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RV-3 Baby Rocket

Rdwrv4

Well Known Member
Just in the process of painting my 3 and starting a new one. I have alot stuff to use up so some of my choices are dictated by what I have on hand. I would like to get advice on somethings and opinion on other
the Project
1. I want to use a cutdown rocket cowling just cuz it is Sexy and I have one
2 . o-360 conical mount cuz I have one off a super D
3 . balanced shortened elevators off a RV-8 again cuz I have an extra set and they are Identical!!! to the 3 except the spar is .180" deeper and has a much better trim tab and I will make a horizantal to match, the cord on the 8 is too big
4. Canopy off a panther or what Todd has that might be better. I want the volumous feel of a razorback canopy that terminates close to the longerons.
5. I have a hartzell off a RV8 but the extra 80lbs, CG issues and complexity is making me lean towards a 3 bladed Catto and I have one of those too
6. tilt back seat 2" at upper longerons and have hatrack shelf storage behind head ,I like this cuz it will offer accessable storage in flight and shelf floor will stiffen fuselage
7. hanging rudder pedals like RV4 without the firewall buckets this will allow pedals to come forward 2" more
8 1" upper longerons will be straight from tailpost to firewall but will have to twist them to allow the skins to lay flat. width at seat increases by a little less than 1/2" due to the wide Rocket cowl although the shortened cowling makes a little smaller firewall than the stock rocket.
9. build the last turtleneck bulkhead in 2 pieces so I can reach in and buck rivets, I ran out of little friends to do this, inspection cover on the belly just aft of the elevator reversing bar so I do not have to climb through baggage compartment.
10. 2 piece aft belly skin to make it much easier to fit.
11. early wingtips and wheel pants cuz I have them I like the way they look too if I had later ones I would like them too I think, free is beautiful
12. small instrument panel sitting on top of longerons , helps ease of entry
13. RV4 gear legs cuz they're two inches longer than 3 I think I found a cheap set
14. Fuselage floor should stay the same except the front forward lower longerons will be 96° angle to account for firewall shape. I may have to widen lower firewall as much as 1 1/2 inch but hoping not too won't know until I cut cowling down


Structural concerns
1 parallel valve O-360 weighs 30lbs more but Catto Prop is light so I will change the the perimeter tubing size on the engine mount from .035 to .049
2. The forward fuselage sides are no longer vertical but more curved and trapazoided out 10° so this is not as strong not sure what to do about this yet. All firewall angles will be 1" instead of 3/4" and I can hang the rudder pedals off of them. the steel firewall engine mount attach gussets will be .063 and slightly larger. and will attach with Hi-shear fasteners where convient.
One area of concern is the fuselage spar opening will be 1/4 to 1/2 inch wider and may interfere with the -3 bolts on the spar

Ideas and Input would be appreciated and spare parts would be loved. I really enjoyed building my last 3 so I hope this won't be frustrating but very enjoyable
thx Robin
 
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With the longer gear legs, don't forget that where they hit the ground, they need to be in the right location with respect to the CG.

Dave
 
Sounds fun! I would look at the other rocket mods, especially to the empennage. A well sorted 150HP RV3 as you know can go past VNE in level flight.
 
the -4 gear legs are only 2 " longer and in the landing attitude move the axles back less then 1/2 " but building my own mount and will place wheels in the correct position, I am a little concerned about the extra stiffness being hard on the mount.
Withhe longer gear legs, don't forget that where they hit the ground, they need to be in the right location with respect to the CG.

Dave
 
Robin,
Add the gussets at the lower corners of the firewall/forward fuselage area ala the RV-8.

Dave P is right...you will need to maintain, at a minimum, the same relationship of the wheel axles to the wing LE, and preferably 2 inches forward of that per Rocket guys Mark F and Vince F to help prevent nose-overs. Because of the longer legs of the RV-4, you will need to change the socket geometry at the engine mount (spread them out). Since you're going to beef up the mount, this will be an easy change...just get the geometry right before welding.

As you know from our last email exchange, I have a full set of Rocket drawings. I could be willing to part with them. Let me know if you're interested, and we can work out a deal.

Sounds like a cool project. Good luck with it and keep us in the loop as you make progress.
 
No substitute...

