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Question about acro capabilities

nohoflyer

Well Known Member
Patron
When I flew acro in the USAF, my tweet was equipped with fuel pumps and an oil system that could handle it. How does Vans (specifically RV-7) deal with it? I ask because I’m about to begin on my fuel tanks and looking at the plans I don’t see anything special about inverted flight or special sumps.

Am I over thinking this?
 
Flop tube

Just exactly what the name implies...it " flops" to stay in fuel when inverted...Vans sells them ...and there is a service bulletin on them also ....you'll need inverted oil system ...RAVEN sells one of the best and fuel injection ( many options ) on engine ( or pressure carb ...but very old school)
 
If you go with a flop tube just a heads up that there isn't an anti rotation bracket in the plans that can lead to issues. Check post #67 here to see how I fixed this. Most guys don't have an issue but this simple fix will remedy it from the get go. I'm just glad I found this before mounting on the wing!
 
Many RV’s don’t have any inverted fuel / oil systems. Just keep the aerobatics positive G and you’ll be fine.
 
Article for "Sport Aviation" magazine, August 2016 (edited for word count.)

Equipping Your RV for Aerobatics
By Ron Schreck

Proper preparation is the key to success in most new endeavors. Properly preparing your RV for aerobatics is dependent upon the level of aerobatics you intend to fly. Recreational or sport aerobatics require a minimum of equipment while success at the higher levels of competitive aerobatics will require a greater investment. When you finish reading this you should be able to make three lists: stuff I need, stuff I don’t need, and stuff that would be nice to have someday when I have the time and/or money.

Note: Equally important to preparing your airplane for aerobatics, preparation of the pilot should not be overlooked. An excellent resource for pilot preparation can be found at the International Aerobatic Club (IAC) web site: iac.ord. Click on the “How to Begin” tab.

So let’s discuss the items you may consider when equipping your RV for aerobatics:

Parachutes:
While there is no FAR requirement for a solo pilot to wear a parachute during aerobatic flight, when carrying a passenger both the pilot and passenger must wear an approved parachute. Pilots flying at IAC events are always required to wear a parachute. Most RV pilots seem to prefer the back pack chutes. Many RV-4 pilots by exception prefer the seat pack chute as the back pack puts them even closer to a panel that many feel is too close to begin with. The seat pack chute is quite hard and you may add some cushioning on top of the pack if headroom allows. I suggest you try both parachute designs to determine which works best for you. Call your nearest IAC chapter representative to inquire about borrowing a couple of parachutes. While a new chute is a significant investment, a used chute in good condition may be a real bargain. There is an urban legend that states that a parachute has a service life of 20 years. There is no basis in fact for this. Continued service life of any given parachute is to be established by a certificated parachute rigger at the time of inspection and repack of the parachute and is based upon the condition of the parachute and compliance with established standards without regard to its age. However some riggers may refuse to recertify a parachute that is over 20 years old so this may factor into your decision to buy an older parachute or the price you pay.

Canopy Release Mechanisms:
Of course there is no point in having a parachute if you can’t get out of the airplane in flight. Tip over canopies can be modified with easily removable hinge pins and slider canopies can be easily jettisoned if the front canopy roller attachment bolts are replaced with quick-release pins. Vans Aircraft provides plans and material for optional canopy release mechanisms for RVs with tip-up canopies. Before flying in IAC competition you may be asked to show the technical inspector the provisions for jettisoning the canopy on your aircraft.

Attitude Reference Systems:
Aerobatics are done with respect to outside visual references so attitude instruments are of no use and they will likely tumble after a loop or two anyway. Electric and mechanical attitude instruments, even when caged can become damaged so it may be advisable to remove the instrument before flying aerobatics. EFIS attitude presentations also may tumble but no harm to the instrument should result. If you fly aerobatics often it may be advisable to replace your mechanical or electric gyro with one of the mini EFIS instruments available from a number of suppliers.



G-Meter:
Knowing your G-loading during aerobatic flight is extremely important and you can’t accurately know your G-loading without reference to a G-meter. All aerobatic RV aircraft are limited to +6 and -3 Gs and most pilots eventually learn to know what a 4 G pull feels like without reference to the G-meter but more aggressive maneuvering requires closer attention to the instrument. Mechanical G-meters, once widely used are now often replaced by cheaper and more versatile electronic meters. The GT-50 model from Flight Data Systems has become quite popular.


Fuel Injection and Inverted Fuel Systems:
Carbureted engines can be flown in recreational aerobatics and even in competition! The carbureted engine will quit producing power immediately when subjected to negative Gs but will resume normal operation once under positive G with a windmilling propeller. Momentary loss of power due to fuel starvation is not detrimental to the engine. Many aerobatic maneuvers can be flown while maintaining positive G on the aircraft. While some figures in competition require momentary negative G to be technically correct they can be flown entirely under positive G with some deduction by the judges. The serious competitor will want to be equipped with fuel injection to be able to maintain full engine power in all phases of flight. An inverted fuel system with a flop tube in the fuel tank is not necessary. There are no IAC figures that require inverted flight beyond a few seconds and that’s not long enough for an injected engine to stumble due to fuel starvation. .

