Apologies for the text; the forum won't let me put a space between paragraphs.
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Apologies for the text; the forum won't let me put a space between paragraphs.
So I'm hoping the collective brain trust here can explain a few things conceptually to me about MAC, centers of balance, and CG.
Robert is still going to do the W&B for me, but in the meantime I need to understand all this stuff - it's my butt in the seat, after all. Plus I hate not understanding this.
So I dug around and found the formulas and even a nifty tool to find the MAC for biplanes, and using my measurements low and behold mine is 25% of the cord of the main wing (which should be between 24 and 28%, so yea team!)
I get what the formulas are doing and I even understand the placement of the center of balance for the wings inherent in the design - one wants the Center of Balance of the wings (and the lift) over the Center of Gravity.
So I took my MAC placement and translated that to a point on my plane from the datum (my firewall). It's just over 19 inches back from my firewall.
I also, naturally, weighed the aircraft and worked up the CG (empty). I added the meat lump and fuel using the standard methods (fine living now has me at the FAA approved 170 pounds!).
Ten gallons of gas and pilot puts the CG at 22" behind the datum, or three inches behind the Center of Balance.
Playing with fuel loads and pilot weight only moves it about about an inch at the most. So it seems to me everything is pretty much in agreement and I'm okay.
The question is why do the MAC calculations at all? Is Robert just validating his design against my build, or is this standard for homebuilts?
I think you may be confused about some terms (or are using them differently than they are typically used). MAC is a length, not a percentage. I do not know what you mean by "center of balance" if you are referring to something other than center of gravity. Your CG varies with different loading cases, and must be restricted to a forward limit and a rear limit to ensure proper stability. These limits are sometimes expressed as a percentage of MAC length (e.g. Fwd limit at 22% MAC, aft limit at 30% MAC). These points can also be expressed as distances from a datum point. The designer must specify the fwd and aft limits. (You can learn more about how to do this in the book "Airplane Performace, Stability and Control".) What Robert is probably doing is confirming that the fwd and aft limits for the design also apply to your aircraft, which may or may not conform to the dimensions of the design. I'm guessing that is why he asked you to supply him with some dimensions.
MAC is Mean Aerodynamic Chord, no way will it be 25% of the main (by which I presume you mean upper) wing chord. MAC is both a length (the average of the upper and lower wing chords accounting for areas) and a location (somewhere between the upper and the lower wing chords).
"Center of balance" is not a term normally used in aerodynamic calculations, and I have no idea what you mean by it. Normally, the center of gravity needs to be a bit forward of the wing(s)'s center of lift for the airplane to be stable.(actually it's the "neutral point" that the c.g. needs to be forward of as the center of lift moves with different AOAs but that's the general idea). But as mentioned in the post above the c.g. range is often given as a range of MAC so I presume that's what your 24-28% is).
I'm sure I'm gibbering-up the terms - this is why most folks who know airplanes start talking slowly and use small words on technical details!
Okay, so here's the "measurement thingie" that is Center of Balance, taken as a screenshot from Excel:
http://www.darts-page.com/images/Nieuport/Mac.jpg
I'm going to have to track down whomever put this together and bow down to them for making something so darned useful.
And here's the bog standard W&B spreadsheet:
http://www.darts-page.com/images/Nieuport/wb.jpg
Someone want to help put some ridges in my smooth brain on this?
This is not taking into account THE GAP beween THE wings,I' send ą Pm next week when I am home
OK, without seeing the underlying calculations, I'm guessing what you have is a spreadsheet intended to help R/C modelers find the desired "balance point" holding the plane with their fingers under the top wing, not something you want to use to determine the proper c.g. of a full scale plane. Most modelers just do a quick balance check of their models that way; if it balances on their fingers at 1/4 to 1/3 of the wing chord, good to go. But it's harder to figure where that point should be on a biplane with stagger, even moss so if the upper and lower areas aren't equal, hence the spreadsheet. The second one you posted helps you find where the c.g. IS, not where it SHOULD be.