Just in the process of painting my 3 and starting a new one. I have alot stuff to use up so some of my choices are dictated by what I have on hand. I would like to get advice on somethings and opinion on other
the Project
1. I want to use a cutdown rocket cowling just cuz it is Sexy and I have one
2 . o-360 conical mount cuz I have one off a super D
3 . balanced shortened elevators off a RV-8 again cuz I have an extra set and they are Identical!!! to the 3 except the spar is .180" deeper and has a much better trim tab and I will make a horizantal to match, the cord on the 8 is too big
4. Canopy off a panther or what Todd has that might be better. I want the volumous feel of a razorback canopy that terminates close to the longerons.
5. I have a hartzell off a RV8 but the extra 80lbs, CG issues and complexity is making me lean towards a 3 bladed Catto and I have one of those too
6. tilt back seat 2" at upper longerons and have hatrack shelf storage behind head ,I like this cuz it will offer accessable storage in flight and shelf floor will stiffen fuselage
7. hanging rudder pedals like RV4 without the firewall buckets this will allow pedals to come forward 2" more
8 1" upper longerons will be straight from tailpost to firewall but will have to twist them to allow the skins to lay flat. width at seat increases by a little less than 1/2" due to the wide Rocket cowl although the shortened cowling makes a little smaller firewall than the stock rocket.
9. build the last turtleneck bulkhead in 2 pieces so I can reach in and buck rivets, I ran out of little friends to do this, inspection cover on the belly just aft of the elevator reversing bar so I do not have to climb through baggage compartment.
10. 2 piece aft belly skin to make it much easier to fit.
11. early wingtips and wheel pants cuz I have them I like the way they look too if I had later ones I would like them too I think, free is beautiful
12. small instrument panel sitting on top of longerons , helps ease of entry
13. RV4 gear legs cuz they're two inches longer than 3 I think I found a cheap set
14. Fuselage floor should stay the same except the front forward lower longerons will be 96° angle to account for firewall shape. I may have to widen lower firewall as much as 1 1/2 inch but hoping not too won't know until I cut cowling down


Structural concerns
1 parallel valve O-360 weighs 30lbs more but Catto Prop is light so I will change the the perimeter tubing size on the engine mount from .035 to .049
2. The forward fuselage sides are no longer vertical but more curved and trapazoided out 10° so this is not as strong not sure what to do about this yet. All firewall angles will be 1" instead of 3/4" and I can hang the rudder pedals off of them. the steel firewall engine mount attach gussets will be .063 and slightly larger. and will attach with Hi-shear fasteners where convient.
One area of concern is the fuselage spar opening will be 1/4 to 1/2 inch wider and may interfere with the -3 bolts on the spar

Ideas and Input would be appreciated and spare parts would be loved. I really enjoyed building my last 3 so I hope this won't be frustrating but very enjoyable
thx Robin

Robin,
Here's a link that might add some light to your thinking...remember that the aerobatic gross weight G loading and VNE of the original RV3 are easily challenged with the mods you list.
The Matronics thread below discusses the same issue including counterbalancing the RV3 elevator.

http://www.matronics.com/archive/archive-get.cgi?RV3-Archive.digest.vol-ab

V/R
Smokey
 
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Angle of Gear Legs

I have a Thorp T-18, and fly my wife's RV-4.
The T-18 has short stiff gear legs and the RV-4 legs feel like wobbly spaghetti to me.
I think you could re-angle the RV-3 mount with those RV-4 legs and be OK. Of course, the new angle will raise the front of the plane a little more when on the ground...
I built an RV-8, I really love the landing gear's behavior, but not the space taken up by the gear towers.
I sure like working on the RV-4 better than the -8, everything is so accessible and easily serviced. An RV-3 must be even better!
Keep us posted on your RV-3 Rocket project!
 
Baby Rocket

My RV-3 was originally built and flown with an IO-360 and CS prop. It does add weight, but it can be done....and the performance....get the heck out!
Dave
 
Baby Rocket update

OK firstly, upon examining the Rocket Cowl in hand I discovered no a chance of putting it over a 360 with a RV3 mount. So I acquired a RV4 mount with long legs. it is a little longer than the -3 by about 4 inches. I think I can make that work but it will require repitching the gear sockets.
So CS prop and 360 apx 100lbs extra up front. Weight in rear needed! , I weighed both the RV-3 tail and RV-8 tail . FYI weights are as follows. (Done with bathroom scales ,weighed myself with and without each part) elevators 2.6lbs vs 6.4lbs each. Rudder 3.4lbs vs 7.6lbs Vertical 6 lbs vs 7.8lbs Horizontal 12.8lbs vs 17.8 lbs total difference 15lbs. That sounds about right considering the moments. Big concern is the larger surfaces may look out of proportion. No one I have asked has expressed any aerodynamic concerns. Using The -8 parts makes it much easier for me to build cuz I have them. Anybody know of any aerodynamic concerns? I will use the last two RV-8 bulkheads and deck at the rear all that should fit harmoniously. The angles of the stringers and Longerons are almost the same.
 
