By design
Early RV's -3 & -4 and even the -6 really where made with lighter prop & engine combos in mind. It was not till late 80's early 90's Van fully embraced constant speed props. The first RV factory prototypes up and including the RV-6 had fixed pitch props, at least at first. Past RV's tended to be nose heavy, since builders tended to put larger engines and c/s props added even more to the nose.
Now comes the case in point, the RV-7. To make it work for a 200HP/C/S combo and make it also work for a O320/wood is a challenge, no doubt. I think it is fair to say the RV-7 is tail heavy with light engine/props. Van no doubt did this from his experience and knowing builders tend to build heaver than lighter. Of course builders being creative are making there FWF setup lighter. What works real well in a RV-6 is on the light side in a RV-7.
Here is an un scientific survey of about 115 RV's (all models RV-4 thru 9):
Total...............MIN..........MAX..........AVG
60....FIX..........874..........1170..........1041
55....CS..........1010..........1244..........1111
41....320..........874..........1168..........1034
60....360..........986..........1189..........1084
14...IO360.......1103..........1244..........1151
32...320Fix........874..........1106..........1019
28...360Fix........986..........1170..........1066
9....320CS........1010..........1168..........1084
32...360CS.......1026..........1189..........1101
14...IO360CS....1103..........1244..........1151
Before you point out that I don't break out models, if its painted or day VFR or Night IFR, look at the trends. The AVG O320/fixed = 1019 lbs; IO360/CS = 1151 lbs. The difference is 132 lbs. Lets assume that weight is mostly influenced by the engine prop combo, which I think is true. Really no surprise fix pitch planes are lighter, and O320 planes are lighter than IO360 (200hp) planes.
Here is the average of 25 RV-7(A)'s:
...............#..........MIN..........MAX..........AVG
RV-7.......15..........1011..........1141..........1073
RV-7A.....10..........1020..........1134..........1092
I am a big fan of the Hartzell constant speed prop, especially the New Blended Airfoil prop made for the RV. Also the Sensenich Fixed is an excellent prop. I guess this is one case where weight is good. Don't get me wrong a light RV with a O-320 and wood prop is awesome, but like big heavy engines on the early RV's, light engines on the RV-7 has W&B considerations. There are tricks to minimize and mitigate the aft CG.
Using light a weight starter, alternator, prop and a smaller engine can get you into a little W&B quandary in the RV-7. The point is when building a light RV, try to put as much equip as far forward as possible. Also keep in mind paint tends to shift CG aft. Watch priming and heavy paint on the back end of the plane. Another 10 lbs on the back is not going to help.
I hate to say it, but ballast is a time honored tradition in aviation. There has been many an airliner that I have flown that needed ballast (usually a spare tire or ballast pallet in the cargo compartment). Also with light loads there are many a time flight attendants have to move people around to get the W&Balance to work out, even in a B737. Trust me, its not a RV-7 thing.
Using a weight (ballast) on the nose (say on the engine between the starter and alternator) could solve your problem, it you indeed even have a problem. Before you get into a moment of inertia and spin characteristic debate of ballast on the nose should be a non issue, and easy to check by similarity to the moment of inertia of a heavy engine/prop combo compared to a light engine/prop with ballast. Always check with Van's aircraft before making any major structural change or modification, but in my opinion a nose weight is not going to be an issue. Also if you upgrade to a Hartzell or Sensenich you can always drop the weight. Also for local flights you may be able to take the weight off for solo flight.
As far as luggage, you may be aft baggage compartment limited with an aft empty CG, but in my RV-4 I used soft duffel's and they where strategically place in the cockpit under the passengers knees. For a long trip, with care you can place some items on the cockpit floor for cross countries. Make some kind of anchors to assure payload does not shift fwd and interfere with the rudder pedals would be a good idea. It adds more payload volume and has a small positive CG effect. Most of the time, if you are like me you will fly solo or two up with no bags.
George RV-4, RV-7
I guess the first thing I will take a look at is whether the dynafocal rings are the same from O-320 to parallel O-360 and do the moment calcs for hanging the O-360 2" further out. That ought to be worth about 800 inch pounds. That's probably way too much, so maybe this boils down to some properly engineered spacers between the firewall and the (6) engine mount points and a bit of fiberglas work on the back edge of my cowl (not there yet either).
