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Not much dicussion on flight testing?

NeilMcLeod

Active Member
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
 
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
 
NeilMcLeod said:
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.

NeilMcLeod said:
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?

NeilMcLeod said:
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.
 
Aft C of G

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

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.
 
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
 
Well It's not like it's an unprecidented creation

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
 
Before your 60th

Frank,
Got mine airborne last March then turned 60 this month.
So there is a target for you.
Pete.
 
Pete

Great accomplishment and congrats.......Early fall I should be done...BUT.....60 in April so ya beat me like a Tazzmainian Devil!!!

Frank @ sgu and slc...
 
I strongly recommend that everyone fully explore their aircraft's characteristics at the extremes of the CG and gross weight envelope.

I know of at least two people who didn't do that (one was a -4 pilot and another was a -6 pilot). Both were very surprised at the handling of their aircraft when they loaded a passenger and/or baggage. I would submit that it is awfully unfair to your passengers if you take them up in a weight and/or CG condition you have not previously demonstrated.

In my case, I created a flight test card with 8 or 10 different weight/cg combinations, with the objective being to gradually step the aircraft's weight up to my planned gross, then gradually move the CG to the aft limit at gross.

There is a huge difference in how these aircraft fly with an aft CG, particularly at pattern speeds.
 
Flight Characteristics

Bob,
I am very reluctant to disagree with you because your posts and attitude deserve great respect.
In this case however, it is not a matter of 'testing' the aircraft stability, but experiencing flying your RV- which is already light on the controls at normal C of G- at AFT C of G and learning how to deal with it.

It's a training exercise.

Pete.
 
I agree with Bob AND the FOD!

:D

I agree with both you guys....we really are doing what amounts to "production flight testing" on the machine....but we are training ourselves how it handles out to the edges of the envelope that we plan to use. I did a lot of interesting flight testing in my 40 because I enjoy that sort of thing...but I probably could have stolen someone else's data to build "the book" on the plane. However, it was really valuable to get the experience in all the corners (especially the aerobatic corners) before I felt really comfortable.....

Paul
 
The training part I agree with

fodrv7 said:
Bob,
I am very reluctant to disagree with you because your posts and attitude deserve great respect.
In this case however, it is not a matter of 'testing' the aircraft stability, but experiencing flying your RV- which is already light on the controls at normal C of G- at AFT C of G and learning how to deal with it.

It's a training exercise.

Pete.

I agree with the training part of the exercise. I did have some major bugs to deal with which are the sort of thing you expect in this kind of test program. They were dealt with and the plane is performing very well. But the training was equally important. I did go up to Vernonia, Oregon and I did one session with Mike Seager which prepared me for the basic flying of the machine (a delighful experience by the way) but day-in-day-out operations under the wide variety of conditions one encounters remained to be learned. I don't think we are that far apart on our views and I do appreciate your kind words.

Bob Axsom
 
Most of us are not qualified Test Pilots....

Interesting how we look at flight testing.

Most of us are not qualified test pilots and I don't pretend to be one. We are test pilots in the sense that we fly what we build, but I wouldn't know where to begin a formal test program, say for FAA certification or to check out a new design.

Once I check the stall speeds and gradually opened the speed envelope for a flutter check, I have a good idea the airplane was built fairly close to spec and trust Van's extensive test program for the rest of it. With the stall speed, I calculate an approach speed and with the flutter test, I know the thing won't come apart on a high speed dive on the red line. The rest of it is getting into performance corners depending on what one wants to do.

It is a good idea to get educated on aft and rear CG flight characteristics but the airplane will not fall out of the sky if you don't. Just don't over control it. Like all the books say, pitch stability is best at forward CG and less so at the aft limit, but not so that the airplane is dangerous or uncontrollable. It just aviates a little differently. Same at max GW vrs flying with 12 gallons of fuel. If you are really concerned about this aspect of the airplane, the best thing you can do is let someone else check your numbers so you do not inadvertantly get outside the CG envelope. It is interesting that there are licensed pilots flying around who do not know how to compute the CG of their airplane. I have helped more than one.

The really, really critical thing about initial flight is the engine. I typically do about 4 hours of extensive taxi work, including a number of high speed runs down the runway, mostly to see if the engine will keep running and how hot it will get. I did have the Subaru quit during this process because of an anomaly with circuit protection and the fuel pumps. That was a great thing to happen on the ground. :)

Other than that, after a couple or three other people have looked at your work to make sure the ailerons are not hooked up backward, its push the power up and let her rip. These airplanes do fly great!

dd
 
Well, good to see some discussion started here! This is great. I'll have more questions when I get time to get my thoughts together. I do believe that some of what we are talking about is more correctly described as flight training or familiarity checks. It is probably a little different for most of us in that we won't have a qualified instructor to show us the edges of the envelope. True these are proven designs but also true that we are not all proven builders and it is possible that our planes are not all rigged the same. The surprise that Vans had with the spin characteristics of the 7 shows that what appear to be small changes can have larger than expected affect on flight characteristics. I don't mind learning this stuff on my own but I did want to do it solo first. BTW I do fly with and have experience with a chute but I do wish I knew if it were possible to get out if nessessary, (7 Slider).

My compaint with the rudder is not the effectiveness but just the high forces. It's no probem for "normal" flight but I find that in a left crosswind that when you bring the tail up on take off that it takes a mighty stomp on the right rudder to stay aligned. Do-able but hard to do with finess. Also higher than I like on spin recoverys and hammerheads. Hard to hold full rudder in those maneuvers. The rudder pedal configuation makes it more difficult too.

