PDA

View Full Version : New to forum



Ivanstein
08-25-2017, 02:12 PM
Greetings,

I am a new to the forum and new to ultralight aviation.

I am an aerospace engineer and have decided to design and build my own ultralight. I got into engineering late in the game and have an extensive history in machining and mechanics (mostly automotive amd heavy equipment). So, I have, at least, the basic skills to take this project from start to finish.

I plan on a full metal craft with a semi monocoque fuselage and a rib and stringer wing.

I have been working from my Senior design class text by Raymer and have mostly completed the rough sizing calculations. I have stared into the conceptual stage where I need to start generating basic lay out drawings (read: the fun part).

I am sure I will have many many questions and would be quite interested in finding someone local(ish) who has been down the same road. I am in Wichita KS, and would love to chew the fat at my design firm office (Starbucks) and learn some insider tricks.

Also, if anyone has a 5 axis mill and a CNC lathe with live tooling just sitting in their garage waiting on something to do....[emoji6]


First serious questions:

Do I pick a reasonable gross takeoff weight (W0) considering my own size ( working on reducing that...) Or do I set a gross​ weight based on an average pilot to set wing area for minimum stall speed requirements? If I design it for a 170lb pilot and consider the spare tire I carry as "crash protection" and live with the higher stall speed, is that reasonable?

Next question:
Are there any power plant considerations which will be about 30-35 hp without breaking the bank? I have seen a Yamaha engine showing up on ebay, but cant find any info on it. Also a reasonable Cayuna on ebay, but that seems to be an antiquated engine and parts may be hard to find.

I appreciate any help and would love to find some new friends of like mind to share enthusiasm.

Thanks.

Sent from my XT1585 using Tapatalk

rwanttaja
08-25-2017, 05:15 PM
First serious questions:

Do I pick a reasonable gross takeoff weight (W0) considering my own size ( working on reducing that...) Or do I set a gross​ weight based on an average pilot to set wing area for minimum stall speed requirements? If I design it for a 170lb pilot and consider the spare tire I carry as "crash protection" and live with the higher stall speed, is that reasonable?
Design it for the weight at which you expect it will be operated, and add a 25% margin on top of that. So if you weigh 200 lbs, design it for 250 lbs. It'll thus be happier a lighter weight.

Ron Wanttaja

cliffo
08-26-2017, 07:55 PM
I agree with Ron on the weight issue as there is always an issue with going over gross, helmets, clothing, a little carry on kit, etc., etc. As far as engines are concerned no matter what you start out with in 10 yrs. if not sooner it will be way behind in the new designs and technology. I have an old 447, and a rebuilt 40 yr. old Cayuna I went thru for a back-up, doing a couple updates in the process. These older engines are tried and true, and parts are readily available.

Bill Berson
08-26-2017, 08:50 PM
Gross weight is your choice, depends on if just one for you or if selling plans to others.
AC103-7 (online) has much info about the weight rules.

Ivanstein
08-27-2017, 01:38 PM
Gross weight is your choice, depends on if just one for you or if selling plans to others.
AC103-7 (online) has much info about the weight rules.
Thanks for that. I am currently running calculations for my altitude +1000' which is right at 2300' msl. So, if I am reading the description correctly, the airspeeds can be corrected for a standard atmospheric day at sea level. This will help a bit on the wing area required to meet stall speed requirements, as with the somewhat thinner air here, the q (dynamic pressure) value is lower requiring more wing area to produce the same lift at sea level.

So, apparently I can suffer the higher stall speed due to thinner air. However, that doesn't help with performance at altitude either. I think, with everything engineered, there will be a trade off.

Sent from my XT1585 using Tapatalk

Dana
08-28-2017, 05:06 AM
If you're designing for Part 103 you will want to use the AC103-7 appendix calculations for speeds. Not as actual design values, but as a sizing guide. The calculations in the appendix are very conservative, and accepted as proof of 103 compliance without actual demonstration. So you can have a legal ultralight with somewhat higher performance than the regulations would suggest.

