Sep 30, 2012, 11:43 PM
Promoting Model Aviation...
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United States, CA, Tehachapi
Joined Nov 2005
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Thanks for the historical references. Definitely good to know info.

I do think a smaller gasser would be perfect. And they would be able to meet their 1.5 hour flight times for sure. But I guess they want to do this with battery power.

I haven't seen any new comments from these guys on their site. Sure would be nice to get some feedback from what we have discussed here and to see if they have decided a different approach.

Frank
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Old Oct 01, 2012, 01:30 AM
Build to Fly? FLY to BUILD!
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United States, AZ, Gilbert
Joined Nov 2009
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Quote:
Originally Posted by Murocflyer View Post
I haven't seen any new comments from these guys on their site. Sure would be nice to get some feedback from what we have discussed here and to see if they have decided a different approach.

Frank
Did I mention that they don't really care to acknowledge help?

An inrunner on a gearbox would work, but in this particular scenario, I think a mid-low kv outrunner with a big, very high pitched prop would be ideal. From a reliability standpoint, there is much less to go wrong with an outrunner than an inrunner with a gearbox. From an efficiency standpoint at any appreciable speed it would be more efficient running a steep prop compared to a shallower one, being that there is very little acceleration required to keep going at that speed.

A steep prop will be less efficient in climb out, but more efficient in cruise.
A shallow prop will be more efficient in climb out, but less efficient in cruise.

The plane would have to be seriously stiff, which isn't too hard in modern times. A wing would be a possible solution, their current plane (the Shrike? I think) is a nifty idea, but its just not going to cut it. The shape of the center section is way too draggy. A bigger wing would be far better for the application.

If the wing's thickness at the center was thick enough to hold all of the gear, with room to spare, there's no reason that they couldn't pack something like 6 or more batteries in the wings with no real consequences.
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Old Oct 01, 2012, 01:32 AM
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They post videos once a week at DiyDrones. They're still trying to master their Ardupilot, telemetry setup. They make little adjustments and additions all the time. I'd expect when they think theyre ready, they'll know what the plane can or cant do and then the search will be for the right airframe/power.
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Old Oct 01, 2012, 05:36 AM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
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While I agree their project may be overly ambitious at the moment, never underestimate a determined person. A model aircraft was successfully flown from Kitty Hawk NC to Ocean Side CA in 1975 by AMA Hall of Fame Member Bob Rich and his wife Doris.

The aircraft used were two Carl Goldberg Models Senior Falcons named "Liberty Bell" in honor of the US 1976 Bicentennial and were modified to carry 32oz fuel tanks.

The flight was made with the sponsorship of many modeling companies and the AMA. One of the Liberty Bell's is now in the Smithsonian Institute in Washington DC and the other is at the AMA Museum in Muncie IN.

There's very little new under the sun

Azarr
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Old Oct 01, 2012, 10:56 AM
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United States, AZ, Mesa
Joined Jul 2007
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Quote:
Originally Posted by C₄H₁₀ View Post
One thing I notice about this project, and about many long-distance FPV flyers in general, is that the preferred airframes are often very inefficient for their purposes. If I had to come up with a plane for maximum flight distance, I would do a few specific things.
Many FPV folks use gliders which are very efficient, but part of the fun of FPV is flying fast and low through the trees or something - it's something you just can't do with a full scale plane. So, many setups are designed for that, and they take them on long distance flights to test their system (distance is a badge of honor in the community). So you have to keep that in mind, that many of us aren't really interested in distance just for the sake of high numbers, and we pick planes that are fun to fly instead. Building a plane that could fly 10 miles away and exceed the limits of your system isn't the goal, but testing the limits sometimes is.

For a cross country flight though, FPV equipment would just be extra weight.

Quote:
Originally Posted by Azarr View Post
While I agree their project may be overly ambitious at the moment, never underestimate a determined person. A model aircraft was successfully flown from Kitty Hawk NC to Ocean Side CA in 1975 by AMA Hall of Fame Member Bob Rich and his wife Doris.

The aircraft used were two Carl Goldberg Models Senior Falcons named "Liberty Bell" in honor of the US 1976 Bicentennial and were modified to carry 32oz fuel tanks.

