Design Questions about the RV-12

In general I like the RV-12 in concept and so far in "proof of concept".

I do have some design questions that I will be researching for answers.

1. Gas tank in the fuselage. I know why Van is doing this and I agree with his design reasons. I just don't know how he is doing this . Like others I?m not thrilled about the idea of a cockpit gas tank but I have flown several airplanes that have cockpit gas tanks (cubs, champs, etc). I?ll be curious as to what safety measures Vans takes concerning the tank. I?m also curious as the final shape and location. Right now it appears to be a tall rectangular tank right behind the passenger?s seat. In addition I have some questions about filling, venting and being able to visually check the fuel level. How do you ?stick? a fuselage tank during preflight to verify the fuel level? Can you see the fuel level if you remove the filler cap? One final thought is how much CG change will occur between full and empty. The primary concerns are any items that can compromise safety so I will be looking for specific design features that address safety concerning the fuel tank.

2. Landing gear. I?m pleased to see a strut style nose wheel and also the large diameter of the nose wheel. Good for rough field operation. I?m curious if anyone has seen an RV with main gear larger than the typical 5:00 x 5 tires. My 1965 Cessna 150 had 6:00 x 6 tires on the main gear and they were great on grass strips. Option for larger wheels would be a nice feature.

3. Flaperons. It sounds like they are effective as ailerons either in the drooped or raised position but I haven?t heard any comments yet about how effective they are as flaps. My 1965 150 had 40 degrees of fowler flap that let you come down like a parachute. I?m guessing the flaperons won?t be as effective as fowler flaps but it would be nice if the do something to lower stall speed and increase drag for landing. It appears to side slip ok in the video of Ken shooting touch and gos.

4. Cab forward seating. I hope Van keeps that feature. For a light sport plane I would prefer a high wing( I like the Cessna LSA) but the cab forward seating in the RV-12 looks like it might satisfy my sight seeing needs. Besides the low wing also helps facilitate removable wings. I?m also curious of the CG numbers associated with cab forward seating. I always enjoyed sailplanes as you sat ahead of the wing but we did have to watch the CG closely because we sat so far ahead of the wing. Some light weight pilots had to add ballast to meet the minimum weight requirement.

5 Removable wings. I for one hope Van retains this feature too as I fit the one scenario where tying down outside is an option for me. Our weather in the Northeast is not that violent in the summer. (We make up for that in the winter) I can get 7 months of tiedown space for the same price as 1 month of hanger rent. In the winter (after daylight savings time ends in November), I?ll remove the wings and bring the bird home (I live 1 mile from the airport). That feature alone will save me $2200 a year in hanger fees. Even if I wanted to pay for a hanger there?s a long waiting list to get one. It?s pretty evident how the front spars attach but I have not seen any detail of how the rear spar attaches yet. I'm curious if its difficult to rig removeable wings as they did comment about a heavy right wing on the prototype.

In general the cab forward seating and removable wings are the differentiating factor for me. Assuming they work out the details to Vans satisfaction and they retain these features then the RV-12 meets my mission statement for light sport flying fun. It will be faster and lighter on the controls than my 1965 150 and the airframe and power-plant will be 50 years newer

I see where Van is presenting ?Flying the RV-12? as a forum at Sun and Fun. Friday morning 9:00 AM. I?m sure there will be standing room only with a lot of people like myself asking questions.

Frank

turn radius

Those are excellent questions. One concern of mine is that without differential braking, whats the turn radius? Might seem trivial, but at small airports there often isn't much room to maneuver (i.e. back taxi - 180 degree turn on a narrow runway)

FrankS said:

In general I like the RV-12 in concept and so far in "proof of concept".

I do have some design questions that I will be researching for answers.

1. Gas tank in the fuselage. ...

2. Landing gear. I?m pleased to see a strut style nose wheel and also the large diameter of the nose wheel. Good for rough field operation. ...

4. Cab forward seating.

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#1 - I agree - I hate the idea of any fuel in / near the cockpit, in particular the tank(s). Wing tanks are more complicated but, in this instance, worth it, IMHO.

