abufletcher

I hate to go on and on here but this introduces yet more ambiguous language. What would "wings level" mean. Most newcomers looking at a flat-bottomed airfoil (as on the Puppeteer) would assume that "level" would mean that the bottom of the wing is parallel to the ground. But in terms of the angle of attack, the true line though the airfoil goes from the middle of the LE to the edge of the TE. So it's actually "tipped up" several degrees relative to the bottom surface of the wing. Which line is to be level?

Linguistic issues aside, why would it be more relevant to balance the model based on "level wings" vs. a "level fuse centerline?" Inquiring minds want to know!

TFF

Thats a problem that advertisers and ARFs downplay because they want "anyone" who wants a plane to buy. The reality is that there is engineering involved in getting a plane to fly, it is a little bit of rule of thumb, calculations, or experience, and some luck. To divert this, have you figured out why the engine died?

tc42

Have always assumed that level is when the fuz (and often the flat part of the wing platforms) is level. My interpretataion of all plans was/is that when I support the plane by the indicated balance point on the wing, it should sit as per the attitude shown in the plans (i.e level).

In retrospect I have always balanced my planes a little fwd of this for initial flights so I probably have been balancing a little nose down.

As I was told once, a 20% aft MAC COG on most planes is fatal no matter how good you are but a good pilot can fly a nose heavy plane not matter how nose heavy (up to the point where it can't get off the ground).

abufletcher

Right, well, the lead's in place. All 484.5g (17oz) of it. (I'm never going to be able to make sense of Bassman's 1oz., so best to just forget it.) This is the weight that was in the cowl in the photo above of me balancing the model. I then melted it down, poured it into a small circular form and then hammered it into a roughly square shape so that it fit in the space between the mount supports. It is then secured with three 3/4" screws. If I feel this is too much after the next flight I can remove some of the lead from this block.

This gives the model a total weight of about 4.1kg.

abufletcher

This has always been my assumption too. The norm in drafting would be to draw the centerline level and so all flying surfaces will show their actual deflection from the centerline. But is this really the attitude that aircraft take in flight? As I understand it, some aircraft tend to fly in a slightly nose-down attitude, while others naturally take a slightly nose up attitude.

abufletcher

I was just going to say, that now that the balance issue has been dealt with I need to return to a "pre-flight" check procedure for the "second maiden." First, I need to see if anything was shaken loose during the flight. Then I need to return the elevator trim to its "pre-emergency" setting.

And finally, I need to give some thought to why the engine died. I had about 1/3 of a tank left when I landed so it wasn't another "oops" moment. It might have been running a tad rich and with all the throttling back and forth to keep the model flying, it just died out. I had taxied around a bit and then had been flying for about 5 minutes, tops. Probably more like 3 mins.

Beyond that, I haven't got a clue or a guess. I suppose all I can do is make sure I give the engine a good tuning again (and maybe get the club Saito expert to tweak it ) and then maybe run a full tank through it while throttling back and forth with the model in different orientations. Maybe I need to tweak the throttle setting and/or trim. This is the same engine I used in the Cub and it was pretty consistently reliable thought I think I had a deadstick or two out of several dozen flights.

vincento

From Flair:

Dear Vince

The COG can be anywhere within these measurements and the model will fly if
the COG is placed closer to the rear of the plane it will make the elevator
control more sensitive and if the COG is closer to the front of the plane
the elevator control will be less sensitive. It can be left to personal
preference as to the exact COG point as to which characteristics you prefer.

I Hope this has answered your enquiry

Regards,

Paul McDonagh
Flair Models Ltd

abufletcher

Sounds like the standard response (and essentially true for any aircraft or aircraft model). And of course it still doesn't address the "glide angle" issue. Besides, I don't think this was a simple issue of elevator sensitivity. This felt like a seriously tail-heavy model, one that was balanced slightly nose down at 138mm for its maiden (as per the instructions as I read them).

Although to be fair, I'm sure it was both. I have 25% exponential dialed on on the elevator. Maybe I need to bump this up to 50% for the next flight.

abufletcher

Well, I think I'm ready to go to the field again.

abufletcher

As a final comment on balance and CG, I'll add that the model as weighted at the moment balances LEVEL at about 120mm back from the LE. THAT's what should be stated in the instructions!

bassman

I finally got around to taking some pictures. In the first you can see my servo installation. In the second and third you can see the engine area. I did make a mistake in the added weight there isn't 1oz there is 1 1/2 oz! I had to find a way to get better air flow over the engine head so in the last two you can see the plastic baffle plate that I made up and attached a picture of a rotary engine too. This forces all of the air flow around the cylinder head. Without it I did get some overheating.

Bassman

abufletcher

That's interesting about the overheating. BTW, perhaps just as important as the dummy channeling air over the cylinder is the fact that it reduces the intake area thus helping to create a "suck through" effect for the air. I was wondering about this myself. The opening at the bottom rear of the cowl isn't very large so hot air would get "trapped" inside the cowling. I thought about maybe doing a cut-off cowl similar to the Snipe or the Camel but it doesn't quite work with the Puppeteer's lines.