The vertical gap between the wings is irrelevant.
I used a biplane formula set, mostly to get an idea if I was going to be way off of CG with my weights. Still waiting on Robert for the definitive answer.
To show at least I did the W&B procedures right, fuel was drained and put into flying position:
http://www.darts-page.com/images/Nieuport/WB001.jpg
Leveled at the longeron by the cockpit.
Then it was a bunch of marks using a plumb bob:
http://www.darts-page.com/images/Nieuport/WB002.jpg
Moving on, the last big thing was mounting the pitot tube. I knew I wanted it on the interplane strut, so while the plane was in flying configuration I bent the tube itself to the angle to match it.
There were three things to consider in my choices:
1) It had to be stable.
2) It had to be simple.
3) It had to be something other than butt ugly.
Well, I've got plenty of 1/4" tubing left over and I did a test piece to see if I could make a mounting flange for the ends. It turned out pretty good.
First I annealed the ends and made two cuts:
http://www.darts-page.com/images/Nieuport/pitot001.jpg
The challenge was to make the cuts to the sides just long enough to go flat without going short and getting a split or going long and having a cut past the flange. Sometimes it's best not to think about things too much and just do it....and in this case it worked out perfectly on both ends.
I made vertical cut that fit the pitot tube firmly, painted it, and ran the tubing up through it and into the pitot tube.
http://www.darts-page.com/images/Nieuport/pitot002.jpg
Pull down snug and mount to the strut with a couple rivets.
http://www.darts-page.com/images/Nieuport/pitot003.jpg
It's solid to the strut and won't be going anywhere.
The ends of the mounting flanges can be bent down a tad to match the curve of the strut, but the hour was getting late and the temperature dropping.
I put an oscillating fan in front of the tube and the ASI jumped around nicely to show it's all connected properly.
I'll post my W&B measurements up later for anyone who wants to chew on them while I wait on the official CG range....
The official word came back from Robert Baslee and....
...I'm ten pounds too light at the tail.
Well, that's better than the other way around! But I've got to figure out how to put some weight back there without doing major surgery. I've a few ideas, some of which aren't Wile E. Coyote in complexity.
Ądding 35lb to the pilot weight might have the same effect :)
You've opened up some delicious satirical replies. How about a tail hook? You could then do banner towing and practice carrier landings. :>;Quote:
Originally Posted by Frank Giger
I forget what you had for an engine and too lazy to search back... if you're hand propping a glider tow hook is useful weight...
1915cc VW (85hp) direct drive.
Oh, and I have a starter....hand propping is "of the Devil" IMHO.
Pics tomorrow on my solution for the weight issue.
[edit]
On snarky comments, I've always been considered heavy in the head and light in the ass. Sort of the definition of a nerd!
:)
Sooo....ten pounds to the tail. Well, let's plan some surgery:
http://www.darts-page.com/images/Nieuport/WB003.jpg
I already had an inspection hole there for getting to the nuts that hold the vertical stab to the fuselage.
So I built a box that rests on the lower longerons and has brackets going across front and back.
It was getting cold, dipping below 50 degrees, so I was going fast to keep warm...and didn't take photos of them.
http://www.darts-page.com/images/Nieuport/WB004.jpg
With the box in place (what a PITA) and the rivets taped over, I put the 12 weight sleeves into the box:
http://www.darts-page.com/images/Nieuport/WB005.jpg
Where did I get lead shot sealed into thick plastic bags of a convenient size that allow me to easily remove weight if I need to?
It's a secret.
http://www.darts-page.com/images/Nieuport/WB006.jpg
Box sealed up and a couple "drop tests" from knee high to see if it shifts (it didn't).
http://www.darts-page.com/images/Nieuport/WB007.jpg
Ready for fabric repair.
http://www.darts-page.com/images/Nieuport/WB008.jpg
A few notes:
The box is well clear of both the elevator control rod and the rudder cables.
