JP Mk5 Nose Strakes

[twinsrus]

Anyone have any info on what the nose strakes on the Jet Provost Mk5 actually achieve? I understand that they were fitted to make the spin less oscillatory. Do they reduce the lift created by the nose section?

[Dan Winterland]

It was the JP5a which had them. The 5s at Finningley used for Nav training didn't. The 5as also had the roughened leading edge which was also part of the fit to make the spin more stable.

I'm not sure exectly how the strakes worked, but the main difference between the 5a and the 3a was the large canopy on the 5a. Also, the 3a had tip tanks which the 5a didn't (except for the Nav training Mk5s). I expect it was something to do with these facts. What I do know is that the 5a burned 5lbs a minute more at low level than the 5.


And I'm not sure they worked that well. Spinning a JP5a one day was the closest I've ever come to parachuting!

[Yellow Sun]

It was the JP5a which had them. The 5s at Finningley used for Nav training didn't.

The JP5 had the strakes. The 5 became the 5A after the avionics refit that introduced ILS and VOR/DME in place of Rebecca. IIRC the IFF equipment was also part of the upgrade. The entire nose section of the 5 was different from the 3/4 with a wider under surface and a more ovoid shape. The best explanation I heard for the addition of the strakes was to reduce the Cl of the forward fuselage and to maintain it at a more constant value under varying conditions. One can also speculate about the inertial effects but it is difficult to arrive at firm conclusions.
I had little to do with the 5B as flown at Finningley, but I seem to recall that the strakes were removed on 3 grounds:
a. Less drag - therefore lower fuel burn (see post above)
b. Limited use for spinning and aerobatics
c. Not usually flown by student pilots
The fitting of the tip tanks also altered the B/A ratio. I don't have figures for the 5 series similar figures for the 3/4 series with fuel in the tips and empty were .48 - 1.52. The comparative figures for the 5A/5B would be of the same order.
It is also be worth considering the effect of the fuselage cross section on spinning characteristics. Although the rear fuselage is most important as a contribution to the "damping in yaw" effect e.g.
Circular - 1
Rectangular - 2.5
Elliptical - 3.5
(all anti-spin effect)
You can see that the change to the forward fuselage would also alter the spin characteristics. I suppose that the bottom line is the fewer "bolt on bits" the better job the designer did!
YS

[Dan Winterland]

Not that I want to sound like a spotter, but what I was trying to say was that it was only the 5s used for pilot training which had the strakes. The 5a wa the new Nav kit mod, but the 5a was used for pilot training and the 5 for nav training. The 5as which were subsequently used for nav training and which had tip tanks fitted and strakes removed were designated 5bs.

WRT B/A ratios, I only flew the 3 at CFS. Can anyone remeber any limitations about spinning with tip tank fuel?

[Jaguar Pilot]

The strakes were indeed to make the spin less oscillatory in yaw.
Apart from the 5, I also flew the 167 Strikemaster for five years.
This too had strakes and was always flown with tip tanks. I can't remember the fuel figures for the 5, but when spinning the 167 the tip tanks had to be empty because of the relatively high B/A ratio.
Incidentally, we also flew it with drop tanks plus tip tanks full - in temperatures of 45C+, it needed about 6000ft of runway to get airborne!!
Mind you, once it was airborne, it went a very long way.

JP

[twinsrus]

Tks for above comments. Did the JP5 suffer from poor or neutral longitudinal stability and if so were the strakes designed to improve this?

[spoff]

Flew the Jp3/5 and Strikie,

Spinning the 3 as memory serves the tips had to be less than half full and balanced

Spinning the strikie used to scare the sh#t out of me, armour plating affected the B/A ratio, VERY nearly had to punch out of one that did not want to recover. Was briefing the ejection when it recovered with a final attempt at centralising controls and praying.

Also seem to recall the party line on the 5 being that the strakes made the spin less oscilliatary[sp?]

