EZ Fuselage Extension for better CG

I'm considering using a rotary engine in my OpenEZ project. Like O-320/360's, this is a heavier powerplant than the aircraft was originally designed for & shifts the CG noticeably aft. I've seen references to people putting ballast in the nose to achieve better CG ranges.

 

What do you think about extending the fuselage by 6"?

 

Option 1: Leave a gap between the backseat & firewall. Scoot the pilot, GIB, nose gear, canard, etc forward, leaving the strakes & wing attachments in the same place.

 

Option 2: Leave the GIB seat in place, just increase the separation between him & his instrument panel (wasn't expecting anybody flying from the back seat anyway).

 

Or is it just better to put some ballast into the nose?

 

Thanks,

 

Firefly

What do you think about extending the fuselage by 6"?

What do you know about the relationship of Aerodynamic Center(s) to Centers of Gravity, and how to determine the Aerodynamic Center of an aircraft?

Or is it just better to put some ballast into the nose?

I like this option!

 

I built a LongEZ with an O-320 and a MT constant speed prop (45 lbs). I was very careful on my weights and went to extreem to move as much weight as far foward as possible.

 

Extend the nose about 9 inches.

brake cylinders in the nose.

Battery moved forward.

electrical system components, master relay, strobe power supply.

 

When I finished, I didn't need any ballast, and my CG was at the aft limit (103.5)

 

(Correction - the Aft limit is 103, not 103.5. edit by Waiter)

 

Look at how I did the nose here:

 

http://www.iflyez.com/LongEZ_Construction_Photos_Nose.shtml

 

Waiter

What do you know about the relationship of Aerodynamic Center(s) to Centers of Gravity, and how to determine the Aerodynamic Center of an aircraft?

I've got a BS/MS in aerospace engineering.... but then immediately went into software.

 

For those playing along at home: the CG is the fulcrum you're trying to balance the aircraft on. The AC is the point where a surface's lift is centered on, generally about the 25% aft of the leading edge. The smaller lift force of the canard/tail is balanced against the large wing lift by the canard having a longer moment arm.

 

This is another reason why I thought an extension might be good, to increase the moment arm of the canard.

 

I shouldn't have said "6 inches", as I haven't calculated any weights & moment arms yet.

When I finished, I didn't need any ballast, and my CG was at the aft limit (103.5)

Very interesting. I'd be nervous at first about the load transfer from putting so much in the nose, but it's apparently working well for you.

 

At the moment I'm still more comfortable with the thought of stretching the bathtub, as it would seem to be structurally simpler. Need to get the TERF CD and look at actual lengths & weights.

As your aware, one of the many issues you'll need to address when you install your fuselage "plug", the published LongEZ numbers, CG, weights, MAC, etc, will no longer be valid for the new aircraft.

 

I believe this is what Marc was getting at, This is not the type of modification that can be made by someone like myself, or the majority of builders.

 

I lack the knowledge of how these items need to be computed and how they interact with each other.

 

For people like myself, its a safer bet to follow the plans and stick with the proven design.

 

Waiter

I've got a BS/MS in aerospace engineering....

OK - a good start.

 

This is another reason why I thought an extension might be good, to increase the moment arm of the canard.

Think about it - you're suggesting moving the AC forward while you move the CG backward. I'll ask again:

 

What do you know about the relationship of Aerodynamic Center(s) to Centers of Gravity?

 

Knowing the definition of each isn't sufficient. Go back and review what the relationship should be, and then think about what the movement of the canard forward will do to that relationship, and then think about why the relationship needs to be what it does.

I'm considering using a rotary engine in my OpenEZ project. Like O-320/360's, this is a heavier powerplant than the aircraft was originally designed for & shifts the CG noticeably aft. I've seen references to people putting ballast in the nose to achieve better CG ranges.

 

What do you think about extending the fuselage by 6"?

 

Option 1: Leave a gap between the backseat & firewall. Scoot the pilot, GIB, nose gear, canard, etc forward, leaving the strakes & wing attachments in the same place.

 

Option 2: Leave the GIB seat in place, just increase the separation between him & his instrument panel (wasn't expecting anybody flying from the back seat anyway).

 

Or is it just better to put some ballast into the nose?

 

Thanks,

 

Firefly

12" has already been done. there is a cozy IV that has been stretched and is flying . the Berkut is a 12" stretched long eze design. they both use the same wing and canard as the long ez.

They both have retracts in the extra 12" space behind the rear seat.

I extended the nose of my highly modified Cozy MkIV fuselage, but made sure that the extension was in front of the canard.

 

The distance between the canard and the wing stays the same -- moment arm of the canard's lift doesn't change.

12" has already been done. there is a cozy IV that has been stretched and is flying . the Berkut is a 12" stretched long eze design. they both use the same wing and canard as the long ez.

They both have retracts in the extra 12" space behind the rear seat.

if they have retracts in the extra 12" behind the rear set I understand that they were stretched in that point so what happened to strakes? were they also stratched? I mean: if you take the centersectionspar 12" aft, you have to stretch the strakes also or you'll have a hole there......