I re-weighed the tail and she's put me in the CG limits, though at the forward end of them, which I'll take all day long.
Hi Frank,
in your CG calculation the position of the mains wheels is at 7.125in, this looks far back to me ?
if the front "leg" is vertical, then from what I make out of the plans this could be max 4 to 4.5in aft of firewall; which results in a CG calculation shift 2 inch more fwd ?
greetings
Johan
I can answer that. Since most of the AA planes are using VW engines, that are lighter than the original engines, the wings are swept back farther than original to move the center of lift, and therefore the C/G, back. Otherwise, a lot of nose weight would be required. Prior to the AA kits, the builders of the Graham Lee Nieuports found that moving the C/G back generated a little problem with ground handling, so many of the early builders of the Graham Lee planes moved the main wheels back closer to the C/G. Sweeping the front landing gear legs back. This helped with ground control. Robert's Nieuport plans (at least mine) show the forward leg being vertical, but the dimensions he gives for the legs result in sweeping the forward legs back to do the same thing.
Therefore, Frank's front landing gear legs are swept back, not vertical as was on the originals.
Now, in my case, I am building the full size AA N17 and since I am using the heavier Rotec R2800 radial, I have removed much of the added sweep in the wings and therefore repositioned the forward landing gear legs back to vertical. I have discussed this with Robert and others who have built Nieuports.
Dale
Dale is exactly right; when I was at the HOP,* Robert suggested we deviate from the plans and bring the gear rearward in order to improve ground handling. It's a mod the KC Dawn Patrol guys all made on their planes with great improvement.
I naturally agreed whole heartedly that we do this; I want a plane that looks like a Nieuport 11 more than I want a Nieuport 11.
* HOP = "House of Pain," a euphemism for the builder's assist program Mr. Baslee puts on, immortalized by Dick Stark in his second book. Robert's shop is climate controlled in the most fundamental way - it's mostly controlled by the climate outdoors. In my case, it was a very warm summer where even the cat was walking around with its tongue out due to the heat. A couple of swamp fans helped, but one rarely found himself in front of them.
Work at the HOP is dictated by the builder - if one is slow not much gets done. Robert and Jim are there to assist and teach, not build one's plane for them. However, Robert doesn't dally about - this is a man that built the four Nieuport 17's for Flyboys from phone call and a blank sheet to airworthy in 60 days. He tends to get one moving quickly from task to task and encourages hustle.
I had the fuselage done and on gear as well as that tailfeathers mounted in four days at the HOP. If I had the means and the cash there is no doubt in my mind that I could have had a flying plane in less than a month with his oversight and help (assuming he would be available for that).
But even for an old soldier like me it was a test. Loads of bending over, repetitive motions, and having to use one's brain while doing repetitive motions. Every skill needed for the build is taught, from basic design to basic tool use to annealing and swagging cables. Worth every dime!
Sigh and a big whew.
When I did the measurements, I didn't really do the upper wing offset, as Robert hadn't made it clear to me. So I came up with it using math to determine sides of a right triangle.
The problem is that the wing doesn't start at the firewall, but is well forward in the center. Instead of an eight inch offset for the upper wing, it's two inches! Recalculate and not only is no weight required to be added, doing so would put me out of the right range.
So pull all the weights out, patch the fabric, and frown at the seams that didn't need to be there in the first place.
The good news is that I did everything over for W&B from scratch and that was the only thing I had wrong. My weights were even the same, which I thought might be different for some reason. They shouldn't be, as I had the same level on the longeron at the cockpit.
I thought ten pounds in the tail seemed like an awful lot, but you sounded so sure...
LOL, I always sound sure.
But that doesn't mean I won't always rely on empirical data over mathematical data whenever possible. So all the math is done and I figured I'd make it easy on myself and make the chart for the POH:
http://www.darts-page.com/images/Nieuport/CG_chart.jpg
The odd thing that might stick out is how much five pounds in pilot weight matter between 180 and 185. This is because the gas tank and the pilot dance around the CG; that's the tipping point where the pilot wins and offsets the weight of the fuel. I may make the one gallon cell on the 180 line yellow, as it's close.