So maybe I need to put together a quickie photo dummy (affixed to the cowl). I can use the same one I made for the Snipe.

bassman

By the way here is my only RC claim to fame from the January 2006 edition of Model Airplane News!!!

abufletcher

Well done! [sm=thumbs_up.gif]

abufletcher

Here's the dummy engine for my Pup. I still need to figure out the details on how to mount it. One possiblily would be to screw it on to the front end of the engine mounting beams. Another idea would be to epoxy it on to the cowl.

I started with a CDROM as the backing for the photo but then realized that that would melt. So I copied the CDROM pattern onto 1/32" ply. This is a little too flexible so I'll probably add some wooden cross-pieces on the back. Then the whole thing needs to be fuel-proofed. I do the back wood with urethane and the photo with Nelson's Clear.

The "missing cylinder" should channel air to the Saito cylinder and I plan to open up the bottom of the cowl a bit more to create adequate flow-through.

TFF

You might need to add some cooling holes to the cowl if you think it is overheating. If the air stagnates in the cowl it will deflect air trying to come in with the cushion. The real pups have those long cutouts mostly on the bottom and I think the Neiuport 28s had some on the side, so I think you can make some "authentic" field modifications.

abufletcher

That's true. There's a large cutout now but the muffler blocks most of that area. The long "smiling" opening might be just the thing to add. The rule of thumb for airflow it to have at least twice as much exit space as entry space.

Other exit area is provided by the holes around the rocker heads and also the opening in the side for access to the glow plug. So with the "chin opening," the gap at the bottom of the cowl, the holes over the rocker heads, and the hole in the side, I think that adds up to more than enough.

BTW, it's certainly counter-intuitive (to the new builder) that the engine could overheat with that BIG ROUND HOLE in front! And with a big "fan" spinning at 10,000 rpms in front of that!!!

TFF

The exit 2 to 1 or better is right, but also if you can direct the air over the engine to the exit can help, if things seem marginal, and you get to the maximum cutout you want to use.

abufletcher

I decided to glue the dummy directly to the cowl. To make it fit I had to shave off about 1/8" off the ends of the engine beams. Now it isn't touching the engine anywhere. It still needs fuel-proofing.

TFF

Looks good.

DrHair

Without starting an IC vs Electric argument, it's interesting that there should be an overheating issue potentially. I don't expect a problem but you never know. I'll let you know once I've maidened mine.
Good work though Abu et al.

abufletcher

I took the Puppeteer to the field but didn't fly. The engine ran reliably and idled well, but it seemed a little flat at full throttle. I tweaked this and that but it didn't seem to solve the problem, so I'll need to ask one of the "club pros" to check it out. Getting an engine tuned just right seems to be as much of an art as building. And I sure don't have the magical touch. [&o]

I did, however, take this opportunity to taxi it up and down the field and got a feel for how to turn it around and how it will be on take-off runs. It takes a good bit of speed for it to get "light on its feet" and it's not particularly squirrely even with the taller, narrower gear. I taxiied it around for almost 30mins without any engine problems. I did discover that I'll need to add a little metal "boot" to the skid since without it, about 1/8" was sanded off skidding around the field!

During the taxiing one of the bolts on the wing struts vibrated loose and fell out, which meant that one of the flying wires fell off too. I'll need to double (double) check all of these again. BTW, this is precisely why I decided to swap out the imperial bolts and nuts that came with the kit for M3 bolts and nuts that I can purchase locally.

The other thing I noticed as I was shooting some more "stills" was that the lower left wing looks like it has a twist to it. You can see this in the last photos. I hadn't noticed this before. It might be something that my music wire rigging introduced as I certainly thought I had built it straight. Anyway between the cross-strut bracing and some minor tweaking to the length of the rear strut I should be able to pull it into place.

What would be the effect of one slightly twisted wing panel on a biplane? I didn't have much time during the first flight to appreciate how it flew but it seemed to respond normally to aileron and didnt look like it wanted to turn or stall.

abufletcher

Maybe this is a clue for you engine gurus out there: As I adjust the needle valve from rich to lean, it goes up to a bit before what my ears hear as "the top" (maybe around 9000) and then the RPMs drop again. The "sweet spot" seems very narrow and it's not the full RPMs I'm looking for (which on this engine is about 9800-10,000)

abufletcher

A little photo analysis shows the lines. I'm not sure where the problem lies and the geometry is a bit mysterious. The top wing looks about right (as "right" as I'm going to get it). And I've checked the length of the rear struts (identical) so I'm not how the twist is possible. It looks like I should shorted the left rear strut by about 1/8"

bassman

How much run time does your engine have on it? If it is a young engine it will get a little stronger as it breaks in. Where does the prop size fall in the recommended range for your engine? If it's at the very high end for diameter that will cut down your top rpm a little. What % ntiro are you running? If you are at 10% you may want to go to 15%.


Your wings look fine don't mess with them. A little twist may induce a little roll. Figure out the other issues first.

Bassman