Help understanding the RV-9A Preview Plans

[BobP]

This is my first post. I have lurked here off and on for the last year. I finally decided to buy the Preview Plans for the 9A and they arrived earlier this week.

While pouring over the Weight and Balance section, I came up with a question about the data presented on Page 14-12.

That page addresses calculating the nose wheel weight based on gross weight and CG. The example given at the bottom of the page results in a nose wheel weight of 362 lbs. using a 100 lb. pilot, 216 lbs. of fuel, no passenger and no baggage. Furthermore, the horizontal line indicating the 362 lb nose wheel weight solution is shown below the hatched area with its lower boundary value of 325 lbs.

In the notes to the right of the example and on page 14-3, in the boxed data, it states that the maximum allowable nose wheel weight is 325 lbs. Is there an error in the maximum allowable nose wheel weight? It doesn?t seem reasonable that with only a really skinny pilot and full fuel, that one could exceed the maximum nose wheel weight allowance.

Also in doing some math, I calculate that in that same example, the nose wheel weight is 339 lbs not 362 lbs. I admit my calculations could be faulty however they still result in exceeding the stated maximum.

Does anyone have any insight into this. Is it possible that this data was reproduced for the 9A from a previous model or is there some other explanation?

Bob Paulsen

 

[IowaRV9Dreamer]

Hi Bob, and welcome! I lurked for 2+ years before starting my build. The only thing I regret in my RV life is the loss of those 2 years.

Have you seen http://www.vansaircraft.com/pdf/Nose_gear_service_letter.pdf
This has a lot of good detail on nose wheel weight. It just came out in November as a response to the NTSB structures study on -A model flip overs. This is where the 325# limit came from (I think).

What you are seeing in your preview plans is pretty typical. Vans doesn't always do comprehensive updates of the instructions.... they sometimes get updated piecemeal. I suspect in this case they put in the new 325# limit without updating the rest of the section. As you build, you'll often find places in the instructions that don't quite match the plans. It's no big deal. Maybe they do it to see if we read the instructions!

Good luck, ask lots of questions, and order that tail kit!

 

[videobobk]

Welcome aboard! You are very observant. Dave is right; not everything gets updated, or at least that is how it appears. Also, I understand that there is a difference in allowable NW weight between the 7A and 9A although they are basically the same fuselage/nose gear. Don't understand that one either.

The bigger question--is this a problem? Probably not, but a little depends on you. Remember that a CS prop, heavy engine (such as the Subie) or other heavy FWF stuff could make it a problem. I have no CG or nose wheel weight problems as long as the pilot weighs over 105 lb. Less than that, then I have to add something to the baggage compartment. I don't even KNOW a pilot who weighs less than 105 pounds.

Bob Kelly

 

[Finley Atherton]

Bob,
To give you a real example. My 9A is about as nose heavy as you would get with an 0-320 and a Hartzell C/S prop. To be more nose heavy you would need an 0-360 with a Hartzell and the 0-360 is not recommended by Vans for the 9, 9/A. Pilot only (me at 173 lb) and full fuel puts 341 lb on the nose wheel. Half fuel brings it back to 311 lbs. Having a passenger aboard makes little difference to the weight on the nose wheel. In practice, I can fill to nearly ¾ tanks before exceeding 325 lb nose wheel weight. Any more fuel and I should add some weight in the baggage compartment. This is no real problem as I normally do not fill over ¾ tanks unless I am going on a trip, in which case I would have some baggage. Solo at full fuel I would need 30 lb baggage to bring the nose weight back to 325 lb. I considered adding weight (9 lb) to the tail so I could never exceed the 325 lb nose wheel weight but I think I will just throw something in the baggage compartment if needed.
This might all sound like an argument for a lighter prop but in reality it is no problem and I love my Hartzell C/S.

Edit; Due to the nose wheel weight SB, if I was building the 9A again with the Hartzell, I would investigate installing the battery further aft than the standard position on the firewall.

Fin
9A Flying

 

[BobP]

Thanks and new info

Thanks for the welcome and the help.

Dave, thanks for the links. They enabled me to learn more and to find VAF threads about the nose wheel issues. That was entertaining.

Bob, as it turns out there isn't a problem now that I understand that the example given is in error. The example loading gave a nose wheel weight of 363 lbs. After doing the correct calculation on my own, it should have shown a nose wheel weight of 321 lbs. That weight is also consistant with the line they drew. It took me a while to figure out where their cg lines vs gross weights were coming from. The real point of the example is that a light pilot, full fuel, no passenger and no baggage transfers the most weight to the nose wheel and one needs to be aware of that. My weight is such that it won't contribute to nose wheel overload.

Fin, thanks for your example. It is consistant with what I now understand relative to the issue. In the beginning, with the example shown, I was concerned that normal flight loadings would be in excess of the nose wheel limit.

Thanks again.

Bob Paulsen

 

[IowaRV9Dreamer]

This might all sound like an argument for a lighter prop but in reality it is no problem and I love my Hartzell C/S.

Edit; Due to the nose wheel weight SB, if I was building the 9A again with the Hartzell, I would investigate installing the battery further aft than the standard position on the firewall.

