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28 more gallons of fuel on an RV-9A

This is our first attempt at building wingtip tanks for the RV-9A. First flight results seem promising! We added winglets to see if it makes any difference. We show the wing and winglet aerodynamics in different stall configurations... The tanks work beautifully and we are super happy with the results :D

Correction: 14 gallons on each tank = 28 gallons total

Check out video here

Ananda
RV9A - 464CP
Engineer at Levil Technology
"Fly straight and Levil"
 
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The main reason for the winglets is to create a high point for the tank vents, reducing piping work. The second reason is that from the analysis, the forward swept winglet is more efficient than other shapes or no winglet, giving 15% drag reduction, keeping the performance the same, even with the additional tanks. In other words... we have now twice the fuel, and no loss in performance... or at least that is the goal.
 
I like the idea of added fuel. When you hold the tank in your hand, it looks great and I can see the shape. Nice glass work for sure. Giving another 90 minutes + safe flight time with no performance is probably more than most of us need, but it is nice knowing it is possible. Thanks for the stall videos. That was really interesting to me. Have fun!
 
I like it Ananda. Do you plan a production run? How difficult/easy to install/plumb/remove on a flying aircraft? Need a beta tester? :)


 
Very interesting. The video suggests a few questions.

What are the forces that the winglet imposes upon the wing structure?

Do those forces account for the winglet stalling, as shown in the video, which would decrease their lift and increase their drag at wing angles of attack below the wing's stall?

Did you make any structural modifications to handle those loads?

How does the winglet stalling affect the angle of climb?

Thanks,
Dave
 
Wait, I recall winglets have been discussed in this forum. One camp was concerned about them because the wing isn't engineered to handle the twisting moment created by wind forces on the winglet's outer forward edge. How have you addressed this?
 
Very interesting and valid questions.. Although we haven't done all the tests to be able to answer all the questions, here are some interesting things we made:

- The tanks actually give 4 more hours of flight at 145 Kts.
- When building the airplane, the main and rear spar were reinforced, to handle the weight of the tank and the twisting moment of the winglet.

How does the winglet stalling affect the angle of climb?
From the tests, the winglet started stalling at 60 kts, which is not ideal, but we normally climb at 80 its, and during our standard climb, the winglet did not stall.

What are the forces that the winglet imposes upon the wing structure?
Don't know.. we made it very strong. More tests to come...

Do you plan a production run?
Negative. This is just for fun and to be able to go the distance.

PS: The RV9 is an amazing airplane as is. It does not need winglets.
 
- The tanks actually give 4 more hours of flight at 145 Kts.

Do the tanks act as Lavatory Storage too? Or you'll need a case of Little Johnnys. :D Doing the basic math, 4 hours @ 3.5 GPH= 14 Gallons. Pretty good fuel burn.
 
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....How does the winglet stalling affect the angle of climb?
From the tests, the winglet started stalling at 60 kts, which is not ideal, but we normally climb at 80 its, and during our standard climb, the winglet did not stall.....

Thank you.

From the video, I'd expect that the winglet would not be stalled at the best rate of climb speed, but that it might be at the best angle of climb speed. It might be worth investigating that.

Do you have any plans to tweak the winglet airfoil or incidence so as to increase its stall margin?

It also might be interesting to see how the plane reacts in a slip as the angle of attack increases. Perhaps the drag of the stalled winglet would increase the effective yaw stability at that point. For example, full right rudder, left yaw (wind in the left ear), the left winglet should have a higher angle of attack than the right one, and might stall before the right one. Its drag should increase as the winglet stalls, thus tending to unyaw the aircraft.

Dave
 
those sure are cool looking!
but yeah.. my range is not determined by the plane... but by my bladder.

Do the tanks act as Lavatory Storage too? Or you'll need a case of Little Johnnys. :D Doing the basic math, 4 hours @ 3.5 GPH= 14 Gallons. Pretty good fuel burn.
 
