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Appears Vans not allowing Sky Design Wing Tank ER Mod

jpkindred

I'm New Here
I was interested in incorporating the Sky Design RV-10 ER FUEL TANK KIT kit mod which increases total fuel from 60 gallons to 83 gallons total fuel. After contacting Vans to make the necessary additions and deletions to my wing kit, I received a form with the following verbiage:

"T-1004 Special Order Form

By signing below purchaser certifies that ribs, stock code(s) T-1004-L
and/or T-1004-R will not be used to install aftermarket extended range
fuel tanks. All T-1004-L and T-1004-R ribs may only be installed as
instructed in Van’s Aircraft Inc’s Kit Assembly Instructions Section 18
for the RV-10 and RV-14."

Sky Designs had just received word that this form was being sent out and was researching it.

Anyone else aware of this issue?

What other fuel storage increased capacity mods have been successfully incorporated in the RV-10s?
 
I don’t think Van’s can dictate what you can and cannot do since it’s E-AB. They can, however, control what goes out in the kits and can stipulate no adds or deletes to a particular kit. Worst case you’d have to suck up buying the wing kit as is and ordering things you do need separately online from “the List”.
 
Welcome to VAF

John, welcome aboard the good ship VAF.

Methinks the message from the factory is a lawyer driven thing-----it would appear that if makes you totally responsible for changes to the design.

Although there have been similar mods in the past, you cant blame Vans for covering their butt.

The added fuel weight and lateral moment are most likely something Vans has not engineered for.
 
My Sky Designs tank kit just shipped yesterday (for my already built wings).

Interested in hearing more about this.
 
Perhaps the engineers at Van’s have reason to worry about such things:
F140697-E-0353-4-A67-A636-3-D3384931-F8-B.jpg

Take the safe road. Build a ferry tank to replace one or both rear seats, keep W&B in spec and fly on.

Carl
 
KEN'S RESPONSE:

I believe that extending the tank skin and tank baffle outboard serve only to increase the bending strength of the wing in the two affected rib bays. Also the torsional stiffness and bending stiffness of the wing are, if anything, increased with ER tanks so there is no reason to expect a reduction in flutter speed.

Additionally, spin recovery is adversely affected by any increase in rolling and yawing moments of inertia but it should be recognized that other commonly added extras - such as air conditioning systems - also increase the mass moments of inertia. Given that spins are not recommended in either RV-10 or RV-14 and that both aircraft have such benign stall characteristics, the increased moment of inertia due to ER fuel was deemed an acceptable compromise.

It is also worth noting that fuel carried in the wing moves the aircraft CG slightly forward whereas carrying fuel in the baggage area or rear seats moves the aircraft CG aft. All other things being equal, a further aft CG tends to degrade spin recovery.

Conversely, removable tanks in the baggage area or rear seats can run counter to safety. I say this because of the necessary increase in fuel system complexity and pilot workload as compared to larger capacity wing tanks. Also, depending on how any fuselage tank is constructed and attached to the airframe, crashworthiness could also be degraded.

The idea of placing extra fuel in the outboard leading edges of RV-10 is not unique to Sky Designs.

Saint Aviation offers two options for long range fuel: 90 gallons and 120 gallons. See: https://www.saintaviation.com/newrv/pricing.html then scroll down to find "SA long range fuel tanks")

Hotel Whiskey offers another means of carrying additional fuel: http://hotelwhiskeyaviation.com/rv10

And finally, AeroCentro also offers 90 gallon fuel tanks for their RV-10 customers:
https://www.aerocentro.com.br/copia-rv-10

What sets the Sky Designs ER Fuel Tanks apart from the rest is that the simplicity of the original fuel system is retained - one tank per wing, one filler cap per wing, no additional plumbing, pumps, or fuel lines are needed.

Finally, Increasing wing fuel capacity is a common modification on certificated aircraft. Here are a few such examples:

https://skyway-mro.com/cessna-206-207-auxiliary-fuel-tank/

https://flintaero.com/kits/internal-tip-tanks/

https://www.planeandpilotmag.com/ownership/modifications/adding-aux-fuel-tanks-to-your-airplane/

Customer safety is of utmost importance to me. So if my designs are unsafe, I need to know about it and am truly thankful for the opportunity to consider this issue more thoroughly.
 
Perhaps the engineers at Van’s have reason to worry about such things:
F140697-E-0353-4-A67-A636-3-D3384931-F8-B.jpg

Take the safe road. Build a ferry tank to replace one or both rear seats, keep W&B in spec and fly on.

