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RVs and Aerobatics Forum, 1:00 PM today.

ronschreck

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.
 
ronschreck said:
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.
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Location is listed in the EAA iPhone App as the IAC Headquarters.
 
Came back yesterday so I won't make it today. If not a recording maybe the presentation can be made available?
 
RVs and aerobatics

1:00 - 2:15pm Steve Johnson
"RVs and Aerobatics"
Steve has been competing in the Advanced
category with his MX2 across the nation and
has been a member of the US Advanced team.
Steve has over 100 hours of instructional flight
time in RV aircraft: RV-4s, RV-6s and RV-7s.
Steve teaches proper energy and airspeed
management in these fast slick airplanes.

Here's a plug for Steve Johnson and RV forum on aerobatics. He's a fantastic pilot, presenter, judge, instructor, and likeable person. I also hope he scores me higher on the next contest. IAC is also offering a 50 percent off on membership for RVers, so ask about it.
;)
Cheers,
Bill McLean
RV-4 slider
lower AL
 
Steve said he was going to post the slides to the IAC website.

So far, I do not see it but one may need to be an IAC member.

Many forums are recorded and can be purchased. This is the info I picked up:



This is the info about the forum requested on the above flyer:

"RVs and Aerobatics"
Steve Johnson
July 23, 2015 1:00 to 2:15 PM
IAC Headquarters
 
AirVenture RV Aerobatics forum presentation

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.
 
Page 33:

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...
 
Snowflake said:
Page 33:



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...
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There's been tons of talk on this, and I've read it all. I, for one, just do not buy it:

There you are in straight and level, unaccelerated flight.

Now you pull up sharply - 4-5G.

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.

Imagine the same maneuver with no gas in the tank. No inertia.

I could be wrong, I suppose, but I'm not going to risk it.
 
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Saville said:
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.
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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.

However, it does mean the wing overall lifts more to carry the weight of the fuel plus the weight of the aircraft, so at the outer end of the fuel tank there is a stress concentration. That's where I wonder if the math has been done.
 
Snowflake said:
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.
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As I've said people can do what they want. For myself, I will be including the weight of fuel in my acro weight calculations.
 
ronschreck said:
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.
Click to expand...

Thanks Smokey. Every IAC class I tried to attend was overflowing and I couldn't shoehorn myself in without being rude so I passed. Based on the attendance and what's being said here, I sorry I missed it. Maybe next year.

Thanks for the PP.
 
Snowflake said:
Page 33:



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...
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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.
 
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ChiefPilot said:
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.
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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.

As a practical matter I would find it difficult to do more than low "G", simple aerobatics above the published aerobatic gross weight limit. In competition I typically fly with enough fuel to fly the sequence and land with a 30 minute reserve, period!
 
ronschreck said:
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.
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It was in a direct email to [email protected] including the quote from the slide and asking the question on Friday with a response received this morning. Aside from that, there's this post from one of the better known Van's Aircraft folks who hangs out here from time to time.

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.
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This does seem to come up often enough (as Ken Scott acknowledged in his reply to me this morning) that an official statement might be helpful. 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.
 
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Saville said:
Snowflake said:
Yes, but that transfer is to the structure *outboard* of the wing... Not to the wing root.
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This makes no sense to me
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Sorry, that was poorly worded. Let me try again. You almost had it with your understanding of how the lift is distributed:

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.
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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.

At every point along the wing, the forces must balance for steady flight. At the wing roots, at 1600lb, and no fuel, you have a 1400lb dead weight (the fuselage), just inboard of the side fuselage skins. On the outboard side, you have 200lb of dead weight (the wings themselves) and 1600lb of lift. Weight = lift, 1400+200 = 1600.

If you add 200lb of fuel, and increase your gross to 1800lb, this changes slightly: You still have 1400lb of dead weight in the fuselage, but you now have 400lb of dead weight in the wing (fuel plus wing weight), and you now have 1800lb of lift. The weights still add up (1400+400=1800).

But notice that the load at the wing root is the same as before... At the wing to fuselage interface the wings are only lifting a 1400lb fuselage. The extra 200lb of fuel is carried by the wing structure, not the fuselage. Counter-intuitive, perhaps, but there it is.

It gets even more freaky when you factor in that the fuel is only carried in the inboard half of the wing... That unloads the spar to a point *below* the stress of the 1600lb aerobatic loading... But only along the fuel tank. At the outboard end of the tank, the stress jumps above the loading at 1600lb, and is probably the area of most concern.
 
Snowflake said:
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.
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Except that the lifting surface is a very small part of the wing and is also the leading edge. The center of lift is aft of the tank. 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.