The extra horsepower is destabilizing, so adding tail area helps.

You could do a basic static stability analysis following any of the older texts out there to get an idea if the CG limits ought to change, and if so, to where. Perkins & Hage's book is excellent and there are others available too, that basically contain all the information you'd need. That and a calculator and you're in business.

Flutter could potentially be an issue with the larger surfaces and their mass balance weights, which all add mass inertia, to the standard tail cone. My thinking is that for some of the flutter modes the stiffness of the fuselage is a contributing factor, and if the inertia goes up and the stiffness doesn't change, the natural frequency goes down - which is in the wrong direction for you.

Is this an issue? Heck, I surely don't know. But it's a factor worth studying. Here, though, I don't have a reference to suggest.

Also, added weight in the nose and tail can significantly change the spin characteristics, and not necessarily in a good way. Just so you know. I think that the added tail area might be beneficial here but this is out of my expertise and can't really say.

Dave
 
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weight

as far as weight goes it shouldn't be any heavier than one of the heavy weight 3's built in the past with an 0-360 and constant speed prop.
 
I wonder about using larger longerons if you go with an -8 tail. The holes for the forward mount points for the HS have marginal edge distance with the stock 3/4" longerons. I added a mount bracket to the back of the forward HS spar because my existing holes were too close to the edges of the longerons. With the larger mass of the -8 tail, you'd have more stress on the longerons where the bolts pass through during engine start (tail shake!) and aerobatics. (Maybe you'd need larger bolts as well-- the -3 uses AN-3 bolts for this, does the -8 use AN-4?)
 
thumbs down on the -8 empennage

Too large. One just like it, but modeled for the -3 size, would be the right ticket (balanced control sfcs).

KatieB is right about the longerons too - go to 1x1". Bigger firewall weldments, etc. Heck - the firewall is gonna be bigger anyway. Easy choice there.

Be careful - John Harmon told me the -3 reverses elev control at about 5G..I cannot say if the HR1 does this or not.

Carry on!
Mark
 
I wonder about using larger longerons if you go with an -8 tail. The holes for the forward mount points for the HS have marginal edge distance with the stock 3/4" longerons. I added a mount bracket to the back of the forward HS spar because my existing holes were too close to the edges of the longerons. With the larger mass of the -8 tail, you'd have more stress on the longerons where the bolts pass through during engine start (tail shake!) and aerobatics. (Maybe you'd need larger bolts as well-- the -3 uses AN-3
bolts for this, does the -8 use AN-4?)
If I use the 8 tail I use the -8 bulkheads and deck at the end . Using -4 sized firewall weldments and 1 1/4 2024 angle already extruded to the more open angle. BTW I bought 1" angle 50 ft, it is too big to bend, trying to find 7/8 angle If not will use 3/4
 
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Can you clarify what 'reverses elevator control' means.
Thanks,

I suspect what was actually being described was a loss of positive pitch stability.

At higher angles of attack (required by the increased amount of lift required to maintain the increased load factor) the center of lift (CoL) moves towards the leading edge. When this happens, the CoL gets closer to the center of gravity and as a result lateral (pitch) stability decreases. As it approaches the point where neutral stability exists, the back pressure required for a given load factor is reduced and there will be no back pressure required to maintain the current load factor. At some point, you might find that you need forward stick pressure to prevent the load factor from increasing. This isn't really control reversal, it's really just negative stability.

ETA: I should add that I've never flown a -3 and the above is a theoretical description in answer to the question. I noticed during phase one on my -6A that stick forces got lighter as I approached 6G but never got the point of neutral, much less negative, lateral stability. Whether one encounters such or not will depend where the CG is located - if you start with something with a very aft CG, you're more likely to encounter it than you are with a forward CG. This is one of the reasons why a aft-limit balance point is specified along with the weight for aerobatic gross.
 
