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Is this Rv-7 even doable?

W

wrongway john

Well Known Member
If I go with a 150 hp or 160 hp 0320, along with a fixed wooden prop, dual electronic ignition, and a tail dragger version, that?s going to make for a very tail heavy plane, I think. Seems like if the problem was nose heavy, it would be easier to fix, since one could always add other lightweight products such as starters, and also relocate the battery aft of CG. I hate to add weight to the nose section such as a heavy prop spacer weight to make up for it, seems counter-productive to me on what we are trying to accomplish by building it light as possible. For those that haven?t started building, and knowing this will probably be a problem, is there some better suggestions out there?

wj
 
I wouldn't call it "tail heavy," I'd call it "nose light." I know, semantics...

You can peruse the records here: http://www.rvproject.com/wab/ and you'll see a handful of -7/-7A's with O-320s and wood props, and you can play with their weight & balance characteristics. See if it's really an issue with your typical loading scenarios.
 
It looks like jcmcdowell just bought a RV7 in that configuration. Maybe he can give you some insight into the cg issues. My RV4 with a wood prop was "nose light" and I did have to watch the aft cg carefully. I have since installed a metal Sensenich prop and it did change the cg issues. If I had to do it over again, I think that I would have gone with a Catto 3 blade and lived with the occasional aft cg issue.

Jim
 
no problems right now....making mine even lighter

My Rv7 has a sensenich prop, O-320, tailwheel, light interior, and supposedly weighed in at W&B at 1026lbs. Not a lot of filler on the paint, and not a lot weight in the interior (no carpet).

I noticed that the lightweight starter was replaced with a regular starter (starter failure is my guess).

I intend on a light weight starter (-10lbs), lose the sensenich for a catto 3 blade (-10lbs), lose the vacuum system and 6 pack gauges (-12lbs), lose the oil seperator (??) and then I'll redo the W&B.

I also intend on a baby seat in the baggage compartment- I'm consulting with EAA techs, A&P's, and other builders here at KFFC to make sure everything is within range and kosher from soup to nuts.

There's a pretty good range of CG to work with on the RV7.

I've been flying with full fuel, 2 men, and she still climbs at 1000ft PLUS off the ramp at a density altitude over 3k here in Georgia (field Alt 800ft).

I think you've got a lot of room to play with...
 
From experience, you won't lose 10lbs from a sensenich to a Catto 3 blade. From one setup to the other (with the crush plates any everything) will be between 3 and 7lb's. (Ours was 3lbs lighter).

I would definely look at getting the longer engine mount and longer cowl that Van's sells for the O-320's. Also consider Fuel injection (a little more weight up front.

Then build the tail light (make sure to cut the lightening holes, trim everything as much as possible), light primer on the tail surfaces if you prime at all.

Then consider a harmonic damner for your wood or composite (3 blade would add a little wieght too...) and you probably will be alright. I know a guy that had lead between two crush plates in front of his prop to balence out.
 
I think you've got a lot of room to play with...
Click to expand...

I hope so. The RV-7 still may be too hot of a plane for me, considering I?ve never flown anything other than the TraumaHawks. I?m still looking at the RV-9A as well, and it may be a more docile plane for me to transition in to. I?m not committed to either just yet.

I would definely look at getting the longer engine mount and longer cowl that Van's sells for the O-320's. Also consider Fuel injection (a little more weight up front.

Then build the tail light (make sure to cut the lightening holes, trim everything as much as possible), light primer on the tail surfaces if you prime at all.
Click to expand...

Yeah, on the tail, I figured I could just prime only the surfaces that needed it, and on the outside paint, I might leave some parts aft of the wings just polished alum which all considered should save me a couple of pounds. I thought of the longer engine mount, just didn?t know if Van?s sold that option till now. I don?t know how much more stress load that puts on the mount by going out further with it, but hopefully with the lighter engine and wooden prop, it wouldn?t be considered a problem. Surely if all else failed to give me the w&b numbers I needed, the longer mount would pretty much get things where one wanted. And it?s nice to know they have the longer cowl to go with it too.

I appreciate all of the feedback.

wj
 
The RV-7 still may be too hot of a plane for me, considering I?ve never flown anything other than the TraumaHawks. I?m still looking at the RV-9A as well, and it may be a more docile plane for me to transition in to. I?m not committed to either just yet.
Click to expand...