I'm not an engineer, and I didn't sleep at any motel chain last night. But I would be concerned about that much weight at the tip of the wing. 84 lbs on each wing, plus the weight of the mod wing tip. Is the Van's spar and wing assembly strong enough for that, say in turbulence? Will there be a twisting load in turbulence? And what about a firm landing with full or nearly full wing tip tanks?

Gee, that all sounds so negative, and I actually like the idea of the experiment!!
 
This is experimental aviation after all...

I'm not an engineer, and I didn't sleep at any motel chain last night. But I would be concerned about that much weight at the tip of the wing. 84 lbs on each wing, plus the weight of the mod wing tip. Is the Van's spar and wing assembly strong enough for that, say in turbulence? Will there be a twisting load in turbulence? And what about a firm landing with full or nearly full wing tip tanks?

Gee, that all sounds so negative, and I actually like the idea of the experiment!!

But there are even more potential issues that where hopefully considered and now need to be tested.

The polar moment of inertia of the fuel weight and heavier tanks at the wing tips, and its effect on yaw stability, spin recovery, etc.
The RV-9 was extensively spin tested. This type of mod. effectively throws all of that test data out the window.
I know tip tanks have been installed on RV's in the past, but with the longer wing span of the RV-9, it makes the inertia factor that much bigger.
 
The RV-9 was extensively spin tested. This type of mod. effectively throws all of that test data out the window.
I know tip tanks have been installed on RV's in the past, but with the longer wing span of the RV-9, it makes the inertia factor that much bigger.


I would love to know more info on the spin testing for the 9. If the spin testing info is available, is there a link to the info?

Thanks
 
Have them engineered.

Nice work guys, buuuut.....

I fly Air Tractors in my spraying business and our wings have a 5,000hr. spar life, then the lower spar cap (steel) has to be replaced by the factory.

There is a winglet manufacturer that makes and advertises them in our trade publications, to create less vortices and so on.

Air Tractor sent out fliers and in magazine articles, that the winglets reduce our spar life by 40% !! ...and we only fly at 140 MPH. Granted, these winglets are quite a bit taller than yours and would then create a stronger twisting force.

At near 200 MPH, the twisting force at the wingtip, where the spar is thinnest, concerns me, sans aeronautical engineering consultants.

Best,
 
The wing structural load would be highest with EMPTY tip tanks and FULL seats in a high G maneuver.

Any positive effect on lift happens at the outboard end of the wing, so ignoring all the twisting, you have to realize that at the same G-load as before, the bending moment on the root of the spar might be quite a bit higher.

The only time the added fuel weight is a bad thing is on landing, but my guess is that that won't be as much of an issue as the added moment with empty tips and high G's.

Did you do a fatigue analysis of your spar mod to make sure it doesn't cause more problems than it solves?

Of course the twisting (there isn't much to an RV rear spar, afterall) and dynamics (polar moment, etc) are different issues entirely that deserve to be addressed as well.
 
RVbuilder if the 9 was extensively spin tested why are we plackarding them for no spins

Van's likely used the FAR 23.221 spin requirements as guidance. FAR 23 (applicable to type-certificated light aircraft) requires that every single engine aircraft be able to recover from a one turn spin, even if the aircraft is not approved for intentional spins. The spin is not fully developed after one turn, so it is more of a test of recovery from incipient spins. If the aircraft is to be approved for intentional spins, you also need to show that it can be recovered from six turn spins.

Note: the above is a rough summary of FAR 23.221 spin requirements, and does not cover all the details, including a "let" for aircraft that are shown to be spin resistant.
 