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Baby Rocket update 2

OK measuring and figuring , It is nice Harmon left his cowling narrow at the bottom. It looks like I can use RV-8 Firewall weldments with some modifications to the lower ones. I am trying to locate a Hartzell prop extension like the one used with the Sam James cowl. Also A 14 to 14.75 spinner , got a line on a super D 14.125" one it should be OK it is 3/8" smaller than the front of the cowl, not sure how noticeable that would be. Longerons ,I bought 1" angle but just looking at it you can tell it would be a b****h to bend, so I am going to cut it down to 3/4" except at the firewall end and leave that 1". my buddy swears his fine tooth carbide tipped table saw will do it perfectly. I really need a spinner and a spacer to get the firewall shape right. Also looks like an RV-8 fuselage end will work perfect and save a lot of time. FYI
 
I sure can!

Can you clarify what 'reverses elevator control' means.
Thanks,

Control reversal means that the stick force used on a particular control surface reverses.

Ex: elev control should continue to be a 'pull' to increase positive G. Apparently, the -3 elev force switches from a pull to a push somewhere around 5G positive. I am also told that the trim direction on the F-102 reverses at some very high speed...no problem if the pilot knows this to be the case..

Clear as mud?

Carry on!
Mark
 
Try this:

Get your hands on a red-tagged Hartzell M2 hub (you won't need an extension), and look for a spinner from a Commander 114 (or 112?). Vince at Flyboy Accys might have the spinner avail in composite soon - or maybe now?

Carry on!
Mark
 
news from the rumor mill ...

omg can we puhleeze stop with the speculation on RV-3 pitch force reversal during high-G maneuvers? In the 20-odd years I've been flying my -3 (and in many acro-formations and dogfights with -4s, -6's and -8s) nobody ever encountered pitch force reversal at any G rating. And we've all got recording accelerometers so we all knew where we were at while yanking and banking. Let me tell you how fast the speed bleeds off in a five and a half G turn in a dogfight ... yeah, just about that fast (been there, done that), unless you are putting on the G while going downhill, and I guarantee you don't want to do that unless you are a master at aerobatics - speed builds up in an RV on the downside faster than you can say "Jimminy Christmas!". I don't want to hear about any RV3 drivers going out to try this unless your ship was FULLY TESTED during phase 1 for high-g maneuvers. We had too many wing separation accidents in the '80s to risk enticing third or fourth-gen owners of RV3's to go out and yank on the stick like King Kong. DON'T DO IT. All respect to John Harmon and his Rockets.

- Steven
(1000+ RV3 hours ... another one last Saturday!)
 
An acquaintance at IAC judging school is "plans building" a Harmon Rocket. He built the longerons from over sized angle and milled them down between the fire wall and empanage ends to keep the edge distance requirements as mentioned.
 
omg can we ******* stop with the speculation on RV-3 pitch force reversal during high-G maneuvers? In the 20-odd years I've been flying my -3 (and in many acro-formations and dogfights with -4s, -6's and -8s) nobody ever encountered pitch force reversal at any G rating.

snip

All respect to John Harmon and his Rockets.

- Steven
(1000+ RV3 hours ... another one last Saturday!)

Steven:
I have not flown an RV3, so I can't say one way or another. I am not speculating either; I am only repeating what John Harmon told me. Could be his version had an aft CG? Smoke oil tank in back? Dunno.

He did turn one into a crumpled pile of aluminum in performing a snap roll at takeoff...could be he knows what he speaks of?

Don't shoot the messenger, even if you don't like the message.

Carry on!
Mark
 
omg can we puhleeze stop with the speculation on RV-3 pitch force reversal during high-G maneuvers? In the 20-odd years I've been flying my -3 (and in many acro-formations and dogfights with -4s, -6's and -8s) nobody ever encountered pitch force reversal at any G rating

giphy.gif


John Harmon is a pretty respected individual and has had lots of experience with RVs through the years, so if he suggested that something was happening at a high load factor I'd tend to believe him although details (weight, CG, etc) are missing.
 
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Baby Rocket update

OK what Have I done, got a -4 engine mount with long gear, IE 6" longer than RV-3 therefore I had to cut it in half and weld it back together to move axles forward 3.5 " ,not a simple job!!! came out great one problem though was in rotating them forward created toe in 1/8" more than recommended. Going to live with it ,could be bent out though. Got a spinner from a Rockwell 112A, OMG it is huge. Got RV8 firewall weldments The uppers will work perfectly but the lowers won't thought I could modify them. Too much work, easier to make new, working on figuring out the firewall shape now A rocket firewall looks good but the footwells are too deep and will hit the mount. I would like to know the thrust line of the Rocket mount but not on the Rocket drawings. A lot of work for little progress but carrying on.
 
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