But at the FAA approved 170 pounds (with clothes on), I'm okay to run out of fuel. Sure the engine will go into whisper mode, but hey, the CG will still be okay for my unscheduled landing!
Even after building several airplanes I always get a couple of experienced friends over and triple check everything. I learned the hard way test flying a friend's Rans S-9. I relied on his calculations and it turned out it was very tail heavy. Made for a very interesting trip around the pattern to say the least with the elevator being extremely sensitive. Don
Forms off in the mail to the FAA for the registration. Why forms have to be notarized is beyond me.
So now the wait for that to come back, putting together the builder's log into hard copy, fleshing out the POH, and trips out to the airport to triple check everything and give it lots of hugs.
Frank, have you been flying much during the build? Make sure you get some time in a Champ or something if you are going to do the test flights. Or find an experienced test pilot to do the first few flights and sort it out. Don
Most likely it is an attempt to discourage abuse of the 51% amateur-built regulation. The FAA cracked down on professional builders several years ago because so many experimental aircraft were popping out of "factories".Quote:
Originally Posted by Frank Giger
Frank, I just completed the registration and inspection process a few days ago and the mistake most often made by builders is not having all your paperwork match EXACTLY when it comes to owner, builder, manufacturer, and model information. All this must match to the letter, no exceptions, or your paperwork will be kicked out for a redo. Your dataplate must also match exactly with the paperwork. The EAA registration packet ($20) is very useful in this regard as well as getting your DAR involved.
Best wishes for a smooth inspection!
I bought the document package before I bought the kit!
They really need to idiot proof the instructions, though. It would be nice if they had in big bold letters MAIL THE 8050-1, 8050-2, AND THE 8050-88 TO THE FAA. KEEP THE OTHER STUFF FOR THE DAR in the instructions.
While it's always a pain to get stuff notarized, there was a nostalgic pleasure to filling out a form that had actual carbon paper between sheets. I was mildly disappointed to see that it did not exhort me to "press hard - you are making three copies" anywhere on it.
On flying, I'm lining up a Champ for some stick time, as well as a few hours with a "foreign" CFI to see if I have any bad habits. I'm a firm believer in getting a CFI I don't know to fly with me and spot things I'm doing wrong (and, hopefully right). While it's not completely analogous, I did get some yoke* time behind a C150 last month.
* Ug. What an abomination! First they put the third wheel on the wrong end of the aircraft and then they put in a goofy steering wheel in place of a stick. I understand why they had wheels in Gotha bombers, but a light plane like a C150? Weird, man, just weird.
Guess I'm an idiot. ;)Quote:
Originally Posted by Frank Giger
I just checked off the boxes in the instructions in the order in which they appeared, did what they said, and everything worked out fine. The best way to avoid mistakes is to talk to your DAR before filling out or mailing any forms. My DAR insisted on filling in some of the forms for me and bringing them to the inspection.
I didn't use any carbon forms. You might be referring to the old version of the Bill of Sale, I used the single sheet version (downloadable as a pdf) in the packet. All forms are available now as downloads from the FAA site.
* Ug. What an abomination! First they put the third wheel on the wrong end of the aircraft and then they put in a goofy steering wheel in place of a stick. I understand why they had wheels in Gotha bombers, but a light plane like a C150? Weird, man, just weird.[/QUOTE]
I fly a couple of 140s and a 150 every once in awhile. The 140 is 10 mph faster that the 150, climbs much better and generally flies a lot nicer than the 150. So much for progress. If you can fly the Champ from the back seat an hour or so. That will really get you tuned up for the test flight. Don
So now that you are getting close to the big day, how to do you feel about the way the build has gone? Would you go with a Baslee kit again if you were starting over? I am about to pull the trigger on a kit from Airdrome so have been following this thread closely. I am in Bama quite often, I hope to see you flying overhead soon!