Carl

Wow!! an extra 138# of fuel did that... I don't think so....:rolleyes:
 
I think Vans may have an issue with many RV-10 and 14 owners deleting a bunch of tank parts and building Ken’s tanks (lost revenue for Vans).

I also think that the guy who did a lot of the design work on the 10 (Ken) knows what he is doing. I’m building and installing the ER tanks soon.
 
Vans need to insure they are not liable

I tried to delete my stall warning (Stall vane) since I was going to use AOA which I have a lot of confidence in and Vans told me for "safety" related issues they could not do this. As mentioned I think Vans is just being proactive in this crazy world of ours. The attorney would appear in front of a jury and ask "So you allowed the purchaser to delete parts that obviously needed?" Yes, "What where you expecting the buyer to do not purchasing these parts?" No reply...."You were expecting him to make an alternative design"...Maybe "I rest my case". Sign what you need to sign. I think I had to sign multiple documents when I deleted parts to use Berringer wheels and brakes and Showplanes composite tail cone. (You can imagine there issues deleting top skins and bulkhead formers).
 
So I’m curious, have any of these companies who manufacture extended fuel tanks done any structural engineering and spin recovery impact studies. In the certified world, you would be required to demonstrate both areas. Some issues don’t show up for thousands of cycles, but results can be catastrophic, i.e. the Comet jet structural failure as an example.
 
I also think that the guy who did a lot of the design work on the 10 (Ken) knows what he is doing. I’m building and installing the ER tanks soon.

Fair assessment.
Having said that, I find it strange that Ken has changed from his former opinions of not being in favor of designing and marketing a mod. such as this while he was at Vans, to now thinking it is fine.
Possibly has something to do with him not having to deal with any fallout that resulted from it….?
 
So I’m curious, have any of these companies who manufacture extended fuel tanks done any structural engineering and spin recovery impact studies. In the certified world, you would be required to demonstrate both areas. Some issues don’t show up for thousands of cycles, but results can be catastrophic, i.e. the Comet jet structural failure as an example.

None that I am aware of, though maybe Ken has and I just don’t know about it (It was only recently that it was introduced).
 
I enjoy the Extended Range Fuel in the wings.

""Take the safe road. Build a ferry tank to replace ONE or BOTH rear seats"", :eek: UMM, I would have nightmares of feeling the (refreshing & cold) Fuel splashing over me and my passenger and watching petrified in slow motion as its passing by headed for the Electrified Panel during a Nose Gear Collapse. :eek: No Thanks for the ferry tank idea in daily use.
 
Fair assessment.
Having said that, I find it strange that Ken has changed from his former opinions of not being in favor of designing and marketing a mod. such as this while he was at Vans, to now thinking it is fine.
Possibly has something to do with him not having to deal with any fallout that resulted from it….?


Scott, can you expand on what exactly you mean by this? Are you referring to Ken not being in favor of other ER tank options, or simply that when he was at Vans he never pursued marketing tanks like he is now. In other words, did he actually come out and say he was against modifying the fuel capacity? Or what exactly was his stance?

I hope these don’t sound like fighting words as that’s not the intent. Just trying to understand what his views were in the past. If I were in his shoes years ago, I can see not being in favor of certain ER tank mods if he didn’t support HOW they did it. In other words, maybe he could not support the extra plumbing or complexity, the engineering, etc.
 
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So I’m curious, have any of these companies who manufacture extended fuel tanks done any structural engineering and spin recovery impact studies. In the certified world, you would be required to demonstrate both areas. Some issues don’t show up for thousands of cycles, but results can be catastrophic, i.e. the Comet jet structural failure as an example.

This is not the certified world. Basic structural engineering would be straight forward to do and might well have been done. As for spin recovery, do you know what Vans has done in terms of spin testing? Have they done a full Part 23 spin program in all configurations combinations of wt, cg power setting, altitude etc etc? That’s a huge amount of work. Companies spend months doing it in the certified world. Or maybe vans just did the corner points of the envelope. I guess most builders assume that they have but probably very few actually know. It is not a certified airplane. So you can’t demand that a mod has been tested to Part 23 standards when you don’t know what the baseline aircraft has been tested to.
 
Wow!! an extra 138# of fuel did that... I don't think so....:rolleyes:

Well, the cat is out of the bag now - the RV-10L. This is the new version for folks who want a really low wing aircraft that sheds the need for entry steps, takes full advantage of ground effect, and doesn't tempt the owner to spend the bones for an AeroCreeper.
 