RVbuilder if the 9 was extensively spin tested why are we plackarding them for no spins

That is what I thought. I would still like to know what the spin testing issues were. I don't want this thread to get off track, so if there is other info about spin testing for the 9, pm or email me. Thanks
 
That is what I thought. I would still like to know what the spin testing issues were. I don't want this thread to get off track, so if there is other info about spin testing for the 9, pm or email me. Thanks

The official company position is that there were no "spin Issues" (not sure why someone thinks they must be "placarded" against spins). Recreational spins are not recommended. This is not particular to the RV-9. It is the same recommendation for all the side by side RV's. It has nothing to do with ability to recover, or unusual techniques needed. It is because the aggressive entry break and subsequent acceleration towards a high rate of rotation will like scare the %&@#* out of most pilots if that let it go very far.
 
The purpose of winglets (usually on high performance aircraft) is to increase low speed lift, reducing spanwise flow, and reduce drag by reducing wingtip vortices at cruise.

None of these are aerodynamic issues on an RV except MAYBE wingtip vortices drag, but even reducing that to zero would be such a small reduction in total drag you wouldn't notice a difference in day to day flying.

Other than the tip tanks for someone who can sit in an RV for 4+ hour stretches... this is a solution looking for a problem.
 
Correction: 14 gallons on each tank = 28 gallons total

Wow, 28 additional gallons...just curious, why so much? I would think 5-8 gallons each tip, for a total of 10-16 additional gallons, would give a very good total range or endurance.
 
64 gallons without resorting to a fuselage/baggage tank?! That is impressive. I too am very curious of your motivation.. just for kicks? cross continent ferry service? looking to exceed Jon Johannson's records? inquiring (nosey) minds want to know :D.

They look great.. congratulations! Have fun experimenting.

Stan
 
RV9 Extra fuel

I have to say putting fuel so far outboard raises significant structual concerns for me. While I don't object to experimenting, I just wouldn't do this particular mod without significant analytical backup.

I too wanted more fuel for my -9A as I wanted to have the same range capability as my Long-EZ had. I decided to keep the fuel weight inside the airplane by building fiberglass tanks that tucked into the space behind the seats. The CG isn't much further aft than the pilot/pass CG. Each tank holds 8 gal, which I've found to only need one tank for the vast majority of my Xcountrys.
I burn this Aux tank off first during the initial climb out when fuel consumption is highest and by the end of the first 45 min or so the tank is empty. It gives me a range of a 1000 miles with reserves.

The tank is directly plumbed into the 3rd fuel port on the standard fuel selector valve. I've regularly used this setup and it works GREAT!
https://picasaweb.google.com/116654282962520736797/BaggageFuelTank?noredirect=1#5224815801258893730
 
Thank you Scott for the answer. The placard comment is what confused me a bit. Thanks again, I appreciate it.

The official company position is that there were no "spin Issues" (not sure why someone thinks they must be "placarded" against spins). Recreational spins are not recommended. This is not particular to the RV-9. It is the same recommendation for all the side by side RV's. It has nothing to do with ability to recover, or unusual techniques needed. It is because the aggressive entry break and subsequent acceleration towards a high rate of rotation will like scare the %&@#* out of most pilots if that let it go very far.
 
64 gallons without resorting to a fuselage/baggage tank?! That is impressive. I too am very curious of your motivation.. just for kicks? cross continent ferry service? looking to exceed Jon Johannson's records? inquiring (nosey) minds want to know :D.

They look great.. congratulations! Have fun experimenting.

Stan

Anyone flying north to Alaska or other similar destinations can use the extra fuel. 99% of the time, having extra fuel is not an issue but, for example, flying the Trench route through BC, from Mackenzie to Watson Lake if you get into weather at the northern end of that leg and have to turn around, it may not be possible to get back to Mackenzie on a "normal" tank of fuel. There are places to land, but no fuel.

Or take Vlad's proposed adventure to the Aleutians and back - another example of a long flight for which it would be very useful to have extra fuel.

Just a couple examples of "why" someone might want to do this.

Greg
 
Guys I'm all for experimenting...and I fly a 180hp -4 so the idea of having a bit of extra fuel is certainly appealing to me. However, 14 gallons per side puts a picture in my head.