I have to say that the Airdrome Aeroplanes kit is the absolute best way for a starter builder without a clue like me to go.
It's all relatively straight forward, with a few exceptions of the things not put into the kit (like the seat), and is the sweet spot between a stack of plans and a materials list to buy and CNC cut and punched pieces. While all the materials are there and the gussets pre-cut, just about everything needs to be trimmed, coped, bent, drilled, and riveted. So there's a lot of minor fabricating going on.
I always pause when someone asks me if it's plans or kit built. It's both.
The fact that the tools are all basic and the skills required are easily learned was a huge plus.
If I were to build another aircraft it would be an Airdrome kit. Indeed, it's crossed my mind that if I had the financial means I'd mothball my current plane and start all over again, making something a step better in finish.
And that's the thing about Airdrome kits. One can do what I did - stick to the plans and make one of the only vanilla models he has out there that is solid, functional, and good(ish) looking - or one can tweak things slightly and have something that's a show stopper and looks more like a replica than a representation of the type.
That SE5a of his is a gorgeous monster, for example, and still LSA compliant!
Not to be understated is the support one gets. Robert Baslee is seemingly always available and gives straight answers to what have been my often vague questions, and others that have built Airdrome and Graham Lee planes are just the Internet away from advice.
The first four days of the build in Robert's shop were invaluable (okay, they had a value in that I paid for it) in teaching me all the skills needed for the build. I had put together a rudder prior to going whole hog, figuring if I could even half a** it I had potential...and I wasn't wrong. But learning all the other things, from how to cope tubing to fit to annealing to how to do maintenance on a pneumatic rivet gun were priceless.
While it's taken me a long time as far as the calendar goes, in large measure that's because I took long breaks from the project owing to weather. We had a summer that was just too hot to work out of doors for any length of time and a bear of a winter as well. Plus I worked slow, just having fun with it. On days where I started early and just cranked it out I got huge amounts of things done; usually, though, I'd go out into the back yard and do one or two things and then put the tools away.
[edit]
That said, I selected the Airdrome kit for three reasons:
1) I wanted my own airplane.
2) I knew I could build an Airdrome plane for around 12K. With do-over pieces and a few other considerations it's now closer to 15K. But it's a far cry for what I'd have to pay to own a decent Champ that didn't need a lot of work.
3) I want to fly for my own pleasure. Low and slow in an open cockpit is the life for me. Forget transportation, night flying, all weather stuff, or aerobatics. Cruising at 55 mph at 1500 feet AGL on a CAVU day with low winds over cow fields and rivers is pure heaven to me....as is an hour of touch-and-goes.
So it met my criteria of price and mission. That it's representational of WWI aircraft and I'm sold. I'm sort of a WWI nut when it comes to airplanes so that was the cherry on the top.
I just finished (are they ever really finished??) an AA Fokker D.VII and have a build site:
http://fokkerd7.com
Here are some thoughts after the first four months of the project:
http://fokkerd7.com/4-months.html
Frank's comments pretty much mirror my impressions, the AA kits are a good value but require enough thought and fabrication to keep it interesting. :)
Although my N17 project is a long way from completion, I concur with both above. Mine is taking much longer than it should. But I knew it would before I started. The main reasons are that I do have another life and my wife and I like to go off several weekends a year and on other adventures. Also, I have changed nearly every area of the kit from "as designed" to something that I feel looks a little more original. When you make one change, you have likely made ten and you have to figure out all to continue. Before everyone goes nuts over that statement, I have conferred with Robert on nearly every change - all that are structural.
The AA kits are definitely builders kits and require a lot of interpretation of the very basic drawings that are the plans. But as said above, Robert is a saint about answering questions and helping decipher some aspect of the build. Also, there are many other builders out there who are a wealth of info.
Dale
Got a postcard from the FAA today!
Hurray, she's officially registered as an aircraft with the gub'ment!
