ronschreck
Well Known Member
Steve Johnson will be giving a presentation on aerobatics and the RV. It's part of the Sport Aerobatics Airventure Forum. Head on over there. Steve sent me a preview of the presentation and it's VERY informative.
Steve Johnson will be giving a presentation on aerobatics and the RV. It's part of the Sport Aerobatics Airventure Forum. Head on over there. Steve sent me a preview of the presentation and it's VERY informative.
Any chance it's being recorded and might be available online at some point?
Came back yesterday so I won't make it today. If not a recording maybe the presentation can be made available?
I get "this page is not available"... Is it just me?For those of you who were unable to attend Steve Johnson's IAC forum presentation on RV Aerobatics, here is the powerpoint presentation. Enjoy.
I get "this page is not available"... Is it just me?
As confirmed with Van's aircraft on 12/16/05, for
any RV which has wing tanks, aerobatic gross
weight does NOT include fuel in the wing tanks.
Said differently, the pilot may compute (and not
exceed) the published Aerobatic Gross Weight
figure for his/her model, then add fuel on top of it
up to the Normal/Utility category gross weight of
the aircraft.
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I'd love to see this posted on the Vans site, or perhaps at the very least a comment from one of the Vans employees who frequents this site. This has been a controversial topic in the past, and i've never seen it confirmed in writing from any official source...
Yes, but that transfer is to the structure *outboard* of the wing... Not to the wing root. The wing root is already being "bent upward" by the lift the wing is generating. The fuel load subtracts from that at the wing root.If there's fuel in that tank, inertia is going to mean that the fuel tries to "stay where it was" meaning a downward force on the structure beneath the fuel. This force will be transferred to the rest of the structure.
Yes, but that transfer is to the structure *outboard* of the wing... Not to the wing root.
This makes no sense to me
The wing root is already being "bent upward" by the lift the wing is generating. The fuel load subtracts from that at the wing root.
This makes a little more sense to me. But remember that the fuselage, and the engine, and you, are pushing DOWN on the wing roots along with that gas, while you are accelerated..inertia makes the fuse etc want to stay where it was. And the gas is adding to that. And I would also add that the downward force of the gas in the tanks - 20 gallons times 6lbs per gallon times (say) 4G is a 500 pound force ahead of the lift vector and therefore is also applying a twisting action to the wing.
For those of you who were unable to attend Steve Johnson's IAC forum presentation on RV Aerobatics, here is the powerpoint presentation. Enjoy.
I believe that the IAC is still offering memberships at half price. Check it out on thier web site.
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I'd love to see this posted on the Vans site, or perhaps at the very least a comment from one of the Vans employees who frequents this site. This has been a controversial topic in the past, and i've never seen it confirmed in writing from any official source...
Check out this post. Additionally, I just received confirmation from Van's that fuel weight should in fact be considered towards the aerobatic gross.
That said, the Steve Johnson's IAC forum presentation slides concern me. Regardless of what Van's said ten years ago, they're not saying that today and perpetuating the statement from 2005 may cause some to believe they have more G margin than what they actually do.
Van's discussion with Randy Lervold in 2005 has been controversial ever since Randy first posted it. I have heard arguments on both sides. I provided the information to Steve Johnson. If, as you say Van has confirmed that fuel weight should in fact be considered towards the aerobatic gross would you please provide the date of that disclosure and the context of the quote.
Better yet, I would hope Van would put it in print. I have always attributed the quote as a statement from Van to Randy and nothing more. If he misspoke or was wrongly quoted I hope he will set the record straight.
I think the responsible thing to do would be to not propagate the statement at all, at least until there's an official word from Van's that says excluding fuel weight is ok.
Sorry, that was poorly worded. Let me try again. You almost had it with your understanding of how the lift is distributed:This makes no sense to meSnowflake said:Yes, but that transfer is to the structure *outboard* of the wing... Not to the wing root.
What you missed is that the fuel and the fuselage are not pushing down in the same place. The fuselage pushes down as a dead weight, with no lift directly above it to offset it. The fuel is distributed right under the lifting surface, spread out along the wing... Just like the wing weight itself.Saville said:But remember that the fuselage, and the engine, and you, are pushing DOWN on the wing roots along with that gas, while you are accelerated.
What you missed is that the fuel and the fuselage are not pushing down in the same place. The fuselage pushes down as a dead weight, with no lift directly above it to offset it. The fuel is distributed right under the lifting surface, spread out along the wing... Just like the wing weight itself.