As for engines, the Cuyuna is not a bad choice. Lots of them still around, parts readily available and far cheaper than Rotax.

Greg Wilson
08-31-2017, 03:51 PM
Bear in mind that the required stalling speed is at the flying weight. Many ultralights have the gross weight set by determining the maximum weight that the required stall speed can be achieved. As Dana said AC103-7 will be of great help in this pursuit.

Dana
08-31-2017, 08:22 PM
Bear in mind that the required stalling speed is at the flying weight. Many ultralights have the gross weight set by determining the maximum weight that the required stall speed can be achieved. As Dana said AC103-7 will be of great help in this pursuit.

I think AC103-7 has you do the calculations with the "standard" 170# pilot and full fuel. But then I never worried about it because I happen to weigh 170.

Bill Berson
08-31-2017, 11:33 PM
The FAA isn't concerned about some overweight, according to an article in Sport Aviation, August 2017.

Norman Langlois
09-01-2017, 02:16 PM
I am the Crazy one that designed and built, then learned to fly the thing all from scratch without any aeronautical knowledge or engineering . I had the skills you mention an industrial fabricator machinist. The first thing you need is to be aware the normal structure is going to be lighter than you would like it to be. You also will be flying with very little around you [ hang cage structure ] therefore Ultra light is harder to get there than you can imagine. The usual tube structure is proven . The usual ladder tube wing design also . If you plan to build an efficient ultra light they do not exist they fly slow not far, they do not glide well . Mostly because weight limits the wing area. To over come area shortage you need speed, that's not allowed ether. The solution is thicker air foils higher drag. Then there is the power plant. I have a new Kawasaki 440 they are around. The lightest power to weight package I could find. I just made the weight with all my considerations.I wanted amphibious I had to give up land base and opted for water only because of extra flotation weight allowance. My base flying design weight was 296 lb the final was 303 lb
I do not have a normal wing structure and I would not give it up . So what are you willing to give up in the venture I assure you there will be comprise. Be careful and be safe I was just LUCKY

edwisch
09-01-2017, 02:28 PM
The FAA's old standard for average weight was 170 pounds, but the ASTM standard pilot weight used for LSA is 190 pounds. Playing a little loose with the precise definition of "average," half the population will weigh more than 190. Me, for example, and I'm not all that big by today's standards. Design for heavier pilots, as somebody else pointed out. Not that many pilots weigh 170 or less any more.

Michael Miles
09-03-2017, 12:15 PM
Hi Ivan:

I'm following your thread with keen interest. I'm also building my first aircraft and have started my own thread. I'm using Raymer's simplified design excel spreadsheet for the preliminary calculations, and have the student version of RDS and his text for when it's time to get down in the mud. I've got a much simpler design task since I'm building a powered paraglider, and the wing already exists. I'm primarily using the design software to help me select a wing at this point.

Good luck, Michael

Ivanstein
09-11-2017, 12:51 PM
I have been faithfully crunching numbers on this and have been getting a bunch of really terrible expected wing area results.

In the order of 220ft^2.

This is all driven by, believe it or not, cruise. I assumed a 40kt cruise speed and it turns out that the wing loading should be around 3.5lb/ft^2. My lowest wing area occurs when I adjust the coefficient of lift to match takeoff wing loading to match cruise.

This is all initial sizing, and will be revised as the design progresses. However, I am unsure how the other popular ultralights keep the wing area so low. They all have calculated wing loading of 3.5-4.5 lb/ft^2, but seem to be only 100-125ft^2 area. Most are right around 500lb gross weight.

More investigation is due.

Sent from my XT1585 using Tapatalk

Ivanstein
09-11-2017, 08:16 PM
6678
6679

Picture of some surfacing I have done. The transparent box is the interior dimension for a 20ft enclosed trailer I looked up on line. One of the design goals is to make it fit in one due to the lack of a hanger in my back yard.

