cg limits for HP11A

Does anyone know the cg limits of the HP11A as percentages of chord, so some other reference?

Originally Posted by

Does anyone know the cg limits of the HP11A as percentages of chord, so some other reference?

Check he

http://www.soaridaho.com/Schreder/HP...culations.html

Brad.

On Tuesday, February 11, 2014 1:25:04 PM UTC-8, Brad Alston wrote:

Check he

http://www.soaridaho.com/Schreder/HP...culations.html

That's the reference that I would have cited. There are clearly some typos that seem to have resulted from the OCR process on the original documents (or rather copies of copies of the originals). However, the clarifications at the bottom of the document seem pretty clear.

The example shown for the HP-18 is also instructive:

http://www.soaridaho.com/Schreder/Sc...976_HP-18.html

It shows some neat algebra for determining the pilot CG location with only a single extra weighing.

As in the past, I disagree with Dick Schreder about the definition of MAC; he seemed to think that it was the same as the average chord, which it is not. However in this case (and for the other HPs), the difference is pretty small, and the CG range he suggests is probably OK. I personally recommend operating at a CG forward of 35% MAC in order to preserve stability margin and keep the stall characteristics relatively docile on these ships.

Thanks, Bob K.

On Wednesday, February 12, 2014 4:46:05 PM UTC-8, Bob Kuykendall wrote:
On Tuesday, February 11, 2014 1:25:04 PM UTC-8, Brad Alston wrote:



Check he



http://www.soaridaho.com/Schreder/HP...culations.html



That's the reference that I would have cited. There are clearly some typos that seem to have resulted from the OCR process on the original documents (or rather copies of copies of the originals). However, the clarifications at the bottom of the document seem pretty clear.



The example shown for the HP-18 is also instructive:



http://www.soaridaho.com/Schreder/Sc...976_HP-18.html



It shows some neat algebra for determining the pilot CG location with only a single extra weighing.



As in the past, I disagree with Dick Schreder about the definition of MAC; he seemed to think that it was the same as the average chord, which it is not. However in this case (and for the other HPs), the difference is pretty small, and the CG range he suggests is probably OK. I personally recommend operating at a CG forward of 35% MAC in order to preserve stability margin and keep the stall characteristics relatively docile on these ships.



Thanks, Bob K.

That is a good usable CG spread sheet, but I doubt it came from Schreder. I remember the first flight of an HP-16, the only thing Dick said was "balance between 25% and 30 MAC"...........nothing else! The builder correctly assumed the mean cord was half way out the constant tapered wing. He then moved the MAC inboard along the leading edge and measured the min/max CG location from the leading edge at the root rib.

Did you catch his mistake?

Yep, the MAC must be moved inboard parallel the wing center line, not parallel to the leading edge. Being a low time pilot, the builder asked a highly experienced pilot to make the first flight. It took full aft stick to keep the nose up as the test pilot hung on in low tow position..............praying for bailout altitude! He released at about 3000 feet and discovered he could hold the nose level at about 80 knots, so he decided to land it at 80. Everything worked out OK and the ship and test pilot both came out unscathed. Needless to say, the CG was moved aft a considerable amount before the next flight.
Cheers,
JJ

On Sunday, February 16, 2014 10:46:32 AM UTC-6, JJ Sinclair wrote:
Yep, the MAC must be moved inboard parallel the wing center line, not parallel to the leading edge.

Well, generally true for most glider configurations, but not quite. It does not project in along the centerline of the wing. It projects straight in, perpendicular to fuselage center line. If you projected it inboard along the centerline of a forward or aft swept wing, you would be just as bad off as the the guy who followed the leading edge on a basically straight wing.. HP wings are generaly straight along their spar, which is typically at about 40% chord.

Steve Leonard

Steve,

First let me say, aaarggg (Pirates Day is coming).

Your brother impressed us all at the Moriarty Region 9 in his HP (build by your dad), last year.

Second let me say, I am now a part owner in an HP-11a (like I need another glider). Just yesterday, our huge resource, test pilot Darrel Watson, helped me and my partner do a good weight and balance measurement for our HP-11a.

The information being provided in this thread has been extremely valuable to us. My take-away is that aft CG is a good thing in the HP, as it is in most racers.

Raul Boerner
DM

On Monday, February 17, 2014 3:07:32 PM UTC-8, wrote:

The information being provided in this thread has been
extremely valuable to us. My take-away is that aft CG
is a good thing in the HP, as it is in most racers.

In my direct experience (HP-11 and HP-18), the Schreder birds are a bit shy on margin of static stability. So at the aft ends of their CG ranges they are more nearly neutrally stable than their European counterparts at equivalent CG locations. That is why I recommend keeping the CG forward of 35% MAC for all of the HPs.

Thanks, Bob K.

On Monday, February 17, 2014 5:07:32 PM UTC-6, wrote:
Steve, First let me say, aaarggg (Pirates Day is coming). Your brother impressed us all at the Moriarty Region 9 in his HP (build by your dad), last year. Second let me say, I am now a part owner in an HP-11a (like I need another glider). Just yesterday, our huge resource, test pilot Darrel Watson, helped me and my partner do a good weight and balance measurement for our HP-11a. The information being provided in this thread has been extremely valuable to us. My take-away is that aft CG is a good thing in the HP, as it is in most racers. Raul Boerner DM

Argh back to you, Raul! Yes, Ron is having oodles of fun with Dad's old HP-18. As to you "needing another glider", well, that is talking to the wrong guy, I suspect. Have a great time with your partner in the HP-11A.

As Bob K said, aft CG will help performance, but at a price. Most recommend something on the order of 2/3rds to 3/4ths of the way back in the manufacturers allowed range will give best performance. The benefit may be a bit more pronounced in the HP series, as the tail geometry requires creation of a larger force normal to the tail surface in order to get the same vertical component of a "flat" horizontal tail. I would start out at 2/3rds back in the allowable, and if all pitch is OK, look at 3/4 back in the allowable range. Any further aft than that, and you likely won't gain much more. And as JJ's tale told, too far forward and you won't be able to get the nose up! I saw an HP-14 that had this problem. Crunched the nose pretty good.

Steve (I think I need another glider) Leonard

On Tuesday, February 18, 2014 9:30:02 AM UTC-8, Steve Leonard wrote:

Argh back to you, Raul! Yes, Ron is having oodles of fun with Dad's old HP-18. As to you "needing another glider", well, that is talking to the wrong guy, I suspect. Have a great time with your partner in the HP-11A.

Is that the HP-18 with the retrofit center stick?

Thanks, Bob K.

On Tuesday, February 18, 2014 11:34:03 AM UTC-6, Bob Kuykendall wrote:
On Tuesday, February 18, 2014 9:30:02 AM UTC-8, Steve Leonard wrote: Yes, Ron is having oodles of fun with Dad's old HP-18. As to you "needing another glider", well, that is talking to the wrong guy, I suspect. Have a great time with your partner in the HP-11A. Is that the HP-18 with the retrofit center stick? Thanks, Bob K.

Yes, Bob. That is the one with your center stick kit installed. Says it made it a much better flying plane. N1054A, serial 089.

And Thank You for those efforts, Bob K!

Steve Leonard