O-470 in an RV-8

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Bert, Sep 16, 2019.

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  1. Sep 18, 2019 #21

    bifft

    bifft

    bifft

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    It depends on how the -8 is built. I built my -8A to be extra light (currently 1010 lbs), but most of the stuff the builder can choose to go lighter on is in the panel or firewall forward. So while most end up nose heavy mine is tail heavy. I can't load it anywhere near the forward CG limit, and am limited by aft CG rather than gross weight. I can't load it to gross without exceeding the aft CG limit.

    Mine is day vfr, O-160, wood prop, SD-8 alternator and small lithium battery. I would agree with other posters that a constant speed prop is worth the weight if you can afford the $.
     
  2. Sep 18, 2019 #22

    TFF

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    His maybe a O-320 too. His wife flys an RV4 I think so he does not care about passengers. They fly both planes places. All three of the ones I have been around have had angle valve engines and CS props. The guy who built the 7 after the 8 used a parallel valve. There use to be an angle valve RV 4 with retracts and CS that flew with no ballast. One of the guys does not have the strength to fight an out of trim plane. He was crippled in a car wreck but holds a regular class 3. A real tough character. He puts about 50 lb in the back if he does not have a passenger. Like the hot rod RV4 above, it’s really outside of why it was designed if using a fixed pitch in an 8. All good if you pull it off, but it does go against The RV recipe for success.
     
  3. Sep 18, 2019 #23

    Bert

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    It really does come down to the proposed mission, doesn't it? From what I have read here so far, putting a 470 in an RV-8 is definitely doable and safe. It will change the handling characteristics of the plane but if you mission isn't hard core aerobatics, it shouldn't make that much difference.

    I will probably follow the advice here and start looking for a 360 but I have to admit that I haven't closed the door completely on using my 470 in it. I will keep reading and learning from other's experiences before I make a final decision.
     
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  4. Sep 18, 2019 #24

    BJC

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    If I were considering using the 470, I would do a careful weight and balance to see what ballast and or battery / equipment relocations would be necessary to keep the empty CG close to design. Don’t forget the custom engine mount, cowl, exhaust, as well as everything else FWF. Then I would calculate the change in the yaw plane and pitch plane polar moments of inertia. With that, I would ask Van’s to comment on the potential impact of the changes, including spin recovery, g ratings, and handling characteristics. I would not build an RV-8 with poor spin recovery or degraded G ratings or degraded handling because the resale value would be too low. Then I would consider the necessary custom parts and added construction time.

    The perceived savings likely will not be worth the complications and concessions.


    BJC
     
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  5. Sep 18, 2019 #25

    Bert

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    Good point that are absolutely right. It isn't a trivial matter to use a non-sanctioned engine but it has been done before so there is data that one can use to make the calculations that you mention. Plus, I seem to remember seeing a 470-engined 8 for sale on Barnstormers for the longest time proving that it can be difficult to sell such an aircraft.

    Having said that, one of the reasons I am leaning more toward a 360 is because of the complications you mention above.
     
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  6. Sep 18, 2019 #26

    Toobuilder

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    Please understand the context of "doable and safe". To me that means the airplane may not be a deathtrap, but the impact on the sweet handling of the -8 will go far beyond "hardcore aerobatics". If done right, the 470 RV-8 will certainly fly without killing you, but it's not going to fly nearly as nicely as any other -8 out there. It will be a pig.
     
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  7. Sep 18, 2019 #27

    Bert

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    Ture. But, then, I have never flown an RV-8 before so I have no yardstick against which to measure its characteristics - with or without a 470. Does a 470-engined aircraft fly better than a 172? If yes, it's a plus!
     
  8. Sep 18, 2019 #28

    ScaleBirdsScott

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    Has anyone done a study on a stretch tail version of the RV similar to the later stretch tail P-40? Could be an interesting experiment for someone qualified to determine the proper rework.
     
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  9. Sep 18, 2019 #29

    BoKu

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    There is at least one, and probably several, out there. One such is Bob Mills' Rocket Six that flies in Sport Class at Reno. It started as a typical RV-6 kit. It now has an IO550, and the tailcone is stretched by about 10". The builder arranged the bulkheads further apart, and fabricated their own skins and stiffeners using thicker material. It probably sounds a lot simpler than it is.
     
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  10. Sep 19, 2019 #30

    BBerson

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    Are you guys using heavy aluminum blades on constant speed props or custom wood/composite blades?
     
  11. Sep 19, 2019 #31

    Rockiedog2

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    I always used AL
     
  12. Sep 19, 2019 #32

    BJC

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    Hartzell aluminum blended airfoil blades.


    BJC
     
  13. Sep 19, 2019 #33

    Rockiedog2

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    Oh shoot why didn't you tell us?
    That changes everything...you won't know what you don't know!!
    Yeah build it!:D

    So SIL came to the family and said "He asked me to marry him. What do you think?"
    Everybody said "Don't do it".
    She said "Why not?"
    So everybody told her all the reasons that were obvious to all but her.
    So yeah, she married him anyway.
    D**n short honeymoon!! LOL

    Bert it was a joke man!
     
    Last edited: Sep 19, 2019
  14. Sep 19, 2019 #34

    gtae07

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    That’s my plan. The composite props look beautiful but the cost is something like 50% greater.

    Were I the OP, I’d sell the 470 and find a rebuildable parallel valve O-360. It can be made into vertical or horizontal induction, with carb or mechanical injection or EFI. Even rebuilding the engine will be less work than adapting a different engine.

    Disclaimer: I may biased as this is exactly what I’m doing on my -7
     
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  15. Sep 19, 2019 #35

    Bert

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    In real life, it is entirely possible that "everyone" is wrong about the man that your SIL wants to marry. Yes, they could be right but such scenarios always remind me of the old adage "Behind every successful man stands a very surprised mother-in-law."

    If I didn't give a rat's backside about what the people on this forum think, I would have never posted this question in the first place. But, what I am asking about isn't new. It has been done many times and I wanted to get the opinions of people whose knowledge on the subject I respect.

    As I mentioned earlier, though, it will be a while before I have to make the decision so I am just in the data-gathering mode right now.
     
  16. Sep 19, 2019 #36

    Bert

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    That sounds like a very good idea. I am not in the aircraft parts sales area, though, so I don't know what the likelihood of being able to sell my engine and prop are. I rebuilt the engine myself under the guidance of a "real" aeroengine mechanic in his shop so it can't be put into a certified aircraft. Likewise, the prop was rebuilt by a certified prop shop but they rebuilt it to homebuilt standards so it, also, may not be installed on a certified aircraft.

    Maybe I'll list the two of them on Barnstormers and see what happens.
     
  17. Sep 19, 2019 #37

    Pops

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    Very well said as usual.
    The reason I weigh in oz and grams. The reason the SSSC and the JMR will not have an electrical system. Percentage wise, its a huge jump in weight.
    The flying weight with me and fuel in the JMR will be about 950 lbs. The is with 112 sq' of wing area and a Cont 85 engine and fuel. The SSSC is a flying weight of me and fuel is 780 lbs with the 60 hp VW engine and 120 sq' of wing area. On the SSSC with the VW at an idle of 900 rpm it doesn't want to come down very fast to land , so all landing is with a hard slip down to flare unless its a very long runway that is rare in this area.
     
    Last edited: Sep 19, 2019
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