CG shift with fuel

Ken mentioned the CG shifting with the amount of fuel in the tanks and although I have not done this for the 10 W&B it's probably similar to the 14. The formula for the moment change is 82.58-((B15-5)*(1.22/45)) where B is the number of gallons loaded. Again this is for a 14 not a 10 but gives you an idea of the moment shift as fuel is loaded. Not that I would consider extended tanks (I am my wife need to stretch our legs every 3 to 4 hours) but is the intent to exceed current gross weight? It seems the 10 can carry additional fuel with doing this especially if it's just one or two people without needing to exceed max gross.
 
Spin Recovery

This is not the certified world. Basic structural engineering would be straight forward to do and might well have been done. As for spin recovery, do you know what Vans has done in terms of spin testing? Have they done a full Part 23 spin program in all configurations combinations of wt, cg power setting, altitude etc etc? That’s a huge amount of work. Companies spend months doing it in the certified world. Or maybe vans just did the corner points of the envelope. I guess most builders assume that they have but probably very few actually know. It is not a certified airplane. So you can’t demand that a mod has been tested to Part 23 standards when you don’t know what the baseline aircraft has been tested to.

That's an interesting question. Looking at Ken's tank mod, the only real unknown would be how spin recovery is affected by the moment of inertia change. Stress and fatigue from the greater weight outboard should be easy enough to calculate. If Vans did minimal testing in spin recovery, it makes it difficult to approve or indict Ken's mod. One of the design challenges with the Vans low wing tank configuration is tank slenderness, and the need to push outward for a greater volume. I'm hoping the RV-15 tank is the large region between the front and rear spar which would allow volume increase with minimal outboard movement.

Additional fuel in the cabin behind the occupants may raise more safety concerns than Ken's tank mod.
 
Builders regularly delete parts from kit orders to add aftermarket parts. I know I signed a some sort of waiver when I did that.

What I don’t remember is signing a waiver specifically indicating I wouldn’t add a certain modification. Do builders who delete upper fuselage skins when adding the Showplanes fastback mod sign a similar waiver? How about the wingtip deletion? Did Aveo do an structural analysis or flight test program on ZipTips? How about Hotel Whiskey?

I can’t help but wonder if this particular mod designed by a highly regarded and very competent former Van’s engineer is getting a different response from Van’s because of who it is - versus a real concern over structural implications or impact on handling qualities?
 
Pointless debate.

Obvious legalese. Sign, buy the parts, be happy.

BINGO!

You are the manufacturer of the aircraft. You get to live with...or die with, the changes you make.

Just be smart about your experiment and don't blame Van's if it doesn't go well.
 
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I am in squarely in Dan's court.
If I owned Van's aircraft I would not allow any changes to the kit so's to keep the lawyers at bay.
They can twist and distort facts so much it will make you sick.
I built houses for 42 years and was an expert in court for many cases against other shoddy builders. I was a hands on builder, not a paper contractor, so had tons experience to draw/testify from.
" I have never been sued" yet.
I believe they are a necessary part of society, But, some are a ruthless bunch of blood suckers.
OK I'll get off my soapbox before I get sued.
Art
 
I saw this in a comment attributed to Ken Krueger above:

“Given that spins are not recommended in either RV-10 or RV-14 and that both aircraft have such benign stall characteristics, the increased moment of inertia due to ER fuel was deemed an acceptable compromise.”

The RV-10 is not aerobatic, but the RV-14 is. This is the first time I have seen something that would indicate spins are not “recommended” in an RV-14. Is this true?
 
I guess...

"...If I owned Van's aircraft I would not allow any changes to the kit so's to keep the lawyers at bay..."

I guess I took Dan's comment from a different perspective; order the parts, be happy and build what you want to build.

I get that Vans is trying to mitigate liability...
 
Showplanes mod

It's been awhile but the only thing I remember signing was the authorization to delete the skins and formers and I was responsible for the outcome. Vans would not let me delete the stall vane but that's peanuts and probably effects 90% of unintentional "envelope excursions" which is fine. At some point Vans will probably ask us to sign "something" that limits liability for any design changes beyond what was proven. I'm ok with that, we are Experimental Aircraft builders after all. Somehow adding 40 gals (240 lbs.) seems not an issue as long as we keep the max gross within design.
 
KEN'S RESPONSE:
...

Also the torsional stiffness and bending stiffness of the wing are, if anything, increased with ER tanks so there is no reason to expect a reduction in flutter speed.

...

Regarding wing flutter characteristics, generally speaking:

- Increasing wing bending stiffness will decrease flutter speed (badness, if there is not enough excess flutter margin to begin with).