[Jaguar Pilot]

Twinsarus:

The JP5/167 was not weak in either longitudinal static or dynamic stability. As I said, the stakes were said to make the erect spin less oscillatory in yaw.
It was designed as a trainer and weak longitudinal stability would have made it difficult to fly in close formation. The short period mode was very well damped but at high altitude (high TAS) it did exhibit (like many aeroplanes) the long period phugoid. It was. however, neutral in roll.
I was fortunate enough to win three aerobatic competitions, one of them international, in a 5 and in my view an aeroplane needed the right qualities
to perform an accurate Derry turn. The 5 certainly did. Structurally the fin post was its' weakest point, and lots of rudder above 150 KIAS was not a place to go.

Spoff:

Where did you fly the Strikemaster and when? I might know you.

JP

[spoff]

Jag Pilot,

Check your PM's Mate.

[sycamore]

strakes

A few points about the J-P`strakes and things...
Mk 3/4 had 3 fuel tanks in each wing (appx1450lbs) and 2 tips( 700lbs); Mk5/5a/Strikey had 4 tanks in each and 2 tips ,2900lbs total. The Strikey could also carry 75/100 gal u/wing tanks.
Spinning limits for 3/4 were- no fuel in tips, balanced fuel in mains<100 lbs between wings , and 1300 lbs max.Up to 8 turns permitted.
Mk5 limits are max fuel 1780lbs <100 between wings and pre mod 1791(wing-tip tank mod.ie fitted) no fuel in the tips.8 turns permitted.
If tips were fitted(post 1791), fuel state was ..no fuel in tips, <100 between wings, and max fuel state 1300lbs. 4 turns permitted.
The Strikey was I think a max fuel of 1600 lbs<100, none in tips, and no underwing stores carried-- store carriers could be fitted.
Strakes were fitted to stabilise the oscillatory characteristics by reducing lift generated by the larger egg-shaped front(Coanda) as was the `concrete ` LE of the wing. The 5/5as also had strakes under and behind the intakes, probably for the same reason, or prevent x-flow in spins.
Memory must play tricks Jag, as Strikeys never had any strakes, as the guns were in the lower part of the intakes, and the ejector chutes probably were as effective(unless of course you can show it different !)
The Mk3/4 were quite smooth spinning, recover well 1/4-1/2 turn, Mk5/a similar but can be oscillatory, and slightly faster to the right , recovery 1/2-3/4 turn. Strikey- slower than others4-5 secs, stable, but flatter, recvers about 1/2 turn.
These are of course done `academically` for airtest purposes, not your QFI FLICKING IT IN THE MIDDLE OF AN UPWARD `WHAT-WAS THAT`...

Edited . Also the Cof G position, ,range, and limits were changed and have a considerable influence on spin characteristics, particularly between Mk5 and Strikey.

[Jaguar Pilot]

sycamore,

Our 167s were unarmed since they were used only for pilot and WSO training but now that you mention it, I now have doubts
about the strakes. Unfortunately I do not have any personal photos since in Saudi Arabia the carrying of cameras just about carried the death penalty.

Incidentally, most of the Strikies spun and recovered very well. Pre-spinning on an air test I always did an unaccelerated wings level stall and held the heavy buffet with almost full aft stick. If the aeroplane rolled more than 30 degrees I wouldn't spin it until after a rigging check. What about yours?

JP

[NigelOnDraft]

Still fly and spin the Mk5A - in fact the prototype one... Strakes still there, but the "roughened leading edges" have been repainted enough times (without sand!) that their effect would be reduced / lost. Seems a little different to what I recall from QFI days, but recovers fine (so far )...

[Jaguar Pilot]

spinning

NigelOnDraft,

quote: ......but recovers fine (so far )...

Then I hope that the escape seat has been serviced and is functional...!!

The best spin recovery that I was ever taught is:

1. mouth fully closed
2. apply full opposite bedpost and observe a two second pause
3. sheets going forward until the rotation stops
4. centralise bedpost
5. if no immediate recovery, apply in-spin bedside light
6. if still no recovery, check height and reach for bedside bucket

JP

[John Farley]

Maybe that would be appropriate for a Jaguar pilot.

