2 Bubbas in an 8

[Veetail88]

With only a few hours left in Phase 1, I'll be spending the weekend pushing out to the weight and balance limits.

It's imperative that I'm able to take my brother in the airplane, and neither of us is "dainty", so that means I have got to push pretty much all the way to the aft and max gross limits with ballast now.

I understand that the pitch forces will become very light and that will make landings a bit more tricky, and I know that the design has been tested and deemed "safe" at the published limits, but I'm wondering. Have most folks gone all the way into the corner of the envelope during testing? Does anyone consider the airplane unsafe there? Does the airplane scare anyone at that point?

Aside from the above, I would appreciate any input or tips on this. I'll go out there a chunk at a time, fly it to altitude and do some stalls and slow flight before landing it at each step.

Currently I've got 140 lbs in the back seat and the thing is extremely pleasant, but I suspect that's going to change quite a bit.

(Image removed by OP for inaccuracy)

[brad walton]

With aft CG, I have experienced a reversal in stick pressure in the flare. With aft CG and trim so there is forward trim pressure on the stick on final, as I flare the forward trim pressure on the stick decreases and actually reverses just before touchdown. In other words, I am holding back pressure on the stick on short final and just before touchdown, without change in elevator, I must decrease my back pressure to 0 and then go to push on the stick to maintain angle of attack. There is at least one thread here on VAF about this. It suprised me first several times I experienced this stick pressure reversal.
Search"RV-8 stick force gradient when landing".

[brad walton]

My empty CG is 79.52 and I can' t come anywhere close to 290 lbs. in my back seat

[akarmy]

So far I've done about 240 in the rear with no baggage. You basically land with cruise trim. As you slow the nose will come right up. I do wheel landings in this config with plenty of speed and it works just fine. As indicated above be ready to PUSH on the stick if needed to keep the speeds up and put the main gear on the runway. It actually lands fairly easy with weight in the back, but 3 point is a bit more tough as the nose will come up quickly when you slow.

[drill_and_buck]

Jesse,
I've flown with max rear cg without any issues. As noted, it does require getting use to both for 3 point and wheel landings. For testing to the max limit cases of plastic pint size water works well for ballast. They stack up nicely in the rear seat and baggage area.

[Andy Hill]

I've seen no issues at/close to aft limit.

However, I would not 100% trust all the figures are right, nor translate between different RV-8s. So build in some testing as above both at aeros aft limit and full aft limit.

I'm sure you'll NB easy to overstress, be wary of rough surfaces (tailwheel discussions with rudder). In general 3 point easier aft CG, wheeler fwd IMO.

[Veetail88]

Just as a follow up data point for future thread searchers, as of this past weekend I've flown the 8 ballasted to a CG of 85.13". 79% aft.

As noted by all who have come before, the pitch stick force becomes 0 at this point and is quite a bit different than I've been used to. With some practice, landings are ok but strange. The tendency to overcompensate in the flare happens even though you expect it and you can't rely at all on stick feed back.

After a bit more practice here I'll load it to 85% aft and I think I'll quit there. As I haven't yet experienced the feedback reversal near the stall, I know my numbers are close enough and that I still have a bit to go to get to full aft CG. At this point I don't want to push it there. I'll just be sure to add ballast to the front baggage compartment to avoid going past that 85% mark.

My take away from this is that I'm glad I postponed pushing these limits to the end of the flight test phase. I've been able to develop a feel for landing the airplane prior to receiving screwed up stick inputs at this critical phase of flight.

[flightlogic]

At what point in the build were you thinking of giving your brother a ride?
I know it is tempting, after pink slip to jump right in and start giving rides in your pride and joy. Might think of logging some more hours at that point with some water bottles in the back.... just to be sure the handling is something you can handle. After all the build effort... it is worth it to wait and protect your investment.... and keep the brothers wife happy too !

[Veetail88]

Yeah, I'm planning on logging quite a few more landings with water bottles before putting my brother's welfare on the line.

I currently have 4 of these in the stack with 2 more on the rear baggage floor.

1 more will be stuck in where a passenger's left leg would go and that will bring me to 85.82", fully 1" forward of Van's limit, which is not anywhere I want to go.

[akarmy]

Looking good Jesse, Your picture reminds me of my testing. I used two of these 5 gallon tanks at times.

Untitled by akarmy, on Flickr