Trim

I am pretty new here....
So maybe asking about old news.

With full flaps I am running out of nose up trim at about 85 IAS. Have 15lbs of lead in baggage area.
I am nose heavy at 55.77" CG empty, I know. But I am hearing from a couple of 3 pilots, this is pretty typical due to a small trim tab.
Are you all experiencing pretty much the same.... and if so, at what speed?
Thanks,
Nickster
N13KE

Hi Dennis

Not flown the RV-3 yet (getting there!) but the issue and cure I would suggest is not the trim / speed etc., but purely the CG position. The RV-8 suffers from this too, solo, if the basic CG is too far forward.

I presume the following still holds true:

13KE is heavy, and nose heavy at 55.77 CG empty, 893lbs. Scaled it twice. I know the Hartzell is mostly to blame. 24lb concord battery ahead of the spar also...
The plane much prefers wheel landings...

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Randy L stated early on with his flying:

Trim speed ? One thing I noticed on my first landing is that I can't trim to approach speed. In the original nose-heavy configuration it won't trim to anything below 95 mph. This of course was one of the clues to a fwd CG condition. With the 25 lbs of lead in the back it behaves better, and pitch forces are lighter on approach, but I still need to hold back stick all the way to landing. My trim tab is getting 20? of deflection, I'll try to change the range to provide a few more degrees...
I'm flying now with the battery relocated aft of the seat. My spreadsheet tells me this shifted the empty CG from 57.08" to 58.05" (will verify by re-weighing the plane soon [57.56"]), which doesn't sound like much. Still, it makes a noticeable difference and the plane feels much better now in all modes and just lighter altogether. This CG location also still leaves ample baggage capacity so I'm happy and consider the CG optimized....
Optimizing CG
In building an RV-3 you really don't have too many options available in controlling the aircraft CG, mainly just the battery. I originally located the battery just forward of the main wing spar so as to preserve as much baggage compartment weight capacity as possible. Also, Van told me "you really don't want to operate an RV-3 near the aft end of the CG envelope".

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I would disagree to the extent that there are other aspects to shift CG, all depending on how radical / how many $$$ you wish to splash out on.

What Randy (and Van) hints at is that shifting the CG aft is not just a mechanical process - it will alter the handling characteristics... As CG goes aft the aircraft will come more "fun" to fly / less stable which by all accounts is where the RV-3 excels. Once / if you get to the point where you do not run out of trim, it indicates the basic CG is as designed [NB RV-3 airframe was designed for a 125HP engine with a light wood FP Prop]

My first target would be that Concorde battery. Replace with a PC680 or LFX18 and you should see a difference? If you'd rather stick PC680, then next step would be move it aft (as you say) - there would be little point in shifting the LFX!

I have some other targets employed on the RV-8 that I will be using on the RV-3 to get CG aft... PM if you want more info

On my RV-3 the elevator is real heavy at full up trim on final, there is no way you could land this plane with the trim only if the elevator control is non-functioning. The cg is right on the money. I was told by an multiple RV builder to increase the size of the trim tab at the build time, but I did not. Now as they say 20/20 hindsight.

Trim Tab Travel.

A lot of folks set the push rod on the trip tab so it travels the same number of degrees up as it does down. RV-8 Folks talk about running out of nose up trim when at final approach speed and forward CG

Based on this and a recommendation from one of the tech guys at Van's, I biased mine so I get more travel out of the trip tab to get more nose up trim and find I can trim the stick forces out when on final. I still have plenty of nose down trim for cruise even with aft CG.

Cheers
Mike

On my -3 I have the battery behind the seat, and the c of g is slightly aft. I have all the trim that I need, and the stick pressure remains light during landing. If you have a metal prop, you might want to change over to wood, much lighter. My trim tab is also the size that is indicated in the plans. Don't know it would make a difference, but do you have a header tank?

This is all good info and it confirms what I have heard and offers some new things to think about.
I had talked with Paul Dye and Rob Holmes about this trim issue and I am now clear on what is going on and what I can do. Paul advised against making the trim tab larger... understandable given the limited flight testing done back then and not wanting to venture into test pilot land. I would love to have a composite light weight prop like he has on Tsam, but it's just too expensive for me to consider at this time.