#2 - Larger size is good - better cushioning on landings, less chance of damage on grass.

#4 - Great. I love the view down from the high wing but miss the canopy. The "seat forward" design gives you better downward visibility than a standard low-wing. I'm not sure what relocating the tanks to the wings would do W&B wise, necessitating moving the seat aft.

jmoylan said:

One concern of mine is that without differential braking, whats the turn radius?

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I've never found it a problem in the hand-brake airplanes I've flown (Thorpedo, CT). Differential brakes allow for tighter turns, but the hand brake seems to be Ok.

The old PA28-140 Cherokee "Flite-Liner" that I learned how to fly in had only a hand brake. I don't recall ever having a problem with them or it, but that was almost 30 years ago. I don't recall a lot from that far back anymore.

Bigger tires = bigger weight and drag. The 5:00 x 5 wheels and tires on the RV-6 have never let me wanting for more on a grass field. With an aircraft that is several hundred pounds lighter, should be even less of an issue.

I'm not of big fan of fuel tanks, or fuel lines, in the cockpit. But most GA aircraft have as a minimum fuel lines in the cockpit - so it's something I have gotten over. If you think about it, a tank behind the main spar is well protected, more so then a header tank and wing tanks, especially overhead wing tanks (Cessna).

Removable wings - yeah I'd use that feature. I don't like flying in the cold (November through April) and wouldn't mind not having to pay storage for 5 or six months. Moreover, the winter is a great time to do maintenance and there is no better place to do that work then in a nice warm garage. Sign me up for removable wings.

I looking forward to flying the RV-12. From it's unique features and it's promised "soul" of other RV's, it should make for a nice plane to own, and a nice plane to teach my kids about flying.

Hi guys, first post here. I'm another one impatiently watching the RV-12 development.

My opinion of the fuel tank location is, I think it's one of the safest places to locate it. If you look at post crash photos, RV or whatever, I think you will find that this area is usually the least effected in a crash. I would think that a fracture would be highly unlikely in a survivable accident. I do think it would be slightly more likely to get fuel in the cockpit with this configuration than with low wing tanks. I think high wing tanks would be more of a concern and forward fuselage tanks like the Cub would be much more of a concern, but a tank failure in a cub seems to historically very unusual.

Landing gear, if the front strut has enough adjustment, larger tires shouldn't be a problem.

Flaperons, I wouldn't count on them being nearly as effective as a 150 with 40 degree barn door flaps, but full span flaperons should be more effective at 20 degrees than most conventional flaps at 20 degrees.

Forward seating, this is of most important concern to me. I'm first concerned with how the fuselage will fold in the cabin in an accident. Second, I'm concerned with weight and balance issues with the occupant forward, fuel aft CG configuration.

It has been stated that the thing will take off at full gross, but how long can you fly it that way and be able to land it? I doubt that those that would like to see more fuel capacity will see that happen.

They have expanded the span of the stabilator, which seems to reinforce my concerns above. I would guess that the first try on the stabilator span was an attempt to make it as trailer friendly as possible. I have no idea what the span is now, but I would like to know.

FrankS said:

How do you ?stick? a fuselage tank during preflight to verify the fuel level? Can you see the fuel level if you remove the filler cap?

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I've been renting a Diamond DA-20 Eclipse to stay current while I finish up my RV. It has a single fuselage mounted tank behind the seats. The filler tube is on the left side, just aft of the wing trailing edge. You can't visually see the fuel in the tank. Standard issue equipment on DA-20s is a wooden fuel stick with markings. Works like a champ.

Of course to use a stick Van will have to ensure that the filler tube to the bottom of the tank is a straight line.

My thoughts:

1. Fuel tank. I agree with the feeling that the area is probably the least damaged in a survivable accident. My concerns are the possible separation of the fuel filler neck or vent, and the implications if you do find yourself up-side-over. Maybe some sort of fitting at the tank that only flows one way or shuts off if inverted/disconnected. Any thoughts??