Don't rule out the RV-7! There are lots of people who flew similar aircraft (Cessna's, Pipers, etc) before stepping right into the RV-7/8! It's a super aircraft and I actually felt safer immediately after transitioning from the Cessna spam can. The key is to get proper transition training. I was on the fence of the 7/9 for the same reasons as you but I am soooo glad I went with the 7A. Any RV is going to be an honest aircraft.
 
From the research I've done, the 320 seems to be a fine fit for the 7. I am leaning more and more this way each day. I am going for a ride in a 7A tomorrow with a 320 in it. That will give me a much better idea of the direction to go.

Personally, I think the 320 is a fantastic engine, and should definitely be considered... :cool:
 
Exactly.... I transitioned from a Cessna 172 right into a 7A. I still fly the 172 every now and again. I feel much safer in the 7A. Bumps and thermals are sooo much better in the 7A. When I get out the 172 it takes me a little while to get the hang of how mushy it feels especially when I get banged around with thermals. The 7 is really fun to fly and a blast to land.
I had my first chance to fly it to oshkosh and I loaded it to the max with camping gear and I expected it to feel heavy. Not so. I was surprised to see it only took about 50 more feet to lift off and handling in route was the same.
Yes the controls are more sensitive but that is really really good. You feel much more in control when in the bumps. The increase in speed over the 172 was no issue to me as the only way I really noticed it was looking at the speedo.
After crusing around at 180 mph plus and slowing down on approach you would think you are at a crawl on final when in fact you are still going 80. Did I say really easy to land?
 
Consider either a 7a or a striaght 9? I don't know why you would limit yourself to a -7 taildragger or a 9a. First decide if you want nosewheel or tailwheel, then decide if you want to do aerobatics or not.
 
Why?

John,

Why are you thinking about an O-320?

From what I have been seeing the O-320 and O-360 run about the same price, new or used.

This engine question is what drove me towards building a -9. I thought it would be cool to build one with an O-235 and motor around at 150 mph on a C-152 engine. In the end I found my O-290-D2 (135HP) for $3,500. My total FwF cost is around $7,500, not counting the prop. That is for a 0 SMHO engine w/ a yellow tagged carb, duel electronic ignition, and all new accessories.

For that I have an airplane with a 760 lb useful load, can cruise at 175 mph (according to Van's) and an engine that should out last me.

Build the airplane you, -7 or -9, TW or NW and when the time is right, start looking for an engine.

Best of luck!
 
Let the numbers speak, no debate, but it seems tail heavy

I don't want to step in it, because several have expressed strong opinions and I am going to disagree, sorry in advance. But a nose "light" RV-7 will have limited baggage capability and Acro CG will always be exceeded with two-UP. :eek: Sorry the numbers don't lie. Granted I picked the worse one, this is From Dan C's web site a W&B data base. This RV-7 has a 320/wood and has a very aft empty CG. I am going to say the 320/wood works but not ideal CG wise for a RV-7. Baggage will be limited and it may even be a single place Acro plane, at least in these examples.

Weight and Balance for Van's RV-7 N203CR

Owner: cary rhodes
Engine: Lycoming O-360 (180 hp)
Propeller: 68" Other 2-blade Wood Fixed Pitch
Number of Seats: 2
Fuel Capacity: 42 gallons
Empty Weight: 1058 pounds
Empty CG: 83.14" aft of the datum
Max Gross Weight: 1800 pounds
Useful Load: 742 pounds
Full Fuel Payload: 490 pounds


Normal: ....CG Range: 78.7" to 86.82" aft of the datum @ 1,800 lbs
Acrobatic: CG Range: 78.80" - 84.50" aft of the datum @ 1,600 lbs
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Sample Scenario 1: Normal Pilot & Pass, Full Fuel, *Max Baggage*

* Note: RV-7's has 100 lb max bag limit normally, but this builder arbitrarily made 60 lbs max, but is still is too much in most loading scenario's.