Another thing, after thousands of hours in my 182 and gliders none of which did this I was surpised to find the 7 to be a tail wagger in turbulance. I hadn't heard anyone mention that before. Probably Bonanza pilots think it's normal.

Neil
 
Slower

Neil,
The amount of rudder required on take-off is proportional to the rate at which you raise the tail.
On my mates -8 if you just leave it alone the tail comes up itself and very little rudder is needed.

My RV7 - on the other hand- has quite a rear C of G and so some forward stick is required. But less is easier.
Pete.
 
I agree that flight testing an RV is more like production flight testing than it is experimental flight testing on an unproven design. But, these are not production aircraft, where each one is essentially identical to all the others. Every RV is unique, either due to builder mods, or builder errors. These differences can have an effect on performance, handling and engine and system behaviour.

In particular, builders should conduct a full series of flight tests at the extremes of their desired weight and CG envelope. Yes, Van provides recommended forward and aft CG limits. But, some aspects of the handling will degrade as the CG moves forward and aft, and each builder must determine within what envelope he finds the handling acceptable. Just because Van considers the handling of the prototype acceptable with the CG at 86.82" does not mean that the builder will find the handling of his aircraft acceptable with the CG there.

Many builders use scales of questionable accuracy when weighing their aircraft, and some do a poor job of leveling their aircraft. The empty weight and CG that the builder calculates may be affected by these issues. Thus when the pilot calculates that the loaded CG is at 86.82", it may very well actually be some other value, due to an inaccurate empty weight and CG. Rather than simply accepting Van's recommended CG envelope without doing any confirmatory testing, builders should carefully test the edges of the CG envelope they need for their aircraft.
 
Interesting about the tail wagging. I have heard some others comment about this, but I have never experienced it in my 7A. Dan C. has commented about it (wagging) and flies a 7 with the original smaller rudder. As far as having to push hard on the rudders, I have never felt it necessary to push abnormally hard to get desired rudder effect. I haven't done any hammer heads, but I do a lot of turbulence and crosswind landings. I do a lot of climbing and hiking. Perhaps my legs don't feel the strain as much. It is more rudder than typical, but I really like the response and effectiveness.

Roberta
 
7 tall tail vrs 7 short tail

re "The surprise that Vans had with the spin characteristics of the 7 shows that what appear to be small changes can have larger than expected affect on flight characteristics."

It is my understanding that to meet utility category spin recovery requirments, the 7 did not stop rotating quite quick enough with the short rudder. They installed a 9 rudder and it did. They then reinstalled the short rudder on the 7, at least the last time I saw the airplane, it had a short rudder. Each 7 builder was given a tall rudder kit so as to meet those spin specs.

I do not think this is a big deal. The free kit is still up on a shelf waiting to be built. My airplane is OK in any cross wind I care to fly in, plus it may even have a smidgen less drag with the short rudder, which is good and more is needed.

I don't know about tail wagging, mine seems to not wag. Maybe you-all are experiencing dutch roll.

dd
 
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Why the heavy rudder?

There is a good reason Van made the rudder pedal forces high.

Unlike the tailplane (and the wing) the Vertical stabilsiser is cantilevered. That is, it sticks out from the fuselage supported only from one end. This imposes much high loads on the vert stab spar and it's attachment to the fuselage. Hence the Vert Stab spar is much more beefy than the Horiz Stab spar and extends below where it attaches to the horizontal stab (and is attached to the fuselage), in order to relieve some of the cantilever effect.

To get an appreciation of the loads on the vert stab, try picking your tailplane up of the floor by holding it at the tip, instead of in the centre.

Additionally because the RVs have such a large speed range, the rudder has to be big enough to be effective at low speeds and is consequently excessively large for the job at high speeds.

Van's high rudder pedal loads discourage you from booting the rudder on the cruise.

Incidently, for this reason, most jet airliners that I flew had either a mechanical limit to rudder throw at high speed or an artificial feel system that increased the rudder loads.

Fish-tailing? Of course. Because the rudder is excessive for it's job at high speed and will respond vigorously to side gusts..... but also damp it out quikly- unlike the V tailed Bonazas. And let's not get into yaw/roll coupling and Dutch roll.
Pete.
 
Thanks for all comments. As far as leg strength, I'm a recently competitive and still active cyclist and work out at the gym twice a week. I'm not a big guy but probably have as much leg strength as the average RV pilot. Maybe my aircraft is not typical. I'll just say I prefer more balanced contol forces between pitch yaw and roll and I have flown aircraft that are like that. If I recall correctly I can barely hold full rudder in a slip at 80 kts. I don't want to go back to the small rudder that is hanging on the wall because I do frequently spin the aircraft and do acro. In spin testing at aft cg's (aerobatic aft limit) I decided I wanted all the authority that the big rudder provides. I still have trouble recovering consistantly on heading.I haven't flown with the smaller rudder though and am curious how much difference there is. I concur that high rudder forces may be "safer" in that it may make it harder to inadvertantly spin the aircraft. I'm not sure I buy the structual argument but not being a engineer I'll defer comment there pther that I agree we don't need to be "booting" the rudder at cruise which is much above blueline. As far as a slower rotation on take off, that is a point well taken and I'll give that a try. I have a strong tendency to want to get the nose down to where I see and get stabilized in the gusty crosswinds we typicaly have here.

Neil
 
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