A Harrier pilot would just get out of bed, walk steadily to the wardrobe and piss in one of his shoes.

[Jaguar Pilot]

spinning v pissed

John Farley,

At least a Jaguar pilot would know what room he was in, and probably walk down the corridor and piss in some other persons shoes!

Cats don't soil their own territory, as any animal psychologist will tell you...

We have met by the way...somewhere...sometime//maybe over the rainbow. I have a murky past.

JP

[sycamore]

Sinking to the low-level `some` of you guys used to operate..truckies could never find the shoes, so the sink would do...
Anyway, back on thread,.. always must do a full stall session b4 spinning, for all those good reasons, and certainly most JP`s, L-29/39S are very similar that you can get full aft stick and just sit there gently `nodding` away... it`s only the fact you are approaching the ground at about 5-6000 ft.min that startles some studes...
If you are spinning a piston a/c , to teach the effects of prop, etc used to go to altitude 8-10000, do the stalling bit, then do a stall, having turned the fuel off(mixture), and then pull up and hope the prop stops. Now demo spinning one way(4 turns), holding full aft stick, full opposite rudder until it spins the other way(4 turns). ;recover at leisure .., open mixture/press starter, etc,etc.

[Mere Mortal]

Greetings all,

Not being a test pilot or normally viewing this forum, the topic caught my eye and I have been following with great interest.

I fly an ex-kiwi Strikemaster here in Oz. This one never had strakes, but I have seen a few JP5s with the strakes and concrete LE. I figured it was a mod. to give the aeroplane a more desirable stalling and spinning character.

If anyone needs clarification about 167 figures, I have a flight manual handy.

Cheers
Mere Mortal

[sycamore]

M-M,G`DAY,Blue,how are they hanging ? Question for you? You probably know about the Strikey fatal in Oz last year As a result of that our CAA have forbidden all aerobatics and spinning until such time as `they` decide otherwise; ie until the report by your CAA comes up with the answers as to why it crashed.The rumour is that the fin/tailplane came adrift,causing a `bunt`, which folded the mainplane down,etc,etc...There are of course,speculation/rumours,etc that the a/c was used` aggressively`, and had no `fatigue life` known,etc, etc.
To put you in the picture about J-P/Strikey operators here, our aircraft are only allowed to fly on a `Permit to fly` which means that one cannot use the a/c for `hire/reward`,pax can be carried,but cost sharing, same as private, can do air displays, and training for pilots wishing to buy one or be in a `group ownership` scheme.This restriction now has meant a slow-down in jet flying, and the CAA couldn`t actually care less, as it`s less work for them,and not much play for anyone else.BAe, the makers/design authority likewise don`t see any profit in helping.....
Soooo..., I know it`s a fast ball, and we still do `body-liners`... is there anything about the state of play in Oz that you could let us know about...?
If you feel you would rather not broadcast in public, then a PM would be useful to go in to bat with against `them`.. are you flying, any restrictions, any truth in any of the rumours,any leads we can follow-up/websites for further info. Much appreciated if you can help...Syc

[Mere Mortal]

G'day Syc,
I was approached by a Police investigator who mainly covers aircraft fatalities. He and the ATSB are of the opinion that the wing departed first at the upper wing attach point. CASA posted a recommendation to all Aussie Strikey and JP operator to limit the g to +4 and no 0g or negative, which is what I flying to for the past 5-6 years. Pax don't need anymore than that to get the thrill.
There is a theory that the aircraft had main gear collapse years ago which may have weaken the wing attach lugs.
I will PM you what I know about the rest. If I can find the prelim. report, I will PM the link as it has photos of the sheered wing attach lug.
Usual problem with sort of thing is sifting through the crap and personal agendas to find some true facts.
Cheers MM

[Algy]

...was this the last JP5A spin loss?

Stude and strukkie jumped out at Cranwell in early '81, from memory, following failure to recover from spin. Aircraft laid out in many, many pieces in Cranwell hangar, much visited by uncharacteristically thoughtful studes for about 24hr until it was locked up.

Not sure what the board eventually made of that one. Presumably the last of its kind???