From what I have read (and been told) it should indeed be possible to build a model with scale fidelity that flies well.

Particularly in the case of WW1 subjects where the RAF-15 Airfoil for instance is apparently very tollerant of the issues caused by Mr Reynolds.

The incidences on your model all sound about right. But I would note that in some cases, the full sized prototype had the vertical Stab offset by about 4° to the right to counteract Engine/prop torque.

There is a factor that we modellers miss out on though regardless of the setup of a model. And that's the seat of the pants feel that told a pilot where to put the stick or rudder bar.
We rely on visual fed back which we then translate to what we think is happenning and what we can do to correct it. So it's only natural that we don't generally fly our models (unless we are very practiced and experienced) as smoothly as a pilot actually flying a full sized SE5a for instance might do.

The SE5a was known as a stable gun platform but with manueverability when needed...

I wonder if my Topfilght SE5a kit will have similar issues.

Cheers,

Hugh

I've heard of that idea but never really paid careful attention to it before. Now that I'm looking for it, I see in the Wylam SE5a drawing (also shown on the forum link someone provided earlier) that the vertical fin is indeed off-set to the right!

That's the thing about going scale. If you're going to go scale, you have to go ALL the way!

*****

Makes me think that maybe I DO have to somehow get more right thrust. BTW, something else that I haven't checked is whether there may be some slight degree of left offset on the model's vertical fin that could be adding to the problem. If there is, I can't change this now, but I could add in a click or two of right rudder.

Using photoshop to measure off the above drawing, it looks like the fin was offset to the right by a bit more than 4 degrees. So...does right engine thrust of 2 degrees = right fin off-set of 4 degree?

Actually Don, that Wylam Drawing is showing the Fin off set to the LEFT! At least that's my interpretation. And I would not take a Wylam Drawing as gospel... There a great many details on his drawings that bear NO relation to reality.

Consider two things.

A) the Tail Moment is about three (maybe three and a half) times longer than the Nose Moment.
B) the Offset motor is PULLING the nose around to the right, while the (right) Offset fin/rudder is REACTING to the airflow by pushing the tail to the left. So possibly, the fin/rudder offset is less effective than the engine offset.
Just postulating... my Aerodynamics might be right up the Khyber.

Cheers,

Hugh

Damn semantics! If you look at the tail post of the fin, it's dead-center. Then look at the "nose" of the fin. It's offset to the right of the center stringer.

You're right there. I just checked on the Replicraft drawings and there is no indication of any off-set on the vertical fin.

I'm assuming that what the vertical fin will want to do in flight is adopt a position of least resistance, i.e. with the LE directly into the airflow. If we take the LE to be on the right side of center, then for the fin to get lined up with the airflow, it will try to swing the tail to the right. So that doesn't make any sense! :confused: I suppose the better way to look at it would be as a vertical airfoil with the right off-set equating to a raised LE. This should (at least in my mind) produce more "lift" ("pressure") on the left side compared with the right side so the fin should move to the right.

That's the opinion of an English teacher.

I agree with that assessment... I think.
Have a look at any GOOD drawing of a Hawker Hurricane. The Leading edge of the tail is offset to Port.

Anyway, as promised, I took some photos of the side thrust on my BUSA Pup.

http://www.rcuniverse.com/forum/atta...mentid=1962768

Very obvious.

Cheers,

Hugh

Thanks. That's about how things looked on my Puppeteer as well.

Well, let's see, progress of sorts. I guess. In an effort to get more than than that silly 1mm of right thrust, I drilled and filed out the holes a bit more. And as an strength improvement added a 6mm think "flange" of fiberglass reinforced material (similar to but tougher than G10) below the ply mounting shelf. So now the ply "shelves" are sandwiched between the metal engine flanges and the fiberglass material.

And so yes, I can now get more right thrust (probably up to what we see in Merlin's photo)...but...it's not exactly equal rotation. Measured on my cable the left side moves forward about 1/8 inch while the right side moves back almost 1/4 inch (both relative to a neutral mark). Obviously the engine isn't rotating around a center point.

And I'm going to make myself not care! :D

Top view.

Quote, "and I'm going to make myself not care!" I tried that once to no avail. Easier said than done.lol

Again using PS for a bit of photo-analysis, the engine is now has between 1.5 and 2 degrees of right thrust. In the case of the SE5a it doesn't matter too terribly much that the crankshaft center is a couple of millimeters off center. That sort of thing is more visible in a "round cowl."