Other one is a 4 view. This is a very rough lay out. I have parametrized the wing and flying surfaces to make easy and quick modifications and have formulas to quickly read out areas and tail volume coefficients. This will definitely evolve as time goes on. I am thinking it may end up being a biplane (due to required wing area) but that will be more difficult to stuff in a trailer. However, I should be able to keep the model parameterized with upper and lower wing data and an option to include one or both.

So, as a matter of personal opinion, should I go for a monoplane? Biplane? High, shoulder, low wing? Canard? Possibly a flying wing? Give me your personal favorites! :)

Bill Berson
09-11-2017, 09:05 PM
Wing area is determined for required stall speed, not cruise.

Ivanstein
09-12-2017, 06:54 AM
Wing area is determined for required stall speed, not cruise.
Not really. Wing loading is calculated for each expected flight regime. Select the lowest, and size the wing to maintain that wing loading. In this case, because the speed envelope of the ultralight category is so limited, the air density causes the greatest shift in dynamic pressure. Thus, the takeoff condition at ground level has a touch higher q value than cruise at 40kts and 1000ft AGL. So, basically the wing loading at cruise must be lower than at take off (stall x 1.1 kts)

It was rather surprising to see this occur, but after thinking about it, it does make sense.

Sent from my XT1585 using Tapatalk

Dana
09-12-2017, 11:13 AM
Not really. Wing loading is calculated for each expected flight regime. Select the lowest, and size the wing to maintain that wing loading. In this case, because the speed envelope of the ultralight category is so limited, the air density causes the greatest shift in dynamic pressure. Thus, the takeoff condition at ground level has a touch higher q value than cruise at 40kts and 1000ft AGL. So, basically the wing loading at cruise must be lower than at take off (stall x 1.1 kts)

It was rather surprising to see this occur, but after thinking about it, it does make sense.

Sent from my XT1585 using Tapatalk

In level unaccelerated flight, wing loading does not change; it's aircraft weight divided by wing area. Well, it decreases slightly as fuel is burned, but that's it.

For Part 103 ultralights, the FAA has published a set of tables (In the AC103-7 appendix) that essentially give the required wing loading (assuming a 170# pilot) to achieve the mandated stall speed for various generic airfoil types. If your ultralight complies on paper with those tables, no further proof is required, even if the actual pilot is a sumo wrestler, and yes, even if the actual performance is outside the 103 limits. As those tables are rather generous, they're a good place to start your initial wing area sizing.

Ivanstein
09-12-2017, 12:55 PM
In level unaccelerated flight, wing loading does not change; it's aircraft weight divided by wing area. Well, it decreases slightly as fuel is burned, but that's it.

For Part 103 ultralights, the FAA has published a set of tables (In the AC103-7 appendix) that essentially give the required wing loading (assuming a 170# pilot) to achieve the mandated stall speed for various generic airfoil types. If your ultralight complies on paper with those tables, no further proof is required, even if the actual pilot is a sumo wrestler, and yes, even if the actual performance is outside the 103 limits. As those tables are rather generous, they're a good place to start your initial wing area sizing.
Thats all correct, except the design is based on the "required" wing loading for best performance at any given regime.

Think of it like this...
At stall, your wing is operating at maximum lift. Indirectly, this is at the maximum coefficient of lift. So, you are using all that wing can possibly create.

Now, give that wing extra speed and you no longer have to operate at maximum lift coefficient. So, in this case you could reduce the coefficient of lift of the airfoil and still have enough lift with less drag due to airfoil thickness or camber. OR...you could decrease wing area and keep the same airfoil resulting in less drag. Either one would be optimal at cruise, but wouldn't get the airplane off the ground at any less than cruise speed. So, it isnt optimal for takeoff.

Another way to think of it is that with higher speed, you can lift more with the given wing and it would be optimal to increase your "cargo" at cruise.