2. I like the strut - especially if it is more rugged and have less issues than the "A" models. (No need to discuss nose vs. tail wheel here - its been done )

3. Flaperons - Van's reports reflect good control - even when drooped. LSA stall speed will indirectly dictate a reasonable level of "flap performance". His goal is "RV-style" handling. I read that as "responsive" and hopefully reasonably light. I trust that he will be fully pleased with results before he starts producing.

4. "Cab-Forward" - As a "high wing" pilot - this low wing stuff will be new to me. I really like the idea of having more unobstructed views downward than a normal low wing would offer. Cool idea. However - as I posted in another thread - I am concerned about CG also. Can I fly it solo... and not run into forward CG issues as my fuel runs low??

5. Removable wings - I am ambivalent. Hangers are expensive here... so I can see the advantage of being able to bring her home for maintenance. I would love to see it stressed for Acro... and think that removable wings will lessen the very slim possibility of that. (I think that the LSA weight restriction will limit the strengthening of the aircraft beyond what we would consider the utility category.)

6. Brakes - I can deal with the handbrake idea. I too am curious about turning radius. I was raised on farm tractors and like differential braking!

Now if we can just get someone from VAN's to feed us some more crumbs of info... I know I'd be happy for the weekend!!

Phyrcooler said:

I would love to see it stressed for Acro... and think that removable wings will lessen the very slim possibility of that.

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Being able to do light aerobatics is a deal breaker for me...and I never assumed that the aircraft would be restricted in this way by the wing design. There are many aircraft (gliders) that have removable wings that can still do "sportsman" type aerobatics.

This statement from Van's site leads me to believe that the aircraft has been rolled:

"even from the ground we could tell the roll rate was pretty snappy. Van said it felt at least as quick as the RV-9:

But then again, they might not be referring to a full 360 degree roll.

RV6junkie said:

This statement from Van's site leads me to believe that the aircraft has been rolled:

"even from the ground we could tell the roll rate was pretty snappy. Van said it felt at least as quick as the RV-9:

But then again, they might not be referring to a full 360 degree roll.

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The statement from Vans is in very standard wording to describe the rate of change of bank angle, which is known as roll rate. It almost certainly describes non-aerobatic manoeuvres, such as a 60 deg change in bank angle from 30 deg left bank to 30 deg right bank.

I have been playing around with some CG numbers just for entertainment while waiting for the last of our snow to melt. I don't have real numbers but I made some up that I thought would be close enough to get an idea about the CG issues of a forward seating design like the 12. I assumed a chord of 54 inches and used an old rule of thumb that the CG should be between 15 and 28 percent of the chord. This gave a spread of about 7 inches. Then I assumed the CG of the pilot/passenger was just 12" ahead of the center of lift and the gas tank and baggage were 22" behind the center of lift. Then I picked a couple of extreme scenarios. I chose a 100# female pilot with full fuel and 50 lbs of luggage. Next I chose two 225# male pilots with no luggage and landing with just 2 1/2 gallons of gas left in the tank. Under these extremes I was able to stay within a 7" CG range. So the "flying" CG seems to be managable with engineering depending how close the center of lift is the wing spar location. Judging from the hints Vans has given along he way I'm sure they already have these numbers worked out and are busy proving them out in flight trials.

The second CG issue is a ground based issue. Before the 100 # pilot boards the plane she has already loaded her 50 # of luggage in the back and topped off the tank. This is extreme aft CG that will be corrected once she gets in the pilot seat. However the landing gear has to be far enough aft of this CG location so the luggage and fuel do not cause the plane to tip back on its tail.
So, one design criteria is to set the wheels back to cover this aft CG scenario on the ground. Now when the two 225# pilots get on board with little fuel left this shifts the CG forward which means the nose wheel has to carry more of the load ands its going to be harder for the stabilator to hold the nose off during landing (or rotate during takeoff).

