PSS Jet Provost

[Dave Cooper 3]

Hi All

Quite fancy a PSS Jet Provost design /build for this winter. Had a look at the Andy Blackburn design (subject of the Mass Build ?) but this is rather small at around 36" span.

Have now sourced another plan plus some scale drawings which look rather promising....not sure about the plan's wing section though which seems to be a member of the NACA semi-symmetrical family. On the slope, I'm wondering about a Selig 7055 or Eppler 205 /374 section ?

I'm after a fast(ish) model with good penetration and energy retention. Probably 'stand-off' scale in terms of detail - light, but strong airframe which can be ballasted up for different wind strengths. I have some carbon, Kevlar, grp and Liteply available (plus good-old balsa !).

Thanks for any assistance from the PSS experts...

Dave

[Phil Cooke]

Hi Dave, agreed the Jet Provost is a little small at 36" span and I too would like to make a slightly bigger one - but its a great model - I'm still flying mine from the 2014 Mass Build venture as are many other of our members.

What sort of size are you thinking of? For me the best thing to do would be to scale it up by 25% or 50% (to keep the maths simple) and go up on stock size from the original drawing to the same factor.

[Andy Blackburn]

> On the slope, I'm wondering about a Selig 7055 or Eppler 205 /374 section ?

Depends on the size, and on what you want. The small Jet Provost wing section is Selig S7055 which works well at that size, it thermals and climbs well but the wing section seems to limit the top speed. Eppler E205 is faster but seems to require a decently-sized wing chord to work properly, I hesitate to speculate but I'd say something around 8-9 inches chord would work well. E374 is similar but a bit faster, and hasn't got a nearly flat rear profile so it can't be built flat on the bench.

One other thing, though - the small JP has a little bit of washout (a degree, from memory) and it normally behaves itself in the tip-stall department; I urge you to at least consider the possibility that a little bit of washout might be a good thing...

(P.S. If it's Ron Collins' plan for a JP Mark 5 that you have, I think it's Eppler 374...)

[Dave Cooper 3]

Hi both - thanks for replying :

Phil - Yep, a straight scale-up is very tempting. We've got the builders in at the moment and all my modelling stuff is up in the loft for safe keeping ! But, I was thinking around 4 foot span and about an 8" median chord. I'm not a very efficient soarer yet and I was thinking that the extra wing area might help me to stay aloft in more marginal conditions.

Andy - yes, I have a Capstan model (E205) of around 6' span and, from memory, it has about 1-2 deg's of tip washout. Not maiden'd it yet but others report that it flies nicely rudder /elevator and very well with ailerons (I've just finished the conversion).

I was wondering if the washout on the JP could be 'blended' into the tip tanks to make it look more scale-like ? I don't think the plan is 'Ron Collins' but, it is a Mark 5. Target weight was around 3-4 lbs if I remember the magazine article correctly. Does this seem ok for wing loading ? Some of our club members have built yours and speak very highly of it's performance.

Dave

[Andy Blackburn]

> I was wondering if the washout on the JP could be 'blended' into the tip tanks to make it look more scale-like ?

Yes, that's what was done on the small one - the tip tank is (or should be!) at the right angle for scale, the washout isn't noticeable.

> I don't think the plan is 'Ron Collins' but, it is a Mark 5. Target weight was around 3-4 lbs if I remember the magazine article correctly. Does this seem ok for wing loading ?

If it's 48" span, then bearing in mind you said that you wanted a "light, but strong airframe that can be ballasted" then 3 lb is probably OK, at a guess. It also depends what slope you fly from - if it's a brick lifter then I wouldn't worry too much, but if you fly from a more normal slope then I'd aim for a wing loading of 15-16 oz/sq ft. You might well have to use some light wood to get that, though.

[Dave Cooper 3]

Thanks for the advice Andy, as a PSS beginner I'll try and do a light build on this one.... ( for some reason my tails often come out a little over-weight !).

The main local slopes are about 600' high and, for PSS, the experienced guys tend to fly in winds of 10-20+ mph. As you say 'brick-lifters'. Nevertheless, I think 15-16 oz/sq ft is a good target for me to aim at.

BTW Andy / Phil I'd like to have a look at Ron Collins's plan - any idea of size and where I could get one from ?

Cheers for now,

Dave

[Dave Cooper 3]

Hi All - a quick update : Having just finished working with the builders to level my garage floor and applied the (very expensive floor paint !), I can now get my modelling projects back on track...

(Andy mentioned an interest in motorsport in an earlier post - so, the level floor is for my 10% wind tunnel. This to give me key lift /drag data for a Le-Mans style sportscar that I'm building. Also, it now gives me reliable 'datums' to take chassis measurements from).

So, finally dug out the plan for the JP and it's a Roger Howells' design for a 40-size power model. About 47" span, and, prettymuch-true-to-scale. If I can keep the wing loading to a reasonable level, it might just work as a PSS job. Wing section looks OK(ish), but, yet to verify the actual section. Will probably need some tip washout to make it nicer nearer the stall plus some lead up front in lieu of motor /fuel etc.

Anybody tackled anything similar ???

Dave

[Mark Kettle 1]

How's it going Dave your JP build? Here's a couple of links to a video or two of a racing JP.

Jet Racer BAC Jet Provost, Nathan Harnagel

See at video time 0.40 & 2.00 Nathan Harnagel Mk5 JP racing at Reno 2019