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  #1  
Old 07-11-2022, 09:00 AM
Lufthans's Avatar
Lufthans Lufthans is offline
 
Join Date: Dec 2017
Location: Hilversum, The Netherlands
Posts: 224
Default HR-I vs RV3

Hi guys,

I own an RV3B that is now taken apart for some serious upgrades. Iím a multiple offender when it comes to building and modding aircraft (and cars for that matter) and am going to put a Subaru conversion on the RV.

Not here to discuss the merits of this engine. Thereís other places on VAF to do so. Suffice to say that Iíve been flying one on my Jodel for the past 15 years, which after three iterations, tons of engineering, money and headaches, I got to function flawlessly and thus far 100% reliably. I have done a few more on other aircraft since and even got to do some serious R&D for an Oregon-based company (not the mothership, there are more companies in Oregon).

Anyway, on the RV3, I will be putting the cooling in a P-51 style belly pod, with proper ducting, and will turbocharge the engine. With that (and modified electrics, fuel system, custom ECU, engine mount, cowlings, instrumentation and a whole bunch of upgraded engine internals), it has the potential of putting out 300 hp.

And hereís where my questions in the Rocket forum come in:

I know that 300 hp is serious overkill on such a small aircraft, and I know that its 210 mph Vne can be reached with half that power. So I will be using the other half to make it climb like a mountain goat with ambitions (which really suits my type of flying anyway - quick dashes to the clouds, play around between them and then drop back in).

However - it would be nice to have a bit more headroom in the speed department.

Iíve sent an email to John Harmon (with much of this text), however am not sure if I can expect an answer from him, since heís apparently no longer supporting the HR-I. So I also post the questions here:

Does anyone here know anything about the specifics of this aircraft?

What did John state as a Vne on the HR-I, and what did he do to safely achieve that?

I believe heís switched to an RV4 tail? Just for the sake of its mass balancing, or is it stronger too? Just the horizontal or the vertical tail as well?

Did he do any other structural modifications to the airframe like thicker skins? Did he modify the wing in any way? (Mine has the B-wing). (And yes, I know about the razorback, I just like the P-51-like looks of the slider more)

Bolting on a more powerful engine is one thing, but making it safe to operate is another thing altogetherÖ.

Curious to know and any tidbit of info more than welcome!

Thanks
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Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #2  
Old 07-11-2022, 10:19 AM
Mike S's Avatar
Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,534
Default

Sounds like a fun project-----keep us informed as you move along.
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Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #3  
Old 07-11-2022, 10:36 AM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,482
Default

Perhaps you could find Dave Anders' discussions about his very fast RV-4. In at least one of them, he outlines the major structural changes he put in. Among other things, he built a new empennage with modifications.

A couple of builders added mass balancing to the RV-3 tail. Generally, as far as I know, those were following the concept from the later RVs. Also, as far as I know, none of them were professionally tested for a higher Vne (i.e., with proper instrumentation and analysis), although one or another of them may have been tested more casually.

Are you going to have a variable pitch propeller? With that much power, it would probably be desirable. Oxygen, of course.

How much does the engine installation add to the weight? That alone might suggest some structural changes, and of course the CG position is always a consideration.

A related alternative is a new build, of the F1 Rocket instead of an RV-3 and installing that engine of yours, and I believe I'd choose that instead. They are updating their website so you'll need to contact Vince directly. vince@f1aircraft.com

Good luck - and please keep us posted.

Dave

Last edited by David Paule : 07-11-2022 at 11:34 AM.
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  #4  
Old 07-11-2022, 10:59 AM
Freemasm Freemasm is offline
 
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Location: Orlando
Posts: 888
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ooh boy. You'll definitely be into the design margins. There's lot to consider but I'll state what I think I know, i.e.wings. The rockets re-station the ribs 1" closer throughout the length. There's also the ~4" wider fuse this also effectively "shortens" the wings. There's the wing skin thickness increase but that's not universal and reportedly for CS versus dimpling ops to save time.

While it obviously results in a stronger wing, the stiffness is improved to decrease structural divergence/increase aero-flutter margin. This is (IMO) the most unforgiving aeronautical design alligator of them all. Proceed with caution.
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  #5  
Old 07-11-2022, 12:40 PM
Lufthans's Avatar
Lufthans Lufthans is offline
 
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Location: Hilversum, The Netherlands
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Quote:
Originally Posted by Mike S View Post
Sounds like a fun project-----keep us informed as you move along.
Unfortunately, I have to finish two car Restomod projects first (work obligations) and build myself a new workshop. So I can only start in 8-10 months from now, at the earliest. Gathering information and keeping my mind sane from lack of aircraft projects in the meantime. But will do, in time.
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Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #6  
Old 07-11-2022, 12:58 PM
Lufthans's Avatar
Lufthans Lufthans is offline
 
Join Date: Dec 2017
Location: Hilversum, The Netherlands
Posts: 224
Default

Quote:
Originally Posted by David Paule View Post
Perhaps you could find Dave Anders' discussions about his very fast RV-4. In at least one of them, he outlines the major structural changes he put in. Among other things, he built a new empennage with modifications.

A couple of builders added mass balancing to the RV-3 tail. Generally, as far as I know, those were following the concept from the later RVs. Also, as far as I know, none of them were professionally tested for a higher Vne (i.e., with proper instrumentation and analysis), although one or another of them may have been tested more casually.

Are you going to have a variable pitch propeller? With that much power, it would probably be desirable. Oxygen, of course.

How much does the engine installation add to the weight? That alone might suggest some structural changes, and of course the CG position is always a consideration.