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 210 / 97.48 / 20470.8
Passenger 160 / 97.48 / 15596.8
Baggage 60 / 126.78 / 7606.8
Total 1740 / 87.24 / 151796.52

CG is 0.42" aft of the aft normal limit. No go
CG is 2.72" aft of the aft acro limit. No go

--------------------------------------------------------------------------------
Sample Scenario 1A: Normal Pilot & Pass, Full Fuel, No Baggage

Weight / ArmCG / Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 210 / 97.48 / 20470.8
Passenger 160 / 97.48 / 15596.8
Baggage 0 / 126./ 78 0
Total 1680 / 85.83 / 144189.72

CG is 0.99" with in normal limit OK
CG is 1.33" aft of the aft acro limit (80 lbs over wt) No go

(Even with lighter pilots or less fuel its impossible to do dual Acro. If solo and a big boy you will be at or aft the Acro CG.)

--------------------------------------------------------------------------------
Sample Scenario 2: Heavy Passenger, *Max Baggage, Minimum Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 30 / 80 / 2400
Pilot 210 / 97.48 / 20470.8
Passenger 300 / 97.48 / 29244
Baggage 60 / 126.78 / 7606.8
Total 1658 / 89.07 / 147683.72

CG is 2.25" aft of the aft limit. No go
CG is 4.57" aft of the aft acro limit (58lbs over wt) No go

--------------------------------------------------------------------------------
Sample Scenario 3: Standard Pilot Weight, No Baggage, Full Fuel

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 170 / 97.48 / 16571.6
Passenger 0 / 97.48 / 0
Baggage 0 / 126.78 / 0
Total 1480 / 84.25 / 124693.72

CG is 2.57" with in normal aft limit OK
CG is 0.25" with in acro aft limit OK

(Full fuel helps move CG fwd. 170lbs is max pilot weight with 28 gal of gas or more.)

--------------------------------------------------------------------------------
Sample Scenario 4: Lightweight Pilot, No Baggage, Full Fuel

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 100 / 97.48 / 9748
Passenger 0 / 97 /.48 0
Baggage 0 / 126 /.78 0
Total 1410 / 83.6 / 117870.12

CG is 3.72" with in normal limit OK
CG is 1.40" with in acro limit OK

--------------------------------------------------------------------------------
Sample Scenario 5: Very Heavy Passenger, *Max Baggage, Half Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 126 / 80 / 10080
Pilot 210 / 97.48 / 20470.8
Passenger 310 / 97.48 / 30218.8
Baggage 60 / 126.78 / 7606.8
Total 1764 / 88.63 / 156338.52

CG is 1.81" aft of the normal aft limit. No Go
CG is 4.13" aft of the acro aft limit (167 lbs over wt) No Go

--------------------------------------------------------------------------------
Sample Scenario 6: Very Heavy Passenger, *Max Baggage, Minimum Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)

Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 30 / 80 / 2400
Pilot 210 / 97.48 / 20470.8
Passenger 310 / 97.48 / 30218.8
Baggage 60 / 126.78 / 7606.8
Total 1668 / 89.12 / 148658.52

CG is 2.3" aft of the normal aft limit No Go
CG is 4.62" aft of the acro aft limit (68 lbs over wt) No Go

--------------------------------------------------------------------------------

You could add one of those weighted harmonic balancers for fixed props to add engine rotational inertia (better idle). Also you could use a heavier battery, starter & alternator.

I think a metal prop (Sensenich) is the obvious choice. Expressing my opinion only, I would go with a Sensenich, its has better performance, prop pitch can be changed in the future and has better product support. Even better its GOING to be faster, in my opinion than a wood prop. A metal prop is a no brainer, especially if you are going to build a RV-7 with a O320/Fix.

Paint makes CG go aft (more surface area aft of CG than fwd). I dare mention priming internally, that will also add more weight aft as well. If going with a real light engine/prop combo, you need to do everything you can to add weight fwd of the spar and as little aft, where possible. You could put some lead ballast on the front of the engine. It does change the "moment of inertia" of the plane in the yaw axis (spin) but its only making up for the light engine/prop.

The ideal make weight and aft CG from a practical stand point for a RV-7 is 1095 lbs and CG of 80" or more fwd. Lighter is fine but CG of 80" or less (fwd) is kind of critical to carry the full 100 lbs in the aft bag area and to stay in Acro CG with two pilots. Fuel helps move CG fwd, but with full tanks you may run into weight restriction, especially Acro wt of 1,600.
 