I don't mean to hijack the thread.... but I think this will be the most difficult decision that I will have to make on the entire project.... much harder than nose wheel vs. tailwheel, slider vs tip-up, etc.

I know there are lots of posts and opinions, but its' great to see reports from flying aircraft... Thanks Fin!

Since I only fly from big paved runways, I'm leaning toward FP (cheaper, lighter, less maintenance).... but I'll change my mind a few times..

 

[BobP]

Dave,
I too am struggling with whether to use a fixed pitch or constant speed prop. On previous planes, I have had only fixed pitch, both metal and wood. I have made my decisions on a slider and a nose wheel and I agree those were easier to make, too.

Fin,
Back to your 9A, in addition to the O-320 with the Hartzell CP, what other firewall forward features do you have? Mags vs EI, etc. Also if you wouldn't mind, would you share your wt and bal data? This kind of info is extremely valuable to me. In building my previous project, I was never able to match the manufacturers weight projections and most others were in the same boat.

Thanks, Bob

 

[Finley Atherton]

Dave,
Fin,
Back to your 9A, in addition to the O-320 with the Hartzell CP, what other firewall forward features do you have? Mags vs EI, etc. Also if you wouldn't mind, would you share your wt and bal data? This kind of info is extremely valuable to me. In building my previous project, I was never able to match the manufacturers weight projections and most others were in the same boat.

Thanks, Bob

Bob,
F/W fwd. everything is pretty standard as per Vans. I have one Slick mag and one LS Plasma III.
Empty weight is 1097 lb at 76.61”. Measured on accurate, regularly calibrated scales. Includes:
0-320
Hartzell C/S
Tip Up canopy
VFR steam gauges
Engine monitor
Two Trio auto pilots
RiteAngle AOA
Backup oil pressure and oil temp gauges
Strobes
Full Flightline interior
Full epoxy interior prime except for a few interior removable covers
Full exterior paint
All fairings
I was pleased with the final weight. I expected it would be more with the Hartzell. I have previously built a Vari-Eze and like all of them, it was overweight. Where possible I tried to keep the weight down during construction of the RV.
I can carry 2 people my weight (about 175 to 180 lb) full fuel and about 100 lb baggage at Van’s gross of 1750 lb. With me as the pilot, the most fwd possible C of G is 8% (of the allowable C of G range) aft of the fwd. limit. The most aft possible C of G (min VFR fuel reserves, heavy passenger and 100 lb baggage) is at 78% from the fwd. limit. The aircraft flies and handles fine at either loading.
Further thoughts on my post #4. The more I fly the aircraft, the more I am impressed with the design and strength of the nose gear assembly. I flew the aircraft before the SB with 341 lb (solo and full fuel) on the nose wheel with no problems. The nose wheel incidents before the SB, have generally happened on landing rather than T/O. Personally, I would T/O from a reasonable airstrip with 341 on the nose knowing that the fuel burn would bring me under the 325 limit for landing. Others may disagree!

Fin
9A Flying

 

[BobP]

Bob,
Empty weight is 1097 lb at 76.61?. Measured on accurate, regularly calibrated scales. <snip>
I was pleased with the final weight. I expected it would be more with the Hartzell. I have previously built a Vari-Eze and like all of them, it was overweight. Where possible I tried to keep the weight down during construction of the RV.
Further thoughts on my post #4. The more I fly the aircraft, the more I am impressed with the design and strength of the nose gear assembly. I flew the aircraft before the SB with 341 lb (solo and full fuel) on the nose wheel with no problems. The nose wheel incidents before the SB, have generally happened on landing rather than T/O. Personally, I would T/O from a reasonable airstrip with 341 on the nose knowing that the fuel burn would bring me under the 325 limit for landing. Others may disagree!

Fin
9A Flying

Fin,
Thank you very much for the data and congratulations on the empty wt especially in final form. I too built a VariEze, I sold it about 15 months ago. Building one of those is excellent training in how to build light. I certainly wasn't able to acheive Burt's numbers for things even though I tried. It came in at 668 lbs.

By the way, I wouldn't fault you for your take off weight philosophy.

Bob

 

[Bryan Wood]

You'll carry stuff in the back anyway

My 9a is set up just like Fins except it is a slider. Even the weights an CG's sound very close! I keep a tool kit in the baggage area that weighs about 15lbs as well as an "M" sized oxygen bottle mounted back there. The tools are purposely kept as far back in the baggage area as they will go. Throw in a couple of quarts of oil and the canopy cover and there is always at least 30 pounds in the back with no exceptions. In real life you will also likely travel or just fly locally with junk in the back of your plane. There's nothing that will make you kick yourself in the rear like not having a tool and getting stuck somewhere. I did that once with a loaded up plug after a fly inn and somebody had to return to help me out. We haven't flown again without tools.

On another note I have two steel plates left over from the build that are about 1/4" thick that were used to back rivet the ailerons and flaps and tail feathers. The idea of mounting one of those on the deck on the back of fuse under the empenage fairing to lighten the nose a bit keeps running thru my mind. I hate to make the plane heavier, but keeping the nose light might make it worth it.

Best,