Enclosing an Evans Volksplane VP-2

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Oct 26, 2014.

Help Support HomeBuiltAirplanes Forum by donating:

  1. May 9, 2016 #81

    flyer alan

    flyer alan

    flyer alan

    New Member

    Joined:
    Jul 12, 2014
    Messages:
    3
    Likes Received:
    1
    Location:
    Gig Harbor, WA, USA.
    Excellent discussion. Having read most of this forum with great interest, and being something of a fan of the VP-2, i would like to make a couple of suggestions.


    First; THRUST and power are both important to the performance of this rather marginal airplane, especially with two up, and given the ‘draggy’ nature of the open cockpit. Thrust is realized by increasing the propeller swept disk area, and this comes from increased propeller diameter. Diameter can only really be increased by decreasing propeller RPM, which implies a reduction gear of some kind. With so many PSRU’s out there, and so much impassioned writing about them i would not presume to recommend, BUT, piston engines produce their power in distinct pulses, and propellers do not rotate smoothly either (turbulence, interference flow etc) so some form of rotational or torque compliance must be built in. Some argue that a belt does this, others add a sprung belt tensioner, some add circumferential springs (like a car clutch plate), but all should be matched to the engines pulse’s at designed RPM, and the number and orientation of the propeller blades.


    All this to say a PSRU on your VW of choice would add significantly to performance, if not adding actual speed. Be aware that this would raise the thrust line of the propeller, and possibly need a taller MLG leg, changing the static stance of the wing/fuselage, a T/O issue.


    Second; i would suggest adding the roll over bar, still steel tube, to the BH behind the cockpit seats, not over the front BH. Its effect would be much the same, and it would not interfere with the compass. Were you to add <>50% perforated screening between it and the rear fuselage, you might reduce drafts in much the same way as modern convertibles. See Audi and BMW 4 seat convertibles for ideas.


    My own VP-2 would have a raised rear fairing, and a radial engine cowling over a PSRU to give a Kinner Sportster look or fairing line.
     
  2. May 9, 2016 #82

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    Thanks, Alan, for your comments. I am not a fan of PSRUs in VWs because I think it gets away from the simplicity that is so appealing, but I agree that the VP-2 needs all the power it can get. The plans call for a 60" diameter prop, so clearly Bud Evans was thinking the same way about maximizing thrust, especially in the takeoff and clime regimes. For comparison, Sonex suggests a 54" diameter prop with the Aerovee at 4000 rpm. With a 60" prop, engine max rpm would have to be kept to 3600 to keep the propeller tip speeds the same.

    On the roll bar question, I have kicked around some options but the more I study the plans the more I appreciated how well Bud Evans designed his planes. My understanding is that you should draw a line from the top of the firewall to the top of the roll bar and extend it onwards into space to see which will take the brunt of a rollover impact, the roll bar or the pilot. The VP-2 manages to satisfy that with quite a short bar forward, though it could probably be raised a few inches to be sure for tall pilots (as it is in my sketches). Put it behind the pilot and now it needs to be much higher and heavier.

    On the turtledeck and canopy, I have gone round and round on that question as you can see, but I think building open-cockpit first with the options to enclose later makes good sense. I think I'd go with a longer-than-stock fairing for looks as much as anything else but also keep it quite low and end it before reaching the rudder. One practical reason to have the turtledeck a little higher than stock would be to have the shoulder harnesses pass up over the rear spar bulkhead to reduce the downward, compressive angle if the harness is called upon to do its job.

    Cheers,

    Matthew
     
  3. Feb 21, 2018 #83

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    Picking up an old thread, I have a question about canopies. I've mentioned before that the very narrow VP-2 cockpit pretty much needs shoulders and elbows sticking out beyond the top longeron if you do take a second person up for a quick hop. That suggests that a canopy on a VP-2 should be more globular than is typically desired in an aircraft canopy, more like a WWII Spitfire and Mustang Malcolm hood as mentioned at the beginning of this thread.

    evans vp-2 sport aviation cover (medium).jpg MalcomHood1.jpg

    Free-blown canopies always have a little bit of this sort of sag, but in this case we'd actually want to magnify the sag. I can imagine that using compressed air to inflate a heat-softened acrylic or polycarbonate sheet, and then quickly letting a little of the air out, might create this effect, but I have no actual experience. Does anyone have any experience with free-blown canopies and how you might deliberately create something more like a Malcolm hood? Or maybe a flat sheet on frames that form about 225 degrees of a circle would makes more sense?
     
  4. Feb 21, 2018 #84

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    Aaagh, you've done it again!!! keeping me up at nights thinking about modding up VeePees.....how about a slab-sided Jodel D112 cockpit canopy or the semi-blown kind fitted to some D117s? or even a canopy like a Condor?
     
    cluttonfred likes this.
  5. Feb 22, 2018 #85

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    also, if you start going down the big cylinder route for VWs, you start getting into serious money. How about one of the less well known Rotaxs, the 670? Could you picture a two-stroke pulling a VP-2 aloft? there are at least two excellent VP-1s with 582s in them and they are excellent performers.
     
  6. Feb 22, 2018 #86

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    Jodel and Condor are great examples of simple canopies but I don’t think they bulge out like a Malcolm hood for that extra inch or two of elbow room.

