iron eagel

Well after correcting my math ( I was a factor if ten off) it not as bad as I originally thought. But still even for charging it take a lot to really be of any usable benefit to you, and then we are only talking 400 mah at that rate it would take you ten hours to recharge the batteries.

iron eagel

A thought regarding wing flex.
I would be thinking of using both a forward spar and one aft as well for your wings. I would make them up with unidirectional carbon fiber spar caps top and bottom of the spars separated with a balsa shear web that is reinforced with omnidirectional carbon fiber tissue (or veil) on both sides of the webbing. With the dual spars on the wings using the carbon fiber as the spar caps should give you a very stiff wing.

As far as battery performance v temperature, is they any data from the previous flights that you have access to, that would help in determining your needed battery capacity, if not do some testing.

BMatthews

WOW! We haven't has such a popular and short term active thread in a long time! Two pages in less than 12 hours!

Your numbers for the size and weight and wing loading all seem just fine. They are right in the ball park with some of the bigger gliders found on the market. But if you can I'd suggest stretching the span and aspect ratio a bit more to something more like 16 to 18. At the size and weight you're looking at the Reynolds numbers will be high and support this somewhat more sailplane like planform for a higher efficiency.

I like the idea of the twin spar design as well. Even if you go with a vacuum bag style wing a pair of inner span forward and rear carbon or similar spars will provide the sort of structural strength and stiffness you need for the tail booms as well as the inner half of the wings.

As noted already the angle of attack is set by the flying speed. I think you meant to ask about the angle of incidence. Ideally you would want the fuselage to sit in the most direct into the airflow angle as possible for the portion of the flight that the model needs the most efficiency by reducing the drag. To my thinking the mission you're considering is a mostly up then down sort of deal with only a minimal portion of the flight at any given altitude while collecting. Then it's "back to the lab". You'll need to crunch some numbers to determine a valid climb angle and airspeed and from that determine what the wing's lift coefficient will be. For motor battery effiency you'll want to look at climb rates that are between the airframe's minimum sink speed and the best L/D speed to see where the max altitude per watt occurs.

I know that for my free flight models the best altitude comes from climbing at as close to the minimum sink speed as I can manage. But those are rather draggy models and the same may not hold for this case. A part of me says "minimum sink" for the climb speed but another part is yelling that you want to cover more distance in the climb so the best L/D speed would give more hieght per watt. You'll want to look into this aspect with more attention since so much of the flight time will be spent climbing under power.

I'd simply forget about the solar cells. I doubt you'll be in the air long enough for any sort of meaningful solar contribution. The way to tell is to figure out how long your flight mission will be. If the solar cells can supply more watt-hours per ounce than a similar weight increase in lithium motor cells can provide then fine. But if, as I suspect, a similar weight added to the battery pack results in more watt-hours of energy carried aloft then your answer is clear. Pack in the lithium cells and to heck with solar cells for this application.

If you feel guilty about not "going green" then cover the roof and one side of the flight support van in solar cells. Aim the whole lot at the sun at your starting point and let the solar cells charge the battery bank which you then use to charge the flight packs for the plane. By soaking up the solar energy and moving it into some storage batteries you'll reduce the amount of solar energy that heats up the inside of the support van. So that'll reduce the amount of air conditioning needed in the van. At the same time it means less gas burned to keep the charging bank up. A win-win all around.

beepee

Here is my thinking ...

Build up a really nice motor/glider and dispense with the BIG batteries, telemetry, and whatnot. Take it to the local airfield and find a guy tinkering with his Bonanza. Offer him this really neat power/glider if he will take you up to gather a few air samples. Much cheaper and quicker way to go about it!

Just kidding, keep at it!

Bedford

bpbrinson

You could "re-invent the wheel" which is fun but often gets in the way of the real project. Or you could purchase this UAS and/or consult Skip Miller Models in Colorado. He has worked w/ several universities. The Tempest has more than enough room for all your FPV/telemetry and anything else you want to stuff in it. Designed just for the type of project that you describe. http://www.youtube.com/watch?v=N8Lb9...RiJ5vA&lf=plcp

http://www.skipmillermodels.com/
http://uasusa.com/ "recently achieved a very successful mission with flights exceeding upward of 10.8 miles above the surface of the earth..... and returned safely to the launch site 38 miles upwind." 57,000 Feet!!!!