At every point along the wing, the forces must balance for steady flight.

Ah but if you look again, I explicitly said that I'm talking about non-steady flight.
 
Saville said:
Ah but if you look again, I explicitly said that I'm talking about non-steady flight.
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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.

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.
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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.

As far as the joint between the fuselage and the wing goes, it only carries the weight of the fuselage and everything in it. It does not carry the weight of the fuel. This concept is difficult to grasp, I know.

In any case, the discussion has digressed quite a ways away from the original topic and is masking the overall point... 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.
 
Snowflake said:
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.
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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.
 
Message to Van

The text of my email to Richard VanGrunsven is provided below:

Hello Van,

I am writing to you in hopes that you would clear up some information regarding proper computation of aerobatic gross weight for RV aircraft. The following quote is attributed to your organization by Randy Lervold:

"There has been some confusion on computing Aerobatic gross weight. As confirmed with Van's aircraft on 12/16/05, for any RV, including the RV-3, 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. The reason for this is that fuel essentially becomes part of the wing structure. Van's is quick to point out however the detrimental effects of higher weights on aircraft performance when operating in the Aerobatic category and encourages pilots to excercise good judgement and caution."

Randy is an EAA Flight Advisor and Technical Counselor, RV builder, President of Cub Crafters, Inc. and a respected authority in the aviation community. The quote is found on page one of his Unofficial RV-3 Headquarters web site.

I have referenced the above quote in a presentation on RV Aerobatics which I gave at the 2015 North Carolina Formation Clinic and more recently it was referred to by Steve Johnson in a forum presentation at AirVenture 2015. Steve and I are both IAC aerobatic competitors and judges. Mike Heuer, President of IAC, has enlisted my help in encouraging RV pilots to participate in IAC competition. As a part of this effort I provide to RV pilots information about the IAC competition environment, safety considerations and the suitability of different RV models for aerobatic competition. Computation of aerobatic gross weight is an important part of this instruction. I want to get it right!

I am requesting that you either confirm or refute the information in the above quote from Randy Lervold. Thank you for your consideration of this important issue.

Very Sincerely,
Ron Schreck
 
ronschreck said:
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.
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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.
 
ChiefPilot said:
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.
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All I want is the RIGHT answer. Who are the "folks"? When did they say it? Why don't they put it in writing?

I have no skin in this game as I always fly aerobatics with considerably less than Van's published aerobatic gross weight. BUT there are others flying with two large people in the airplane that justify their actions because they discount the fuel weight based upon a 2005 quote attributed to Van's organization. I'm sure Randy Lervold would be happy to remove the quote from his web site if Van's refuted the information. And if Van's does so I will personally ask Randy to do just that.
 
ronschreck said:
All I want is the RIGHT answer. Who are the "folks"? When did they say it? Why don't they put it in writing?
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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?

I'd add that Snowflake is correct - the responsible thing to do is remove the statement until it can be confirmed. As it is, it is really nothing more than hearsay that has been refuted several times by the factory.
 
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ChiefPilot said:
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?
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Great! Please post the email.
 
ronschreck said:
Great! Please post the email.
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From Ken Scott on Monday 8/3:
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.
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So there you go - word from the factory a few days ago vs. hearsay based on something that may or may not have been said a decade ago. Which is more authoritative?
 
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ronschreck said:
Great! Please post the email.
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And here's the relevant portion of Scott's post to get it all in one place:
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
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Is canopy ejection mechanism required for SBS tip up?

(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,
 
Roy Thoma said:
(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,
Click to expand...

Section 2.3 of the IAC Official Contest Rules does not require any sort of canopy ejection mechanism. (It does address cabin type aircraft, but not tip up canopy aircraft.) And the Official Tech Inspection Form does not address the issue.

As a practical matter it would seem that the requirement that all competitors must wear a parachute implies that the wearer know how to use it and has the means to exit the aircraft. That said, it may likely be the case that the tip up canopy can be opened when the aircraft is out of control as normal air loads might no longer be holding it in the closed position.

Personally, I would sure like to know that I could jettison that canopy in any and all situation should I need to make a hasty exit.

I cannot say that a savvy tech inspector might not ask how you intend to exit your tip up canopy enclosed cockpit in an emergency. If you have no good answer there may be a reason to exclude you from competition.
 
Roy Thoma said:
(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?
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It is a reasonably common requirement. Checkout this thread in the IAC forums :
http://www.usnationalaerobatics.org/IACSafetyForum/default.aspx?g=posts&t=376

Excerpt:
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.
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