    Ewww, no, the VP in my head does not come with a two-stroke whine and CG location would be a challenge. If I did want a cheap and easy, plans-built, two-stroke two-seater, there are still some out there including several Fisher models. A Milholland Cabin Eagle with the right two-stroke might be fun, too.
     
  7. Feb 22, 2018 #87

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,440
    Likes Received:
    3,176
    Location:
    Memphis, TN
    What is really needed is angling the aft cabin bulkhead so the pilots are not so upright. Streamlining and cabin should be much better. Shoulders need to be closer to the top longeron.
     
  8. Feb 22, 2018 #88

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    Dare I say, add the extra width at the building stage and make the airframe wider by a couple of inches, at the spar line? is that possible?......engine-wise, a Corvair with two pots blanked off to give you a four banger of about 80 hp. If you can't lift two people, with 80 hp and the -2 on a diet, as suggested above, you may throw your hat at it and fly it as a single seater. With the canopy, how about angling out a framed canopy like the Pazmany Storch. If it's elbow room, rather than a vertical view, that you want then a simple inverted fibreglass armrest on either side would do, with vertical canopy sides arcing over to join in the centre like a d112 canopy.
     
  9. Feb 22, 2018 #89

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    The more I mess around with this, the more I think that my original idea is actually pretty good.

    1) Make the windshield span the full width of the front spar bulkhead/instrument panel with straight sides and circular arc at the top up to the level of the top of the pilot's head.
    2) Raise and round the top of the roll bar to match or, better yet, eliminate the roll bar in favor of a strong windscreen bow to serve the same purpose.
    3) Provide a raised, rounded rear turtledeck to the same height as the windscreen.
    4) Build a light, removable, side-hinged wooden or aluminum tubing canopy frame to match the windscreen and turtledeck and fit it with a bulged Malcolm hood blown canopy much like the Mustang above.

    Now you have a more sheltered open cockpit with the option of full enclosure when the weather gets chilly. The effect is basically to put a removable Malcolm hood on this French VP-2.

    French VP-2.jpg
     
  10. Feb 22, 2018 #90

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,650
    Likes Received:
    430
    Location:
    Flint, Mi, USA
    I would still add a second roll bar behind the pilot, likewise drawing a line from the aft tip of the fuselage to the rear bar.
    A bad crash could have enough momentum to bring the tail up and over and into the ground.
    Plus it gives you a place to attach the turtle deck.
    For cockpit width, it's viable to just build the fuselage a couple inches wider without causing problems.
     
  11. Feb 23, 2018 #91

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    The Jodel D-9 had the option of a blown sliding canopy for winter and open top for summer. I was told that the French builders got glider manufacturers to blow them from cut-offs from the original moulds for two-seat gliders. Some D117s and D120s have curved windshields and blown canopies, again blown by canopy makers for the glider crowd.
     
  12. Aug 28, 2018 #92

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    jim scoles vp-2.jpg

    Despite the title, this thread evolved into a discussion of all sorts of potential modifications to the VP-2, so I think this is a good addition.

    Canadian Jim Scoles did not originally build his VP-2, but he rebuilt it twice including adding a Subaru engine, shortening the chord of the ailerons, and trying out a fixed fin and rudder over the course of 20 years of ownership. Jim's modified VP-2 is featured in the two YouTube clips by Nathalie Fortin below.

    https://youtu.be/Vhmzb0PJ2o0

    https://youtu.be/34aHMzxdd9s

    I was recently able to connect with Jim thanks to Nathalie. Jim provided a wealth of commentary on his experience with the VP-2 and gave me permission to share his thoughts with other enthusiasts. Here is Jim's initial message and a follow-up, both dated August 27, 2018.

    And here is Jim's reply to some follow-up questions from me.

     
    Last edited: Aug 28, 2018
  13. Aug 28, 2018 #93

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    Nice one!
     
  14. Aug 30, 2018 #94

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
    @cluttonfred, have you seen the 3-view of what is called a VP-chel ? A VP-2 lookalike built using the methodology of the Pouchel types.
     
  15. Aug 30, 2018 #95

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    Nope, I don’t think so, got a link?
     
  16. Aug 31, 2018 #96

    Twodeaddogs

    Twodeaddogs

    Twodeaddogs

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    823
    Likes Received:
    233
    Location:
    Dunlavin, County Wicklow,Ireland
  17. Aug 31, 2018 #97

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,350
    Likes Received:
    2,220
    Location:
    World traveler
    Thanks, I had not seen that, looks like a single-seater, not sure what the advantages might be other than meeting European microlight limits.
     
  18. Sep 1, 2018 #98

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,650
    Likes Received:
    430
    Location:
    Flint, Mi, USA
    Pretty neat but those top-mounted struts bug the crap outta me.
     
  19. Sep 1, 2018 #99

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    11,674
    Likes Received:
    2,190
    Location:
    Port Townsend WA
    Is it the looks of the struts? Or a concern about strength?
     
  20. Sep 1, 2018 #100

    Sockmonkey

    Sockmonkey

    Sockmonkey

    Well-Known Member

    Joined:
    Apr 24, 2014
    Messages:
    1,650
    Likes Received:
    430
    Location:
    Flint, Mi, USA
    Partly looks and partly because they screw up the airflow over the top of the wing.
     

Share This Page

arrow_white