I am sure with UASUSA's background working w/ universities would give a leg up in the approval process w/LSU.


Brooks

Shoe

Definitely consider Hofstadter's law in this project:

Hofstadter's Law: it always takes longer than you expect, even when you take into account Hofstadter's Law.

You can make an aviation corollary to this law by replacing "takes longer" with "costs more".

Seriously, I think a manned option might be cheaper, quicker, and more flexible in terms of accessible airspace (not saying this just because I make a living flying airplanes). I do suspect the manned option might be more administratively burdonesome (getting your payload approved for wing mounting) and less fun.

rmh

A little food for thought
We have designed a number of models for contests whre the total outlay in time and money -for the flyer - is substantial.
The biggest single part of each design was always "how do we reduce weight whilst retaining necessary strength.'
fussing about best airfoils? - - just make it as thin as possible .
The higher you go - the faster it must fly-to get same lift - so the airfoil is a compromise -always. Ideally the wing would have an adjustable camber - but THAT is heavy.
The one thing that is a proven constant - the lighter it is the less the airfoil matters .
Once you get all the hardware sorted out - get a guys who is really sharp at structure and then layout the strongest ,lightes setup
if it is light enough -the other 'fine points don't matter.

IflyPATTERN

Hey Guys,

Im glad yall like the idea of a double wing spar- I already had that in mind. Now, as for the solar cells- i will have to do more research and calculating.

Bpbrinson, the glider you have shown looks nice! However, i believe you underestimate the air sampling capability this thing needs. We arent just talking about strapping on some pitree dishes outside- no, its a lot more complicated than this. A plane designed for this application in mind will collect better data- and that fact is even more important than the altitude it reaches. Thanks though!! Im really liking the info im getting guys- keep it coming.

as for the construction of this bird... Well luckily im neighbors with two of some of the countries best- Bryan hebert and Randy Hicks. i will have plenty of good advice in that department...
www.hebertcompetitiondesigns.com

Brandon



As for the full scale solution- this a has already been tried. Though it sorta works, no one has yet to build a full scale plane meant for this application- so once again the quality of the data suffers.

shoe, I like your law! Ill have to add that one to murphy's

iron eagel

I have to agree with Dick's and B Matthews last posts, the most bang for your buck is going to be to keeping the structure as lightweight as possible, while maintaining the strength.

And just to throw out another option rather than using a full scale aircraft is, if speed is not an issue what about a dirigible type of delta aircraft? With the need for high lift offset by by gas in internal bladders your AUW would not be as much of an issue. You may see now why balloons have been the staples of both weather and atmospheric research for years.

While the engineering challenges of such a project may be daunting, it is by no means impossible...

bpbrinson

I have worked as a consultant for many years on UAS projects. If you could be more specific as to payload/equipment, perhaps I/we could be more help. I have seen a project that resembles what you may be describing. In the late 90's, a group of UT students brought out a 1 meter square fine nylon"screen" in a pvc pipe frame to my dropzone and asked/hired a couple of skydivers to freefall with it. Never heard the results, but did see some very small spiders w/web and a grasshopper in the screen. I could see the problems w/ that method, took several thousand feet for the skydivers to get it stable (huge drag). The "vertical sample" being the biggest problem to sort out. Contamination from close to ground during landing. Loss of material if not handled properly by the skydiver landing with it (turned backwards) ect... More details would be helpful.

Brooks

BTW, my wife is a LSU '90 grad, CJ degree

IflyPATTERN

Specs thus far: ( all theoretical at this point )

Wingspan: 14Ft
Wing Area (main wing- 2028 sq in) + ("t-canilizer winglet"- 250 sq in)= 2,278 sq in
Total TRF weight projections: 15-20lbs.
Batteries: 2x5S 25C 5,000-6,000 mah
Motor: 3,000 watt (likely a Neu motor
Propellor: Folding ??x??

iron eagel

A couple of my fellow club members work for this outfit: http://www.aurora.aero/Index.aspx
you may see something there that gives you some ideas.

Yes, for what your doing the double spar seem to be the way to go, you may want to add diagonal ribs as well for torsional strength. With your wing twist and flex are going to be an issue.