- Increasing wing torsional stiffness will increase flutter speed (goodness).

- Increasing both wing bending stiffness and torsional stiffness will need some analysis/assessment/testing to determine whether flutter speeds go up or down.

- Adding (fuel) weight forward of the Elastic Axis of the wing (as these leading edge tanks do) will increase flutter speed.

- Adding (fuel) weight aft of the Elastic Axis of the wing will decrease flutter speed.

- Adding (fuel) weight outboard will reduce the wing bending frequency (usually good for flutter), but will also reduce the wing torsional frequency (bad for flutter).

Note that many of the above effects are interrelated, and cannot happen individually (e.g., cannot increase wing torsional stiffness without increasing wing bending stiffness to some degree.)

Therefore analyses/assessments/testing should be done which include all of the above effects to determine whether adequate wing flutter margins exist with the extended tanks.
 
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Folks, FYI we'll be adjusting the language in our documents related (generally) to the sale and use of our parts for purposes other than designed-and-tested-by-Van's cases. I had a good quick chat with Ken on Friday and we're all essentially on the same page. We do have to ensure that we either limit changes or deny certain parts sales (in some cases) or require the customer (in other cases) to acknowledge the risk and accept and liability of using the parts and other items we make/sell in ways/designs for which they were not intended.

These airplanes are complex enough to warrant careful testing and design, and we put a lot of work into that for the things we build for safety purposes, of course. The designs and parts do change over time, and we at Van's (just like any other manufacturer) observe and learn about real-world experiences that affect how we design, change, support, approve and allow our parts and materials to be used. Plus, the fact is that some aircraft systems are considered to be more critical than others, relatively speaking. At any rate, working on it here so please give us a couple of days. I'll post again soon with an update of sorts.

greg
 
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These airplanes are complex enough to warrant careful testing and design, and we put a lot of work into that for the things we build for safety purposes, of course. The designs and parts do change over time, and we at Van's (just like any other manufacturer) observe and learn about real-world experiences that affect how we design, change, support, approve and allow our parts and materials to be used. Plus, the fact is that some aircraft systems are considered to be more critical than others, relatively speaking. At any rate, working on it here so please give us a couple of days. I'll post again soon with an update of sorts.

greg

Vans Definitely has the best engineered airplane kits in the Experimental amateur built market and definitely very conscientious of the safety of their products. Since it Experimental aviation the builder is still free to make changes to the Vans supplied kits. Call it legalese or CYA but I think it is very professional for Vans to provide the builder with a bit of understanding of the risk of making changes that they did not account for in their engineering.
 
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I had a good quick chat with Ken on Friday and we're all essentially on the same page. We do have to ensure that we either limit changes or deny certain parts sales (in some cases) or require the customer (in other cases) to acknowledge the risk and accept and liability of using the parts and other items we make/sell in ways/designs for which they were not intended.

These airplanes are complex enough to warrant careful testing and design, and we put a lot of work into that for the things we build for safety purposes, of course.

It's totally understandable that in this very litigious world, vendors/manufacturers need to explicitly state these kinds of things to limit their liability for what others do with their products. I'm glad there's agreement on the prinicple that the user takes on certain risks when modifying the use case, and not simply an attempt to block that use.
 
While the liability issues are there and real I also understand Vans position just for reputation. They have a stellar reputation for reliability and safety and they rightfully want to protect that. Any excursion from the plans creates risk at varying levels. Any accident impacts their reputation, so understandable they want to give clear warnings to builders as they go down that path, assuming they may not understand them, or outright discourage it if possible to help protect that reputation. They walk a fine line in this area. It's easy to see how an RV having it's wings ripped off in flight may land on Vans eventhough modifications were made that caused it. Seems unlikely the NTSB would catch that. People think of RVs as complete kits, at least from a structural standpoint, and not just a guideline for scatch building truly experimental stuff.

Example for impact not to assume this mod would cause that.

Larry
 
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While the liability issues are there and real I also understand Vans position just for reputation. They have a stellar reputation for reliability and safety and they rightfully want to protect that. Any excursion from the plans creates risk at varying levels.
Larry

And this is why, when you ask the factory about many builder modifications, the answer is something like: "We have not tested such a modification and cannot/do not offer advice specific to that modification."

That doesn't bother me in the slightest.
 
Just received word from Sky Designs Engineering and it looks like Vans reversed their decision the ER Wing Tank Mod:

"Hello John,

Forgive me if this is a redundant message but things have been a bit crazy...
We have good news. Vans contacted us and told us they have reversed their decision on withholding their ribs to our customers.