When I finished, I didn't need any ballast, and my CG was at the aft limit (103.5)

Waiter

Don't forget that CP #37 made a change (LPC #116) from 103.5 to 103!

 

Dave

The Berkut moved the passenger forward of the centersection spar 6 inches. The pilot and canard were moved 12 inches forward of the centersetion spar.

The centersection spar did not change position.

 

If you are adding retracts, the Velocity/eRacer style eats up that additional room between the firewall and the passenger. The Infinity style of retracts leaves that area open and is usually used as a reserve fuel tank or large sump.

 

A lot of canard builders are stretching the strakes even without a stretch mod. Mine extend to the instument panel.

Correct, The Aft CG limit was moved from the original limit, 104. To the new limit, 103.

 

I'm at the aft limit, 103, not 103.5

 

Waiter

OK - a good start.

 

Think about it - you're suggesting moving the AC forward while you move the CG backward. I'll ask again:

 

What do you know about the relationship of Aerodynamic Center(s) to Centers of Gravity?

 

Knowing the definition of each isn't sufficient. Go back and review what the relationship should be, and then think about what the movement of the canard forward will do to that relationship, and then think about why the relationship needs to be what it does.

I'm actually trying to get a net CG change of zero relative to the wing. The idea is that the shift forward will counteract the heavier powerplant.

 

Moving the canard forward will increase the moment arm of the canard lift force, producing greater pitch moments. If the CG is the same relative to the wing, the wing moment remains the same. I'm not sure what you're driving at.

 

Moving the canard forward will increase the moment arm of the canard lift force, producing greater pitch moments.

so should you reduce the canard span not to have a great lift(nose up) at high speed?

 

......A lot of canard builders are stretching the strakes even without a stretch mod. Mine extend to the instument panel.

I would like to know if this affect CG: if you stretch the fuselage and the strakes 12" forward, the fuel tanks also come 12" forward, does not it give a bigger CG difference between full tanks and low level tanks?

this is the reason why I asked about the berkut strakes(stretched or not).

I would like to know if this affect CG: if you stretch the fuselage and the strakes 12" forward, the fuel tanks also come 12" forward, does not it give a bigger CG difference between full tanks and low level tanks?

this is the reason why I asked about the berkut strakes(stretched or not).

 

Air,

 

Any time you make any change it has the ability to affect the CG.

 

Please don't take the next sentence as a personal attack. It is meant to inform, not only you but others on a subject that may prove less than livable.

 

If you are not a pilot, you will learn about W&B. If you are, your basic instructor neglected to make you understand what CG and it's calculations actually are.

 

Please, for your sake, and the sake of your aircraft and the reputation of the E-z types--- Learn all you can about W&B-- perhaps corner an instructor to help you.

 

With the knowledge of how W&B is calculated, you should be able to tell what will happen when you make various changes.

 

In certified aircraft, when new radios are put in or even one is changed, the CG is recalculated and recorded.

 

Anytime you put any kind of weight anywhere other than on the CG itself, it will change the CG (Of course the weight changes too).

 

If you know the weight added (subtracted) and know the distance from the DATUM, you can calculate your new CG. This calculation will tell you if you have to use some sort of counterweight, if your change will put you within the CG envelope, or if you decide to hang a V-12 Cylinder Mercedes engine on the back, what you have to do to the engine mount and other changes to keep the aircraft within the appropriate CG envelope.

 

Of course after you finish the plane you will do a weighing CG--- Vital for your airworthiness certificate. It seems that they don't really care if the aircraft falls apart as long as you show them a good CG sheet.

 

Again don't take this personally. This type of question comes up all to frequently.

 

Understanding W&B is as important as understanding glassing technique.

so should you reduce the canard span not to have a great lift(nose up) at high speed?

Lift is a function of wing area and angle of attack (... and dynamic pressure, etc), so you could just reduce the angle of attack of the canard by pitching the stick / trimming. I wouldn't think changing the structure or the fixed pitch angle of the canard would be necessary.

 

Changes to takeoff trim would have to be determined, but if we're talking a few inches on a 8? foot moment arm, without crunching numbers I don't see it causing a big impact (<-- Well, that's a bad phrase to use).

 

Of course there's the dynamic modes to think about. I'll have to dig out some stability & control books.

Lift is a function of wing area and angle of attack (... and dynamic pressure, etc), so you could just reduce the angle of attack of the canard by pitching the stick / trimming. I wouldn't think changing the structure or the fixed pitch angle of the canard would be necessary.

 

Changes to takeoff trim would have to be determined, but if we're talking a few inches on a 8? foot moment arm, without crunching numbers I don't see it causing a big impact (<-- Well, that's a bad phrase to use).

 

Of course there's the dynamic modes to think about. I'll have to dig out some stability & control books.

 

Hey, great Idea:mad: :mad:

 

If you do the trim situation, you may find that you run out of downward trim or downward force on the canard with a rear CG, and possibly duplicate the B-2 accident.