If it flies well...and after I get used to how it flies...I might consider moving it back to 0-0.

Don, it's a beautiful model. But if you can't fly it (that is to say, if it cannot be flown), then you may as well donate it to a museum...

I'd be living with the off centre prop for a month or so:D.

Cheers.

Hugh

So, I have some experience with scale bipes. One thing to do is find a friend that has a bipe that flies really well, and compare notes and airframes.

Right thrust will help, but only so much. How much does your airframe weigh? If it is really light, with drag a strong motor will make it torque out hard if you don't have much aileron travel. Differential aileron and mixed in rudder can pretty much tame most bipes that be have badly. Your airframe looks beautiful. I can't imagine it is some really radical alignment flaw.

just my 2 cents

billrad

Agree with MerlinV the fin offset is to the wrong side on the Wylam drawing. (I pulled my best of wylam and mine shows same error). Hurricane and Corsair both have 3 degrees of offset to the port side. (My pictures at work so can't post). Definition: the nose of the fin is to the left of center line while rudder post is on the centerline. This is done on purpose to cause a slight right yaw of the plane to counteract anticipated engine thrust and make balanced flight easier on the pilot. Designers usually calculate how much offset required on the "cruise speed" as that is when most of the flight is expected to occurs. Pilot has the advantage of feeling all of this in the seat of his pants.

I have never seen the vertical fin having what wylam has shown as it is on the wrong side and thus will cause yaw to the left. A bad thing! That does not help counter engine torque but adds to the problem and will make you plane fly squirrelly. (It just occurred to me we are assuming the propeller turns the same as our models. Was perhaps the full scale prop turn the other direction. I don't believe so?)

Your SE-5 with dead center fin is correct. Go with that and do not worry about it again. Your new right thrust will give you an entirely new plane and it will fly great based on your changes. Your plane is ASAP and will be awesome in the air!

That's a good point. Remember that there were both geared and ungeared versions of the SE5a. Perhaps the prop on the geared versions turned the other direction. I'm also just guessing. On the Wylam drawing there is a note saying "Counter-clockwise propeller rotation" (which I take to mean from the pilot's seat).

I feel confident that I've gotten rid of any set-up problems. Now I just need to do a few minor things to "button it up" and then get it out to the (new club) flying field. Actually, it would be foolish just to fly any model that has been sitting for over a year. Solving these problems has re-familiarized me with my model.

It's a little work but since you now know your wings, stab and fin are true you just block fuse on its side... 'zero' the fin and stab... then attach the incidence meter. By 'zeroing' I mean to consider any fin offset and stab incidence. I will say I sure learned a lot flying FF models! They are much more difficult than RC. Currently, sailplanes are teaching me a lot about 'energy management' and how to be even more exacting about model set ups!

You'll find you can have more discrepancies with engine thrust and fly comfortably. Rigging is a whole different ball game! My little Curtiss 'Pusher' didn't have enough 'up' thrust so that when power added it tended to 'mush' downwards. If power suddenly pulled it would balloon. I shimmed more 'up' thrust and solved the issue.

That just seems like too much work (even Les' idea of hanging it). Anyway, I think the model is now well within the ASAP range.

To be honest my main worry now is that I haven't flown ANYTHING in almost a year (since my Puppeteer crashed due to a broken wire in one of the transmitter gimbles). I'd sure be a lot happier if I could give an ARF a few whirls before flying the SE5a again.

The only things remaining are to re-check the balance and re-check all the radio set-up. Here's the discussion on balance on my RC GROUPS thread:

http://www.rcgroups.com/forums/showt...363887&page=73

I feel like determining balance is my Achilles heel. I very frequently get it wrong on the maiden and the position indicated on the plans is most definitely wrong. I just barely got the model back in one piece with it "balanced" at that point.

I think part of the problem is the different ways that different modelers used the term "balanced." To me, that word means that the model is "level" (for example, with the stab parallel to the ground). Other modelers talk about "balancing nose down." Well, that's not really balanced it is. Can you imagine people using a weight balance like that and saying "balance it with the left side down a little bit?"