Inverted Oil System:
You should consider some sort of inverted oil system to protect your engine if your aerobatics involve zero or negative G maneuvering. While momentary loss of oil pressure is unlikely to cause any damage to your engine it will invariably cause loss of oil through the oil vent tube and make a real mess of your RV’s belly. If you have a constant speed propeller loss of oil pressure can cause the propeller to drive to low pitch which may cause the engine to overspeed if you don’t immediately retard the throttle. If you have a fixed pitch propeller and your only concern is to minimize oil loss, installation of an oil separator or only the canister portion of a Christen or Raven inverted oil system may suit your need. A small oil accumulator of the type commonly used on race cars can provide oil pressure during brief periods of negative or zero G flight. Of course for more complete protection from oil pressure loss a full inverted oil system which includes the oil separator canister and an oil valve that supplies oil to the pump in upright and inverted flight is appropriate.

Constant Speed Propeller:
There are many aerobatic airplanes that do just fine with a fixed pitch propeller and the RV is no exception. Considering the cost and complexity of a CS propeller it may be the last thing to consider when equipping for aerobatics. There are two basic types of CS propellers to consider and the difference is the action of the propeller when oil pressure is momentarily lost. An aerobatic CS propeller uses counterweights on the prop hub to force the blades to high pitch when oil pressure is lost. A non-aerobatic propeller does not have counterweights and the blades will drive to low pitch when oil is lost and an engine overspeed can result. Aerobatic CS propellers are heavier, more complex and costlier than non-aerobatic types which are more commonly preferred despite their susceptibility to overspeed.

Sighting Device:
Aerobatics are flown primarily with reference to the horizon and most all aerobatic figures require the aircraft to be flown along a precise line on a vertical, horizontal or 45-degree climbing or descending line in reference to the horizon. I don’t know of any sighting devices commercially available for the RV but the serious competitor can fashion a homemade device out of bits of aluminum and carbon fiber arrow shafts. A simple alternative that serves quite well is simply to apply automotive striping tape to the canopy at appropriate angles.

Ratcheting Lap Belt:
Normally a ratcheting lap belt is the second belt in a dual seat belt harness system. Per the IAC rules:

“Dual seat belts with separate attach points and a shoulder harness are mandatory for
Advanced and Unlimited (power and glider) categories. The same equipment is strongly
recommended for Primary, Sportsman, and Intermediate power categories, but is not
mandatory except when IAC Technical Monitors deem them necessary for the sequence
being flown in these categories.”

I have found that the ratcheting seat belt that I have installed in my RV is the one piece of equipment that has contributed the most to my advancement in aerobatic skill level and enjoyment of the sport! That’s high praise for a simple piece of equipment but when I tighten that ratchet I feel that I no longer just sit in my RV rather I put it on and the airplane becomes an extension of my body.

Summary:
How you equip your RV for aerobatics can be approached the same way you may have approached the purchase or build of your RV. First, determine the mission and if there are multiple missions determine their priorities. Are you interested in recreational or competition aerobatics? Are you willing to forego weighty accessories in favor of a nimble aerobatic performer? Next, determine the resources available to you which may be expressed as financial resources or a commitment of time and effort. Limited resources may require you to seek bargains in second hand equipment or use your skills to install inverted systems or fashion such things as a ratcheting seat belt or sighting device on your own. Finally, make choices based upon the priorities and resources available. A lucky few may have the resources to equip for serious competition without delay. If your resources are limited or you are unsure if aerobatics is right for you a more measured approach may be suitable. Whatever you decide and however you proceed do it with safety always on your mind. I have enjoyed the company of like-minded aerobatic pilots and the challenge that every flight brings as I never cease learning to become a better pilot. If you are up for a challenge, aerobatics may just be what you are looking for.
 
All great replies. Thanks. I have no intention of doing competition acro. Just some loops and rolls. If I have some skills left, I should stay in the positive G regime 99% of the time.
 
What's the difference between the Christen and Raven inverted oil system?
Can you recommend one over the other or are they more or less equal?

Do inverted oil systems have disadvantages over conventional systems when not flying acro?

Malte
 
What's the difference between the Christen and Raven inverted oil system?
Can you recommend one over the other or are they more or less equal?

Do inverted oil systems have disadvantages over conventional systems when not flying acro?

Malte

They are basically the same, Raven is less expensive.

An inverted oil system is two oil scavenge and breather systems ported into one pump. When erect you would not know the inverted portion was there. An inverted system is heavier and more expensive. Oil changes will take longer as the scavenge filter now flows from the out side. When installing an inverted system a different spring will be required in the oil pressure relief valve to bring the OP down.
Pete
 
A video is worth a thousand words. Basic RV-4 with carb and normal oil. Had planned on including inverted system later but for fun acro this is all that was needed. Ended up removing flop tube since it wasn't needed and it had started wear marks into bottom tank skin. If you want hardcore acro get a Pitts or Laser.

https://www.youtube.com/watch?v=KOKfAnHTjyA

Cheers, Hans
 
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