 

If you reduce the angle of attack of the canard, you will have that effect, however, at a certain point of reduction, and a certain point at the CG, because the canard will be at a lower angle of attack, with respect to the wing, than the original design, the wing may stall before the canard and you will float down to the ground ever so slowly, unable to get out of the deep stall that the scheduling of the stall angle of attack of the canard is supposed to prevent. However if this happens, you really won't probably have to worry about fixing it:sad:

 

If you decide to change the angle of the canard, do it with plenty of advice from those who know and best from those who have done it and have thoroughly tested their aircraft in more configurations than just straight and level

 

the CG envelope is there for a very important reason. See my previous post about W&B.

 

The only purpose that the nasal augmentation serves, other than appearance is to enable you to use less weight to get your CG in the proper place (the arm is longer). You might find that the weight involved in the enhanced proboscis is equal to or greater than the weight that you would need in the standard configuration. But then you would have had the fun of the added construction. This CG change can and should be calculated before you go into surgery.

 

Just trying to keep you safe.

If you decide to change the angle of the canard, do it with plenty of advice from those who know and best from those who have done it and have thoroughly tested their aircraft in more configurations than just straight and level

 

Exactly, which is why I am *not* recommending changing the pitch of the canard. The canard has to stall before the wing, no discussion or arguments necessary.

 

You raise a good point about having enough downward pitch available. I wonder what the minimum lift generated by the canard is?

To my knowledge, the shortening of the canard was never associated with the Long-EZ design. This was something that came out of a mod of that design (the Cozy)

I'm actually trying to get a net CG change of zero relative to the wing.

But that's not what you SHOULD be trying to get. See below.

 

The idea is that the shift forward will counteract the heavier powerplant.

Yes, and either putting more weight in the nose, or extending the nose so that a lesser weight at a longer moment arm can counteract the weight in the rear is something that is commonly done, as neither has a major affect on aerodynamics. The aircraft (Berkut, Esselstyn O-540 COZY MKIV with Velocity Retracts) that have been stretched 12" BETWEEN the wing and canard have different CG ranges than aircraft that are not stretched. between the aerodynamic surfaces.

 

Moving the canard forward will increase the moment arm of the canard lift force, producing greater pitch moments.

Which is destabilizing. Hence the need for the understanding of the relationship of the aircraft Aerodynamic Center to the CG range.

 

If the CG is the same relative to the wing, the wing moment remains the same. I'm not sure what you're driving at.

If you move the canard forward, you change the aerodynamic center of the AIRCRAFT - the main wing is not the only lifting surface. Keeping the CG in the same position relative to the MAIN WING is meaningless - it needs to be in the correct position with respect to the aerodynamic center of the AIRCRAFT.

 

So, unless you understand the relationship of aerodynamic center (of the AIRCRAFT, NOT just the main wing) to the CG, and unless you know what moving the canard forward by an arbitrary amount will DO to the Aerodynamic center of the aircraft, you have no idea where the CG SHOULD be, and therefore have no idea whether moving some "stuff" forward to attempt to counteract the extra weight in the back is a good idea or not.

 

That's what I'm driving at, and what you're not picking up on. This is non-trivial, and even moreso with canard aircraft than with conventional ones.

Argoldman, W&B is of course basic pilot stuff, but I think what we're talking about is beyond that: here the canard moment arm has been increased and the shape of strakes is changed, considering also that the strakes have been changed from a flat surface to a lifting profile(even if the flat surface has a little amount of lift too) this lead to a change that is not just trivial.....

anyway I don't consider yours as an attack to anybody, eventually as a suggest: thank you for you reply!

Argoldman, W&B is of course basic pilot stuff, but I think what we're talking about is beyond that: here the canard moment arm has been increased and the shape of strakes is changed, considering also that the strakes have been changed from a flat surface to a lifting profile(even if the flat surface has a little amount of lift too) this lead to a change that is not just trivial.....

anyway I don't consider yours as an attack to anybody, eventually as a suggest: thank you for you reply!

Even without any modifications at all, you still need to do your w&b clculations to validate the placement of the datum before your first flight and FAA inspection. Same with all of the other published specs of the design you are building (all of your 'V' nubers, etc.)

Argoldman, W&B is of course basic pilot stuff, but I think what we're talking about is beyond that: here the canard moment arm has been increased and the shape of strakes is changed, considering also that the strakes have been changed from a flat surface to a lifting profile(even if the flat surface has a little amount of lift too) this lead to a change that is not just trivial.....

anyway I don't consider yours as an attack to anybody, eventually as a suggest: thank you for you reply!

My original comment was based on the fact that the position of the canard was not changed.

 

The real question is what effect on changing the C/L the lenghtening of the nose and modification of the strakes has.

 

Assuming that you don't change the wing/canard distance (which Marc talked about in a prior post), It would seem that the elongation of the nose might push the C/L aft somewhat. Not being an aeronautical engineer (but I play one on the web), I have no idea how much if even appriciable.

 

Now back to the CG point. Since we have a good idea of where the W&B should be for a stock Cozy, If the nose extension modification is made, even if not, it is important to do the initial test flights with the CG in the middle and test fly from that point expanding the envelope until the CG causes the instability.

 

I think that this conversation is a great opportunity for all.