IflyPATTERN

Also, on the building light/strong sugestions: being a pattern pilot will help me in ths area. WE all know the means us pattern guys go to indorder to save an gram or two, let alone an ounce. I hope I can really build this ship even lighter than fifteen pounds... but I am still being conservative for the time being, which is why I threw the 15-20lb range for now. I dont expect my "microbial" equiptment and FPV system to add any more than 2-3lbs to the equation... I will try to recaulcute more wight numbers on that though...

Brandon

bpbrinson

"Anything else im leaving out?" Designing an airframe before or without payload data and sample requirements is kinda putting the cart before the horse. Please, more detail as to equipment and sample requirments.

Brooks

iron eagel

Deltas can fly pretty slow they not all about speed as a matter of fact my first speed plane in many years is a delta/flying wing hybrid. It had an excellent slow speed cruise at 20% power that would give a flight time of about 50 minutes on a 3 cell 3200 mah battery. The speed of a delta is dependent on your AOA and how much gas you give it.
What I was talking about is essentially a delta shaped blimp you would have the best of both worlds where your airframe and payload weight is offset by the gas and you still get the aerodynamic lift as well when you get into thinner air.
The craft you have described sounds like you have a good candidate for what your trying to do.

BTW I am also into pattern as well, not at the competition level, just because I like it...

bpbrinson

@ 1 oz of lift per Cubic foot of helium(not counting weight of containment) this will get huge just to help carry a fraction of the weight. Doable and good idea, but gonna get real big to make any difference. Bigger=more drag = more power to move = heavier=more power=heavier.......
80 cubic feet to carry 5 lbs, not counting weight of containment. Now you gonna build a blimp or an airplane? Both may work.

Brooks

iron eagel

I don't think that high speed is what he needs so the power requirements wouldn't be all that bad. Where he looking at a sailplane type of design with a 14 ft span I don't think size is all that much of an issue either.
Your right a hybrid blimp/airplane would be fairly large, but you have both the gas and aerodynamically generated lift working for you.
But all in all the sailplane approach my be the easiest.
I'm just throwing out some food for thought...

IflyPATTERN

Brooks,

The only person trying to put the cart in front of the horse is yourself...I have clearly stated multiple times in this this that the design concepts/parameters are fully CONCEPTUAL and THEORETICAL. In the upcoming weeks I will begin a detailed design. Its all part of the engineerng method, and currently I am on steps 2or3 of 7 total steps. I will be ready to share more information when that information becomes known and set. For now, I am interested in hearing more theory on how I can perhaps better my design- this includes ideas regarding wing geometry, construction techniques, etc... I dont mean to sound harsh- I want to hear your input. Lets just take things one step at a time. I realize thought that I will get better feedback with the more info I give you guys... So I apolagize for that.

Now,

I have already begun sketching 2D drawings of top and side views... hopefully in a day or two I can transfer these pencil sketches into an autodesk inventor sketch .ipt so you guys can crituque some from there before I begin a 3d rendition. Until then, I am still gathering data- and that is just that, nothing more, nothing less.


My thoughts/conceptual ideas on the fuse/wing construction is this: keep in mind- I am only building ONE of these airplanes, so that is equated into my ideas...

1. The "nose area" will be very low draw, and will likely be built on Inventor and printed in a very "thin" shell...yes, PRINTED. I have experience with using the 3D printer at LSU. So, the nose will be printed in a very light/thin plastic material, the glassed of top with light fiberglass and/or CF tissue.
2. the main fuse area- the area which is the "torso" of the plane will be Lite ply formers and sheeted with balsa and then have a layer of fiberglass/CF on top.
3.The tail booms will each have 2 CF rods that will run from the fuse to the tail section. The CF rods will be encapsulated with a thin foam "shell" that will be balsa sheeted and glassed/CF.
4. The vertical and horizontal stabs will be foam core. So will the main wing and winglet. All wings will also be balsa sheeted and glassed.
5. Main wing contruction: I will likely speak to my friend, Bryan Hebert about this, since he has good experience with building strong and light thin wings (take a look at his Shark Design build- website link posted in previous post). But I expect to have a center section of the main wing permanantly attatched to the fuse... this will give me a strong, solid base, and also serve as a platform for my impact collection method. The center section will also have a slightly thicker airfoil- this is only so that I can fit in my retracts and other equiptment. This leaves me with having a two piece wing-set for the left and right wing. I plan to use a double spar- as already discussed. This could possibly mean using two wing tubes as well- I havent got that far to say for sure. The wings foam core will have proper bracing with sub-spars and other reinforcements. How will they be braced? that is to be answered later on- likely to be answered when I talk to Hebert.