Now to firm up the rest of the paperwork and get a DAR to sign off on her.
Translated this thread into the builder's log.
258 pages of pedantic murmurings with a lot of poorly taken pictures.
Now to make an index for it (otherwise I won't be able to find any particular thing in it if needed) and the POH.
Saturday is "come find stuff wrong with my airplane" day, with my EAA chapter brothers sharpening their knives and grinning at the prospect.
Should be interesting - most of them have been through the inspection process and have long experience with homebuilts, and know that a tough rehearsal is the surest way to get a good show when the time comes.
Lots of fun on Saturday - my chapter is the reason I'm in the EAA, not the folks in Oskosh. The list of gigs isn't very long and I worked off most of them on the spot - but all of them were gigs to be fixed before inspection.
I also got a letter from the state of Alabama asking for a bill of sale so they can tax me 2% on the aircraft. I'm going to call them for some amplification on this....running afoul of the tax man is on my "do not do" list.
[QUOTE=Frank Giger;53860]
I also got a letter from the state of Alabama asking for a bill of sale so they can tax me 2% on the aircraft.
2% only ? I am facing 21% + import taxes, and I paid last week 960 euro (1000usd) to the CAA so they can inspect my shop and building materials ....If all goes well I will be allowed to start with the rudder, If the gents from Brussels are satisfied with the work, only then I can move to THE next item, make another appointment for inspection and so on, .....
good luck with your DAR inspection
johan
Quote:
Originally Posted by Frank Giger
Frank,
Pay 2% of the amount on your bill of sale via your Alabama income tax form (line 18e) and you will be good to go. The tax is referred to as 'Use Tax' on Form 40. Reply to the Revenue Department that your tax will be paid with your income tax return.
My friendly FAA inspector has all my documents "for review" and should be calling the beginning of next week to schedule a time to come out and look at her.
And my EAA chapter is just the best. It's no accident that they volunteered me to give a presentation on the Test Flight Pamphlet for our next meeting. That is probably the most non-subtle way of them showing me the love.
One of the things the pamphlet says is to drain and check the oil before and after the first flight. I was thinking of doing that anyway (at least before the first flight), but there is was in black and white - not just a good idea but a best practice.
As always, there's a kind of story to go with changing the oil. Since I don't know what wrong looks like, one of my EAA brothers with a lot of VW experience came by to lend a hand. My five gallon oil drain catcher needed some surgery to shorten the pipe going up to the catch pan so it'd fit under the airplane.
Huh. So I whip out my Harbor Freight dremel tool, put a cutting wheel on it, hack some off, run the edge on the sander, and call it done. He just gave me a look and said "I'd of used a tape measure."
"They only complicate things," I replied in my best deadpan.
But I did measure the oil cooler under the engine when he wasn't looking, grabbed a bit of scrap sheet, ran some lines down it in a sharpie, and whipped out the butane torch.
"Whatcha doing?"
"Annealing. I don't want to have any fuss out of this sheeting." When the mark disappeared, I just quick-quenched it with water, put the edge on the side of the table, and whacked out some bends with a rubber mallet on both sides and then the end.
I put a line of rare earth magnet buttons along the lower edge and put it on top of the oil cooler, a clean shop rag into the catch basin of the oil can thingie and then put both to the side, and grinned.
"We should warm the engine."
"Yep, that's the best way."
So I taxied around the hangars twice, because what's the fun of just having it sit there idling?
Put all of it back, pull the plug, and two little tiny slivers of metal, each maybe a third the with of a hair and less than 1/4 inch long stuck to the magnet, and we didn't find anything else on the rag. So nothing that would cause concern out of a new engine.
No word from the FAA inspector this week - emails and phone calls unanswered. I figured he must be out of the office for some reason (maybe TDY somewhere), but a note from him saying such would have been nice.
You're lucky that He agreed to inspect it. In our district the FISDO says they are way to busy to do inspections and that we have to use a DAR to the tune of $650 plus travel expenses. Don