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When the gear is tall the fulcrum length is greater (the "weight" on the end of the fulcrum is the prop thrust pulling foreward) and the aircraft feels tippy, so some up elevator is going to be required. How close to the CG the wheel axle is also plays a big part in the tippiness also when the airplane is running or landing "tail up" as in a wheel landing or during the take off run when the tail lifts. If the model is generously powered holding up elevator on the TO run is risky and must be done carefully or the model may start to fly before it's ready and stall,OOPS! On a wheel landing the model will tend to want to pitch foreward when the wheels touch as even if they rotate very freely it sort of applies the brakes and will pitch the model fwd and if you apply up elevator to compensate the model may fly again if it wasnt really going slow enough to land. Practicing and perfecting slowing down and three pointing the model will help in all respects as then the tail is down the GC is rocked back behind the axle and we're going slow enough to stay on the ground at that attitude.
As far as using the Vanessa there isnt much to say, support the model and twist the dowel untill it is level (I dont use a lot of nose down, as you said "more chemical in one tray) balanced is self explanitary so if you want more weight on the nose select a further foreward balance point. If the pointer isnt where you want it add weight to the deficient end and re level and check the spot of the point. Repeat as necessary to get the plumb to indicate the desired spot.

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I'm not sure but did anyone mention that a bubble level needs to be used with the Vanessa? I used a level spot on the fuselage to place the bubble level. To move the Cg forward, I placed a weight on the nose then turned the Vanessa to re-level the bubble. The plumb bob (fishing weight) then proved the Cg was shifted forward. Likewise for moving the Cg aft.[ATTACH]1979483[/IMG]

I am absolutely sure and you can take it to the bank unless you want to make a friendly wager! Just imagine an extreme case scenario of the LG being mounted on the rudder post and your airplane has the correct CG for this application. It will fly once airborne but you will never get it off the ground under its own power!

You can calculate and balance a model for any arbitrary 'c.g.'. The fact of the matter is that conventional aircraft, i.e., those with a rear stab/elevator, fly best with balance point at ~25% MAC. It is a matter of spin recovery. I had a buddy who had a Pitts. We put it on the scales and he calculated its balance point. He decided to move c.g. rearward by moving the battery. The goal was to make it a little more responsive. He got up to altitude and entered an inverted spin and couldn't get out of it until he reached denser air which was ~3000' above sea level!!! If his tail feathers were a little bigger he 'may' have gotten out of the spin sooner. He certainly had his Pitts at the limit! There are lots of variables. Your Snipe is a scale model of an airplane that was designed to be twitchy for the most part... it wasn't a B.E.! Get it balanced at the 25% point then add/remove a little nose weight at a time. You'll find a 'sweet spot' eventually. as you well know, most WWI airplanes had LG located in such a way that the models will be 'tippy'. We land our models in an uncut hay field relative to what the full scale ones do so no wonder they want to nose over. The ideal field would be a felt covered flat surface... right?

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I use blue painters tape to keep the cord from sliding. You want the model to pivot when you rotate the dowel.

The plumb bob always points directly at the CG! It doesn't matter if the plane is hanging level, nose up, or nose down...the bob always is pointing directly at the CG. The CG of a plane is located in 3 dimensions, not just fore and aft. It is located somewhere within the volume of the plane. The reason that you level the plane is to determine where the CG falls in relation to the wing chord. Actually, leveling the fuselage is just an approximation...what you really want is the wing to be at the same angle it will be when the plane is flying straight and level...usually several degrees positive angle of attack. When the wing is at this orientation in the V rig the plumb bob points to a location on the wing that is directly above or below the actual CG (depending on if its a high wing or low, or both). The idea is to adjust the weight of the plane so that this point is in the proper location (approx 25-30% of the chord line).

When he says level, he's referring to the datum line.

"When he says level, he's referring to the datum line."

Not quite. The datum line is just that. A line from which all "data" is taken.

When one speaks of level, it usually refers to the horizontal stabilizer being horizontal, in the attitude of "normal" flight.

Les

p.s. I believe that with the SE5, that means slightly nose down, to provide the pilot with some view over the nose.

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Hey guys...finally found this graphic I got from Duncan Hutson years ago..I have used this method very successfully for years and have never had any exciting moments on my first flights...it works very well.http://www.rcuniverse.com/forum/atta...mentid=1979771

Well, a lot of that is pretty confusing. The "till it's level" was referring to the model, or the stab but a bubble level really isnt required, the good old mark one eyeball will work fine. Establishing where it should be balanced has nothing to do with checking the CG with the V rig. The rig tells you where it is balanced and you need to know where to put the weight to bring it to where the "where it should be calculations" have indicated. The support harness (ropes, cords, nylon strap whatever) should not slip around on the model so something needs to be done about that. The rod (large dowel/broom handle) needs to be large enough to provide traction for the "wraps" of the harness, a length of music wire isnt a good choice for the rod. It needs to provide a stable surface for the cords. The rig your Puppeteer is dangling from looks suitable, I'd prefer a larger dowel but that one will prolly work. And yes with 5 degrees of positive incidence in the stab and lower wing the SE 5a fuse needs to be at least 5 degrees nose down, that's a no brainer.
If the axle of the LG is near the CG it (the model) doesnt have to tip very far fwd to put the CG ahead of the axle and at that point you better have enough airspeed so your elevator can control it or its a prop strike. Both scales of my N28s are sensitive to this as the gear on both models is scale in dimension, location and function. Wheel landings need to be done at a slow enough speed so elevator can be used to keep the tail down without the model flying up again. So check Chris' recommendation on CG and do a little math and see where 25% of MAC is and compare and maybe do some adjusting if it looks like it could be a bit further back. All the calculations are is a starting point anyway as eack model will likely differ somewhat from another, flying it is what tells you if the CG is OK/
Doc

You want the plane to hang in the same attitude that it flys in normal level flight. Usually this means the horizontal stab will be "level"....but it really depends on the airplane's characteristics.

Due to the way the model is suspended in a V rig the plane "must" move if you add weight to the tail or nose! Look at the attached drawings. In the first you see the model suspended in the V rig harness. The CG of the model is located directly under the dowel and the plumb bob which is also attached to the dowel points directly to the CG.

In the second view, I added 2 lbs to the tail of the model. As a result the CG has moved back drastically. The new CG must fall under the dowel also. You can see how the model moved nose up in order for the new CG to fall under the dowel.

In the third view, I have leveled the model by rotating the dowel. Although the model moved the CG did not...it's still directly under the dowel and the plumb bob is still pointing to the CG.

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I agree that there is a HUGE difference between calculating where a CG should be and where it actually is! What counts most is the difference, if any, between those two points and how the flight is effected by that difference.

Y'all sure take a simple thing and make it complicated! However, that's your pleasure! I can balance twenty airplanes in the time it takes you to type all of this stuff! Don't get sore but I'm just sayin'.... ;)

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'Bit by bit' (?) and you discount my silkspan tail feathers idea. Shame!!!! Well, it's all good. Just remember that the stab is what you want to level first before putting the balance point at ~25%MAC.

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