The flight was made with the sponsorship of many modeling companies and the AMA. One of the Liberty Bell's is now in the Smithsonian Institute in Washington DC and the other is at the AMA Museum in Muncie IN.

There's very little new under the sun

Azarr
Yeah I knew somebody had already done this... I was 4 years old and I still remember
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Old Oct 01, 2012, 12:12 PM
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United States, FL, Lehigh Acres
Joined Aug 2011
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i'm not seeing it but good luck.
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Old Oct 01, 2012, 12:59 PM
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Beaumont tx
Joined Oct 2004
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FWIW, we had a guy in the club who flew a Kadet Sr on an old K&B .19. Took forever to get off, but once airborne, it flew forever on a 6 oz tank. That is "flying on the wing." I've gotten 45 mins on 6 oz on my Seniorita/OS 20 combo.

howell
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Old Oct 02, 2012, 05:52 AM
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United States, FL, Masaryktown
Joined Jun 2008
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Originally Posted by Murocflyer View Post
I bet they could do this if they map a route of AMA fields across the US from the west coast to the east coast. Then they could have a large field to land on and no worries about people getting in the way.
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Originally Posted by Murocflyer View Post
And with 2,500 AMA clubs all around the USA
Forget using AMA chartered club fields if it is not flown under AMA guidelines. If the intent is to set or establish some type of record the aircraft design criteria is not allowed in aeromodelling but is allowed in the UAV category (See attached). If the AUW can be kept under 5kg (11 lbs) it would qualify as U1a Electric.

Regards
Frank
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Old Oct 02, 2012, 09:58 AM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
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Again, for special projects the AMA issues specific waivers for a worthy purpose. They do this many times a year for different events and could be persuaded to do so here, I'm sure.

Same with the FAA. Get a heavy-hitting Senator to catch fire and watch 'em knock themselves out trying to help. They're apt to have some mighty good ideas too.

The FAA as enemy thing is a whole-cloth creation of the AMA in its drive for membership. Don't buy that pig. The FAA can be bureaucratic but it is not inherently evil. The AMA may tend to demagoguery and taking credit for deeds not their own but they also are not inherently evil. Both organizations can be perverted to do good with the right carrot and the right cattle prod.
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Old Oct 02, 2012, 10:08 AM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
Using 5 pounds and 1.5 hours flight as fixed data points, the rough available power would be about 20-25 watts per pound. This comes from using a 6 cell LiPo pack of 8000mah, the best fit battery I can come up with to meet the fixed data points of weight and duration.

70MPH on 20-25 watts per pound... this would be a good trick.

It never fails to amaze me how a "goal" is set (like the grand cross-country flight) and then options that should be variable to achieve the stated goal become fixed themselves... making the first goal an impossibility. Focus on the goal and anything is possible. Focus on an assortment of goals and things get overwhelming very fast. (Kind of reminds me of what it's like to do business in this world of heavy regulations today - no wonder so many things seem impossible ;-))
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Old Oct 02, 2012, 03:24 PM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
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I read these guys as practical and flexible. That means they will adjust and go toward their goal of flying coast to coast. They'll make whatever changes they need to make the flight possible, both in equipment, specifications for the flight and in legal matters.
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Old Oct 07, 2012, 11:01 AM
Promoting Model Aviation...
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United States, CA, Tehachapi
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Originally Posted by Rockin Robbins View Post
Again, for special projects the AMA issues specific waivers for a worthy purpose. They do this many times a year for different events and could be persuaded to do so here, I'm sure.
Yup, I don't see a problem with it at all. I'm sure any club would be happy to participate in this adventure.

Frank
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Old Oct 07, 2012, 03:24 PM
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Wilkes-Barre/Scranton, Pennsylvania, United States
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Should they succeed in this effort it would not be recognized as a record. To qualify the flight must be witnessed by an official within the FAI framework.

BM
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Old Oct 07, 2012, 05:20 PM
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ohio
Joined Oct 2010
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Originally Posted by Murocflyer View Post
Yup, I don't see a problem with it at all.
I do, all it will take is for this thing to go out of control and kill someone while it is flying over a park or population center and we can kiss this hobby goodbye.
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