So it appears everything is restored to normal and for that we are very grateful.
Thanks so much for your support.

Kind regards,

Susan"
 
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Vans profits off parts

Someone mentioned that Vans looses some profit by deleting parts and this is why they might not want to delete parts. Now after 2 complete airframes ordered from Vans (And deleting a lot of parts) I found they are more than willing to delete a part and give you credit. (Except for that stall vane and mount which set me back 20 bucks........) They give very decent price reduction on the parts and could make it a lot worse for us. Deleting parts takes time from the order process to the picking and packaging process and I applaud there willingness to do this.
 
Someone mentioned that Vans looses some profit by deleting parts and this is why they might not want to delete parts. Now after 2 complete airframes ordered from Vans (And deleting a lot of parts) I found they are more than willing to delete a part and give you credit. (Except for that stall vane and mount which set me back 20 bucks........) They give very decent price reduction on the parts and could make it a lot worse for us. Deleting parts takes time from the order process to the picking and packaging process and I applaud there willingness to do this.

Yeah, I agree that it's not a profit thing on Van's part. I've already built my standard tanks, and then bought a whole other set (+4) of ribs and other parts. Ken's tanks use a lot of pieces from Van's, and they don't miss out on much money if someone chooses to go with his option. They make plenty more money when people who already have standard tanks opt to buy the parts to build new ones.
 
Any update on when the liability release form will be available for the T-1004-L&R ribs to ship?

I am doing the ER as a retrofit and I was not required to sign anything. All I did is go to the website and order my parts based on Ken's list.
You should not have a hold up.
 
Don't think so

I am doing the ER as a retrofit and I was not required to sign anything. All I did is go to the website and order my parts based on Ken's list.
You should not have a hold up.

This was true some time ago, however, it now says "Call to Order" when you shop for those parts on the Van's web store.

I'm curious if a waiver or liability release is being (or has been) required if you buy an RV tail or wing kit that will be used to build a Rocket? If not, the optics of this particular requirement look a lot more "personal" than "legal".
 
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Any update on when the liability release form will be available for the T-1004-L&R ribs to ship?

I am doing the ER as a retrofit and I was not required to sign anything. All I did is go to the website and order my parts based on Ken's list.
You should not have a hold up.

This was true some time ago, however, it now says "Call to Order" when you shop for those parts on the Van's web store.

I'm curious if a waiver or liability release is being (or has been) required if you buy an RV tail or wing kit that will be used to build a Rocket? If not, the optics of this particular requirement look a lot more "personal" than "legal".

Yes, I placed an order for all of the needed parts in the online store. I was able to order every single part on Ken's list except for the T-1004-L & T-1004-R ribs. Those two part numbers specifically said "call to order," which I did.

When I called, they took my order but I was told the parts would not ship until the legal release form was available. I was told there would be a "considerable delay."
 
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Yes, I placed an order for all of the needed parts in the online store. I was able to order every single part on Ken's list except for the T-1004-L & T-1004-R ribs. Those two part numbers specifically said "call to order," which I did.

When I called, they took my order but I was told the parts would not ship under the legal release form was available. I was told there would be a "considerable delay."

Well, I thought I was not in the same boat but I am. When I made my order, parts were not "backordered" including the in the email received right after the order, they were not marked as backorder like some other parts. All of a sudden they are. I am giving them a call Tuesday to see what's up.

I also want to see what Ken thinks about this, I don't know if they are holding a grudge of some sort.
 
Well, I thought I was not in the same boat but I am. When I made my order, parts were not "backordered" including the in the email received right after the order, they were not marked as backorder like some other parts. All of a sudden they are. I am giving them a call Tuesday to see what's up.

I also want to see what Ken thinks about this, I don't know if they are holding a grudge of some sort.

Given that I've never heard of Van's requiring builders to sign a form that says "I promise not to use these parts to build XXX" - it sure has the appearance of something like that.

With Ken's knowledge, skills and talents - it wouldn't be too difficult for him to develop a workaround if this situation doesn't get resolved soon.
 
I ordered my parts according to Ken's list and was also told they would ship the T-1004-L & T-1004-R ribs after I signed the legal release form which hasn't been produced yet.

Perhaps we should start calling them every week until they produce it?
 
I ordered my parts according to Ken's list and was also told they would ship the T-1004-L & T-1004-R ribs after I signed the legal release form which hasn't been produced yet.

Perhaps we should start calling them every week until they produce it?

Let's do it. I am calling first thing Tuesday morning.

Who else can call Vans on Tuesday for a status update?
 
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