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heavy prop hub

For the reasons mentioned above, that's why I added a 24 lb prop hub behind my lightweight Catto prop. Even though it was not cheap, it was the best way to get weight out front and make the most of it. Adding a second battery only changed the CG by 1/2" if I recall (after I did the calculations). My prop hub came from Saber Mfg... Sam is a good guy to do business with.
 
wrongway john said:
I hope so. The RV-7 still may be too hot of a plane for me, considering I?ve never flown anything other than the TraumaHawks.

<<snip>>

I appreciate all of the feedback.

wj
Click to expand...

My first airplane was a Tomahawk, my second was an RV-6. Other than getting the tailwheel endorsement, I found the transition between the two aircraft surprisingly easy, with the following noticable comments:

The RV has much more torque on takeoff, so your right leg gets more exercise. The pattern speeds and sight pictures are similar, as are the glide ratios are similar if full flaps are applied. The RV stalls about 5 knots slower, which helps a little.

Obviously, the RV has far more performance...
 
The sensenich metal prop will eliminate any possibility of acro on an O-320. There is a SERIOUS harmonic vibration above 2600 rpm, and users are forbidden to enter that area.

It will be difficult, or impossible to prevent rpm above 2600, if you do acro in an RV-7. Which is why I would suggest wood, composite, or C/S

P.S. the cost of used and core 320's is becoming much less than 360's as everyone is going for the bigger engine. There are deals to be had out there, if you just keep your eyes open.
 
Jconard said:
P.S. the cost of used and core 320's is becoming much less than 360's as everyone is going for the bigger engine. There are deals to be had out there, if you just keep your eyes open.
Click to expand...
I have to agree with John here! I've recently been looking thru the ads for core 320's and 360's, and many of the 320 cores are half the price of 360 cores. There are exceptions, of course, but I haven't come across a 360 core for $3500 yet...
 
Stephen, I just figure the 7 as more of a sportster with the taildragger version, and, and if I was to convince myself I had the skills to fly this plane, I?d think I?d go that route and plan on more grass landings as well. The 9A seems a bit more tame and appropriate to me with the nose wheel, if I can?t convince myself I could fly the 7. Hadn?t ruled out any 7A either. Kyle seems to have made the transition from Tomahawk to the taildragger RV just fine. Maybe when I get back into flying again, I?ll start to feel more comfortable with the hotter RV?s. I just received the RV-7 preview plans, will need a couple of more months before purchasing the empennage of either the 7 or 9. One thing that sobered me up, was the other night, I was reading through Dan?s site, and going over the NTSB lists for Van?s aircraft. The planes seem to hold up just fine. But it looks like there were a lot of experienced pilots with many hours in type, that still managed to get themselves in trouble, so, I just want to approach with caution.

George, I appreciate the dissenting opinion. Not always easy to do, when the board is going in another direction.

Bill, I?m just leaning towards the 0320 for the slightly lower fuel burn, and less weight. I?m not as interested in all out speed as I am economy. I also like what Kent Paser was able to do with his 0320. If I manage to get well into my RV kit, I?ll start getting more serious as to which direction I want to go here. Sure a lot of decisions to be made for engine and prop, that is for sure.

wj
 
wj,

I think you need to establish exactly what you want to do before you start tackling the problem of how to do it. My suggestion: go fly some other airplanes besides a Tomahawk. See if you can get some acro and landings time in a Citabria or Decathalon. That will let you be able to decide whether you want to do acro at all (some people just don't like it) and it will also get you familer with taildraggers to some extent.

If acro isn't your mission, but you still want an edgier efficent airplane, the -9 is a great x-country bird that handles the 320 engine with ease, no CG issues.

If you like the acro, then you simply need to look at making a -7 do what you want it to, which, in spite of the naysayers, isn't all that hard. Remember, these are experiementals, just modify where you put stuff until it works. As mentioned above, a solid heavier prop extention is a innovative solution to a light nose, which someone already did. All kinds of other possibilities exist.

If you can't (or don't want to) handle the taildragger, but still like acro, the -7a is an option, the nosewheel would help balance out the light engine to some degree.
 
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