X-Pert (oz7662)


X-Pert (oz7662) by Herm Stroup 1969 - plan thumbnail

About this Plan

RCM X-Pert. Radio control pattern model. For .40 power and 4 channel radio. Uses a foam wing.

Quote: "The third and final construction phase of the RCM Flight Training Course presents the logical conclusion to the series - the competition aircraft. By HL Stroup.

Wanna put your tank in a tiger? This is it! Yet, with a mild .35 engine it becomes a very well behaved pussycat performing class A and B maneuvers easily and smoothly. For the brute power maneuvers in the Class C pattern it needs a .40.

The RCM X-PERT was developed for two specific reasons:

1. For those who have followed the RCM Flight Training Program, from the Basic Trainer through the Advanced Trainer, the X-PERT is the next natural step to a truly high performance but easily handled aircraft. You may use the same wing, stab, and fin that you have on your Advanced Trainer.
2. It has long been my conviction that precision pattern aerobatics could be performed with a smaller aircraft than has been generally used. The new, miniature proportional systems help make this feasible, and the steadily rising cats of balsa and fuel make it highly desirable! I do not believe, however, that the "ultra" small designs recently appearing in several of the magazines are capable of performing smooth pattern maneuvers. They are rather 'jumpy' or must get their 'grooviness' from excessive speed because of the low Reynolds numbers 'involved. The RCM X-PERT with over 500 square inches seems about as small as we can get and still expect smooth responsiveness.

The .40 powered X-PERT is capable of performing FAI and Class C maneuvers with smoothness and precision. It will snap roll or spin in either direction but has no snap rolling tendencies at the bottom of outside loops or if slowed up too much in a landing approach. In fact, if the weight is kept at 4-1/2 pounds or less it can be dragged in for slow nose high, main gear landings. The blunt airfoil very effectively slows it down when the power is reduced as well as helping to reduce excessive speed build-up in "nose down" maneuvers.

The X-PERT is tolerant of CG location. It has been flown with a CG location variation of 25% to nearly 50% of chord requiring elevator trim adjustment only. It is NOT however, tolerant of errors in decalage! Prototype No. 1 was flown with 3 degrees positive wing incidence and the ailerons were virtually blanked out. So, make very, VERY sure the wing and stab are at 0 - 0 degrees. Inverted flying upwind is nearly 'hands off,' the rolls are axial, and it is soft on elevator when properly trimmed.

In short, we have found no bad habits with the X-PERT. Maneuvers may be performed slowly, close in, and low, but it has plenty of power to pull straight up for vertical maneuvers. I must insert a word of caution at this point - it is not a beginner's airplane! The RCM Basic Trainer and Advanced Trainer are for the beginner. The X-PERT is not hard to fly, nor is if temperamental, but it is a fully acrobatic and highly responsive aircraft.

The fuselage inside diameter is 3 inches so that the older style servos may be mounted crosswise. The battery/tank compartment will accommodate up to a 10 ounce tank but there is not enough space for the older style 7 cell battery packs. The nose block could be hollowed out and/or a lower balsa block could be added to look like an air scoop to fit in one of the larger battery packs.

The fuselage was designed around equipment installation with the lowest drag exterior configuration I could devise. When you think about it, a fuselage has no real aerodynamic purpose. It does have two very practical functions:

1. To hold the wing, tail sections, and power source at correct relative angles and distances.
2. To provide a 'housing' for the radio and tank.

The fuselage was not made 'deep' in order to execute the knife edge maneuver. Since a Clam C ship is expected to execute a total of 30 maneuvers, designing a fuselage configuration suited to one maneuver at the expense of several others doesn't seem practical. Successful designs are the best possible set of compromises.

If you have looked at the plans you probably noticed 1/4 inch fuselage sides. Before you decide I have lost my mind, let we explain..."

Direct submission to Outerzone.

Update 02/05/2016: Added article, thanks to RFJ.

Update 6/9/2023: Replaced this plan with a clearer version, thanks to Pilgrim.

Supplementary file notes

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X-Pert (oz7662) by Herm Stroup 1969 - model pic

  • (oz7662)
    by Herm Stroup
    from RCMplans (ref:396)
    May 1969 
    54in span
    IC R/C LowWing
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 21/04/2016
    Filesize: 297KB
    Format: • PDFbitmap
    Credit*: JohnPapandreou, Pilgrim
    Downloads: 1545

X-Pert (oz7662) by Herm Stroup 1969 - pic 003.jpg
X-Pert (oz7662) by Herm Stroup 1969 - pic 004.jpg
X-Pert (oz7662) by Herm Stroup 1969 - pic 005.jpg

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User comments

This model is a good example of a fine design ruined by "progress". Back in the day, I cut a lot of foam wings for all kinds of models. Foam of the type we used was cheap and available, but it ain't the same anymore. All that's available in my area is the "recycled" stuff, unsuitable for aircraft use. It seems all the foam producers have found that they can empty their foam scraps, up to 15 % of volume, into the next vat of new foam and it still retains its insulation value. It's a great deal for them, no waste at all, but for us it's bad news. The foam scraps produce hard places in the foam, ruining the smooth path of hot wire cutters. It just doesn't work. An extensive search of all local foam suppliers failed to find "virgin" foam available. We were able to locate expensive virgin material about a hundred miles away if we met a minimum order of $250.00 and drove a truck to get it. Shipping costs were so high as to make the whole idea uneconomical. A minimum order would completely fill my truck, not enough room at home to store it. That's not all, nice A-grain balsa suitable for wing sheeting ain't easy to find these days. Hobby shops aren't carrying much balsa anyway so you need to order anything more than a couple of sheets, and they won't pick it for you. So for me, I might as well retire my foam cutter and re-design my wings to use balsa construction. I hate ARFs, that's why I love Outerzone, still some builders in the hobby....
DougSmith - 02/05/2016
Thanks Doug, this is really interesting. Does everyone have this problem getting hold of suitable materials these days?
Mary - 02/05/2016
Attached is a photo of the X-PERT made from the plan found on your website [more pics 005]. For anyone who is interested, the engine is a MVVS 40.
BobCherry - 12/10/2017
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  • X-Pert (oz7662)
  • Plan File Filesize: 297KB Filename: X-Pert_RCM396_oz7662.pdf
  • Supplement Filesize: 5950KB Filename: X-Pert_RCM396_oz7662_article.pdf
  • Supplement Filesize: 560KB Filename: X-Pert_RCM396_oz7662_previous.pdf
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