A related alternative is a new build, of the F1 Rocket instead of an RV-3 and installing that engine of yours, and I believe I'd choose that instead. They are updating their website so you'll need to contact Vince directly. vince@f1aircraft.com

Good luck - and please keep us posted.

Dave

Quote:
Originally Posted by Freemasm View Post
ooh boy. You'll definitely be into the design margins. There's lot to consider but I'll state what I think I know, i.e.wings. The rockets re-station the ribs 1" closer throughout the length. There's also the ~4" wider fuse this also effectively "shortens" the wings. There's the wing skin thickness increase but that's not universal and reportedly for CS versus dimpling ops to save time.

While it obviously results in a stronger wing, the stiffness is improved to decrease structural divergence/increase aero-flutter margin. This is (IMO) the most unforgiving aeronautical design alligator of them all. Proceed with caution.
I KNOW that this is not something to take on lightheartedly. Hence my questions about the HR-I. What was its Vne, and what was done (and how was it proven) to make this possible? Without this, mine will keep its 210 mph Vne and the power will then only be for climb performance (which would be fine with me as well, quite frankly).

I know of 4 RV-3's with counterbalanced empennages, RV-4 style. Wondering what was done to the HR-I, exactly.

Constant speed MTV-12 prop is on its way here as we speak. Same one I have on my Jodel, and a large part of its awesome performance. That thing just hauls, especially with the low RPMs that I am running it. (Cruise on the Jodel is 4200 engine rpm, which translates to only 1800 rpm on the prop).

Normally aspirated, the EJ-25 setup, including radiators and the like is comparable to IO-320 weight. Maybe a few lbs heavier. Adding a turbocharger will bring it to parallel-valve IO-360 weights.

CG-wise I have it easy. For one, the radiator setup is behing the CG, offsetting the weight penalty up front. Plus the CG of the engine/gearbox combo itself sits closer to the firewall than that of a Lycoming. And then there is the battery to play around with. All in all, the CG is not all that hard to get just right.

Oxygen is useless for me. I can't go higher than 9500 ft anywhere in this country, and I need to fly out of my way to get even that. Typically, I am limited to 6500 ft.It's all class A above that.

And building an F1 rocket now would kind of defeat the purpose of this build. I've got an RV3 that I want to upgrade, and I'll work within the limits of what that airframe will allow me to do.

And Scott, are you sure about the modified wing? They are on the HR-II. The mods on those are well-documented and well-known. But these are based on the RV4. But how about the RV3/ HR-I?? As far as I know, the only mods are RV4 empennage, fastback, wider firewall and angle-valve IO-360. But I need to be sure before I feel safe to raise the Vne limits on mine.....

Anyway. thank you for the insights!!!!
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Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #7  
Old 07-11-2022, 04:15 PM
Lufthans's Avatar
Lufthans Lufthans is offline
 
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Location: Hilversum, The Netherlands
Posts: 224
Default

I actually just got some (brief) answers from John Harmon himself:

Tail of the HR-I was a regular RV-3 tail, albeit with .020 skins on the elevator and mass-balanced in the same way the RV-4 is balanced.

Vne of 210 knots, cruise 190 knots (241 mph / 218 mph)

No other changes to the airframe....
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Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #8  
Old 07-12-2022, 06:31 AM
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Capflyer Capflyer is offline
 
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Location: Gaithersburg, MD
Posts: 1,133
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Looks like John's first HR1 is for sale on BS. There are some logbook entries shown in the pics. One indicates a top speed of 218 kts in level flight was obtained and flutter tested up to 260mph.
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HRII - Building
RV8 Hot Rod "Drone Killer" - Built & Flying
RV8 Blue Nose "Look'n Good" - Sold
RV4 - FAST & FUN! Rebuilt, Flown, Sold
RV-7A Built, Flown, Sold
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  #9  
Old 07-12-2022, 07:28 AM
Freemasm Freemasm is offline
 
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Location: Orlando
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Quote:
Originally Posted by Lufthans View Post
.....And Scott, are you sure about the modified wing? They are on the HR-II...
Thank you for catching me on that. I tend to skim especially when viewing on the phone. I believe my info to be correct though not relevant to your question; story of my life. That said, sounds like my warning was already in your memory banks but I'll reinforce it. Can't speak directly for this design but the approach is common. Flutter, both aero surface and that related to structural divergence, for the (vast?) majority of EAB world was determined empirically. Dive the aircraft and smack the stick to try and force a function. Go not too much further back in aircraft development history and many of these limits were written in blood. There may be a few more but IIRC, the Glasairs were one of the few that got shaker table testing and some surprises were uncovered. I believe they were ex-Boeing engineers.

Again, sorry about the mistake. Keep us up to date on your progress. Wouldn't your project be much more fun with a direct drive diesel (he said hopingly)?
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  #10  
Old 07-12-2022, 03:35 PM
Lufthans's Avatar
Lufthans Lufthans is offline
 
Join Date: Dec 2017
Location: Hilversum, The Netherlands
Posts: 224
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Quote:
Originally Posted by Capflyer View Post
Looks like John's first HR1 is for sale on BS. There are some logbook entries shown in the pics. One indicates a top speed of 218 kts in level flight was obtained and flutter tested up to 260mph.
VERY interesting. Thanks!!
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Hans Teijgeler
Hilversum, The Netherlands


PH-KLT Resurrecting an RV-3B, with Subaru EJ25
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-SUM RV-4; Imported and upgraded. Sold my share :-(
PH-EIL RV-4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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