Imagine sitting on the ramp at an air show and seeing two 84 pound kids jumping up and down on your wingtips using your wings like spring boards...at the same time! That's essentially the force your wing structure and spare would need to endure on a rough landing. Would you worry about your airframe structure if you saw this happen at an air show? I would.

I also can't imagine putting two, yes two, 40 pound bags of concrete in EACH of my wing tips and taking off.

Again, I'm not an engineer so excuse the non-technical perspective but it has served me well thus far in my flying career. Sorry to be a downer on this...I love that we can experiment but this one makes me uncomfortable.
 
Anyone flying north to Alaska or other similar destinations can use the extra fuel. 99% of the time, having extra fuel is not an issue but, for example, flying the Trench route through BC, from Mackenzie to Watson Lake if you get into weather at the northern end of that leg and have to turn around, it may not be possible to get back to Mackenzie on a "normal" tank of fuel. There are places to land, but no fuel.

Or take Vlad's proposed adventure to the Aleutians and back - another example of a long flight for which it would be very useful to have extra fuel.

Just a couple examples of "why" someone might want to do this.

Greg

Someone running mogas may also want to have good out-and-back range. The extra fuel I'm including should provide me enough fuel to fly out to maximum normal bladder range, stop, and return (plus reserves) without having to buy avgas at the stop.
 
Wow, 28 additional gallons...just curious, why so much? I would think 5-8 gallons each tip, for a total of 10-16 additional gallons, would give a very good total range or endurance.

We have family and property in South America. The long range tank design is to be able to make it from my base airport KSFB (Orlando, FL) to SA with only one stop (Dominican republic). Without the extra fuel we have to either stop in Miami, DR and cross our fingers that there is no headwinds on the long route over water all the way to Vzla, or stop on some of the islands, which end up making the trip super long.
 
We have family and property in South America.

Oh, very good reason. Someday when my RV is no longer a builder but a flyer, I'd like to consider that. May install something in the baggage compartment then. Always wondered why Vans didn't make the tanks a little bigger for the RV-9.
 
My motivation is out & back on home-fueled tanks. <$4 vs >$6 per gal * 10 gal/hr can be a strong motivator.

Charlie
 
I think someone wanting extended fuel range would be better off extending their leading edge tank by a bay or three. That keeps the load closer to the fuselage, further forward for better CG, and uses all of the skills you're already using when building. No need for advanced fibreglass work... :)
 
That's more or less how I did mine (copied the idea from a couple of -9 builders who had already done it. Skipped one rib bay & left the outermost bay dry. Used the spar itself as the back baffle. (Same technique used by the Bushby Mustang II when going from fuselage header tank to wet wings.)

Intent was to keep the original tank system as 'stock' as possible, and gain as little weight as possible (maybe 3 or 4 lbs).

In retrospect, it might have been easier to build a narrow one-bay wing extension tank that would bit between the end of the wing and the wing tip. CG seemed more difficult to manage, though.

Charlie
(Don't do as I did; violates Van's and other natural laws, etc etc.)
 
Guys, we used to sell Cessna Agwagons and Agtrucks so we spent quite a bit of time at the factory and at seminars. An engineer told our group that the 310 series had a lighter spar because of the 55 gallon tip tanks and that they effectively "strengthened" the spar since it didn't help bend the spar UP if the fuel had been inboard.

Jon Johanson had more fuel in his -4 wingtips (17 gal each) and flew it around the world twice, in opposite directions, plus 50 gallons in the back seat!

He did mention landing it full had to be done carefully though.

Best,
 
I like it :) Im undecided about the winglet, but I like MORE fuel. I think the 9 could be the new long EZ as far as range... And it can take off and land on grass... :)

win win...

just my opinion, I could be wrong... :)

D


We have family and property in South America. The long range tank design is to be able to make it from my base airport KSFB (Orlando, FL) to SA with only one stop (Dominican republic). Without the extra fuel we have to either stop in Miami, DR and cross our fingers that there is no headwinds on the long route over water all the way to Vzla, or stop on some of the islands, which end up making the trip super long.
 