These are not impossible issues to engineer around but you have to appreciate Van for taking on this engineering challange for the sake of forward seating and removeable wings. It would definitely make the engineering task easier to place everthing as close to the CG as possible. There has been mention of adjusting the main gear location and the size of the stabilator so they are busy tweaking the design for both the air and ground CG issues.

The other item that I have been giving more thought about is the gas tank. Right now its a tall retangular tank behind the passenger back rest. At first I thought it would be more advantage to make is a flat retangular tank as low as possible in the baggage compartment. In essence it would become the baggage floor. However, just below this region are all the routing of controls for flaperons, rudder and stabilator. Having ready access to these controls is imperitive for annuals, maintenance, etc so covering them up with a gas tank is not a good idea. One other item I noted in some of the pictures is a battery directly behind the spar next to the gas tank. I'm even less comfortable with this scenario. I'm hoping the weight and balance works out so the battery (i.e a sparking device) can be moved back to the firewall (as far away from the gas tank as possible).

Being an automotive engineer I am very curious how Van is going to work out the details of these various engineering compromises. I am looking forward to the day when I say "so , thats how they accomplished that".

As for the balance of the plane it appears that Van has stayed true to his word that he designed this plane for ease of manufacturing. Constant chord wings, flaperons and stabilator means simple rib designs. Simple in the manufacturing world means low cost tooling and high volume production (i.e making a lot of the same parts like ribs) and that all translates to lower overall cost which is the most difficult challenge in the aviation community. Others say the 12 is at best "plain" looking. Some think its "ugly". I look at is as another engineering marvel from Vans and the beauty is in the design work. Besides all that I happen to likes the looks of the design. As we have seen with many a design a paint job in the hands of an artist can trick the eye and create a beauty where others could not see it. (That is why venture capitalists spend more money creating pretty pictures for marketing than they do on engineering. How many "pretty designs" never fly. Van chooses to engineer first , paint later.)

The entertainment value for me is the 12 is not just another "me too" copy cat of traditional low wing LSA. It has some unique features that bring with them unique engineering challenges and it will be neat to see how they are resolved.

Frank

How in the world did Mr. Vangrundsven ever design airplanes before this forum existed?
So many people here know so much more than Van, he probably won't be in business much longer.

I very much appreciated the previous post by FrankS wherein he made some W/B calculations. I, like others, have been interested in how sensitive W/B issues would be with the RV-12. And while his numbers are based on suppositions - what Frank did for me - a new pilot and NOT an Engineer - was give me a greater understanding of how and why what Van has done is possible.

I have not doubts whatsoever that Mr. Vangrundsven is a highly capable designer and engineer. I also do not believe that he is designing this in a vacuum - and quite possibly these posts are being read by him or his staff. I can hear their musings now. "Yeah guys... I know you are a bit uncomfortable with the fuel tank or battery thing... it's a POC and we are looking at all options - and do have your safety in mind". I am sure he is listening to his audience because frankly folks... he is running a business... and good businessmen know that if you want to sell a product... you have to make what they want to buy.

For the rest of us watching very interested from the sidelines... for now we discuss what is going on - comparing notes, expressing likes and dislikes, etc. and for me - learning and understanding more and more about aircraft design and the long road from an idea, to a POC... to the aircraft I hope to be rolling out of my garage in the future.

So - while I took Mel's comments as a bit of tongue in cheek razing of us chasing this RV-12 idea... I did chuckle a bit.

But I also want to express my thanks to Frank, Mel and everyone else from whom I have learned so much at this site.

DJ

Has anyone thought of building an 9 with pulled rivets? I wonder how it would change the performance numbers and if it would then meet LSA requirements?

Pulled rivets on a -9 would certainly make it build much faster, but at a much higher cost, and it still wouldn't meet LSA requirements. Still way too fast and way too heavy.

Interesting idea though. If you ever wanted to get a -4/-6/-7/-8/-9 in the air QUICKLY, and you really don't care about a smooth exterior, I guess you could do the whole thing with pulled rivets. Anyone ever hear of this before?