Another idea is, maybe the aircraft can give away a bit of slow speed performance to gain range or loiter performance. In this case the wing may be sized down to be more efficient at cruise to extend range or time aloft but will have a higher takeoff speed and required runway distance.

So, yes, once the wing is designed, wing loading is weight divided by wing area. But during initial sizing, you run scenarios of the optimal wing for each flight regime and the different wing loadings which are best for each. Then you select the lowest required and size the wing for that. If I had assumed stall is the determining factor (which I had, initially) I would have lost a measure of efficiency, which in this category, is very important due to limited weight and flight envelope.

Sent from my XT1585 using Tapatalk

Michael Miles
09-12-2017, 04:21 PM
...
have been getting a bunch of really terrible expected wing area results.

...
More investigation is due.

Sent from my XT1585 using Tapatalk

Hi Ivan:

Raymer has some assumptions about structural weights that I don't think apply well to ultralights. I had to fudge his spreadsheet with values I knew (like the 254 pound empty weight - his W0 was ending up in the 2000-3500 pound range). Thinking about your question, I realized that I have to recalculate his empty weight constant "a." I had a similar issue as you with CL-max, but his simplified spreadsheet doesn't differentiate the CL at takeoff vs. cruise, it just uses CL-max.

Michael

Ivanstein
09-12-2017, 05:33 PM
Hi Ivan:

Raymer has some assumptions about structural weights that I don't think apply well to ultralights. I had to fudge his spreadsheet with values I knew (like the 254 pound empty weight - his W0 was ending up in the 2000-3500 pound range). Thinking about your question, I realized that I have to recalculate his empty weight constant "a." I had a similar issue as you with CL-max, but his simplified spreadsheet doesn't differentiate the CL at takeoff vs. cruise, it just uses CL-max.

Michael
You are correct. Cruise assumes only enough lift to balance drag and with a prop driven craft, the best range comes at best L/D, so drag is the driving parameter. With a high camber airfoil as needed in an ultralight, that is substantial, even at low angle of attack.

Sent from my XT1585 using Tapatalk

Michael Miles
09-12-2017, 11:29 PM
Hi Ivan:

Lost my thread post, so here goes. I reviewed Raymers textbook against his homebuilders book and I'm definitely going to recommend his homebuilders book to you since he addresses questions you've raised (like wing placement) in ways not covered in his bigger book:

https://www.eaa.org/en/eaa-shop/media/aviation-books/2264021500000__simplified-aircraft-design-for-homebuilders

I also like Chris Heintz's book (Zenith aircraft founder/designer) - good stuff about structures and stability:

https://smile.amazon.com/gp/product/1425188281/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I also like Snori Gudmansson's (gotta love that Scandinavian name - takes me back to my time in Sweden :) book on GA aircraft design:

https://smile.amazon.com/General-Aviation-Aircraft-Design-Procedures-ebook/dp/B00FFFZ3N4/ref=mt_kindle?_encoding=UTF8&me=

I really like Gudmansson's book for all the design process. I primarily bought these books as a way to help me evaluate homebuilt designs. Snori's book (he's not boring - check for his youtube videos) was especially good. I found out a design issue (I think a pretty big one) in a plane that was being hawked at Oshkosh. You should have seen the look of worry on the hawker's face when he saw me noticing the cludgy features of the plane's wing. I kept my mouth shut - Caveat Emptor, his potential customers should buy the books too. The hype sales approach should have been their first warning though (mine too). I recently referred to the Gudmansson book about issues I saw on powered paragliders with front castoring wheels. I wanted to see what he said about geometry and shimmy. If you read the reviews on Amazon, they laud the fact that he has the derivations of the formulas too. His language is straight forward like Raymer, and he covers a ton of issues around small aircraft design. I've actually got both an electronic version and a hard cover version since the diagrams in the hard cover version are only in black and white. It also gives me the opportunity to do detailed searches electronically. The physical book is huge, like a reference should be.