I like it :) Im undecided about the winglet, but I like MORE fuel. I think the 9 could be the new long EZ as far as range... And it can take off and land on grass... :)

win win...

just my opinion, I could be wrong... :)

D

Or just build a -14...it already has a much longer range, has a nearly identical fuel burn at the same speed, is much roomier, is aerobatic............;)
 
Maybe Scott can tell us what the -14A burns at 155-160 KTS?

I am not going to answer with specifics, because for this comparison to be meaningful, we would need to specify a few other details that aren't being mentioned (at what altitude and OAT in particular).

As reported previously I have routinely seen 170 Kts TAS at 8.7-8.8n GPH in the RV-14A at 10K to 11K ft.
Based on that, it's speed fuel flow at that altitude would would be very similar to whats was quoted for the RV-9.
 
Wait, I recall winglets have been discussed in this forum. One camp was concerned about them because the wing isn't engineered to handle the twisting moment created by wind forces on the winglet's outer forward edge. How have you addressed this?

Nice work guys, buuuut.....

I fly Air Tractors in my spraying business and our wings have a 5,000hr. spar life, then the lower spar cap (steel) has to be replaced by the factory.

There is a winglet manufacturer that makes and advertises them in our trade publications, to create less vortices and so on.

Air Tractor sent out fliers and in magazine articles, that the winglets reduce our spar life by 40% !! ...and we only fly at 140 MPH. Granted, these winglets are quite a bit taller than yours and would then create a stronger twisting force.

At near 200 MPH, the twisting force at the wingtip, where the spar is thinnest, concerns me, sans aeronautical engineering consultants.

Best,

I think Sid and Pierre are right. I recently had the opportunity to watch a set of winglets get installed on a 737 wing that did not have them before. The process and the structural modifications were dramatic. It was not just a case of unscrew the old wing tips, install winglets and go flying. The wings were de-skinned from the tip to practically the engine pylon in order to instal the additional structure needed to handle loads imposed on the wing by the winglet. Granted, the RV wing is not a swept wing design but I would proceed with a cautious flight test program.
 
Flight to Oshkosh

Flight Update on RV9 with Winglets:

The RV9 had a successful non-stop Orlando-Oshkosh flight with full tanks (28 additional gallons of fuel) using the new winglets. Had to go around some storms, and we caught some bad weather towards the end of the flight and we still had fuel to spare! Here is a picture:

Photo%20Aug%2009%2C%2012%2016%2013%20PM.jpg
 
Cool. Would you mind posting specifics? (Total burned, altitude, avg ground and air speeds, etc.)

Also, at what weight? Did you raise gross weight by the extra fuel weight? What's the handling feel like with the tanks full? I've got leading edge aux tanks in my -7, but haven't flown yet.

Thanks for the update,

Charlie
 
RV9A winglets

The trip from Oshkosh to Orlando-Sanford lasted 7.5 hours at 11500 ft.
Fuel burn was 7.5 gal average. The speed was 145 true.
This is the same speed and fuel bun before the Tank-winglet modification.
The navigation guidance was performed by a BETA Trutrack ECO (RC $50 servos).
I performed stall test (with parachute) with one tank full and the other one empty.
No adverse stall was found, only trim correction was needed for level flight.
 
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Firstly, I think the winglets look good.. *shrug*

I have thought about doing this to the RV-10 which by all accounts already has a bladderbuster fuel reserve as it is.. but still something nice to have..

My concern is with how it might add an untested load to the wing spars..

Vans themselves say don't do this.. (or that's what they said on the 10 anyway)..

How do you know its safe? This is math that is beyond me =)
 
Just a dumb question here... I would like more fuel in my 9A sometimes.
On the winglet work you did.... would you do it over again? If it goes the same speed and uses the same fuel, what are they for?
I did Sun N Fun to PHX one time in a day. I sure was tired when I got home.
 
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