Marcel Kuhnt's HS748 model problem

[hobby]

Here I am again back "flying" the HS748, this time the model is by Marcel Kuhnt in FS9. As one begins to taxy on the apron the aircraft seems to be not under control - it appears to skid from left to right and vice versa, almost as if the wheels were not in contact with the ground. At the start of the take off run the nose seems to move of its own volition left to right and vice versa. With 10* flap once past 80 kts the aircraft rudder seems to become more effective but way past 98 kts the stick really has to be hauled back an extraordinary amount to lift the nose, increasing the speed still further the acft will eventually, and suddenly, leave the ground at a most unrealistic angle! Feels as though the tyres are stuck in thick tar on the runway!

Adding small white lights at the relevant contact points for the nosewheel and two mainwheels as given in the original acft cfg shows the nosewheel contact point to be below and behind the image of the nosewheel while the lights positioned as per the contact points for the main wheels are also below and behind the image of the main gear as seen on the screen. I repositioned my small lights so that when viewed on the screen they appeared to coincide with the nose and main gear centrelines with the latter lights positioned between the tyres so that their new positions would indicate the correct contact points on the ground for the undercarriage.

Altering the values of the gear contact points on the acft cfg to new values shown by the white indicator lights caused the aircraft to leap up and down completely out of control to such an extent that I have had to abandon attempts to "correct" the contact points and to put up with awful nosewheel steering and treacle like runway surfaces!

Can any of our FS9 simulator engineers help me to solve the problems outlined above?

I do realise that Rick produced a very fine HS748 many years ago for I was in early correspondence with him about that aircraft prior to his issuing the first version.

[Scorpius]

The quickest and best way to solve this one is to use the definative model here, Rick's 748.

Problem solved!

Nev

[hobby]

Thanks Nev. I don't like giving up on challenge which could lead to my understanding the mysteries behind FS models!

[DaveB]

Wish I could say something meaningful Hobby but I'd tend to go with Nev's suggestion. Airfiles have never been my strong point I'm afraid. I guess you could (as a start) look at the values of both aircraft.cfg's as a comparison though this won't be the whole story as some of what you're seeing may be directly related to their respective airfiles. You could also try swapping airfiles between Marcel's model and Rick's to see what happens in the sim though what you might gain I really don't know. There are many ways to skin a rabbit

ATB
DaveB

[Airspeed]

..... I guess you could (as a start) look at the values of both aircraft.cfg's as a comparison though this won't be the whole story as some of what you're seeing may be directly related to their respective airfiles. You could also try swapping airfiles between Marcel's model and Rick's to see what happens in the sim though what you might gain I really don't know. There are many ways to skin a rabbit

ATB
DaveB

I'm rather like Hobby, I get hooked on trying to fix stuff, and bash away until I either solve it, or fall on my face, saving it up for a future time when I get over it. I hate to give up.

I do like your suggestion, Dave, particularly the early bit.

Here it comes, the stupid bit....you could go for a Welsh Rabbit, they don't need skinning at all.

EDIT: Looked around for the offending download, but only found fleeting references to it. One mentioned that it was for FS2002/2004, but couldn't see where it was available.
PLAN B: use Rick Piper's model (or did someone aleardy mention that?)

[cstorey]

Have you examined the CG position of the aeroplane as loaded? It sounds to me as though you have the CG way forward and probably out of limits, so that in taxying it is "wheelbarrowing" , and of course requires up elevator approaching if not beyond the limits of authority to rotate it .

[Scorpius]

The 748/780 (Andover) was the first aircraft I ever worked on when posted from training to RAF Thorney Island. Rick's version is absolutely spot on from a cold dark cockpit to starting the Darts, water methanol injection and fuel at altitude calculations. Even the E190 weather radar display is correct.

Try a STOL takeoff with the stick in your lap and full power with the brakes on, then release them. Watch it go!

I'm not biased at all Hobby!

Nev

[petermcleland]

I agree with most people here...Whenever I have downloaded an aircraft that has serious problems, if it is not easily and immediately fixable I just bin it. In this case with a perfect alternative model like Rick's available...Bin!

[hobby]

For C Storey: Being a great fan of the HS748 I have carried out quite a bit of work on Marcel Kuhnt's original acft cfg. The current CofG of that model is at precisely one third of the wing chord as shown on the diagram that comes up when one presses the 'fuel and load' button.

There are times, when I want to get on with the flying part of the FS hobby, when I 'fly' an FS aircraft which is not in effect a procedural trainer - i.e. all the RW procedures to be followed to operate the aircraft. Long ago in FS95 and 98 days I was fascinated by a procedural FS aircraft model of the Shorts 330 or 360 made by a Welsh gentleman. Rick's HS748 is a cracking model that I have flown in the past and that I will fly in the future.

However as I wrote previously I do like to leap into a simpler aircraft and carry my virtual cargo or passengers wherever my fancy and available time takes me. I also enjoy poking about the acft cfg to try to bring that cfg to a closer imitation of the real world aircraft. Sometimes one succeeds, sometimes one does not! In the MK HS748 case it looks as though I shall not succeed.

Long ago I read of a similar case in which it was found that the contact points of an FS aircraft had been set during the construction of the model at what would always be below runway level. That model did fly but in effect the FS was dragging a chunk of runway with it during the take off run!!!