Do you know of any online forums for using Raymer's programs/spreadsheets? I don't know if you want to keep yours propriatary (in case you develop a plan set, for example), but maybe we could cross check each other's work. PM if you want to.

Enjoying watching the evolution of your design,

Michael

Michael Miles
09-12-2017, 11:30 PM
and please keep in mind that I'm a mathematician and scientific programmer and not an engineer...

Michael Miles
09-13-2017, 12:08 AM
Jeez - hard copies of Gudmundsson's book were hard to find:

https://www.biblio.com/book/general-aviation-aircraft-design-applied-method/d/708946526?aid=frg&utm_source=google&utm_medium=product&utm_campaign=feed-details&gclid=EAIaIQobChMIlJ7V9r6h1gIVQ0OGCh1vYg-TEAkYASABEgKIwfD_BwE

In addition to the Kindle electronic version, it's available on Google Play for the same price as Kindle ($120).

Ivanstein
09-13-2017, 09:54 AM
Jeez - hard copies of Gudmundsson's book were hard to find:

https://www.biblio.com/book/general-aviation-aircraft-design-applied-method/d/708946526?aid=frg&utm_source=google&utm_medium=product&utm_campaign=feed-details&gclid=EAIaIQobChMIlJ7V9r6h1gIVQ0OGCh1vYg-TEAkYASABEgKIwfD_BwE

In addition to the Kindle electronic version, it's available on Google Play for the same price as Kindle ($120).
Same with Airframe Structural Design by Niu. Pricey.

Anything with stress concentration factors (Like Peterson's) is highly expensive as well.

My Raymer book was about $300 from what I recall...

Sent from my XT1585 using Tapatalk

Michael Miles
09-13-2017, 03:58 PM
Raymer's text book with the student software is $160 on amazon (so a bit cheaper than your school):

https://smile.amazon.com/gp/product/1600869211/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I've got both, but prefer his spreadsheet for my project. If I go light sport, I'll probably try using the RDS software. I've heard it has some display issues in Win 10.

Michael Miles
09-18-2017, 03:15 PM
EAA membership qualifies us for a free version of Solidworks, but I'm not sure if it does FEA. There's an online FEA,CFD simulation software at https://www.simscale.com/ - its use is free if your design is posted for open use on the website.

Ivanstein
09-18-2017, 09:14 PM
EAA membership qualifies us for a free version of Solidworks, but I'm not sure if it does FEA. There's an online FEA,CFD simulation software at https://www.simscale.com/ - its use is free if your design is posted for open use on the website.
I have all the tools I need for that. I can do a fair amount of hand calcs to preserve the months long headache of FEA and get pretty close yet stay conservative. When the time comes, I will break out the advanced mechanics of materials book and refamiliarize my self with Castigliano and work-energy methods.

CFD isn't particularly important unless you're looking for world class drag estimates or designing a very specific airfoil. I can use XFLR5 for a decent estimate of airfoil qualities. Stability and control can be done in AVM with some work. Both of those are capable and free. Drag estimates are usually handled through historically based estimates and refined with some basic aero-theory. Also free.

As for CAD, I am very familiar and proficient with CATIA. I used to be a research assistant at NIAR during school and took nearly every one of the classes. I can take another class, which work will pay for, and get a temporary license through it when the time comes.

Being that I am a fledgling engineer (I started school at 35) and still paying back an inordinate amount of student loans while raising three boys as a single father, this project must necessarily be low cost.

I appreciate your suggestions and will look into the website you mentioned. However I would be wary of posting an aircraft design on open source due to possible liability issues...?

Sent from my XT1585 using Tapatalk

Michael Miles
09-20-2017, 12:14 PM
Hi Ivan:

Thanks for the additional resources - I'll check them out. I appreciate the budget approach, and I suspect ultralight folks mostly share that in common. In fact, I think that's probably a driver for most homebuilders. It certainly is for me. Didn't think of the liability issue, but I'm not an engineer. Curious to see how you design the fuselage - not sure how you're going to avoid making it out of aluminum foil given FAR 103.

