Not much dicussion on flight testing?

[NeilMcLeod]

I've done the 40 hours met the requirements for the log book endorsement but my flight test continues. I'm surprised that there isn't more dicussion about flight test and flight characteristics especially at the edges of the envolope. For one, how are people doing testing at gross weight and aft cg. I put 100 lbs of sand in the baggage and 100 lbs in the passenger seat which was as much as I was comfortable strapping in. That gets me 60 lbs shy of gross with full fuel but nowhere near aft. Less fuel moves the cg aft but not much. For practical flight test purposes I can't get much further aft than 85 in. (aft limit 86.82) With 5 gals of fuel and a 369 lb passenger (!?) I can almost get to aft cg and gross wt. What surprised me was how much different the plane flew with a relatively aft cg and near gross wt.. It's true that it flys much nicer light but also it is nicer at mid to slightly foreward cg. I'm not sure I'd like it at all at the aft limit. I like the way the plane flys for the most part but not everthing is perfect. For example with the new big rudder and fin on the 7 I think the rudder pedal forces are very high, too high for my liking any way.

Neil McLeod N748M
#70048 58 hours

[Ironflight]

Neil,

I think maybe it's cause once people get to flying, they are having to much fun at the airport to come back and write test reports!!

Are you flying an -8? When I tested mine, I had 100 lbs in the aft baggage, and I think I put 150 in the back seat - I agree, fastening down more than that just seemed really "iffy". And I don't enjoy the handling when the CG is that far aft. Stick forces get a bit light for my taste.

Paul

[Kevin Horton]

Originally Posted by NeilMcLeod

I've done the 40 hours met the requirements for the log book endorsement but my flight test continues. I'm surprised that there isn't more dicussion about flight test and flight characteristics especially at the edges of the envolope.

Yeah, a full flight test program takes a lot more than 40 hours. I am continually amazed at the folks who talk about "flying off the 25 hours". I wonder how well they know the edges of their aircraft's envelope, and how many things they do the first time with a passenger on board.

You are right, there is hardly any discussion in this part of the forum at all. But I'm happy to talk flight testing all day long. I am starting a trip back home today, and won't get there until Friday PM, so I'll only have internet access at a couple of times in that period.

Originally Posted by NeilMcLeod

For one, how are people doing testing at gross weight and aft cg. I put 100 lbs of sand in the baggage and 100 lbs in the passenger seat which was as much as I was comfortable strapping in. That gets me 60 lbs shy of gross with full fuel but nowhere near aft. Less fuel moves the cg aft but not much. For practical flight test purposes I can't get much further aft than 85 in. (aft limit 86.82) With 5 gals of fuel and a 369 lb passenger (!?) I can almost get to aft cg and gross wt.

Van's recommended weight/CG envelope is big, to try to offer a useable envelope no matter which engine and prop you have. It looks like you have no need to clear the envelope all the way back to 86.82". Figure out what aft limit you need and stop there. Change your POH to show that as your aft limit. If the heavy weight/aft CG part of the envelope is not useable in your aircraft, then you can draw a weight/CG envelope that has an angled line at the top right corner, and only worry about testing to the edges of that envelope.

Do you have a way to tie down the ballast in your baggage compartment?

Originally Posted by NeilMcLeod

What surprised me was how much different the plane flew with a relatively aft cg and near gross wt.. It's true that it flys much nicer light but also it is nicer at mid to slightly foreward cg. I'm not sure I'd like it at all at the aft limit. I like the way the plane flys for the most part but not everthing is perfect. For example with the new big rudder and fin on the 7 I think the rudder pedal forces are very high, too high for my liking any way.

The stick forces in pitch will get lighter as the CG moves aft. That is, you'll need less stick force to produce a given manoeuvre in pitch, and the aircraft will become quite sensitive. It won't trim at a desired speed as nicely, as a tiny bit of stick force will move it off the trimmed speed. Is this the sort of thing you were noticing, or did you spot some other characteristic?

At aft CG the stalls might be a bit sharper, and more forward stick might be needed for recovery. The spin characteristics may be worse too.

[fodrv7]

Weight and Balance testing.
RV7.
I calculated the amount of weight need to move the C of G to the aft limit and then progressivley added it by carrying water containers (full of water) that I purchased from the local camping store. Being an Aussie (litres and Kilograms) there was no need to weigh the water. One litre is one Kilogram.

It is also easy to load water, as you can throw in an empty drum and then fill it up. (I suspect Kevin uses water for ballast in his job)

It is all still a bit approximate. Where is the C of G of a passenger? Not centred on the seat, that is for sure. I put some (10KG) on the floor to allow for the weight of his legs)

Eventually, I had my RV7 ballasted at what I calculated was the Aft C of G limit.

The aircraft was not pleasant to fly, but it was positively stable. Just!
On the cruise, if I raised the nose and then left it stick free, it eventually, after a series of phugoids, returned to the trimmed condition.

Some may thinks this a bit over the top, but I did not want to discover the aft limit when I was loaded up with a friend, baggage and full tanks on a long trip.

I subsequently set off with a 90KG friend, plus me (90KG) plus max allowable (C of G limited baggage) and full mains and Full tips tanks on a 6hr trip.
It was reassuring to know that the aircraft would be within limits. What became apparent was the C of G moving forward as the Tip Tank fuel was burnt and aft as the mains were burnt off.

Pete.

[robertahegy]

Rudder force is high, but you will find you don't need rudder input for coordinated turns. You will, however, love that big rudder in crosswinds and taxiing.

Roberta

[Scott Will]

One of the things holding me back on doing full testing was my airspeed indication. I knew it was off from the start. I recently changed from flush ports to the type that Van's calls out on the plans. Still have more testing to do to see if this is the final fix (I suspect so) but after that, I can start to do more intensive testing.

Also, trying to wait for the right conditions (e.g. standard day, or as close to it as you can get). I also plan to do some testing as the weather warms up to see what 'hot day' performance looks like. But I know it's not as critical as say our Atlanta - Tokyo service where our department had to request to move up the departure time to the morning (when it's a lot cooler) so we could get more weight off the runway.

[Mel]

Peter,
The normally accepted cg of a NORMAL person seated at a NORMAL configuration (not supine) is considered to be at the belly button.

[fodrv7]

Thanks Mel.
Of course I was limited by the shape of the containers. 50 L and 15L and the need to secure the 50L with the harness and the 15L on the floor.
I think it would have been pretty close to the belly button, but if any thing a bit aft, which means my flight test condition would have been slightly aft of that with a passenger.
Thanks, again Mel.
Pete.

[fstringham7a]

Peter

Would that be 1 ml of H2O = 1 gram of H2O = 1 cc @ STP.....ya got to love metrics

Frank @ sgu and slc RV 7A can't wait to start the testing

[Bob Axsom]

This is a little overdone I think. If you build an RV like the drawings there simply is not as much to "find out" as when you are creating an new design - the concept and the basic design implementation have been thoroughly tested. What we are doing is more of a manufacturing test flight sequence.

Bob Axsom