Everyone seems to think that pulled rivets are round head. The come in flush style just like AN rivets do. My Moni Motorglider was designed with flush pulled rivets. Pulled rivets are MUCH heavier than solid rivets, thereby making the weight limit even more of a factor.

daverv9 said:

Has anyone thought of building an 9 with pulled rivets? I wonder how it would change the performance numbers and if it would then meet LSA requirements?

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How many extra pulled rivets would you have to add to equal the strength of the solid rivets? You could use CherryMax rivets to get the strength, but they have less fatigue life than solid rivets. CherryMax rivets need very accurate holes, and the correct grip to get the spec strength though, so they are less tolerant of small builder errors.

The cruise performance "problem" of the RV-9 vs the LSA specs can be solved by putting a fine pitch prop on it. The biggest problem is weight. The RV-9 is too heavy.

If you want an LSA, build an LSA. If you want an RV-9, build an RV-9. Don't confuse the two.

jmoylan said:

Those are excellent questions. One concern of mine is that without differential braking, whats the turn radius? Might seem trivial, but at small airports there often isn't much room to maneuver (i.e. back taxi - 180 degree turn on a narrow runway)

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I have been giving this landing gear thing some thought recently. The three type of steering (for tri-cycle landing gear) that I am familiar with are 1. Cessna, steerable nose gear with spring loaded rods to the front strut. 2 Piper Cherokee with solid rods to the front strut and 3. Grumman, differential braking with free castoring nose gear.

It maybe because of what I am familiar with but I prefer the the Cessna style. The good news is with the flexible link you can execise the rudder without having to turn the nose wheel. So with a cross wind take-off you can hold rudder to keep the plane tracking straight and the nose wheel will track staight down the runway. Works the same on landing. A Cherokee on the other hand goes where the nose wheel is pointed so you drive it on the runway and fly it in the air. If you land a Cherokee holding rudder for a crosswind you better have it straight before the nose wheel touches the runway or your in for a surprise.

The bad news with the Cessna system is if the springs to the nose wheel are weak then you can push full rudder and the nose wheel doesn't necessarily make a full turn so you need a little differential brake to swing the nose around in a tight turn while taxiing. I tried to taxi the 172 Saturday without differential braking and it just didn't work, especially where you had to make tight 90 degrees turns off the runway on to the taxiway, etc.

So, I expect the 12 will either have a stiff steering link to the nose wheel like a Cherokee or if it's spring loaded like the Cessna I would prefer stiffer springs for more positive steering around the ramp.

I still like the simplicity of the hand brake system (for installation and maintainance) so I'm hoping the nosewheel steering works out a good compromise that allows this concept.

Thats one of the items on my list to check out at Sun and Fun in a couple of weeks.

Frank

RV12 fuel capacity

It sure is nice to get more info on the RV12. I hope that by moving the engine forward and changing the C.G,they might consider a bigger fuel tank. With the fuel burn numbers they are giving your range isn't going to much more than a C150. At C172 speeds, I would like to use an RV12 as a cross country machine.

Asymmetric vortex generator condition

I just watched part 4 of the RV-12 stall/spin video and I heard the pilot mention a slight roll tendency due to an "asymmetric vortex generator condition."

Is he talking about VG's on the RV-12 wing or something else? Does anyone know what he meant by that?

Just curious.

DJ

RE: Vortex generators

From Vans website:

We experimented fairly extensively with corrective measures. We tried vortex generators in many configurations and placements. We even made full-span leading edge cuffs that increased the camber of the wing. Neither improved the stall speed -- and just to make things more frustrating, the cuffs actually reduced the cruise speed.

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Strakes?

I wonder if strakes have been considered. THey have proven to lower stall speeds on other planes and Vans designes specifically.

Kahuna said:

I wonder if strakes have been considered. THey have proven to lower stall speeds on other planes and Vans designes specifically.

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Has anyone done flight testing with and without strakes with a flight test airspeed system that would allow stall speed to be determined in CAS? Or has all testing only been able to look at stall speed in IAS? There can be a significant difference, and a reduction in IAS at the stall may not relate to the change in CAS at the stall.