As for the blimp/delta wing ideas. Yes, I agree they have their pros over what I am doing... but they also have cons IMO. I still believe the modified sailplane/glider platform is the best compromise here. It will allow me to easily test a LARGE volume of air at various high and low altitudes and give me relatively long flight times.

Lets keep the info coming,

Brandon

The Gopher

My Feedback: (1)

Food for thought, Imagine the entire uper wing surface as a solar panel

jessiej

Terrific thread. Geaux IflyPATTERN! I couldn't (resist).

jess

bpbrinson

1st question is always " What do you want to carry and what do you want to do with it?" I was simply trying to get to that. You have been very vague, but asking for help. There are some professionals on this forum that have been doing this for decades (30 years for me). Answers like "I have my reasons" are not helpful for you or anyone that does this type of thing for pay, but is volunteering our services. Your title "Maximum Altitude" is not accurate as to your goals, obviously. Yes, high aspect ratio is the answer and is the most flexible as to speed range, deltas are effecient in a more limited range. Pusher is structurally problematic and a bit less efficient. There are some pusher folder spinners on Esprit Models website. That is all I have for you with the information you have provided.

Brooks the gift horse

iron eagel

I like the center section as part of the airframe that will save you a ton of weight if you do it right.
Dual tubes yep.
Rather than typical lite ply for the formers I found that 5 sheets of balsa stacked is a lot lighter and stronger, balsa stacked so the two outer pieces are parallel to each other, the next two 45 degrees to those one left one right and the center piece 90 degrees to the two outside pieces (it is also twice the thickness of 4 other pieces). This balsa ply seems to be very strong and lightweight.

With careful design for this size airframe I bet a built up wing could be made much lighter than foam core, for your two outboard panels. Foam isn't all that light and with proper structure all that filler doesn't really buy you much. I would use the stressed skin approach for this aircraft more work yes, but can be done very light were your strength is where it will do the most good, that is where the bending forces are at their max and your further form the center. I look at foam as the easy way out as far as construction so bear with me please.
Also look at your center section wing root and fuselage as a one larger shape and assembly rather than separate components (if you understand what I mean) ...

IflyPATTERN

Fair enough, I titled this thread maximun altitude because my main goal of this whole deal is to design a glider/sailplane which is best uited for flying at low and high altitudes.... And for me, determinining x,y,z that will allow me to reach the highest altitude possible is my biggest unknown. The thread is shifting gears now since I have got some good data from this thread (ie wing loading, wing geometry,AR, and building techniques).

i want to carry a payload of about 15 lbs in altitudges ranging from 100ft-15K (15K being lowest acceptable altitude- i want to go higher!). The plane will be pusher style becuase I want to avoid contaminating my data collected with unnatural air vortexes that a normal propellor system produces.

Why is pusher less efficient? i would like to hear more about this.

gopher, I may elect to surface the winglet with solar cells. Surfacing the entire wing = enormous cost. That is the main constraint to that idea!

off to class,

Brandon

iron eagel

Brooks delta do have their issues that goes without saying. One of these is that they hemorrhage airspeed in a turn or a pull out from a dive. We wont even get into the loss of power on takeoff, and the list goes on. But they can fly slower at any given AOA than any conventional plane form. Now as far as their efficiency being in a narrow range, I not so sure that is true, where this plane form is found in both GA aircraft and high speed craft like the Valkyrie, Concord and Shuttle.
I can envision a 8-10 ft wingspan delta that has a wing loading in the 4-5 oz range, and carry the type of payload that he need to get airborne and be functional for a long duration flight. Where his requirements for speed isn't that high he wouldn't need a lot of power to get it or keep to airborne and it would be able to shrug off over speed conditions where a high aspect sailplane pieces would be fluttering to the ground.

iron eagel

Brandon a pusher is less efficient because it is in "dirty air" because of the turbulence of the airframe ahead of it.