Actually, from a structural standpoint, all we care about is the steady state configuration... Even a high-G pullup is steady-state, just for a brief duration. The wing doesn't care if it's holding 1600lb at 6G for a second, or 5 minutes. The wing is designed to carry 1600lb at 6G, plain and simple.Ah but if you look again, I explicitly said that I'm talking about non-steady flight.
Okay, consider this: The fuel is hanging off the front of the spar, yes, but the weight of the wing itself is hanging off the back. With *zero* fuel, you'd have the wing weight hanging off the back side of the spar. With fuel, you'd have a net twist forward on the spar. The spar is symmetric front to back, so clearly a forward vs. backward twist is irrelevant... It's been designed to take it.That gas is torquing the spar and that means the torque is transferred to the spar bolts.....right where you, the fuselage, the engine and everything else is also pushing down.
The *latest* word from the factory is that aerobatic load *does* include fuel, and it may be prudent for the presentation from Oshkosh to be taken down until it can be revised to reflect that.
The latest word from the factory is SILENCE! If Van wants to weigh in on this I am listening. Right now the latest word from Van is a 2005 quote provided by Randy Lervold which was repeated in the Oshkosh presentation. If the quote is wrong I will invite Van to dispute it.
The factory is happy to speak to this issue if you ask - I know, because I did and got an answer back fairly quickly. Folks directly associated with the factory have relayed the message that Ken Kruger said it was necessary to factor in fuel weight when figuring gross weight for acro. I feel like this is a case of people wanting one answer and being reluctant to accept a different one.
All I want is the RIGHT answer. Who are the "folks"? When did they say it? Why don't they put it in writing?
Scott McDaniels has written it on here, as well as relaying information from Ken Krueger - a link to the actual post has been provided in my previous comments on this thread. Ken Scott has stated it in e-mails from the factory as well just a few days ago after conferring with Van's engineering staff.
Not sure what more is required - perhaps a notarized statement?
Great! Please post the email.
This question has been going round and round for a long time and even here we don't have
an exact answer. I'm not sure about the history of it, but the last time I asked the engineering
staff they said the weight of the fuel should be included in aerobatic gross weight calcs.
Great! Please post the email.
rvbuilder2002 said:Does fuel need to be factored in when calculating gross weight for aerobatics? Ken Krueger, Vans head of engineering has told me it does.
Van has apparently in the past said that it didn't need to be for the RV-3. I think that is related to its wings originally being designed for the use of a fuselage fuel tank. I think a miscommunication happened somewhere, and a statement Van made may have been taken out of context. I don't believe Van ever meant to say you didn't need to consider fuel in aerobatic gross weight for all models. But I can't speak for him.
The issue is that fuel in the tanks does reduce the bending moment on the wing, but as Kevin pointed out it only effects the portion of the wing where the fuel is. In an RV, the portion of the wing outboard the tank would be loaded higher than intended. If the wings were originally test to 9 G's using the aerobatic gross weight value, then the wing is only proven to that load value. If you fly at a weight higher than that, but with all of the extra weight in the cabin area, it is true that you have downward fuel load (induced by G's) counteracting the upward bending moment of the wings. It is possible that it would make the bending moment at the root end of the wing no higher than it would have been at a lower weight. The problem is that the portion of the wing without fuel actually does have a higher bending moment on it; beyond what was tested.
Regardless of what you have heard, or where you have heard it... my opinion is that you are reducing your safety margin if you do aerobatics at higher than the published gross weight Period
(At the risk of starting another debate about what should be done....) I have heard that to participate in an IAC event, side-by-side RV's with a tip up canopy are required to have the ejection mechanism functional. The presentation does not mention this?
Is it a requirement to have the tip up ejection mechanism functional in a side-by-side RV to participate in IAC events?
Does "Aerobatic Airframe" imply having a functional canopy ejection mechanism for a tip up RV?
Regards,
(At the risk of starting another debate about what should be done....) I have heard that to participate in an IAC event, side-by-side RV's with a tip up canopy are required to have the ejection mechanism functional. The presentation does not mention this?
Is it a requirement to have the tip up ejection mechanism functional in a side-by-side RV to participate in IAC events?
Does "Aerobatic Airframe" imply having a functional canopy ejection mechanism for a tip up RV?
As a contest safety director, I would not allow that airplane to fly. Without installing the emergency release, there is no way to get out of that airplane while in flight, thus making wearing a parachute pointless. If the airplane had an installed and current airframe parachute, that would be OK in my perception, as then there would be no need to exit the airplane.