Anyway, the number I seem to be coming up with for the CoG is 9cm behind the LE of the upper wing. If I put my fingertips at that point, the stab is about level (I think since I can't really see it properly and hold it at the same time). If I place my fingertips at the 12cm point marked on the plans the model adopts a significant nose-down attitude with the stab also pointing downward.

Radio and throws look good.

Here's a tip - hold the model in front of a mirror when balancing. It gives a different perspective and allows for a better look.

Don. Of course I am interested in your conundrum from an SE5 / builder standpoint. Lots of good tips and info. so far,. It is obvious from the last frontal photo that things have gotten rather "out of true". Good thing you have a Robart incidence meter.
Your frontal pic shows two major issues that I can see.
The incidence on your Starbord side ( yes= right side if you are the pilot sitting in plane) is more positive than your Port side.
This will of course in create more lift on that side, thus the Port side roll effect.
Also your cabane is not symetrical which may be causing some alignment problems to begin with but I doubt that this is causing you any major attitude problems.
On my Recent 1/4 Fleet rebuild I spent 15-20 hrs. adjusting the incidence to get all wings within 1/10 of a degree of their proper amounts.
This necessitated making all new wing root inserts so that the wings would be at the correct setting WITHOUT any cable adjusting help.
I then firmly held the wings in place as I made my cables and made sure I had the same incidence once all was removed.
For the first time in my building career I tried "0" degrees engine side thrust and "0" degrees down thrust...
Let me just say that it flew like it was "on rails" on the first flight which made me a firm believer in getting all incidences as close to identical as possible and also not worrying too much about side and down thrust.
But of course every model has it own dynamics.
Hang in there, Eric

Here is a simple way to set the CG that I have used for years. Set the model up so the center line is level, NOT the horizontal stab the center line running the length of the fuse. With the air still..no fans running ect. lift the model while balancing it at the correct CG point. If the tail drops add weight to the nose or remove weight from the tail. If the nose drops do the opposite. Repeat this a few times until when lifting the model at the correct CG point on the wings the model does not change attitude and remains level on the center line. I like this method because one person can preform this procedure and you will get it balanced exactly. It is very important that you know for certain where the CG point is supposed to be and best not be guessing where it should be. With all the hard work you have done this should be a walk in the park. After you get the model flying you can, if you choose, make small adjustments to the CG until the model flies the way you would most like it to.

All of these issues have now been corrected (see the finished rear view on page 4).

...within 0.1 of a degree??? What kind of meter are you using? I can maybe discern half a degree on the analog scale of my Robart meter but that's it.

There was a slight discrepancy in the winglets but I wasn't willing to do any "re-building' to resolve that. At any rate, all the incidences are now equal.

My model doesn't have any down thrust but after a nerve-shattering last flight where it just immediately cut left and wouldn't turn right even with sustained full right aileron, it's just prudent to put in some right thrust. If it flies well...and after I get used to how it responds to rudder, I may slowly move it back towards zero.

As Shakespeare would say: "Aye, there's the rub!" This kit is definitely still at the prototype stage. I'm only aware of one other CDScaleDesigns SE5a that has flown (Teus' model) and I don't think more that a dozen were ever sold. The plans show the CG at 12cm back from the leading edge and that's where it was for the maiden flight...which was a disaster as the model was absolutely uncontrollable and I have no idea how I managed to get it back on the ground more or less in one piece.

Using the calculation shown on the RC Groups page above, I came up with the new position of 9cm back from the LE. I then held a dowel spanwise at that location (to avoid the influence of my fingertips) and added weight to the dummy radiator. See the first of the balance photos above. Technically this is slightly "nose down" since with the fuselage center line would be perpendicular to the TE of the rudder (and the stab is actually a +3 relative to the centerline).

You are correct about the stab relative to the centerline that is exactly where it should be. I empathize with your dilemma being a designer and a scratch builder I have been there more than once. I have Dave Platts' plans for and exact 1/6th scale Se5 and he shows CG to be 2.7 cm back of the top wing leading edge. My intuition tells me that this too far back but in reality I do not know for certain. With all the Scale Se5s that are flying go with what these knowledgeable modelers recommended for they truly must know for certain and base this on reality not theory or math. It is also correct that the nose should be at a slight nose down attitude. I would be very interested to know where it ends up as someday I plan on building the Se5 kit that is tucked away in storage. Good Luck !