Michael

Ivanstein
09-20-2017, 02:49 PM
Hi Ivan:

Thanks for the additional resources - I'll check them out. I appreciate the budget approach, and I suspect ultralight folks mostly share that in common. In fact, I think that's probably a driver for most homebuilders. It certainly is for me. Didn't think of the liability issue, but I'm not an engineer. Curious to see how you design the fuselage - not sure how you're going to avoid making it out of aluminum foil given FAR 103.

Michael
Well, if you've heard the phrase "Boeing builds 'em better", you probably have a good idea how that will work.

The 737 fuselage has skin panels as thin as 0.040" thick and that holds pressure and contributes to the structural make up of the fuselage. Inside are stringers and frames attached to the skin with tension clips and shear ties.

Methinks if 0.040" thick aluminum works for a 189,000 gross weight craft, probably some 2024-T3 clad foil will do the trick. Most likely 0.016" thick or there about. I will also, more than likely, use some aluminum angle or U channel about 0.050" thick or there about for stringers. I suspect I will end up figuring out how to form some frames with a home made rubber box or bladder press and a pressure washer. My initial thoughts are 0.050" thick on that as well.

Amazingly, it appears most 103 aircraft look like they are "sized for stiffness" and not built optimally for weight. Analysis and trade studies will tell the tale soon enough.

I don't think I will get into sizing for 20,000 flight cycles, except on the critical baseline structure that is difficult to access and repair. I am guessing that, If I can use a semi monocoque design, inspection will be easy and any cracking will be readily apparent so I won't have to do a lot of damage tolerance analysis. Especially if I can design for inherent damage tolerance.

I am open to any good sources of indestructium alloy if anyone has any. Also need plans for a turbo encabulator...the one with twin spurving bearings.

Sent from my XT1585 using Tapatalk

Michael Miles
09-21-2017, 02:02 PM
Quite a few trouble shooting issues with the Quicksilvers related to hard landings:

http://www.ultralightnews.com/quicksilver-mx-ultralight-aircraft-troubleshooting/quicksilver-mx-airframe-troubleshooting-reports.html

I think Ultralights tend to be floaty due to their light weight, and susceptible to even light gusts on landing. It's one of the reasons I'm building a quad rather than a trike after seeing too many wobbly paraglider trike landings. Good aileron authority at stall should help, but light is still easy to blow around. Structural consideration around the landing gear might be important - I'm agonizing over it myself.

You mention inspection. I saw a youtube video about using an inspection camera for aircraft:

https://www.youtube.com/watch?v=VEHJLXdHSLo

If you build with this in mind, you may gain access to all of your internal areas for inspection.

Ivanstein
09-22-2017, 09:10 AM
Niu has a pretty good write up on design loads for aircraft landing gear. I will be consulting that when the time comes.

Aileron sizing is usually done to keep good authority at low speeds. I suspect some dihedral and good rudder authority will help as well. However, that doesn't help much in a paraplane, presumably.

As for crosswind landings, it would seem that a bird with a stall speed less than 30kts in a mild breeze could land on a sidewalk...the short way!

As for inspection, I have (or had) a flexible bore scope from my auto mechanic days. They are indeed handy and can be had for a reasonable price. Probably a good investment for ultralight owners.

Sent from my XT1585 using Tapatalk

Michael Miles
09-26-2017, 02:48 PM
Hi Ivan:

I've gotten hold of an older copy of Niu, so thanks for that pointer. I thought I remembered a plane similar to yours, and I found it again:

https://flyhummel.com/ultra-cruiser/

Plans are $260, but they've got a construction video for $18. Looks like the design has been around for 20 years, so there should be good info on the interwebs about experience with the design.