N13KE is an older build from back in '82. A newer O320 engine, Hartzell CS prop and front mount governor was installed in '95 and that added a lot of forward weight. The original Prestolite starter is also heavy as is the Concord batt just ahead of the spar.

I plan to take much of the collective advise. Move the battery aft and maybe use a light Lithium Iron unit. Next will be a light SkyTech NL type starter. Those two things should get me closer to the 58 inch range I hear is about right. I am heavy as pilot weight goes... and need to loose some tonnage anyway, so that will help also in more ways than just CG!

Though I already enjoy the flight handling of my 3, it will be nice to feel the improvement as CG moves aft.

Thank you all for helping me with this. I appreciate the value of this forum.
Dennis Nickson

Nickster said:

Have 15lbs of lead in baggage area.

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Nickster said:

Move the battery aft and maybe use a light Lithium Iron unit.

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OK, so if you are moving the battery to adjust the CG, what is the purpose of going to a lighter battery???

If you get the battery in the right spot, maybe you can get rid of the lead ballast, with the lighter battery, maybe not.

Hi Dennis

I am heavy as pilot weight goes... and need to loose some tonnage anyway, so that will help also in more ways than just CG!

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Regrettably not! Pilot is aft of CG [81"] so heavy pilot will bring CG back.

After your post I expanded my RV-3 spreadsheet to "guess" where the CG will be. Datum starting point was Randy L's aircraft, since he documented the equipment and CG well. The output is an 800lb BW and 58" CG is possible, albeit I suspect some of my savings are optimistic. I put N13KE in with some guesses and it came out as 877/55.86 which is not far off I believe?

As above, battery aft will help if you go PC680. As Mike says, little point with Lithium, and the added cable will add as much weight (or more) as the battery weighs!

Best "bang for the buck" is the tailwheel. Every added 1lb there will pull basic CG back ~0.2". So ensure you have a nice solid tailfork (e.g. Bell), and avoid these new fangled "lightweight" tailwheels. People talk of clamping a weight around the tailfork?

The other area to look at is the alternator / flywheel. If you can get rid of a 40A Alternator up front, move to the Sky Dynamics featherweight (no pulley) flywheel you can lose 6lbs or so, even with a replacement Vacuum Pad Alternator (B&C SD-20, SD-8 or Plane Power 30A). If you can go to a lighter alternator, better still...

Next will be a light SkyTech NL type starter

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They now do a XLT - 3lbs lighter than the NL and 2lb lighter than the LS.

Mike and Andy are on point as to CG...
My motivation is not only to move CG aft but also reduce weight. An Odyssey or Lithium iron battery in the rear of the baggage area is not going to have as much affect as moving the Concord back there, I know. And the added cable from back there will add weight. Hmm.
I also recognize that if I loose weight, it makes CG worst.... what to, what to do.....
Maybe I just change out the Prestolite starter for a Skytec.... moves the CG aft and saves nine pounds or so...then remove the 15lb ballast... and forget the diet ? ;-)

Diet Plan Optimization

Please someone tell me the perfect pilot weight to be to have good CG in the 3. I'm a little pudgy and want to make sure I balance the importance of 3B C.G. versus the importance of the new FAA weight limits...

Be as light as possible! Live long and prosper....

Nick,

The lighter starter will help a bit. Have you looked into a composite prop yet? That will save more weight and also shift the CG back.

Please shoot over to KVCB, I'd love to see it now that it is up and flying.

Cheers,
Brant

Whirlwind Aviation Prop

What do you guys think about the WW 200RV prop for use on a 3? I'm not sure how light it would be with the governor and all, but it would give CS performance and a fairly light prop, no?

What do you guys think about the WW 200RV prop for use on a 3? I'm not sure how light it would be with the governor and all, but it would give CS performance and a fairly light prop, no?

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WW say 41lbs inc spinner, + ~2lbs for Governor.

Their 151-H is nearer 32lbs inc spinner, and used by both Randy and Paul/Louise. The MT MTV-11 is also about that weight. If you want lightweight, those 2 props seem the best options (only) to me?